Management of the Electricity Supply in Alderney
Abstract
The energy system in islands usually relies upon the fossil fuel importation and, consequently has low security of supply as well as high and fluctuated costs. An alternative to address these problems is the development of a Renewable Energy (RE) system which can provide the whole electricity demand and can be funded through community owned investment. This master thesis aims to assess the feasibility of supplying the electricity demand of the Channel Island of Alderney by a combination of RE with energy storage. The island of Alderney is the most northerly of all the Channel Island and its location is perfect to harness onshore and offshore renewable resources. After assessing the different renewable resources and current energy storage technologies, this report proposes an energy system of 1.5MW anaerobic digester plant and a 475 kW solar PV park with NaS batteries to reduce the dependency on diesel and generate the Alderney electricity supply of 1.5MW. The feasibility of supplying the Alderney's electricity demand by the proposed energy scheme is assessed and it is concluded that the RE system is technically feasible. However, the main roadblock to its implementation is the socioeconomic constraint. This could be solved through community owned renewable energy system or with more community involvement in the Alderney's energy decisions such as the funding mechanism for the necessary grid upgrades to allow the safely operation and the connection of the RE system. The report concludes, after analysing different energy fuels such as diesel, hydrogen and other RE resources, that there are multiple options to supply the electricity demand in Alderney with important advantages in terms of cost, reliability and environmental impact. The proposed RE system could be one of the best alternatives to supply the island electricity with low-carbon fuel, high security of supply and stable prices.
Full text
CRANFIELD UNIVERSITY Albert Sancho Balsells Management of the Electricity Supply in Alderney School of Energy, Environment and Agrifood MSc in Offshore and Ocean Technology with Offshore Renewable Energy MSc Thesis Academic Year: 2014 -2015 Supervisor: Dr. J.V. Sharp Industrial Supervisor: James Lancaster Sep 2015
CRANFIELD UNIVERSITY School of Energy, Environment and Agrifood MSc in Offshore and Ocean Technology with Offshore Renewable Energy MSc Thesis Academic Year: 2014 -2015 Albert Sancho Balsells Management of the Electricity Supply in Alderney Supervisor: Dr. J.V. Sharp Industrial Supervisor: James Lancaster Sep 2015 This thesis is submitted in partial fulfilment of the requirements for the degree of Master of Science © Cranfield University 2015. All rights reserved. No part of this publication may be reproduced without the written permission of the copyright owner.
i ABSTRACT The energy system in islands usually relies upon the fossil fuel importation and, consequently has low security of supply as well as high and fluctuated costs. An alternative to address these problems is the development of a Renewable Energy (RE) system which can provide the whole electricity demand and can be funded through community owned investment. This master thesis aims to assess the feasibility of supplying the electricity demand of the Channel Island of Alderney by a combination of RE with energy storage. The island of Alderney is the most northerly of all the Channel Island and its location is perfect to harness onshore and offshore renewable resources. After assessing the different renewable resources and current energy storage technologies, this report proposes an energy system of 1.5MW anaerobic digester plant and a 475 kW solar PV park with NaS batteries to reduce the dependency on diesel and generate the Alderney electricity supply of 1.5MW. The feasibility of supplying the Alderney's electricity demand by the proposed energy scheme is assessed and it is concluded that the RE system is technically feasible. However, the main roadblock to its implementation is the socioeconomic constraint. This could be solved through community owned renewable energy system or with more community involvement in the Alderney's energy decisions such as the funding mechanism for the necessary grid upgrades to allow the safely operation and the connection of the RE system. The report concludes, after analysing different energy fuels such as diesel, hydrogen and other RE resources, that there are multiple options to supply the electricity demand in Alderney with important advantages in terms of cost, reliability and environmental impact. The proposed RE system could be one of the best alternatives to supply the island electricity with low-carbon fuel, high security of supply and stable prices. Keywords: Renewable energy; Electrical energy storage; Alderney; Anaerobic digester; Solar PV energy; Hydrogen.
ii ACKOWLEDGEMENTS I would like to thank Alderney Electricity Ltd for their assistance and patience throughout the course of this project providing me with data and valuable information about the current situation of the electricity supply and future energy projects in Alderney. Especially, I want to thank James Lancaster who provided me the opportunity to visit the island and live the reality of this small and charming community. In addition, thanks to the different institutions which spent time discussing the thesis and other ideas to lead to a change in Alderney’s energy system. I thank my supervisor Dr. J.V. Sharp for his continued advice and helpful knowledge as well as for his flexibility and understanding of my personal situation. Many thank to all my friends who collaborate in this thesis by sharing their knowledge, experience and academic resources to provide me with the necessary background. To my family for supporting me during my year studying in Cranfield and helping me to succeed in this master thesis. Finally, I want to thank Alstom Wind who allow me to realize this master thesis with the required flexibility meanwhile being part of its organization.
1 ABSTRACT ......................................................................................................... i ACKOWLEDGEMENTS ...................................................................................... ii LIST OF FIGURES ............................................................................................. 3 LIST OF TABLES ............................................................................................... 4 LIST OF GRAPHES ........................................................................................... 6 LIST OF PICTURES ........................................................................................... 7 LIST OF EQUATIONS ........................................................................................ 8 LIST OF ACRONYMS ........................................................................................ 9 1 INTRODUCTION ........................................................................................ 11 2 INTRODUCTION TO ALDERNEY .............................................................. 12 2.1 Geographical location .......................................................................... 13 2.2 Current electricity situation .................................................................. 14 2.3 Alderney Electricity Grid ...................................................................... 19 2.4 Challenges and future for the Alderney's islanded energy systems .... 21 3 AIM AND OBJECTIVE OF THE PROJECT ................................................ 25 4 RENEWABLE ENERGY RESOURCES AROUND ALDERNEY ................ 26 4.1 Introduction to the current renewable energy systems ........................ 26 4.1.1 Solar photovoltaic energy ............................................................. 26 4.1.2 Wind energy.................................................................................. 27 4.1.3 Hydropower .................................................................................. 28 4.1.4 Marine energy ............................................................................... 29 4.1.5 Thermal energy generation ........................................................... 30 4.2 Alderney characteristics for the integration of RE systems ................. 31 5 SIZING AND SELECTING A FEASIBLE RENEWABLE ENERGY SCHEME IN ALDERNEY ................................................................................................. 33 5.1 Solar .................................................................................................... 34 5.1.1 Cost analysis ................................................................................ 36 5.1.2 Reliability analysis ........................................................................ 36
2 5.1.3 Environmental analysis ................................................................. 37 5.2 Onshore wind ...................................................................................... 39 5.2.1 Cost analysis ................................................................................ 40 5.2.2 Reliability analysis ........................................................................ 40 5.2.3 Environmental analysis ................................................................. 41 5.3 Tidal stream ........................................................................................ 42 5.3.1 Cost analysis ................................................................................ 42 5.3.2 Reliability analysis ........................................................................ 43 5.3.3 Environmental analysis ................................................................. 43 5.4 AD ....................................................................................................... 44 5.4.1 Cost analysis ................................................................................ 44 5.4.2 Reliability analysis ........................................................................ 45 5.4.3 Environmental analysis ................................................................. 45 5.5 Proposed locations to host RE developments in Alderney .................. 46 5.6 Conclusions: Proposed RE system for the Alderney case study ......... 50 6 ELECTRICAL ENERGY STORAGE ........................................................... 55 6.1 Introduction to EES systems ............................................................... 55 6.2 Characteristics and selection of the most suitable EES technologies . 59 7 FEASIBILITY OF SUPPLYING THE ELECTRICITY FROM RE IN ALDERNEY ...................................................................................................... 62 8 CONCLUSIONS ......................................................................................... 65 8.1 Required grid improvements and funding strategies ........................... 65 8.2 Economic, environmental and reliability assessment of other fuels and energy scenarios ........................................................................................... 67 8.3 Final conclusions and recommendations ............................................ 72 9 FURTHER WORK ...................................................................................... 75 10 REFERENCES ....................................................................................... 77 11 APPENDICES ........................................................................................ 89
3 LIST OF FIGURES Figure 2-A: Map of Alderney [4] ........................................................................ 13 Figure 2-B: Geographical location of Alderney [8] ............................................ 13 Figure 2-C: Alderney's electricity transmission system [11] .............................. 19 Figure 2-D: Initial layout of the FAB link [22] .................................................... 23 Figure 2-E: ARE developments location [20] .................................................... 23 Figure 4-A: EU power mix 2014 (MW) [32] ....................................................... 28 Figure 5-A: Comparative reflection analysis [59] .............................................. 38 Figure 5-B: Annually Wind direction distribution at Alderney airport ................. 39 Figure 5-C: Different proposed locations in Alderney to harness RE ............... 50 Figure 5-D: Characteristics of the RE ............................................................... 51 Figure 5-E: Proposed Location for the solar PV park ....................................... 52 Figure 5-F: Proposed location of the two WTs ................................................. 53 Figure 11-A: Power curve of the T400-34 ........................................................ 97
10 Photovoltaic (PV) Pumped Hydrogen Energy Storage (PHES) Renewable Energy (RE) Round Trip Efficiency (RTE) States of Alderney (SoA) Tidal Stream Turbine (TST) United Kingdom (UK) United States (US) United States Dollar (USD) Vertical Axis Wind Turbine (VAWT) Wind Turbine (WT)
11 1 INTRODUCTION During the last decades, Renewable Energy (RE) technologies have improved their performance and reliability. Consequently, their share in the electrical market has been increased. Specially, they are emerging as an alternative in isolated systems like an island where the electricity generation was based on fossil fuels as diesel. As a result, several examples of electrical isolated system with an important RE integration can be found. Furthermore, there are some cases as the Island of Samso [1] in Denmark as well as the Isle of Eigg [2] in Scotland where the whole electricity demand is generated through RE. Another example is the Island of Hierro in Spain which became the first isolated system in the World to supply the whole electricity demand during 4 hours through RE [3]. This thesis assesses the potential of Alderney to become one of the first in the World with 100% RE integration into the electrical system. Usually these kind of developments is highly linked to community owned systems where the community owns the RE system. Apart from funding the investment, the community actively participates in the development and receive several advantages of it as saving the money of the electricity bills, getting some grants from the governments, the creation of new jobs for the community and the increase of the local economy. Firstly, this master thesis introduces the island of Alderney and its characteristics as the location, the current electricity situation and the electrical grid. Then, it is generally presented the different RE and available Electrical Energy Storage (EES). After assessing these, a RE energy systems with EES is proposed and its feasibility is analysed in two different scenarios. Finally, the thesis concludes by introducing the different funding strategies as well as comparing the proposed system based on RE fuels against other energy fuels such as diesel, hydrogen and other RE.
12 2 INTRODUCTION TO ALDERNEY Alderney is the third largest and most northerly Channel Island. Despite it is part of Europe, it is independent from the European Union (EU) as well as the United Kingdom (UK). However, the Alderney inhabitants are considered British citizens and there are other influences as in the language and the official currency that is the Pound Stirling [4]. The government of Alderney is ruled by the State of Alderney (SoA) but since 1948, when Alderney became part of the Bailiwick of Guernsey, the States of Guernsey has financial and administrative responsibility for some public service such as the airport, the breakwater, police, social service, health and education [5]. As a result, Alderney pays to Guernsey for that service as well as it requires approval from Guernsey for large financial expenditure. Alderney has a population around the 2000 residents which the majority of them live in the capital of the island, St. Anne. Nowadays, this population can be divided in two groups where approximately 2/3 of the inhabitants are normal demographic families and the other 1/3 are people at the last stage of their career [6]. As a result of this third, the population in Alderney has been decreasing along the recent years. In addition to those residents, the population in Alderney peaks at 3000 people during the summer period, especially during the Alderney Week in August, due to touristic attractions as ecotourism, war history and sailing. Apart from the tourism, the economy of the island is mainly based on e-gambling as well as on small businesses [7]. Below, it can be seen a map of Alderney with the airport in the southwest, the main harbour, Braye Harbour, and the capital of St Anne.
13 Figure 2-A: Map of Alderney [4] 2.1 Geographical location As explained before as well as displayed in the Figure 2-B, Alderney is the most northerly of all the Channel Island located at 60 miles from the south coast of England as well as at 20 miles northeast away from the island of Guernsey. In addition, the Alderney Race separates the island from the closest French mainland, the Cherbourg Peninsula, which is located 8 miles west of Alderney. However, the nearest British port, Poole, and French port, Cherbourg, are situated at 110 km and 30 km from the island respectively. Figure 2-B: Geographical location of Alderney [8] The island itself is 3.5 miles long and 1.5 miles wide, having a total area of 3 square miles. Moreover, Alderney's territorial waters extends 90 nm2 around the
14 island and due to the third United Nations Convention of the Law of the Sea it has the right to claim for a total of 500 nm2. In spite of the benefit of having more territorial waters to harness RE resources, the SoA is not planning to claim that right due to the higher legal responsibilities such as ship transport and buried munitions of the World War II [9]. Despite the small territory, the island of Alderney and its surroundings have a huge diversity in flora and fauna, especially in birds that use the island for reproduction and during the migration routes. As a result, there are three conservation reserves that differ dramatically between them, two conservation reserves and one Ramsar site, which are managed by the Alderney Wildlife Trust (AWT) in order to protect these zones in a long term [10]. 2.2 Current electricity situation Currently, the electricity demand in Alderney varies between 1.1 MW and 0.4MW with the peaks of demand during the Alderney week and August (weeks 31 to 33) and winter periods (weeks 50 to 52 and 1 to 4) [11]. The electricity peak demand it has been decreasing along the last 7 years and it is forecasted to continue decreasing in the following years as displayed in the graph. Graph 2-A: Peak power demand recorded and forecasted by the AEL [11] 0,800 0,900 1,000 1,100 1,200 1,300 1,400 1,500 1,600 2010 2012 2014 2016 2018 2020 2022 2024 Peak Recorded/Predicted Load (MW) Year AEL Peak Demand (Load) Forecast, 2010 - 2024 Week 1 Week 32 Week 52
15 In terms of energy, it has been a significant decrease from the 6,912 MWh of 2013 to the 6,648 MWh of 2014 and the forecasted 5,800 MWh of 2015 [11]. Apart from the August and winter peaks, the energy demand is quite stable between seasons as it can be seen in the following figures extracted from the demand analysis realized in the Appendix A. Graph 2-B: Power demand evolution during average days. Graph 2-C: Energy demand evolution during average days. 400 500 600 700 800 900 1000 1100 1200 1300 0:00 6:00 12:00 18:00 0:00 Power demand [kW] Power demand evolution W7 W18 W32 W43 125 225 325 425 525 625 725 0:00 6:00 12:00 18:00 0:00 Energy demand [kWh] Energy demand evolution W7 W18 W32 W43
16 As it can be stated, the electricity demand peaks during the midday and afternoon/night period in all the different weeks. This demand mainly comes from residential properties and small business consumption as well as from the hospital and the generation power plant [7]. Nowadays the power generation in Alderney relies upon diesel due to all the electricity supply being provided through a diesel power plant run by Alderney Electricity Limited (AEL). AEL has been run as a non-profit company for many years and its primary purpose is to meet the energy needs of the island on behalf of the community. AEL was created at 1938 and in 1953 received the exclusive right to supply electricity in the island that is provided by means of a diesel power plant [12] [13]. This plant is located close to the Braye Harbour where the ships with the diesel and kerosene, for the heating system, arrive via Guernsey which has the highest priority. Then the fuel is pumped through a pipeline to the power station where it is stored in 13 tanks, which provide at least 3 weeks of reserve with an average cost of £8K/yr [7] [14]. Picture 2-A: Diesel and kerosene storage tanks From those tanks, the diesel is supplied to one of the seven generators where the diesel is burned to obtain the electricity. This power plant had an annual consumption of 1.8 million litres in 2014 with a cost of 0.397GBP/L and an efficiency of 3.56 kWh/L. There are installed three different kinds of generator: three Paxman generators of 2MW from 1999 installed in 2007 and four Blackstones generators two of 450kW from 1968and another two of 750 kW from 1972 [6] [15].
17 Picture 2-B: Paxman (left) and Blackstones diesel generator (right) The Paxman generators require top overhauls every 10,000 engine hours with a cost of 54,000GBP and major overhauls which are realized in Colchester with a cost of 120,000GBP every 30,000 engine hours [14]. In the case of small maintenance such as oil and injector changes and major overhauls of the Blackstones can be realized inside the power plant with the spare parts stocked in the top of the plant. Following the maintenance schedule predicted by the AEL, by 2020 as a maximum two Blackstones generators will be decommissioned and it will be required a new generator which should cost around £350k [15]. Picture 2-C: Spare parts to realize minor maintenance and repairs Currently if all the generators are run in parallel, they can provide a maximum of 8.4 MW and hence, the system is over-sized. It has to be stated that to minimise the maintenance cost, AEL employs the Paxman during high demand periods with balanced loads and the Blackstones generators with lower demand periods [15]. Nowadays, AEL is making a small profit for the electricity supply that it shares with the different shareholders which mainly are the SoA [4]. The current cost of
18 energy is around 37p/kWh with the following breakdown between generation and distribution costs [16]. Graph 2-D: Energy generation and distribution cost breakdown [12] The majority of these costs such as infrastructure, oil storage and maintenance, administrative and staff costs are independent of the oil price. As a result, reducing the Alderney's electricity demand by installing private RE systems such as solar photovoltaic (PV) roofs panels will lead to a higher cost per unit due to those fixed costs as well as the higher oil prices related to the smaller amount of fuel importation [6]. 74% 26% Power station Distribution 45% 41% 6% 0% 8% fuel staff maintenance depreciation 63% 19% 4% 14% staff maintenance other depreciation
19 For the above reasons, in the near term and long term it is very unlikely to see huge reductions in the electricity cost [6] until a new grid connection links to the mainland or distributed generation like RE microgeneration systems with energy storage are developed. Those developments will provide a more affordable, secure and sustainable energy supply. However, they will require severe improvements in the current electrical grid connection that will be detailed in the following points [6]. 2.3 Alderney Electricity Grid Nowadays Alderney's electrical grid system is an isolated grid due to not being linked to any other surrounding electrical grid as the ones in Guernsey or to the French mainland. As a result, all the electricity supply is provided from the power plant and it is distributed through a grid distribution system of 11 kV. This electricity distribution system, which is displayed below, is mainly buried underground (except one overhead section in the northeast of the island) in order to avoid the severe weather conditions of Alderney. In that figure, it can be seen as well the 20 different substation where by means of 100 - 500 KVA transformers the high voltage electricity is reduced to 1000 V and then to 440/250 V [15]. This low voltage electricity is transmitted to the different consumption points by underground lines. Figure 2-C: Alderney's electricity transmission system [11] Despite it was estimated that the current grid system can support loads of a maximum 6MW and the asset management programme launched in 2007 by
26 4 RENEWABLE ENERGY RESOURCES AROUND ALDERNEY The geographical location of Alderney offers the opportunity to exploit many onshore and offshore RE resources to get electricity. In order to exploit those resources while preserving the surrounding environment, different commissions, groups and companies such as the Alderney Commission for Renewable Energy (ACRE), Alderney Renewable Energy (ARE) and AWT have been created during the last years. The ACRE was created in 2007 and it has the power to "licence and regulate the operation, deployment, use or management of all forms of renewable energy in the island of Alderney and its territorial waters" [23]. For example, ACRE has collaborated with the creation of guidance for decommissioning RE systems [24] or for the licensing and consents process [25] which facilitates the development of RE systems in Alderney. In the case of ARE, it is a tidal energy developer founded in 2004 that tries to maximise the tidal resources in Alderney's territorial waters which has secured a 65 year licence from the ACRE of 48 square miles [26]. In addition, several documents regarding RE in Alderney have been created such as [4] [6] [7] [27] with the collaboration of different Alderney associations. In this section, it will be generally introduced all the RE resources that can be exploited with the current technology and their potential in the case study of Alderney will be assessed. 4.1 Introduction to the current renewable energy systems 4.1.1 Solar photovoltaic energy Solar PV energy is based on the energy conversion of solar radiation into electricity in the PV cell through the PV effect. This cell is composed by two thin semiconductor layers, which absorb the maximum incident light in order to stimulate enough the electrons to cross the potential barrier and then generate electricity. This technology has been enhanced from the first silicon cell converter in 1954 to the current one by increasing the solar cell technologies, reducing the
27 thickness and improving their reliability and cost. During the 1990s the first PV roofs and power station were installed as a result of the fast evolution led by the use of solar PV in spaceships and satellites [28]. Along the last five years, the use of PV solar cells has increased by 55% per year because of the reduction in panel prices due to manufacturing improvements and the intense competition between manufacturers especially after the boom of Chinese companies. At the same time, the price per watt has been decreased thanks to efficiency enhancements [29]. As a result, solar PV cells have been installed specially in Europe which accounts for 73% of the global market [7]. These cells are employed in isolated installations as well as in electrically connected systems as household solar panels or solar farms in order to sell the generated electricity [28]. 4.1.2 Wind energy Wind energy is based on the conversion of kinetic wind energy into mechanical energy through the lift effect on the blades of the Wind Turbine (WT) and then it is transformed into electricity by the generator. Along the last years the WT's technology has been enhanced by increasing the tower height, the blade length and the power coefficient as well as by improving blades' design, new materials, reducing noise emissions and cost reductions on CAPEX and O&M. As a result, the wind energy has been expanded in new countries especially in the relatively new markets of China, US and Latin America [30]. Regarding the consolidated EU market, Germany and UK are leading in the installation of new onshore and offshore WTs. At the end of the 2014, as displayed below in the figure 6, the EU total wind capacity was 128,751.4 MW representing the 14.1% of the EU power mix with Germany, Spain and UK leading respectively the installed wind capacity [31].
28 Figure 4-A: EU power mix 2014 (MW) [32] WTs can be installed in an onshore or offshore environment where the blade length constraints are lower than onshore and allow the installation of higher capacity WTs. Basically, as a function of the axis configuration WTs are divided into horizontal axis WTs, which are more deployed and have better performance, and vertical axis WTs. In addition, as a function of the power capacity, WTs can be classified as micro WT (up to 1.5 kW), small WT (up to 50 kW), medium WT (50 - 500 kW) and big WT (up to 8 MW) [33] [34]. 4.1.3 Hydropower Basically, hydropower systems convert the kinetic energy as well as the potential and pressure energy carried by the water into mechanical energy through a turbine and then into electricity. Hydropower is the most mature technology and the most common form on the RE sector with a global capacity of 1,055GW in 2014 [32]. Despite its maturity, hydropower capacity has grown during 2014 to 39 GW mainly because of the development in China. In mature markets as in the EU, despite the growth being smaller, in 2014 it was the first RE in terms of capacity with 140,683.3 MW (15.5%) [32]. This increase is related with renovating old plants as well as with the installation of Pumped-Hydro Energy Storage (PHES) systems [28] [32].
29 As a RE, hydropower is the most reliable and efficient system, however the required investment and its impact on the surrounding environment are important drawbacks to consider before the construction of a new plant [7]. 4.1.4 Marine energy 4.1.4.1 Tidal energy As a kind of hydropower energy, tidal energy systems convert the energy carried by the surge of the ocean during the rise and fall of tides into mechanical and then into electricity. Tidal energy can be harnessed in two different ways: tidal range or tidal stream. Tidal range systems have been producing electricity from the water's kinetic power since 1966 [35]. Despite being more mature than the stream one, only a few projects are underway due to the required high investment and their impact on the environment. In the case of tidal stream, the kinetic energy of the current, especially from the sea, is exploited in a similar way to wind energy but with a fluid thousand times more dense. Along the last years tidal energy is emerging as an alternative RE with a few turbines installed and some planned or under construction. As a result of the government grants and facilities, several technology improvements have been done in order to extract this low-carbon, predictable and reliable energy source. Especially in countries like the UK and France that have some of the most suitable locations to develop tidal stream systems [36]. 4.1.4.2 Wave energy Waves can be originated by different factors but the most common is due to the influence of the wind on the ocean surface. Wave energy converters are very immature technologies, which intercept the potential and kinetic energy of the waves by pitching, heaving and/or surging their structure. Then, this motion is converted into electricity through different power take-off systems and delivered to the grid. It is estimated there is a global wave potential of 1TW, however the different kinds and designs of wave energy converters are still in a very low
30 technology readiness level with a few devices in the commercial and system testing phase [37]. 4.1.4.3 Other Apart from tidal and wave energy, there are other marine energy systems as ocean thermal energy and ocean osmotic energy which are in a research stages. Ocean thermal energy systems exploit the high temperature difference between the water surface and deeper areas to generate electricity and they have an estimated global potential of 10000 TWh/year, mainly in tropical waters. In the case of osmotic energy, the salinity gradient between fresh and sea water in the river's mouth is exploited to produce an estimated global power potential of 2000 TWh/year [38]. 4.1.5 Thermal energy generation Thermal power plants are the most common electricity generation systems which are usually run by fossil fuels as coal, diesel and gas or nuclear resources. These plants are based on thermodynamic conversions to generate electricity from the heat produced by the combustion of fossil fuels as well as renewable resources. The most important renewable thermal power generation systems are geothermal power, thermodynamic solar power as well as cogeneration and Anaerobic Digestion (AD) from biomass [28]. In the case of geothermal power, it uses the temperature gradient within the Earth, which can reach 1000ºC/km, and it is presented as hydrothermal or hot dry rock resources. Another renewable thermal resource is the solar radiation which can be concentrated to a specific point of the thermodynamic solar plant, by special designs of mirrors and collectors as towers, in order to increase the fluid's temperature and hence the thermodynamic conversion efficiency. Furthermore, the necessary heat to generate electricity can be produced by burning biomass and waste. 4.1.5.1 Anaerobic digestion (AD) The AD process is based on the conversion from biomass to biogas in a digester with absence of oxygen by means of 4 microbiological and biochemical
31 processes: hydrolysis, acidogenesis, acetogenesis, methanogenesis [39] [40]. The inputs of the process or feedstock are organic material from the agriculture and farm like animal manure as well as from different organic waste like industrial and food processing waste [41] [42] [43] [44]. The outputs of the process are biogas and thermal energy which the amount of biogas per tonne of feedstock and the different calorific characteristics can vary in function of the mix of feedstock introduced into the digester [42] [43] [44]. Then, the biogas is burned to produce renewable power and heat and the remaining material can be used as fertiliser [28] [41] [42] [43]. 4.2 Alderney characteristics for the integration of RE systems As introduced before, the location of Alderney allows the exploitation of diverse RE resources making technically feasible the idea of transforming Alderney into a green island as discussed on [7]. In terms of solar irradiation, Alderney has a Global Horizontal Irradiation (GHI) around 3.4kWh/m2/day with a year optimal inclination angle of 37º and an annual irradiation deficit due to shadowing almost 0% in all the territory [45]. In the following section, PV technology will be analysed and selected the different tracking options, the total peak PV power and the most suitable locations for the construction of a solar PV park. Regarding wind energy, based on the measurements at the Alderney airport the average wind speed is 13kts with a variation slightly higher than 30% [46]. Despite offshore WTs having higher energy capacity, the following studied locations will be onshore due to the characteristics of onshore WT suiting better the low energy demand of Alderney with lower capital and operational expenditures. Despite ARE having the right to exploit the best Alderney's territorial waters, the tidal currents in the other areas are high enough to consider the installation of a single or a small array of turbines to supply the required velocity. The deployment of wave energy converters and other marine technologies as a electricity source is discarded due to their low maturity and reliability which will not allow to supply the required demand with enough energy security.
32 Hydropower energy systems are not considered due to the mainland space limitation and the huge capital investment. However, in later stages the suitability of a PHES will be assessed. Alderney soil is mainly composed of sedimentary volcanic rock as Granodiorite and Bibette Head granite which are covered by superficial sands and gravel [7]. This kind of soil generally has the following properties: Mean thermal conductivity (W/mK) Mean thermal diffusivity (mm2/s) Mean heat capacity (MJ/m3K) At 20ºC 3.62 1.69 2.15 At 80ºC 3.42 1.36 2.53 Table 4-A: Characteristics for the Alderney's typology soil [47] Despite these characteristics permitting the possibility of exploit geothermal energy, this kind of energy system is not further discussed due to the high installation cost and the necessity of having skilled staff [48]. Finally, the development of an AD in Alderney can provide the island with a reliable and secure electrical and thermal energy, at the same time as solving the waste management problem. Therefore, the feasibility of an AD plant, like the estimated in [49], is compared against the other suitable RE resources in the next section.
33 5 SIZING AND SELECTING A FEASIBLE RENEWABLE ENERGY SCHEME IN ALDERNEY After introduced the different RE systems and their suitability in the case study of Alderney, for the chosen RE schemes (solar PV, onshore wind, tidal, geothermal power and AD) a rough estimation of their cost of energy, reliability and environmental impact is carried out. Then, based on those estimations, a feasible combination of these REs is chosen to supply the electricity in Alderney in an affordable, sustainable and reliable way. In terms of cost, the RE are compared with its different Levelised Cost Of Energy (LCOE) which is estimated based on previous studies and extrapolating the results as accurate as possible in the Alderney case study. The LCOE is a parameter used in the industry to compare the cost of electricity produced by different generation systems. The LCOE takes into account all the systems' lifetime costs like construction, fuel and maintenance among others and divide them per the lifetime power output. Furthermore, two more parameters as the lifespan and the capacity factor of the system are assessed. In terms of reliability, the RE are compared by system and output reliability. The system reliability takes into account the number and how often the system fails. In the case of the output reliability analysis the output fluctuations depend on external parameters as well as the requirements for an EES. Finally, the different RE systems are compared in terms of Green House Gas (GHG) emissions as well as their positive and negative impact to the surrounding environment. Despite it not being required since Alderney is not a member of the EU, an environmental assessment of RE [27] was carried out to protect Alderney's environment. That report realizes an exhaustive Environmental Impact Assessment focused on marine and onshore wind energy which identifies the different stressors with possible cumulative effects to the Alderney's receptors and proposes some mitigation works [27]. As recommended by AEL, the RE system should not be oversized due to the batteries that can be charged from the current diesel generators easily as well
34 as these generators can supply the gap between the RE production and the demand during peak times. 5.1 Solar The fundamental components of a solar PV park are the PV cells. These are arranged in parallel as modules to increase the current and then in series as panels to have enough high voltage for the inverters. The inverters are responsible to convert the DC power generated by the PV panel to AC power that can be fed back to the grid or consumed. In addition to these components, a solar PV installation could require other power converters as transformers and choppers in order to adjust some magnitudes as well as the active and reactive power [28]. In terms of solar cell technologies, there are different options in function of the material and structure. The most common material is silicon which can be crystallised as a single or several crystals or not crystallised as amorphous silicon. Single crystal silicon cells have the higher standard efficiency and the higher costs, followed by polycrystalline and amorphous silicon. As alternatives to silicon cells, new technologies as CIS, CIGS and CdTe has been developed with generally lower cost, efficiency and lifespan than the crystalline silicon ones [28]. The following table displays a summary of the different solar PV technologies.
35 Table 5-A: Characteristics of the different available solar PV technologies [28] Based on the information described above in terms of cost, efficiency, lifespan as well as technology maturity, performance degradation, available data, energy pay-back and global warming potential [50] [51]; polycrystalline silicon cells are chosen for this study. Furthermore, in order to estimate further the electricity output of the solar PV park a panel of 230Wp of peak power is selected from the available standard solar cells [52]. The chosen solar cells will be installed on a mounting system which can be fixed to the ground or allow the movement by a single or dual axis solar tracker in order to optimize the panel position daily and seasonally as a function of the solar radiation. Then, an estimation of the electricity production in Alderney for the fixed mounted structure with optimum slope, vertical axis solar tracker and dual axis solar tracker scenario is carried out with the following results: Monthly average of Global Irradiation [kWh/m2] Fixed structure 120 Vertical axis tracking 104 Inclined axis tracking 140 Dual axis solar tracker 162 Table 5-B: Monthly average global irradiation for the 4 different tracking systems [45]
42 In addition to the residents close to the farm, the consequences of these stressors affect directly to the wildlife by increasing the collision risk and indirectly by habitat disruption and displacement [69]. It is generally accepted that WTs increase the bird mortality significantly, however, several studies found that the mortality rate due to the WT is twenty times lower than fossil fuels rate [69]. The bats colonies, as the ones in Alderney, are more affected by the wind farm development with a significant increase on the mortality rate [69]. Other plants and animal species are affected during the construction, operation and decommissioning of the wind farm as well as the geological and archaeological features [71]. Moreover, the installation of WTs near airports will require a specific safety assessment because WTs can affect the safety of aircraft operations due to the produced electromagnetic interferences and the physical presence of the turbine [71] [72]. 5.3 Tidal stream As previously stated, the RE system should have the maximum reliability due to the constraints related with Alderney location. Despite tidal stream not being a mature technology, the chosen turbine should be a proven technology with a robust design which minimises the failure rate of the system. Therefore, an horizontal axis Tidal Stream Turbine (TST) is selected because of its higher reliability and the ease to predict and solve the O&M challenges. Furthermore, horizontal axis TSTs are more efficient and can harness high amounts of energy with simpler and more reliable designs than vertical axis turbines [36]. In this case, a three-bladed horizontal axis TST is chosen with a monopile structure and gravity base foundation. The rated power output of the turbine should be around 1MW at current speeds above the 2.60 m/s and it is preferred a yaw system and a fixed pitch. 5.3.1 Cost analysis In the case of a three bladed horizontal axis TST with a gravity base foundation in a remote location as the one studied on [36], it can be roughly estimated the following costs:
43 Capital cost Operational cost LCOE 0.15 £/kWh 0.001 £/kWh 0.158 £/kWh Table 5-E: LCOE, annual OPEX and output reduction for the Alderney tidal scenario [36]. It can be highlighted that the 63% of the CAPEX comes from the cost of the support system and the turbine as well as that 62% of the OPEX is planned [36]. 5.3.2 Reliability analysis Tidal current cycles and their current velocity are very predictable and therefore the power output of the Tidal Stream Turbine (TST). Despite this very reliable power output, a single TST can not supply the electricity demand of Alderney due to the low current periods along the flood-ebb and spring-neap cycles as well as the down time caused by a component failure. In spite of tidal stream technology using proven technology from the wind energy, the extreme loads and conditions of the harsh subsea environment can lead to higher failure rates. Because of the poor reliability data available from TST, the failure rates are predicted based on the previous experience from WT. In that case the most vulnerable subsystems are the ones with moving parts and electrical and hydraulic systems as the generator, rotor blades and the yaw control. Furthermore, it is estimated for different TST subassembly possibilities a failure rate range from 1.5 to 2 times higher than WT of similar size [73]. Apart of higher failure rate than WT, the downtime related with those failures will be higher as a result of the weather conditions which make the access to the site, the transport, installation and O&M. 5.3.3 Environmental analysis The development of a TST affects the surrounding environment by means of different stressors along the installation, transport, operation and decommissioning [27]. One of the most important stressor is the underwater acoustic emissions generated by the TST, the required ship and seismic surveys which can produce loss of hearing in animals and influencing their behaviour. The physical presence of the device alters the seabed, food
44 availability, predation and reproduction patterns by becoming an artificial reef which will increase the habitat and the predators and the consequently risk of collision [74]. Other stressors related with the TST development are the energy removal effects on the sediment erosion, chemicals released by anti-fouling paints and the fuel of ships or the electric and magnetic fields generated by the cables and the device [74] [75]. These stressors can affect several environmental receptors that are presented and some protected in Alderney as fishes, marine birds, marine mammals and the benthic and pelagic habitat [10] [27] [74] [75]. As a low carbon energy, the generation of electricity from currents contributes to reduce the GHG emissions compared to fossil fuels and other energy schemes with a full life cycle mean GHG emissions of 15g CO2-eq/kWh [61]. 5.4 AD As stated before, the AD plant discussed in this report is based on that proposed on [49]. In this example, the AD plant uses as a main feedstock clean wood chip apart of typical farm materials and "blag bag waste" to produce 1.5 - 2MW and the associated heat [49]. An annual supply of 12,000 tonnes of wood is estimated for Alderney that can be transported via Southampton to the island through 20ft containers with 10 tonnes [15]. 5.4.1 Cost analysis In terms of costs, it can be extracted different estimations based on EU experience and adapting them to the Alderney scenario. In this case, the following cost and revenues are estimated based on the formulas presented in [76]: CAPEX (€) OPEX (€/ton) Revenue (€/ton) 155,455 3,828 19.7 Table 5-F: CAPEX, OPEX and revenue for the Alderney's AD scenario
45 Regarding the LCOE, selecting that the Alderney plant will have high substrate cost (high fuel costs) and it will work 7,000 h/year at full load, it is obtained a LCOE between 0.18 - 0.20 €/kWh [53]. 5.4.2 Reliability analysis The production of power from biomass through biogas has a steady and reliable output along the approximately 30 years of lifespan [67]. However, the production of biogas depends on the feedstock mix and it can affect the electrical output. Despite this, the output variance is not as high as in the case of solar PV, onshore wind and tidal stream. In terms of plant availability, it can be learnt from experience that high availability can be achieved as 98% (without taking into account the planned maintenance) along 16 years [77]. Moreover, the plant's annual availability can be around 90% due to routine maintenance [77] [78]. However, in the Alderney case study is estimated a worse scenario with higher down times due to the limited access to the island and the lack of spare parts and skilled personnel. 5.4.3 Environmental analysis The development of an AD has several impacts to the environment which can be different as a function of the employed feedstock, the kind of fuel that the biogas substitutes and the use of the digestate which can be used as fertilizer. Regarding the GHG emissions, some studies have considered that biomass plants are carbon neutral due to the produced GHG having the same amount that the plants and trees have captured before from the atmosphere [61]. However, AD with wood chips feedstock are estimated to have between 54 - 108 gCO2eq/kWh [61]. In addition, AD have a beneficial impact to the environment because the use of waste as a feedstock allows to reduce or eliminate the GHG emissions related with landfill practices which are around 90gCO2eq/kWh over a 25 year lifespan [39]. Furthermore, the reutilization of the digestate solid will reduce the consumption of toxic fertilizer in the agriculture.
46 5.5 Proposed locations to host RE developments in Alderney Before deciding which are the most suitable RE systems for the Alderney case study, the different possible locations to host those systems should be analysed. This selection takes into account as realistic as possible the area, network and environmental constraints as well as the current infrastructure. In the case of the solar PV park, this could be located in many of the fields around the island. Especially, this assessment is focused on the fields surrounding the airport due to its height, no shadowing, the grid connection point as well as the current low usage of this area. Picture 5-B: Surrounding fields to the airport Regarding the WT farm, one of the best location could be in the south-west of the island where 4 gun emplacement from the World War II could be used as a foundation. In addition, this area is located out of the airplanes landing and take-off area and it is an area without infrastructure interference. Picture 5-C: Proposed South-West WT location
47 However, this area has to be refused due to environmental constraints because it is situated in front of the les Etacs Ramsar site where live Gannet colonies [79]. Picture 5-D: Views of les Etacs and the Gannet colony from the proposed WT location An alternative could be on the breakwater but there will be problems with the foundation of the WTs [79]. Finally, a field area on the middle of the island is selected as the most suitable due to the high wind on that area meanwhile not interfering with the flight path neither with the environmental constraints. The main drawback is the proximity to residential areas, which requires a deeper visual impact of the WTs. Picture 5-E: Finally recommended location for the WT In the case of the TST, the optimum location should meet the following requirements [36] [80]: Fast flowing water, mean spring peak higher than 2 m/s. A water depth above the 15m at low tide and no more than 40 or 50m at high tide. Uniform seabed to minimise the turbulence.
48 As close as possible to an onshore grid connection point. Should affect as low as possible the environment and any protected areas. Should not disturb the activities developed by other stakeholders and sea users as fishing zones, shipping lines and local communities. However, it has to bear in mind that ARE owns the 50% more suitable blocks of the Alderney's seabed. Between the four possible locations selected on [4] to exploit economically the tidal stream resources, the north eastern part of the Swinge area is chosen due to the other three being exploited by ARE. In addition, this area is very close to the power station and a grid point connection. The characteristics of this site are a water depth up to 45m and a mean spring tidal currents of 2.2 m/s [4]. However, before the deployment of any tidal device on that area should be analysed the impact on the sand banks due to AWT predicting some sedimentation problems in the Swinge area [79]. Picture 5-F: View of the Swinge area, proposed location for tidal stream array Finally, the AD could be located in different sites of the island such as the northeast area in the Mannez Quarry close to the old train station and the light house. The main problem of that area is the space availability because currently there is the green waste disposal and the converter station of the FAB link should be located on that area.
49 Picture 5-G: Mannez quarry, proposed location for the AD Another probable location for an AD could be the recycle station just in front of the power station. This location has many benefits like its proximity to the port which will ease the transportation and storage of the clean wood chip as well as the digestate solids to be sold as fertilizer. Furthermore, this location close to the power plant, the hospital, the fire station, the port and some residential areas will permit the use of the produced heat in the AD to be used as a district heating. Picture 5-H: View of the recycling centre from the power plant, proposed location for the AD As a summary, an Alderney map with the different proposed locations is displayed below.
50 Figure 5-C: Different proposed locations in Alderney to harness RE 5.6 Conclusions: Proposed RE system for the Alderney case study The following table summarises the different RE assessed previously in order to select the most suitable mix for the Alderney case study. Solar PV Onshore Wind Tidal stream AD LCOE (€/kWh) 0.079-0.098 0.084 - 0.107 0.223 0.18 - 0.20 Lifespan (years) 20 - 25 20 25 25 Capacity factor (%) 20 30 20 80 Output reliability /EES requirement Very high (day/ night fluctuations) High Very high Low System reliability/failures Medium High Very high Low Environmental impact Medium Negative Negative Positive GHG emissions (g CO2-eq·kWh1) 78.7 - 91.1 34 15 90 Other requirements Harsh environment and O&M difficulties Waste management benefit and saving Table 5-G: Summary of the characteristics of the RE analysed
51 In order to make the decision easier, the different parameters are arranged as a function of the priority from the highest, LCOE, to the lowest priority, GHG emissions. Moreover, a colour-coded criteria is used to facilitate the decision taking, where the dark green is the best one and the dark red is the worst one. Solar PV Onshore Wind Tidal Stream AD LCOE System reliability Environmental impact Lifespan Capacity factor Output reliability GHG emissions Figure 5-D: Characteristics of the RE As stated before, a mix of RE is selected in order to avoid the energy dependence on one source as a function of the different priorities which can change depending on the assessment preferences. In this case, the main RE system chosen is an AD with a capacity of 1.5MW which uses clean wood chips as a main feedstock and it will have occupy 5.25 acre [81]. The main benefits of this system are the low output fluctuations, the high reliability and maturity compared to other RE systems. Furthermore, using part of the organic waste as feedstock will reduce the waste disposal cost that in the case of Alderney is approximately £500k per year [15]. Despite that benefit, this analysis is considering a constant feedstock of only clean wood chip without other components in order to approximate better the biogas production and electricity output [42] [43] [44]. The relative high cost of energy could be decreased by using the outputs of the AD apart from the biogas and getting some revenue. For example, the remaining digestate rich in phosphate is generally exported as fertiliser to EU countries with a phosphate deficiency [82]. In addition to this agricultural use, the digestate can be employed as livestock bedding, compost, fuel pellets, and construction material [83]. Moreover, the produced heat can be utilised within the plant to improve the AD efficiency or exported outside [82].
58 5,000$/kWh)-Lower maintenance cost -Monthly self-discharge (>20%) -Mature technology discharge -Higher costs than other proven BESS Ni metal hydride (NiMH) Bridging Idem as NiCd BESS except -Power rating (900W/kg) -Improved efficiency -Lifespan (1,500 cycles) -Monthly self-discharge (>30%) -More environmental friendly -Very high selfdischarge (inefficient for long-term energy storage) Zn-air BESS Bridging -RTE (50%) -Costs (up to 200 €/kWh) -Low lifespan (100 cycles) 450–650 Wh/kg - Negligible self-discharge -Difficulties to recharge efficiently - Low lifespan and efficiency Flow Batteries Energy Storage Energy & Power Different types: zinc (ZnBr), sodium (NaBr) and Vanadium (VBr). -Power rating (up to 25MW) -Quick response time -Discharge duration (hrs) -RTE (60 - 80%) -Long lifespan (1,000 - 13,000 cycles) -Mature technology -Costs (up to 800$/kWh) -Negligible self-discharge -Increased capital and running cost due to the necessity of a chemical plant. -Low power density Table 6-B: Discarded EES technologies based on [19] [88] [89] [90] [91] [92] [93] To sum up this general assessment, some of the most common EES technologies have been discarded in this analysis due to the author of the report deciding based on the available information and their main characteristics that they are not the most suitable one for the Alderney case study. However, as stated previously, there is not an optimum solution for the Alderney energy challenge and this challenge can be achieved by using other EES. For example,
59 ARE was working on the possible development of a tidal PHES in Fort Albert by means of the construction of a 6m high tank of 50,000 m3 filled by sea water [94]. Picture 6-A: Current image of the forth Albert's inside Despite this could be a viable solution for the Alderney scenario, this report is more focused on smaller and more efficient EES options as Lead-acid BESS, Li-ion BESS and NaS BESS. 6.2 Characteristics and selection of the most suitable EES technologies Finally the following EES are the ones selected as the most suitable for the Alderney case study. EES Technology Application Characteristics Lead-acid BESS Bridging -Quick response time (ms) -Power rating (up to 10MW with peak power 700W/kg) -Energy density (30 - 50 Wh/kg) -Discharge duration (min-hrs) -Charge duration (between 8 to 16hours) -RTE (75%) -Lifespan (200 - 300 cycles with 80% discharge) -Monthly self-discharge (5%) -Maintenance required approximately every 6 months -Mature technology
60 Li-ion BESS Bridging -Quick response time (ms) -Power rating (up to 10MW with peak power between 500 - 1,000W/kg) -Highest energy density (100 - 200 Wh/kg) -Discharge duration (min-hrs) -Charge duration (<4h, usually around 1h or less) -RTE (almost 100%) -Lifespan (500 - 200 cycles with 80% discharge) -Monthly self-discharge (<10%) -Maintenance not required -Commercial technology NaS BESS Energy & Power -Quick response time (ms) -Power rating (up to 10MW) -Energy density (100Wh/kg) -Longer discharge duration (hrs) -Longer charge duration (hrs) -RTE (89%) -Lifespan (2,500 cycles at 100% discharge) -Negligible self-discharge -Minimal planned maintenance -Operating temperature around 325ºC -Mature technology Table 6-C: Summary of the most suitable EES technologies for the Alderney's scenario [19] [88] [89] [90] [91] [92] [93] [95] Li-ion BESS is the leader in portable electronic devices and now it is taking a share in the RE's EES market. Thanks to its higher efficiency and high energy density [90]. Despite the maturity in this sector, Li-ion BESS are an unproven technology for long term applications with power ratings of MWs. Furthermore, the deployment of Li-ion BESS requires a precise control of the charge management as well as a high investment [90]. As a result, in this assessment it is discarded but it has to be stated that in the upcoming years Li-ion batteries will be employed for this functions due to the several technology developments [90]. Lead-acid BESS are the oldest chemical energy storage and nowadays they are still used in several isolated systems as detailed in [19]. Furthermore, this study suggest that lead-acid BESS are the most suitable for isolated systems with rating lower than 5MW and discharges up to 12h. However, in this report
61 lead-acid are discarded due to the limited lifespan, high failure rate with continuous cycling and the required O&M [90]. Therefore, a 1MW (6MWh) NaS BESS are suggested as the most suitable technology for the Alderney scenario due to the following advantages: NaS BESS Advantages Most widely deployed BESS with 182 projects (316MW) [89] and consequently it is a mature technology particularly for grid-scale and RE integration functions [96]. Better discharge duration, lifetime, efficiency and minimal maintenance as well as more suitable for energy management [92]. Similar €/kWh than lead-acid BESS but better costs per charge-discharge cycle [92]. Disadvantages Over dimensioned due to this technology can support loads higher than 50 MW and discharge times up to 24h [19] [96]. Hazards due to the operation temperature (over 300ºC) and the spontaneity to burn with air and moisture of Na [88] [90]. Table 6-D: Advantages and disadvantages of NaS BESS As a conclusion, it can be stated that NaS BESS have several economic benefits compared to the lead-acid BESS specially in the cost per charge cycle and lifecycle cost due to their longer lifespan and durability as well as higher availability. Moreover, NaS BESS are more reliable because of the technology maturity and experience as well as the minimal maintenance. As a chemical storage, despite that during the operation the environment is slightly affected by the heat generated from the internal and isolated heaters, the disposal of the electrodes and electrolytes will have an important footprint in the environment. However, because of the higher energy density, the impact of this development affects a smaller area.
62 7 FEASIBILITY OF SUPPLYING THE ELECTRICITY FROM RE IN ALDERNEY Once the selected the energy system of 1,5MW AD, 475kW solar PV park and 1MW NaS BESS, the technical feasibility of the scenario is assessed as detailed in the Appendix C. The inputs of this analysis are the energy demand, the solar irradiation and the amount of clean wood chip. Regarding the energy demand used the weekly energy produced in 2014 supplied by the AEL. Then, the demand every half an hour is calculated through a weekly average demand of the month. By assuming that the daily demand is independent from the weekday as well as the hourly distribution is the same along the year. In the case of the solar PV park, the electricity output is calculated every 30 minutes and it takes into account the GHI for a daily sample of each month. In addition, different losses are considered such as PV degradation, temperature losses, inverter losses, availability and grid connection losses among others. For the AD scenario, the electricity output depends on the amount of clean wood chip as well as the conversion efficiency of organic fraction to biogas, the methane production per kg of biogas, the calorific values and the conversion efficiency to electricity. The electricity output is supposed to be constant along the year with a capacity factor of 80%. Finally, it is assumed that the energy accumulated on the NaS batteries at the beginning of the month is always constant and equal to half of its capacity, 3000kWh. In addition, if the energy level on the batteries is lower than 600 kWh the 450 kW diesel generator will start running at full capacity 30 minutes later. In order to make the use of the generator more efficient, once the generator is started it will continue until the energy on the batteries is higher than 3000 kWh. Taking into account these considerations, as explained with more detail in the Appendix C, the results of this scenario are the following ones:
63 In the case of the solar PV park, the electricity output is calculated every 30 minutes and it takes into account the GHI for a daily sample of each month. In addition, different losses are considered such as PV degradation, temperature losses, inverter losses, availability and grid connection losses among others. For the AD scenario, the electricity output depends on the amount of clean wood chip as well as the conversion efficient of organic fraction to biogas, the methane production per kg of biogas, the calorific values and the conversion efficiency to electricity. The electricity output is supposed constant along the year with a capacity factor of 80%. Taking into account these considerations, as explained with more detail in the Appendix C, the results of this scenario are the following ones: Table 7-A: Summary of the results obtained in the Appendix C for the scenario 1 Hence, based on this analysis, it can be concluded that this scenario is technologically feasible. However, taking into account that no diesel is required as well as the high level of energy storage capacity, this system could be optimised. Therefore, a second scenario with lower clean wood chip fuel is assessed. In this case, a 1MW AD which uses 8,000tn of clean wood chip as feedstock is analysed in the same way as the previous case. The following results are obtained taking the same considerations as before: Scenario 1 Fuel 12,000 tones clean wood chip Batteries usage 20,400 kWh (9% of the total demand) Batteries working time 54% of time Batteries energy storage level 68% of the full capacity Saving compared to the current scenario 1,867,112L of diesel (741k GBP) Extracost compared to the current scenario 12,000 tn of wood chip and BESS investment
64 Scenario 2 Fuel 8,000tn clean wood chip and 14,005 L of diesel Batteries usage 45,639 kWh (21% of the total demand) Batteries working time 59% of time Diesel generator usage 54,900 kWh (25% of the total demand) Diesel generator working time 22% Saving compared to the current scenario 1,853,107 L of diesel (736k GBP) Extracost compared to the current scenario 8,000 tn of wood chip and BESS investment Table 7-B: Summary of the results obtained in the Appendix C for the scenario 2 In the feasibility analysis of this scenario, diesel supply is required to meet the electricity demand and usually the diesel generator works around 5 hours every 24 hours. However, more diesel supply will be necessary especially during the months of higher energy demand such as January, February, August, November and December due to at the end of the day the energy storage level on the batteries is quite low compared to the initial one. This scenario with a mix of fuels could be an intermediate stage of the change from the current situation to the scenario 1 RE system.
65 8 CONCLUSIONS 8.1 Required grid improvements and funding strategies As stated before, the current Alderney electric grid requires several upgrades in order to fulfil with the current health and safety standards as well as to improve the energy security of supply. Apart from these improvements, the proposed scenario of RE with EES needs further updates as the installation of high voltage cable at least in the area affected by this development. Therefore, an important budget is required to fund all these improvements. The accelerated programme to update the Alderney's electrical grid is scheduled in different phases to ease the funding mechanism. Following the different funding strategies under study for the Alderney accelerated programme are introduced [17] [18]: Philanthropic donation. 3rd party investment or loan. Revenue funding which will lead to a 15-20% price increase. Lease funding between AEL and SoA. Offering new shares to shareholders. Grant funding from SoA. SoA purchase the network and at the end of the project own the assets. AEL borrow the money and improve the network while SoA pay back the money and the interest (5%). At the end of the project SoA will own the assets and SoA will grant AEL to operate it. So far, AEL is looking the last option as the preferable one for funding the accelerated programme. Regarding the funding strategy for a RE system in Alderney, the different options should be very similar to the previous ones. Specially, it has to be highlighted the probable predisposition of the SoA to invest in infrastructure, with short-medium return period, and grant AEL to operate it [9]. In addition, there is a very interesting funding alternative which is developing the project as a community owned and operated system. There are several examples of
66 Community Owned Renewable Energy (CORE) projects around the World particularly in European countries such as Denmark and Germany where CORE represents a big share of the energy market [97]. Examples of CORE systems around the World can be found in the following literature [1] [2] [6] [97] [98] [99] [100] [101] [102] [103] [104] [105] [106] [107] [108] [109] [110] [111] [112]. In the UK, CORE developments have been growing very fast and in 2012 there were 43 CORE planned, underdevelopment or constructed [105]. This report wants to highlight some examples of Green Islands with CORE projects as the isle of Eigg in Scotland and Samso in Denmark. The isle of Eigg through the community owned company Eigg Electric became the first standalone energy system in the World with a production from RE higher than 90% [2] [104]. In this Scottish small island, the electricity is supplied from three hydroelectric generators, four small WT and a small PV array [2]. Regarding the Samso example, the power capacity of the CORE developments is higher and they are connected to the Danish mainland. In this case there are installed 10 offshore WTs, 11 onshore WTs and 4 district heating systems [1]. As a result, the community since 2007 is selling electricity to mainland grid [98]. From these two experiences and other CORE, it can be extracted the main benefits of CORE systems: Community benefits Educational benefits as awareness of the technology to invest and the environmental benefits for the community. Promotion of stronger and healthier communities by working together to achieve one goal. Public acceptance by involving the citizens in the decisions. Promotion of using efficiently the energy. Creation by the developer of small scale community initiatives in the CORE area as playgrounds, trails and buildings among others As owners of the system, the financial benefits stay in the community. Environmental benefits Reduction of the GHG emissions and the climate change effects Local economy benefits Creation of new jobs during the construction and maintenance. Harnessing residents’ skills.
67 Table 8-A: Benefits of CORE systems [1] [6] [102] [103] [112] Coming back to the Alderney case study, there are different ways to achieve a CORE project. Firstly it should be promoted among the community and create an awareness of the benefits of RE for the community. Moreover, a group within the community should be proposed to represent them in front of companies and institutions as well as to manage the energy system. As operator of the energy system, the community will require technical knowledge and capacities to manage properly the system that could be provided through collaborating with the AEL. In addition, this community involvement can lead to other CORE projects to power other energy systems such as the heating and transportation ones. Furthermore, an awareness of the energy consumption can benefit the community by promoting energy efficiency, improving the buildings insulation or decreasing the electricity consumption. 8.2 Economic, environmental and reliability assessment of other fuels and energy scenarios After the RE and EES assessment and selection for the Alderney case study, it is compared as a conclusion the chosen energy system which uses clean wood chips and solar irradiation as a fuel with three different scenarios: the current one using diesel fuel, adding a EES to the current situation and one buying hydrogen and using it as an energy fuel. In the first scenario there is an important dependency on diesel and the related cost fluctuation and uncertainties. Despite the current relative low cost of fuel, it is expected to increase again in the following years and hence the Alderney cost of energy. Nowadays the LCOE with that system is around 33.5 p/kWh which the major part of the cost is independent of the oil price. It can be highlighted that nowadays the fuel cost is around 0.397 GBP/L and its average storage cost is 8k GBP/year. In addition, there are expensive major maintenances for the Paxman generators which have to be realized outside the island, every 30,000 engine hours. Furthermore, it is important to bear in mind that with the current scenario in 2020 2 Blackstones generators will be retired
74 highlighted the community benefits of CORE systems. Apart from that, another option to promote the active participation of the community in the energy system could be linking a representative group to the AEL as shareholders or consultants. That community involvement and the related energy awareness are key factors for the future energy developments in Alderney. This could lead to reducing the energy demand by improving the building insulations and the appliance efficiencies. In addition, with this community participation, the arduous goal of converting Alderney into a Green Island will be much easier to achieve. In conclusion, Alderney is a small community but big enough to lead a worldwide change and become more energy sufficient and sustainable. The island offers different RE resources to be harnessed and the community and the responsible institutions should take this opportunity, which has not been taken in the past, before it is too late. Maybe the upcoming CAPEX investment in a new generator by 2020 could be the trigger to start investing and promoting other energy systems. As discussed as part of this paper, the Alderney's electrical system can be improved with minor changes to the current system such as optimising the diesel transport, using the generated heating or adapting the generators to the current demand which is more suitable for Blackstones than Paxman generators. Alternatively to those small and beneficial changes, major developments can be done such as powering the electrical system through RE resources as well as the transportation and heating systems. However, these developments are very difficult and there is not an instant change. In this paper a technical and technological feasible RE system, based on clean wood chip and solar energy fuel with NaS batteries, is proposed which should be the first stage to change Alderney into a Green Island. In order to assure the electrical generation with energy sufficiency and no diesel dependency, different transitory scenarios should exist where the energy generation is not the most efficient one but the experience gained of that time will facilitate the optimum dimensioning of the RE system and its batteries. In this case, two scenarios has been suggested to facilitate the migration to a fuel that will be price stable, more sustainable and reliable for the foreseeable future.
75 9 FURTHER WORK The time and word constraints do not allow the author of this thesis to assess as detailed as desired the Alderney case study. Hence, several points can be improved in further analysis such as the LCOE estimations that can be based on real data provided by suppliers for this special case instead of previous studies adapted in the Alderney scenario. In that case, more accurate efficiencies, capacity factors and power outputs could be extracted. For the feasibility study, more precise and real data and simulations will optimise the capacities of the RE, EES and diesel back-up system. Moreover, the evolution of some parameters such as the weather conditions, demographic characteristics and energy demand has to be assessed and forecasted. This is because they influence the inputs and hence, the design requirements of the energy system. In addition, the fuel comparison can be improved by analysing deeper the different scenarios in order to ease the selection as a function of the main priorities. Especially, those fuels that can supply energy to the electricity, heat and transportation systems at the same time that energy independence such as hydrogen and biogas. In the case of the biogas and methane generation, the possibility of using other feedstock with higher biogas yield as suggested in [6] [42] as well as other generation process like gasification and pyrolysis could be analysed in order to find the most cost-efficient, energy independent and reliable solution. Other RE resources, especially wind and tidal, should be analysed deeper to determine their feasibility in Alderney as well as other EES systems like Li-ion BESS whose technology had several improvements in the last months. As stated in the conclusions, a RE system is technically and technological feasible to supply the Alderney's electricity demand. However, some roadblocks have to be sorted out to achieve that goal. One of them is the inclusion in the legislation of an Environmental Impact Assessment framework taking into account the environmental and socioeconomic characteristics for Alderney in order to assure the sustainability of the upcoming developments [79]. Another roadblock is the socioeconomic constraint, which has to be assessed deeper to
76 propose a strategy to involve more in this important change either the community, the government and other institutions and companies. This plan should comprise different actions such as a promotion, education and training schedule into the local community, a financial analysis of the required expenditure, assessment of possible financial support from the governments and the expected revenues and return period of the project. Furthermore, the current RE policy framework could be analysed and improvements proposed to promote community developments in Alderney and other Channel Islands. Converting the Alderney's electrical system into a more sustainable and reliable network by introducing RE fuels is the starting point of a more ambitious goal that is Alderney becoming a Green Island. Therefore, a further analysis of the transportation and heating system as well as different energy reduction actions has to be done in order to propose a sustainable energy system for Alderney aligned with the electricity developments. These developments are not easy and an integration plan should be defined. Hence, different stages should be developed in order to assure that the Alderney's energy demand is met by the different fuel combinations at any time. This is a difficult and long term project, but the community of Alderney has the opportunity to use its fantastic RE resources to lead a worldwide change and they should take it.
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90 A.1.2 Energy Data In terms of energy demand, along the week 7 there was a total energy consumption of 130,590 kWh with a daily average of 18,655.71 kWh. The energy evolution along the week is the following one with a maximum demand of 660 kWh and a minimum of 341.8 kWh: Graph 11-B: Energy evolution along the W7 A.2 Week 18 Energy Analysis During the week 18, there was a diesel fuel consumption of 34,562 L with a daily average of 4,937 L and an efficiency of 3.52 kWh/L. The power and energy evolution were the following ones. A.2.1 Power Data In terms of power week 18 had a peak of 1,028 kW and a minimum power of 428 kW. The evolution along the week is the following one: 0 100 200 300 400 500 600 700 800 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 Energy kWh Energy W7
91 Graph 11-C: Power evolution along the W18 A.2.2 Energy Data In terms of energy demand, along the week 18 there was a total energy consumption of 121,530 kWh with a daily average of 17,361 kWh. The energy evolution along the week is the following one with a maximum demand of 560 kWh and a minimum of 150 kWh: Graph 11-D: Energy evolution along the W18 0 200 400 600 800 1000 1200 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 Power [kW] Power W18 0 100 200 300 400 500 600 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 Energy [kWh] Energy W18
92 A.3 Week 32 Energy Analysis During the week 32, there was a diesel fuel consumption of 39,766 L with a daily average of 5,681 L and an efficiency of 3.60 kWh/L. The power and energy evolution were the following ones. A.3.1 Power Data In terms of power week 32 had a peak of 1,204 kW and a minimum power of 495 kW. The evolution along the week is the following one: Graph 11-E: Power evolution along the W32 A.3.2 Energy Data In terms of energy demand, along the week 32 there was a total energy consumption of 143,180 kWh with a daily average of 20,454 kWh. The energy evolution along the week is the following one with a maximum demand of 820 kWh and a minimum of 180 kWh: 0 200 400 600 800 1000 1200 1400 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 Power [kW] Power W32
93 Graph 11-F: Energy evolution along the W32 A.4 Week 43 Energy Analysis During the week 43, there was a diesel fuel consumption of 35,419 L with a daily average of 5,060 L and an efficiency of 3.53 kWh/L. The power and energy evolution were the following ones. A.4.1 Power Data In terms of power week 43 had a peak of 1,193 kW and a minimum power of 433 kW. The evolution along the week is the following one: Graph 11-G: Power evolution along the W43 0 100 200 300 400 500 600 700 800 900 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 Energy [kWh] Energy W32 0 200 400 600 800 1000 1200 1400 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 Power [kW] Power W43
94 A.4.2 Energy Data In terms of energy demand, along the week 43 there was a total energy consumption of 124,900 kWh with a daily average of 17,843 kWh. The energy evolution along the week is the following one with a maximum demand of 850 kWh and a minimum of 120 kWh: Graph 11-H: Energy evolution along the W43 A.5 Summary and Seasonally Comparison Finally, an average day per week is calculated in order to compare the power and energy between seasons. As it can be seen in the following figures, the energy and power demand are very similar along the different weeks with slightly higher values during the Alderney Week (W32) and the winter weeks. 0 100 200 300 400 500 600 700 800 900 0:00 0:00 0:00 0:00 0:00 0:00 0:00 0:00 Energy [kWh] Energy W43
95 Graph 11-I: Power evolution along a day Graph 11-J: Power evolution along a day 400 500 600 700 800 900 1000 1100 1200 1300 0:00 6:00 12:00 18:00 0:00 Power demand [kW] Power demand evolution W7 W18 W32 W43 125 225 325 425 525 625 725 0:00 6:00 12:00 18:00 0:00 Energy demand [kWh] Energy demand evolution W7 W18 W32 W43
96 Appendix B : Dimensioning the Solar PV Park and Wind Farm In this annex, the dimensions of the proposed solar PV park and wind farm are estimated. In the case of the solar PV park, the dimensions are estimated as follows by selecting a standard 230W PV panel [52] and fixing the rated power output of the park at 475 kW. As a result of these assumptions, it is estimated that should be necessary 2065 panels of 1.632x0.995 m [52] which require a total area of PV panels of 3,353.58 m2. However, it is estimated a real area of 1.6 times the panels area due to inclination losses, distance between panels and perimeter fences. Hence, the solar PV park will require 5,366 m2 of area which in the example was divided approximately in a rectangle of 160x35 m. Regarding the wind farm and turbine dimensions, firstly it is assumed a measured wind at 10m height of 13 knots [46] with an air density of 1.225 kg/m3, equivalent to an air temperature of 15ºC. Then, the hub height of the turbine is fixed by selecting a WT of 34m hub height and 34m of rotor diameter [85]. The selection of the turbine characteristics is realized by trying to minimise as possible the visual impact to the surrounding areas while having a costefficient energy output. Once fixed these parameters, a hub height velocity of 11 m/s is estimated by using the log law with a terrain parameter of 1.5 (equivalent to suburbs and small town areas) [86]. Equation 11-A: Log law equation Then, a rated power of 250 kW is obtained by using the hub height velocity in the power curve of the selected turbine.
97 Figure 11-A: Power curve of the T400-34 In addition, a power coefficient of 0.337 is estimated through calculating the total power in the wind at 11 m/s which is 741.29 kW. Equation 11-B: Total power in the wind Equation 11-C: Swept area of a WT Finally, two WTs are proposed which can supply 250 kW each at the average hub height of 11m/s. A separation of 136m (4 turbine's diameter) is estimated in the perpendicular direction to the prevailing wind [87].
98 Appendix C : Feasibility Analysis As explained along the paper, this feasibility analysis compares the energy produced by the RE systems against the energy demand in order to determine the storage level in the NaS batteries as well as the necessity of diesel. In this annex, first it will be detailed how the inputs of the assessment are calculated and then the detailed analysis for the different months and scenarios. C.1 Energy demand calculation The energy demand estimations are based on data supplied by the AEL such as the energy demand of all the weeks along the 2014 and the daily demand for 4 different weeks during 2014 and 2015. From the first document, the different weeks are arranged according to the calendar in the 12 months in order to get an average weekly and daily demand per month as follows: Week Energy demand[kWh] Weekly average energy [kWh] Daily average energy [kWh] 1 138,010 133,561 19,080 2 131,040 3 131,690 4 132,340 5 134,723 6 134,190 132,490 18,927 7 134,560 8 131,140 9 130,070 10 127,440 126,748 18,107 11 128,170 12 127,600 13 125,380 14 125,151 15 122,880 122,885 17,555 16 122,940 17 123,760 18 121,960 19 121,290 121,715 17,388 20 118,050 21 123,310 22 124,210
99 Week Energy demand[kWh] Weekly average energy [kWh] Daily average energy [kWh] 23 121,250 120,790 17,256 24 120,159 25 121,052 26 120,700 27 123,826 127,763 18,252 28 123,694 29 125,922 30 128,629 31 136,746 32 143,520 135,571 19,367 33 137,690 34 130,580 35 130,495 36 125,753 123,877 17,697 37 122,616 38 124,440 39 122,698 40 118,878 122,992 17,570 41 120,650 42 123,567 43 126,693 44 125,170 45 127,560 128,930 18,419 46 127,550 47 130,240 48 130,370 49 139,010 136,815 19,545 50 137,790 51 138,400 52 132,060 Table 11-A: Energy demand during the different weeks, month and a daily average Once the daily demand per month is estimated, from the detailed weekly demand, the proportion of energy consumed every half an hour is calculated for the weeks 7, 18, 32 and 43. Then, a constant average energy demand distribution along the day is chosen due to the similarities between the energy consumption per hour between the weeks as shown below.
106 C.3 Energy generation from the AD Regarding the energy generated from an AD, this will depend on the amount of clean wood chip used. In this case the 12,000 tonnes are converted to electricity by means of the following efficiencies: Conversion of organic fraction to biogas 70% Methane production (m3) per kg of biogas 0.31 m3/kg Methane calorific value 35.7 MJ/m3 Conversion efficiency to electricity 32% Table 11-E: Estimated efficiencies for the AD [39] [125] Once calculated the annually electricity production from the wood chips, the capacity factor of 80% is applied and the value divided per 365 in order to get daily production. Finally, the energy every half an hour is calculated by diving the daily per 48 and it is constant along all the hours and months. C.4 Scenario 1: AD (12,000 tonnes) and 475 kW solar PV park After explaining how the different inputs are calculated, a monthly example is displayed in the following pages where it can be seen the energy evolution along the month of January. As shown in that table, the energy storage in the batteries at the beginning of the day is half of the total energy storage capacity and in order to protect the batteries the energy stored is fixed between 200MWh and 5800MWh. In the analysis, the energy stored in the batteries increase or decrease depending on the energy produced and the energy demand.
107 Time Solar PV [kWh] AD [kWh] Energy generation [kWh] Energy demand [kWh] BESS energy [kWh] Required diesel 0:00 0.00 376.89 376.89 279 3,000 - 0:30 0.00 376.89 376.89 277 3,100 - 1:00 0.00 376.89 376.89 299 3,178 - 1:30 0.00 376.89 376.89 243 3,312 - 2:00 0.00 376.89 376.89 247 3,442 - 2:30 0.00 376.89 376.89 233 3,586 - 3:00 0.00 376.89 376.89 242 3,720 - 3:30 0.00 376.89 376.89 231 3,867 - 4:00 0.00 376.89 376.89 251 3,992 - 4:30 0.00 376.89 376.89 221 4,148 - 5:00 0.00 376.89 376.89 243 4,282 - 5:30 0.00 376.89 376.89 214 4,445 - 6:00 0.00 376.89 376.89 306 4,516 - 6:30 0.00 376.89 376.89 299 4,594 - 7:00 0.00 376.89 376.89 272 4,698 - 7:30 0.00 376.89 376.89 383 4,692 - 8:00 3.90 376.89 380.79 431 4,642 - 8:30 6.53 376.89 383.42 448 4,577 - 9:00 9.84 376.89 386.73 544 4,419 - 9:30 12.64 376.89 389.53 478 4,330 - 10:00 15.01 376.89 391.91 513 4,209 - 10:30 16.84 376.89 393.73 478 4,125 - 11:00 18.15 376.89 395.04 519 4,001 - 11:30 18.96 376.89 395.85 457 3,940 - 12:00 19.25 376.89 396.15 450 3,886 -
108 Time Solar PV [kWh] AD [kWh] Energy generation [kWh] Energy demand [kWh] BESS energy [kWh] Required diesel 12:30 18.96 376.89 395.85 531 3,750 - 13:00 18.15 376.89 395.04 537 3,608 - 13:30 16.84 376.89 393.73 424 3,577 - 14:00 15.01 376.89 391.91 460 3,510 - 14:30 12.64 376.89 389.53 420 3,479 - 15:00 9.84 376.89 386.73 465 3,401 - 15:30 6.53 376.89 383.42 474 3,310 - 16:00 2.63 376.89 379.52 415 3,274 - 16:30 0.00 376.89 376.89 401 3,250 - 17:00 0.00 376.89 376.89 448 3,180 - 17:30 0.00 376.89 376.89 407 3,149 - 18:00 0.00 376.89 376.89 644 2,882 - 18:30 0.00 376.89 376.89 546 2,713 - 19:00 0.00 376.89 376.89 446 2,644 - 19:30 0.00 376.89 376.89 495 2,526 - 20:00 0.00 376.89 376.89 514 2,389 - 20:30 0.00 376.89 376.89 430 2,336 - 21:00 0.00 376.89 376.89 465 2,248 - 21:30 0.00 376.89 376.89 468 2,158 - 22:00 0.00 376.89 376.89 419 2,115 - 22:30 0.00 376.89 376.89 423 2,069 - 23:00 0.00 376.89 376.89 352 2,094 - 23:30 0.00 376.89 376.89 336 2,134 - Table 11-F: January example of the energy management using the scenario 1
109 Once analysed all the different month, it is conclude that diesel supply is not required in this scenario and hence there is saving of 1,867,112 L of diesel and 741k GBP. In addition, a summary table is realized where appears different parameters regarding the usage of the NaS batteries. January February March April May June July kWh battery use 2629.35 2347.72 1507.82 1025.35 928.02 846.06 1388.67 %battery usage 14% 12% 8% 6% 5% 5% 8% %battery time 66% 64% 55% 43% 43% 38% 51% %battery full 0% 0% 0% 0% 0% 0% 0% %BESS energy level 58% 60% 69% 75% 77% 78% 71% August September October November December Total/ Average kWh battery use 2196.56 1179.83 1311.82 2076.59 3012.29 9777.10 %battery usage 11% 7% 7% 11% 15% 4% %battery time 64% 47% 53% 64% 66% 59% %battery full 0% 0% 0% 0% 0% 0% %BESS energy level 62% 73% 71% 63% 54% 65% Table 11-G: Scenario 1 summary table
110 C.5 Scenario 2: AD (8,000 tonnes) and 475 kW solar PV park Regarding the second scenario with 8,000 tonnes of clean wood chip, the only input that is different compared to the previous one is the amount of feedstock used which now produce 251.26 kWh. As a result, in this scenario some diesel supply will be required to meet the energy demand as well as to recharge the batteries until the energy level surpasses the initial 3,000 kWh. Following, the summary table and the January example are displayed. January February March April May June July kWh battery use 4630.37 5106.34 3456.78 2910.46 3052.63 3010.96 3418.53 %battery usage 24% 27% 19% 17% 18% 17% 19% %battery time 60% 62% 55% 57% 57% 57% 57% total kWh diesel 4950 4,050 4950 4500 4500 4050 4500 %diesel time 23% 19% 23% 21% 21% 19% 21% total L diesel 1262.7551 1033.1633 1262.7551 1147.9592 1147.9592 1033.1633 1147.9592 August September October November December Total / Average kWh battery use 4492.56 3144.26 3494.63 4330.14 4664.59 20126.18 %battery usage 23% 18% 20% 24% 24% 9% %battery time 62% 57% 57% 60% 60% 59% total kWh diesel 4500 4500 4500 4500 5400 54900 (25%) %diesel time 21% 21% 21% 21% 26% 22% total L diesel 1147.9592 1147.9592 1147.9592 1147.9592 1377.551 14005.12 Table 11-H: Scenario 2 summary table In this case 14,000 L of diesel are required with a cost around the 5,560 GBP which compare to the current scenario will suppose a saving of 1,853,107 L and 736k GBP.
111 Time Solar PV [kWh] AD [kWh] Energy generation [kWh] Energy demand [kWh] BESS energy [kWh] Required diesel [kWh] 0:00 0.00 251.26 251.26 279 3,000 0 0:30 0.00 251.26 251.26 277 2,974 0 1:00 0.00 251.26 251.26 299 2,927 0 1:30 0.00 251.26 251.26 243 2,935 0 2:00 0.00 251.26 251.26 247 2,940 0 2:30 0.00 251.26 251.26 233 2,958 0 3:00 0.00 251.26 251.26 242 2,966 0 3:30 0.00 251.26 251.26 231 2,987 0 4:00 0.00 251.26 251.26 251 2,987 0 4:30 0.00 251.26 251.26 221 3,018 0 5:00 0.00 251.26 251.26 243 3,026 0 5:30 0.00 251.26 251.26 214 3,063 0 6:00 0.00 251.26 251.26 306 3,008 0 6:30 0.00 251.26 251.26 299 2,960 0 7:00 0.00 251.26 251.26 272 2,939 0 7:30 0.00 251.26 251.26 383 2,808 0 8:00 3.90 251.26 255.16 431 2,631 0 8:30 6.53 251.26 257.79 448 2,441 0 9:00 9.84 251.26 261.10 544 2,157 0 9:30 12.64 251.26 263.90 478 1,943 0 10:00 15.01 251.26 266.27 513 1,697 0 10:30 16.84 251.26 268.10 478 1,487 0 11:00 18.15 251.26 269.41 519 1,237 0 11:30 18.96 251.26 270.22 457 1,050 0
112 Time Solar PV [kWh] AD [kWh] Energy generation [kWh] Energy demand [kWh] BESS energy [kWh] Required diesel [kWh] 12:00 19.25 251.26 270.52 450 871 0 12:30 18.96 251.26 270.22 531 610 0 13:00 18.15 251.26 269.41 537 342 0 13:30 16.84 251.26 268.10 424 636 450 14:00 15.01 251.26 266.27 460 892 450 14:30 12.64 251.26 263.90 420 1,186 450 15:00 9.84 251.26 261.10 465 1,432 450 15:30 6.53 251.26 257.79 474 1,666 450 16:00 2.63 251.26 253.89 415 1,955 450 16:30 0.00 251.26 251.26 401 2,255 450 17:00 0.00 251.26 251.26 448 2,509 450 17:30 0.00 251.26 251.26 407 2,803 450 18:00 0.00 251.26 251.26 644 2,860 450 18:30 0.00 251.26 251.26 546 3,016 450 19:00 0.00 251.26 251.26 446 2,821 0 19:30 0.00 251.26 251.26 495 2,577 0 20:00 0.00 251.26 251.26 514 2,314 0 20:30 0.00 251.26 251.26 430 2,136 0 21:00 0.00 251.26 251.26 465 1,922 0 21:30 0.00 251.26 251.26 468 1,706 0 22:00 0.00 251.26 251.26 419 1,538 0 22:30 0.00 251.26 251.26 423 1,366 0 23:00 0.00 251.26 251.26 352 1,265 0 23:30 0.00 251.26 251.26 336 1,180 0 Table 11-I: January example of the energy management using the scenario 2
113 Appendix D : Conclusions calculations D.1 Calculations current system with EES The main benefit of using the Paxman generator at full load is the higher efficiency compare to the current scenario. In this case and based on [14], the efficiency of the generator should be equal or lower to 4.4 kWh/L. Then, the litres of diesel required along the year are 1,318,182 L if a annually consumption of 5,800 MWh is assumed [11]. Hence, a saving of 548,930 L and 218k GBP is estimated, taking into account the current diesel cost of 0.397 GBP/L [16], compared to the current scenario. D.2 Calculations hydrogen scenario In order to calculate the kg of hydrogen required, an annually energy demand of 5,800 MWh and a hydrogen fuel consumption of 33 kWh/kg [117] [118] is assumed. As a result, an annually hydrogen demand of 174,017 kg, monthly of 14,501 kg, will be required. This amount of hydrogen should cost around 266,682 USD per month if a hydrogen generation cost and transportation of 1.39 USD/kg and 17 USD/kg are assumed respectively [116]. Compared to the current scenario and taking into account an exchange rate of 1.556562 USD/GBP, there will be a cost increase of 109,557 GBP.