A Solar Dually PVT Driven Direct Expansion Heat Pump One-Year Field Operation Results at Continental Climate

Citation: Sanz, A.; Martín, A.J.; Pereda, A.; Román, E.; Ibañez, P.; Fuente, R. A Solar Dually PVT Driven Direct Expansion Heat Pump One-Year Field Operation Results at Continental Climate. Energies 2022, 15, 3205. https://doi.org/10.3390/ en15093205 Academic Editors: Alba Ramos Cabal, María Herrando and Alessia Arteconi Received: 1 April 2022 Accepted: 25 April 2022 Published: 27 April 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). energies Article A Solar Dually PVT Driven Direct Expansion Heat Pump One-Year Field Operation Results at Continental Climate Asier Sanz 1,2,* , Antonio J. Martín3, Ainhoa Pereda 1, Eduardo Román1, Pedro Ibañez 1and Raquel Fuente 2 1TECNALIA, Basque Research and Technology Alliance (BRTA), 48160 Derio, Spain; [email protected] (A.P.); [email protected] (E.R.); pedr[email protected] (P.I.) 2Applied Mathematics, Faculty of Engineering, University of the Basque Country UPV/EHU, 48013 Bilbao, Spain; [email protected] 3Energy Panel, 14900 Lucena, Spain; [email protected] *Correspondence: asier[email protected] Abstract: The high energy-consuming building sector needs to meet both electricity and heat demands. In a nearly zero energy building scenario, most of the consumed energy would be generated locally by means of renewable solutions that nowadays seem not to provide an attractive performance or cost-competitiveness. Solar-based technologies tend to be the most promising ones, but for high densely populated areas, the usual photovoltaic or thermal single approaches may not be efficient enough. The current work is focused on the analysis of the dual use of the solar resource by means of hybrid PVT collectors and their smart combination with direct expansion heat pumps through predictive control strategies. To that end, a system was developed, installed in a real-use single-family house at a continental climate for domestic hot water application, operated and monitored for one entire year. The average day indicator results show 83% renewable energy share, 220% self-sufficiency ratio, 41% heat pump self-consumption and 46% of the solar fraction. Keywords: photovoltaic-thermal; PVT; PV/T; heat pump; HP; hybrid; system; control; field results 1. Introduction Global energy consumption is projected to return quickly to pre-pandemic levels [ 1 ]. The reference for 2020 was around 600 quadrillion British thermal units with a 50% estimated increase by 2050 driven by non-OECD economic growth and population. The European Commission states [ 2 ] that buildings are responsible for 40% of the energy consumption and 36% of CO 2 emissions, and pretends to reduce their impact through different actions. Most of those buildings need to meet both electricity and heat demands, for domestic hot water (DHW) and space heating/cooling (H&C). In the close, nearly zero energy building (nZEB) scenario, most of the consumed energy would need to be generated locally by means of renewable resources. Unfortunately, current renewable solutions seem not to provide an integral, simultaneous and local solution to this need, ensuring energy supply guarantee and cost-competitiveness. However, solar energy is available all over the face of the earth. Thus, buildings should try to take higher value from every beam of light reaching their envelopes. Today, photovoltaics (PV), and in the past, solar thermal (ST) applications, are becoming widely used for built environment on-site generation. Nevertheless, for high densely populated and shadow restricted areas, these kind of single approaches are not enough to satisfy building energy needs. Detailed analysis of solar resources in built environments shows that not only roofs but also façades should be considered with higher efficiency solar conversion devices such as PVT [3]. Harnessing solar energy should be a must for new and refurbished buildings [4–6] , but when the sun is not shining and energy stores are empty, solar base solutions always require back-up systems, which reduces their competitiveness. The electrical grid makes Energies 2022,15, 3205. https://doi.org/10.3390/en15093205 https://www.mdpi.com/journal/energies Energies 2022,15, 3205 2 of 23 things easier for loads, but thermal needs are still highly fossil fuel-dependent in a great part of Europe [ 7 ]. However, heat pumps (HP) seem a promising technology for a reduction in building thermal comfort-related CO 2 emissions and enable the use of the electrical infrastructure to use them as a back-up source [ 8 ]. Therefore, if solar and HP are individually suitable for electricity and heat generation, merging them in a unique hybrid system will enable obtaining even higher benefits [ 9 – 11 ]. Anyway, it is usually hard to inter-compare technologies and quantify those real benefits to simply conclude which one shows overall greater performance. Thus, within the current work, an experimental approach is proposed to shed some light on the real field performance of such systems. 1.1. PVT Dually Coupled HP Technology The proposed solution is a solar hybrid PVT dually coupled HP. It is a fully integrated system comprising an unglazed hybrid solar collector, a direct expansion solar assisted HP (DX-saHP) and an overall system control (Figure 1). The base of the technology has been widely studied before by different research groups for comparative analysis [ 12 , 13 ] and experimental studies [ 14 , 15 ]. The union of PV and solar thermodynamic technologies in one collector enables simultaneous electricity and heat generation and in a kind of symbiosis both technologies work optimally without mismatching the other’s performance [ 16 ], as occurs in conventional PVT where a trade-off between the thermal and electric performance is needed. Thus, the dually assisted HP significantly increases the total annual use of the solar resource while primary energy consumption is reduced. Energies 2022, 15, x FOR PEER REVIEW 2 of 23 require back-up systems, which reduces their competitiveness. The electrical grid makes things easier for loads, but thermal needs are still highly fossil fuel-dependent in a great part of Europe [7]. However, heat pumps (HP) seem a promising technology for a reduction in building thermal comfort-related CO 2 emissions and enable the use of the electrical infrastructure to use them as a back-up source [8]. Therefore, if solar and HP are individually suitable for electricity and heat generation, merging them in a unique hybrid system will enable obtaining even higher benefits [9–11]. Anyway, it is usually hard to inter-compare technologies and quantify those real benefits to simply conclude which one shows overall greater performance. Thus, within the current work, an experimental approach is proposed to shed some light on the real field performance of such systems. 1.1. PVT Dually Coupled HP Technology The proposed solution is a solar hybrid PVT dually coupled HP. It is a fully integrated system comprising an unglazed hybrid solar collector, a direct expansion solar assisted HP (DX-saHP) and an overall system control (Figure 1). The base of the technology has been widely studied before by different research groups for comparative analysis [12,13] and experimental studies [14,15]. The union of PV and solar thermodynamic technologies in one collector enables simultaneous electricity and heat generation and in a kind of symbiosis both technologies work optimally without mismatching the other’s performance [16], as occurs in conventional PVT where a trade-off between the thermal and electric performance is needed. Thus, the dually assisted HP significantly increases the total annual use of the solar resource while primary energy consumption is reduced. (a) (b) Figure 1. A representation of the PVT dually coupled HP technology: (a) Physical scheme of main system elements; (b) Solution square view following IEA procedure [17,18]. 1.2. Solution Innovations The proposed solution incorporates innovations focusing on the main critical elements impacting the entire system’s cost-performance. 1.2.1. PVT Collector Deep research has been carried out during recent decades on solar hybrid PVT collectors [19] and their integration at a system level [20]. The last advancements are continuously presented [21,22] and future trends are discussed [23,24] by the scientific community. In parallel, a wide set of commercial products are available [25–29], covering almost all different types of collectors [30] and applications [31], but the cost is significantly linked to the thermal efficiency [32,33]. However, for HP-based systems the cold side temperature is not required to be close to the application one. Thus, directly PVT coupled HP solutions could benefit from a non-high temperature collector field thermal output while Figure 1. A representation of the PVT dually coupled HP technology: ( a ) Physical scheme of main system elements; (b) Solution square view following IEA procedure [17,18]. 1.2. Solution Innovations The proposed solution incorporates innovations focusing on the main critical elements impacting the entire system’s cost-performance. 1.2.1. PVT Collector Deep research has been carried out during recent decades on solar hybrid PVT collectors [ 19 ] and their integration at a system level [ 20 ]. The last advancements are continuously presented [ 21 , 22 ] and future trends are discussed [ 23 , 24 ] by the scientific community. In parallel, a wide set of commercial products are available [ 25 – 29 ], covering almost all different types of collectors [ 30 ] and applications [ 31 ], but the cost is significantly linked to the thermal efficiency [ 32 , 33 ]. However, for HP-based systems the cold side temperature is not required to be close to the application one. Thus, directly PVT coupled HP solutions could benefit from a non-high temperature collector field thermal output while ensuring proper operation [34], even just by driving the HP with PVT thermal contribution [35]. According to these premises, a new PVT collector has been proposed (Figure 2). The collector pretends to be closer to a conventional c-Si PV module in terms of cost, with an Energies 2022,15, 3205 3 of 23 additional single residual heat recovery unit. This lightweight solution is manufactured by means of a directly one-step lamination on top of a hard-anodized roll bond thermal absorber, that achieves cost competitiveness while enhancing the heat transfer between PV cells and HP refrigerant. To enable further heat transfer with ambient air [ 36 ], the collector has no extra backsheet, thermal insulation or any further mechanical components. Energies 2022, 15, x FOR PEER REVIEW 3 of 23 ensuring proper operation [34], even just by driving the HP with PVT thermal contribution [35]. According to these premises, a new PVT collector has been proposed (Figure 2). The collector pretends to be closer to a conventional c-Si PV module in terms of cost, with an additional single residual heat recovery unit. This lightweight solution is manufactured by means of a directly one-step lamination on top of a hard-anodized roll bond thermal absorber, that achieves cost competitiveness while enhancing the heat transfer between PV cells and HP refrigerant. To enable further heat transfer with ambient air [36], the collector has no extra backsheet, thermal insulation or any further mechanical components. (a) (b) Figure 2. The innovations introduced in the PVT system under study: (a) The unglazed one-step manufactured PVT collector; (b) the overall control system implemented in a Beagle Bone Board. 1.2.2. Overall System Control The solar PVT-based solutions controllers have been traditionally left in a second plane [37,38]. The classical systems hardly require high-powered active elements during operation, where excluding electric back-up systems, the only present loads are the solar field circulation pumps. In such conventional systems, the thermal generation is simply delivered to the tank and the electrical energy is injected into the grid [39]. The recent selfconsumption regulation advances are pushing towards more complex system architecture combinations, where PV and ST are combined with HP or other components [9]. These entire solutions must be controlled integrally for ensuring a proper global energy performance, considering not only the thermal but also the electrical generation [40–42]. Furthermore, in an nZEB scenario, the local energy generation will not be the only problem to be solved. Thermal and electrical energy supplies will need to be smartly handled to satisfy user needs technically and economically. However, the current solar hybrid solution controllers seem not to be capable of ensuring the required performance [43,44]. Consequently, a new overall system control is presented (Figure 2). The innovative control strategy considers a day ahead DHW consumption prediction routine integrated into a high-level control layer that maximizes the HP operation with just solar resources. Thus, higher solar fractions and self-consumption figures could be achieved, optimizing the overall system performance without affecting end-user comfort or grid impact. 2. Materials and Methods In order to prove the previously exposed potential benefits, a prototype of the proposed solution was developed, installed and operated for one entire year in a real-use application. The objective of the test is double. First, to experimentally determine the technical performance of the whole solution by means of accurate monitoring. Second, to validate the robustness of the system under extreme working conditions. Figure 2. The innovations introduced in the PVT system under study: ( a ) The unglazed one-step manufactured PVT collector; (b) the overall control system implemented in a Beagle Bone Board. 1.2.2. Overall System Control The solar PVT-based solutions controllers have been traditionally left in a second plane [ 37 , 38 ]. The classical systems hardly require high-powered active elements during operation, where excluding electric back-up systems, the only present loads are the solar field circulation pumps. In such conventional systems, the thermal generation is simply delivered to the tank and the electrical energy is injected into the grid [ 39 ]. The recent self-consumption regulation advances are pushing towards more complex system architecture combinations, where PV and ST are combined with HP or other components [ 9 ]. These entire solutions must be controlled integrally for ensuring a proper global energy performance, considering not only the thermal but also the electrical generation [40–42]. Furthermore, in an nZEB scenario, the local energy generation will not be the only problem to be solved. Thermal and electrical energy supplies will need to be smartly handled to satisfy user needs technically and economically. However, the current solar hybrid solution controllers seem not to be capable of ensuring the required performance [43,44]. Consequently, a new overall system control is presented (Figure 2). The innovative control strategy considers a day ahead DHW consumption prediction routine integrated into a high-level control layer that maximizes the HP operation with just solar resources. Thus, higher solar fractions and self-consumption figures could be achieved, optimizing the overall system performance without affecting end-user comfort or grid impact. 2. Materials and Methods In order to prove the previously exposed potential benefits, a prototype of the proposed solution was developed, installed and operated for one entire year in a real-use application. The objective of the test is double. First, to experimentally determine the technical performance of the whole solution by means of accurate monitoring. Second, to validate the robustness of the system under extreme working conditions. 2.1. Experimental Set-Up 2.1.1. Real-Use DHW Application The demonstrator baseline is a single-family house located at Jablonec nad Nisou, Czech Republic (Figure 3). The new solution has been installed to fully supply hot tap water Energies 2022,15, 3205 4 of 23 for a 3-member family, replacing the previously existing gas boiler. However, the boiler has not been removed during the test period as it still covers space heating energy needs and may be punctually used as a back-up system, if needed, during the heavy winter season. Energies 2022, 15, x FOR PEER REVIEW 4 of 23 2.1. Experimental Set-Up 2.1.1. Real-Use DHW Application The demonstrator baseline is a single-family house located at Jablonec nad Nisou, Czech Republic (Figure 3). The new solution has been installed to fully supply hot tap water for a 3-member family, replacing the previously existing gas boiler. However, the boiler has not been removed during the test period as it still covers space heating energy needs and may be punctually used as a back-up system, if needed, during the heavy winter season. (a) (b) Figure 3. The single-family house considered for the test previous to the intervention, located at Jablonec nad Nisou (50.7N, 15.1W coordinates): (a) Outdoor view of the building south rooftop and façade; (b) Indoor room with existing boiler and further household appliances. As part of a preintervention study, the building usage patterns have been analyzed according to user questionaries. The household accommodates 2 persons during workdays and 4 during weekends. The daily average hot tap water consumption is around 200 l, distributed in early morning showers, short mid-day cooking/washing, and night additional 10 min showers. According to the collected information, Table 1 shows the estimated energy requirements to be satisfied. Table 1. Household expected DHW day and month energy demands, according to historical average maximum/minimum ambient and tap water temperatures. Month T amb, max (°C) T amb, min (°C) T tap water (°C) Q DHW (kWh / Day) * Q DHW (kWh) * January 0.4 −5.4 4 10.672 331 February 2.7 −4.0 5 10.440 292 March 7.7 −1.0 7 9.976 309 April 13.3 2.6 9 9.512 285 May 18.3 7.1 10 9.280 288 June 21.4 10.5 11 9.048 271 July 23.3 11.9 12 8.816 273 August 23.0 11.7 11 9.048 280 September 19.0 8.7 10 9.280 278 October 13.1 4.3 9 9.512 295 November 6.0 0.2 7 9.976 299 December 2.0 −3.3 4 10.672 330 Year 12.5 3.6 8.3 9.686 3534 * Calculated at 50 °C. Figure 3. The single-family house considered for the test previous to the intervention, located at Jablonec nad Nisou (50.7N, 15.1W coordinates): ( a ) Outdoor view of the building south rooftop and façade; (b) Indoor room with existing boiler and further household appliances. As part of a preintervention study, the building usage patterns have been analyzed according to user questionaries. The household accommodates 2 persons during workdays and 4 during weekends. The daily average hot tap water consumption is around 200 L , distributed in early morning showers, short mid-day cooking/washing, and night additional 10 min showers. According to the collected information, Table 1shows the estimated energy requirements to be satisfied. Table 1. Household expected DHW day and month energy demands, according to historical average maximum/minimum ambient and tap water temperatures. Month Tamb,max (◦C) Tamb,min (◦C) Ttap water (◦C) QDHW (kWh/Day) * QDHW (kWh) * January 0.4 −5.4 4 10.672 331 February 2.7 −4.0 5 10.440 292 March 7.7 −1.0 7 9.976 309 April 13.3 2.6 9 9.512 285 May 18.3 7.1 10 9.280 288 June 21.4 10.5 11 9.048 271 July 23.3 11.9 12 8.816 273 August 23.0 11.7 11 9.048 280 September 19.0 8.7 10 9.280 278 October 13.1 4.3 9 9.512 295 November 6.0 0.2 7 9.976 299 December 2.0 −3.3 4 10.672 330 Year 12.5 3.6 8.3 9.686 3534 * Calculated at 50 ◦C. 2.1.2. System and Components Sizing The DHW application that has been chosen for validation purposes determines the strategy to be used for system sizing. Thus, according to the expected DHW day demand and its consumption profile, the thermodynamic bloc comprising the HP and the thermal energy store (TES) is selected. Traditionally, for DX-saHP, the key parameter to look at at this point is the time interval needed to ensure the entire tank water is heated at the Energies 2022,15, 3205 5 of 23 set point. Usually, a maximum time is established. Then the HP and TES are selected to guarantee that in the worst-case scenario the elapsed time needed to reach the setpoint is below the defined one. For the current case study, at the coldest, lower solar resource and higher DHW demand months of January and December, with a 2.5 kW of heat output HP and a 200 L TES the elapsed period is 1.65 h. However, the new solution to be tested pretends to run mainly on solar resources. For this reason, an inverter HP has been selected. Even at its maximum regime, an output of 2.5 kW of heat would be reached, it will regularly work at lower operation points. Thus, a slightly higher TES volume has been selected. The final volume is 300 L, increasing by 50% the TES capacity and enabling us to heat it up during solar resource availability periods. Thus, the risk of reaching premature HP stops due to the maximum TES temperature being reduced. Finally, for the selected thermodynamic block, the collection field is sized according to the required cold power for the HP in the previously commented winter period worst-case scenario. For the current case study, with a conventional DX-saHP system, a total of 2.72 m2 (2 units of 1.36 m 2 ) of black painted roll bond solar thermodynamic collectors would be enough. However, the new solution is based on PVT collectors and the front layer might have a lower heat transfer capacity. Thus, the selected collection area is increased up to 4.8 m 2 (3 units of 1.6 m 2 ). Even though 2 units might be enough to thermally run the HP, the additional collector is supposed to add a plus for the critical winter season. To avoid undesired excessive summer HP suction temperatures, independent blocking valves are added to each one of the collectors. An additional PV module is also added in order to enable a comparison of electrical yields. The prototype key components’ main features are summarized in Table 2for the PVT collector and PV module, and in Table 3for the thermodynamic block comprising HP and TES. 2.1.3. System Installation The selected system has been successfully installed in the household (Figure 4). The outdoor unit comprising the solar field has been installed in the same rooftop plane, almost south orientation ( − 13 ◦ ) but in a high tilting configuration (70 ◦ ). In terms of solar resources, the selected plane compared to the optimal (37 ◦ slope and 0 ◦ south) reduces the annual irradiation by 12.6% but still offers an acceptable winter performance with a 6.3% decrease (for December). Apart from the non-optimal collection plane, there is not any additional significant mismatching in the horizon profile that may affect the energy collection. Energies 2022, 15, x FOR PEER REVIEW 6 of 23 Table 3. HP and TES main features. Features Value Heat output 340 .. 2500 W Electric consumption 240 .. 580 W Compressor DJ75F0F-20UB Inverter PSD101021A Expansion valve E2V09USF10 Coefficient of performance 1.4 .. 4.3 Auxiliar heating resistance na Refrigerant R134A Volume 300 l Maximum working temperature 60 °C * 1 Operating temperature range −5 .. +42 °C Dimensions (length × width × height) 2008 × 550 × 601 mm * 2 Maximum working pressure 6 bar Heat mean transfer 0.025 W/m·K Material Stainless steel Isolation Injected polyurethane * 1 For HP operation mode. * 2 Including HP. 2.1.3. System Installation The selected system has been successfully installed in the household (Figure 4). The outdoor unit comprising the solar field has been installed in the same rooftop plane, almost south orientation (−13°) but in a high tilting configuration (70°). In terms of solar resources, the selected plane compared to the optimal (37° slope and 0° south) reduces the annual irradiation by 12.6% but still offers an acceptable winter performance with a 6.3% decrease (for December). Apart from the non-optimal collection plane, there is not any additional significant mismatching in the horizon profile that may affect the energy collection. The solar field composed is of 3 PVT collectors and the additional PV modules (displayed on the east side) have been installed with identical fixing solutions, so no potential heterogeneity is introduced. In order to measure the potential gap in electrical performance, independent maximum powers for tracking have been deployed for each one of the collectors and modules, based on 2 units of the dual input microinverter APS YC500i. (a) (b) Figure 4. The single-family house after the intervention: (a) Outdoor view with the PVT/PV units installed and under operation; (b) Indoor room with the HP, TES and monitoring instrumentation. Figure 4. The single-family house after the intervention: ( a ) Outdoor view with the PVT/PV units installed and under operation; (b) Indoor room with the HP, TES and monitoring instrumentation. Energies 2022,15, 3205 6 of 23 Table 2. PVT collector and PV module main features. Features Value Maximum peak power 250 W Maximum power point voltage 29.53 V Maximum power point current 8.45 A Open circuit voltage 37.60 V Short circuit current 8.91 A Cell Normal Operating Temperature 45.0 ±2◦C *1 Short circuit current temperature coefficient 0.04%/◦C Open circuit voltage temperature coefficient −0.32%/◦C Maximum power temperature coefficient −0.43%/◦C Operating temperature range −40 . . . +85 ◦C Backsheet collection area 1.63 m2*2 Maximum working pressure 10 bar *2 Refrigeration input/output connectors SAE 1/40 0 /3/800 *2 Dimensions (length ×width ×height) 1645 ×990 ×40 mm Weight (PVT/PV) 30/26 kg *1Valid only for PV. *2Valid only for PVT. Table 3. HP and TES main features. Features Value Heat output 340 . . . 2500 W Electric consumption 240 . . . 580 W Compressor DJ75F0F-20UB Inverter PSD101021A Expansion valve E2V09USF10 Coefficient of performance 1.4 . . . 4.3 Auxiliar heating resistance na Refrigerant R134A Volume 300 l Maximum working temperature 60 ◦C *1 Operating temperature range −5 . . . +42 ◦C Dimensions (length ×width ×height) 2008 ×550 ×601 mm *2 Maximum working pressure 6 bar Heat mean transfer 0.025 W/m·K Material Stainless steel Isolation Injected polyurethane *1For HP operation mode. *2Including HP. The solar field composed is of 3 PVT collectors and the additional PV modules (displayed on the east side) have been installed with identical fixing solutions, so no potential heterogeneity is introduced. In order to measure the potential gap in electrical performance, independent maximum powers for tracking have been deployed for each one of the collectors and modules, based on 2 units of the dual input microinverter APS YC500i. The refrigerant circuit from the HP to the collectors has an initial common segment of 7 m in length, which is later divided into 3 identical parallel sections of 2 m reaching the collectors, so the different circuits are compensated. Blocking valves have also been included to enable a potential manual disconnection of each one of the collector’s thermal outputs. The return of the circuit is performed in the same way but without any compensation. All the refrigerant pipes are thermally isolated with a 1cm polyethylene. The indoor unit has been adapted to the available room constraints. Thus, the TES is placed close to the existing gas boiler, so the tank pipes are directly connected to the household DHW circuit. Energies 2022,15, 3205 7 of 23 2.1.4. Instrumentation and Data Acquisition The experimental activity requires accurate monitoring of energy fluxes and further relevant boundary variables to determine the technical performance of both system components and the complete solution. Thus, different kinds of sensors are displayed along the prototype (Figure 5). The most significant variables to measure meteorological conditions, energy collection (solar field), conversion (power electronics for PV and) HP and store (hot water tank) are summarized in Table 4. Energies 2022, 15, x FOR PEER REVIEW 7 of 23 The refrigerant circuit from the HP to the collectors has an initial common segment of 7 m in length, which is later divided into 3 identical parallel sections of 2 m reaching the collectors, so the different circuits are compensated. Blocking valves have also been included to enable a potential manual disconnection of each one of the collector’s thermal outputs. The return of the circuit is performed in the same way but without any compensation. All the refrigerant pipes are thermally isolated with a 1cm polyethylene. The indoor unit has been adapted to the available room constraints. Thus, the TES is placed close to the existing gas boiler, so the tank pipes are directly connected to the household DHW circuit. 2.1.4. Instrumentation and Data Acquisition The experimental activity requires accurate monitoring of energy fluxes and further relevant boundary variables to determine the technical performance of both system components and the complete solution. Thus, different kinds of sensors are displayed along the prototype (Figure 5). The most significant variables to measure meteorological conditions, energy collection (solar field), conversion (power electronics for PV and) HP and store (hot water tank) are summarized in Table 4. (a) (b) Figure 5. Sensors distribution in the prototype under test: (a) Local meteorological conditions, PVT collectors and PV module operation temperatures; (b) Indoor instrumentation integrated in the front of the HP unit. The selected monitoring architecture is based on in-site measurements that are immediately transduced into Modbus over RS-485 by the sensors themselves. Then the data is remotely requested and handled by a datalogger service in the same Beagle Bone board where the control is implemented. The 69-variable monitoring register is gathered every minute and stored on a daily basis in csv files. The control and data logging board have an internet connection by means of a router with a VPN. A remote copy of local content is created weekly. Table 4. A selection of the most significant monitored variables, including the instrument used for the measurement and some additional relevant information. Instrument Units Description Symbol Range and Units Accuracy MET calibrated cell (Atersa) 2 Global plane of array irradiance G PoA 0 .. 1400 W/m 2 ±2.2% 1 Ambient temperature T amb −20 .. 100 °C ±0.8 °C 1 Wind speed ws 2 .. 140 km/h ±3% * 1 1 Crystalline silicon PV module reference temperature T PVref −20 .. 100 °C ±0.8 °C Figure 5. Sensors distribution in the prototype under test: ( a ) Local meteorological conditions, PVT collectors and PV module operation temperatures; ( b ) Indoor instrumentation integrated in the front of the HP unit. Table 4. A selection of the most significant monitored variables, including the instrument used for the measurement and some additional relevant information. Instrument Units Description Symbol Range and Units Accuracy MET calibrated cell (Atersa) 2Global plane of array irradiance GPoA 0 . . . 1400 W/m2±2.2% 1Ambient temperature Tamb −20 . . . 100 ◦C±0.8 ◦C 1Wind speed ws 2 . . . 140 km/h ±3% *1 1Crystalline silicon PV module reference temperature TPVref −20 . . . 100 ◦C±0.8 ◦C RTF-100-S4B-5.0-C8 PT100 (Labfacility) 3 2 at collectors and 1 at module Middle absorber/backsheet temperature TPVT,2 TPVT,3 TPV −50 . . . 150 ◦C±1% VMU-E DC energy meter (Carlo Gavazzi) 4 one per collector Voltage VPVT/PVm,X 0 . . . 400 V ±0.5% *2 Current IPVT/PVm,X 0 . . . 20 A ±0.5% *3 Power PPVT/PVm,X *50 . . . 8 kW ±1% Energy EPVT/PVm,X *5na kWh ±1% EM110 AC energy meter (Garlo Gavazzi) 3 Grid balance PV generation HP consumption Energy EGrid EPVm EHP na kWh ±1% *4 µPC HP controller (Carel) 1 Compressor voltage VComp na V±1% Compressor current IComp na A±1% Evaporation temperature TEva −50 . . . 100 ◦C±1◦C Suction temperature TSuc −50 . . . 100 ◦C±1◦C Discharge temperature TDis −50 . . . 100 ◦C±1◦C Condensation temperature TCon −50 . . . 100 ◦C±1◦C TES load temperature TTES,load −50 . . . 100 ◦C±1◦C TES middle temperature TTES,mid −50 . . . 100 ◦C±1◦C Condenser outlet temperature TCOut −50 . . . 100 ◦C±1◦C * 1 The accuracy for wind speed is valid for 15 . . . 140 km/h range, but always greater than ± 1 km/h. * 2 The accuracy for DC voltage is valid for 10 . . . 400 V range. * 3 The accuracy for DC current is valid for 0.05 . . . 20 A range. * 4 The accuracy for AC energy is 1.5% for a range of 0.25 . . . 0.5 A, according to EN50470-3. * 5 The term EPV is left for the total solar field electrical output. The selected monitoring architecture is based on in-site measurements that are immediately transduced into Modbus over RS-485 by the sensors themselves. Then the data is Energies 2022,15, 3205 8 of 23 remotely requested and handled by a datalogger service in the same Beagle Bone board where the control is implemented. The 69-variable monitoring register is gathered every minute and stored on a daily basis in csv files. The control and data logging board have an internet connection by means of a router with a VPN. A remote copy of local content is created weekly. 2.2. Data Analysis, Cleaning and Processing The applied methodology is essentially based on the analysis of experimental data. The monitoring activity provided dataset is postprocessed to enable a better interpretation and further discussion. The gathered system performance is first analyzed in detail. The day-based files have an automatic checking algorithm. The procedure only enables us to filter entire day performance days with all dataset variables in range. Furthermore, all days are carefully manually analyzed using specific timeseries templates to filter any additional errors. Thus, days with partial operation, monitored variable outlyers or additional reported phenomena are removed at this stage. Any kind of gap filling is not considered. The analysis continues only with the valid-day dataset. For this selection, several intraday parameters and day-aggregated energy values are calculated. Additionally, day representative key performance indicators (KPI) are obtained. Finally, day representative KPIs are once more aggregated in a monthly-based approach. For this analysis, the average, median or accumulated values of day-based KPIs are considered for monthly-based periods. 2.3. Key Performance Indicators The determination of these KPIs is performed according to the common agreed procedure established within different Tasks of the International Energy Agency Solar Heating and Cooling programme [45]. 2.3.1. System Level A set of four main KPIs has been considered to characterize system operation. The renewable energy share represents the local non-fossil fuel potential: RES =Z . QHP PGrid,NC (1) where QHP is the HP heat output, which for the current DX-saHP solution is not directly measured but calculated based on the compressor manufacturer data and monitored T Eva , TCon and HP controller compressor frequency. The self-sufficiency ratio shows the real solar field output potential to cover the HP electric consumption needs: SSR =ZPPV PHP (2) where PPV is the aggregated electric output of the three PVT collectors and the corresponding one for the PV module. PHP is the HP consumption, which considers the compressor but also additional devices. The self-consumption ratio to determine the real PV output potential to cover the HP electric consumption needs: SCR =Zmin(PPV,PGrid) PPV (3) where PGrid is the system grid consumption in the scenario of non-PV production. Energies 2022,15, 3205 9 of 23 Finally, the solar fraction, to obtain the utilization ratio of the solar resource at the energy collection field: SF =ZPPV +. QPVT 4·APVT/PV·GPoA (4) where APVT/PV is the aperture area of the PVT collectors or PV module, in this case identical. QPVT is the PVT collector field heat output, which, as in the case of QHP , could not be locally measured and has been obtained as a function of monitored T Eva ,T Con , HP frequency and manufacturer tests data. The ambient gain for PVT collectors due to below ambient operation is included in this calculation procedure and should be removed for genuine SF obtention, but there is still no confident procedure to decouple it. 2.3.2. PVT Collectors The quantification of the performance gap between the PVT collector and the reference PV module is the goal of the following two specific KPIs that are proposed. One of them is focusing on the potential performance ratio increase: ∆PRPVT PV = ∑3 i=1(PRPVTi) 3−PRPV PRPV (5) where PRPVTiis calculated for each one of the collectors as follows: PRPVTi=ZPPVTi·fPVTi PV APVT/PV·GPoA (6) with fPVTi PV as the maximum power point deviation correction between each one of the collectors and the PV module used as reference. PPVT is the electrical output of the 3 PVT collector-field. The electrical characteristics of each collector and module have been obtained with an indoor flash tester and in the same way the PRPV: PRPV =ZPPV APVT/PV·GPoA (7) The second KPI tries to clarify if the PR deviation is correlated with the expected lower operation temperature of the PVT collectors [ 46 ]. Thus, the day’s average PVT collector temperature difference with the PV module reference is calculated: ∆TPVT PV =TPVT −TPV =∑3 i=1TPVTi 3−TPV (8) where TPVT/PV is calculated for each one of the collectors and modules as follows: TPVTi/PV =1 N N ∑ t=0 TPVTi/PVt(9) Additionally, conventional conversion efficiencies are proposed. In the case of the PV module just considering the electric output power: ηPV =ZPPVm APV ·GPoA (10) where PPVm is the electrical output of the PV module, and for the PVT collector adding the heat outcome: ηPVT =ZPPVT·. QPVT APVT·GPoA (11) Energies 2022,15, 3205 16 of 23 Energies 2022, 15, x FOR PEER REVIEW 16 of 23 Figure 13. Monthly average daily mean energy magnitudes. Figure 14. Monthly average daily mean DHW consumption and the energy source. The entire year aggregated energy by type is listed below: • 𝐸 = 1050 kWh; • 𝑄 = 855 kWh; • 𝐸 = 431 kWh; • 𝑄 = 1287 kWh; • 𝐸 = 220 kWh; 3.4. Monthly Average Daily KPI Analysis 3.4.1. System Level The four main KPIs selected to characterize entire system performance are displayed in Figure 15 for the average day values. The RES is above 60% for the whole period, reaching its maximum of 92% for the month of May. The SSR shows the expected greater variability, with a maximum in August (470%) and a minimum in December (18%), affected mainly by the annual fully decoupled DHW energy demand and solar resource. On the opposite side, the obtained SCR is maximum for the winter period (94% for December) while is reduced to 17% for the month of August. The higher values are linked to low irradiance and long HP operation days. Finally, the SF is in the range of 22–159% for August and December, respectively. Days with almost no irradiation but high PVT thermal output, due to wind and infrared energy collection, leading to above 300% values are saturated. 0 1 2 3 4 5 6 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Energy (kWh) Epv Ehp Qpvt Qhp Egc Egi Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec -60% -40% -20% 0% 20% 40% 60% 80% 100% -6 -4 -2 0 2 4 6 8 10 Energy distribution (%) Energy (kWw) Esc Qpvt Egc Egi Qdhw Figure 14. Monthly average daily mean DHW consumption and the energy source. The entire year aggregated energy by type is listed below: •EPVac = 1050 kWh; •QPVT = 855 kWh; •EHP = 431 kWh; •QHP = 1287 kWh; •EGC = 220 kWh; 3.4. Monthly Average Daily KPI Analysis 3.4.1. System Level The four main KPIs selected to characterize entire system performance are displayed in Figure 15 for the average day values. The RES is above 60% for the whole period, reaching its maximum of 92% for the month of May. The SSR shows the expected greater variability, with a maximum in August (470%) and a minimum in December (18%), affected mainly by the annual fully decoupled DHW energy demand and solar resource. On the opposite side, the obtained SCR is maximum for the winter period (94% for December) while is reduced to 17% for the month of August. The higher values are linked to low irradiance and long HP operation days. Finally, the SF is in the range of 22–159% for August and December, respectively. Days with almost no irradiation but high PVT thermal output, due to wind and infrared energy collection, leading to above 300% values are saturated. Energies 2022, 15, x FOR PEER REVIEW 17 of 23 Figure 15. Monthly average daily mean system-level KPIs. For the entire year’s performance, the obtained system-level average day KPI results are 83% for RES, 220% for SSR, 41% for SCR and 46% for SF. The same KPIs obtained for integration of the entire year are 86%, 204%, 28.5% and 25.7%. The previously commented day and month-based results are reduced for the entire period analysis, especially for SCR and SF. The reason is that the high energy resource summer days with short HP operation are too weighted in this annual analysis. The high RES is basically based on HP performance and enhanced by solar field contribution. The obtained SCR shows good underlying control performance. The obtained SSR and SF results are huge, but somehow artificially boosted due to summer season high solar resource weight and DX-saHP ambient heat collection, respectively. 3.4.2. PVT Collector Versus PV Module The conversion efficiency of PVT collectors is higher than the same size and identical PV technology modules [30] due to the additional thermal output. However, the final energy performance usually depends on the application or the PVT operation mean temperature and on the classical efficiency versus heat quality dilemma. The period conversion efficiencies determined for the testing period are shown in Figure 16. Apart from the coldest month peaks, due to low resource and ambient energy collection, the rest of the winter months show higher PVT values with a significantly greater thermal side contribution. However, for the high irradiation and hot month of August, the PV influence on efficiency is larger than the electrical one. In annual terms, the PV converts 13.9% of incident solar energy, while PVT reaches 37%. 0 1 2 3 4 5 0.00 0.33 0.66 0.99 1.32 1.65 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec SSR (pu) RES, SCR and SF (pu) RES SSR SCR SF ↑ 0.77 ↑ 1.36 0.0 0.1 0.2 0.3 0.4 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Efficiency (pu) Effpv Effpvt Figure 15. Monthly average daily mean system-level KPIs. Energies 2022,15, 3205 17 of 23 For the entire year’s performance, the obtained system-level average day KPI results are 83% for RES, 220% for SSR, 41% for SCR and 46% for SF. The same KPIs obtained for integration of the entire year are 86%, 204%, 28.5% and 25.7%. The previously commented day and month-based results are reduced for the entire period analysis, especially for SCR and SF. The reason is that the high energy resource summer days with short HP operation are too weighted in this annual analysis. The high RES is basically based on HP performance and enhanced by solar field contribution. The obtained SCR shows good underlying control performance. The obtained SSR and SF results are huge, but somehow artificially boosted due to summer season high solar resource weight and DX-saHP ambient heat collection, respectively. 3.4.2. PVT Collector Versus PV Module The conversion efficiency of PVT collectors is higher than the same size and identical PV technology modules [ 30 ] due to the additional thermal output. However, the final energy performance usually depends on the application or the PVT operation mean temperature and on the classical efficiency versus heat quality dilemma. The period conversion efficiencies determined for the testing period are shown in Figure 16. Apart from the coldest month peaks, due to low resource and ambient energy collection, the rest of the winter months show higher PVT values with a significantly greater thermal side contribution. However, for the high irradiation and hot month of August, the PV influence on efficiency is larger than the electrical one. In annual terms, the PV converts 13.9% of incident solar energy, while PVT reaches 37%. Energies 2022, 15, x FOR PEER REVIEW 17 of 23 Figure 15. Monthly average daily mean system-level KPIs. For the entire year’s performance, the obtained system-level average day KPI results are 83% for RES, 220% for SSR, 41% for SCR and 46% for SF. The same KPIs obtained for integration of the entire year are 86%, 204%, 28.5% and 25.7%. The previously commented day and month-based results are reduced for the entire period analysis, especially for SCR and SF. The reason is that the high energy resource summer days with short HP operation are too weighted in this annual analysis. The high RES is basically based on HP performance and enhanced by solar field contribution. The obtained SCR shows good underlying control performance. The obtained SSR and SF results are huge, but somehow artificially boosted due to summer season high solar resource weight and DX-saHP ambient heat collection, respectively. 3.4.2. PVT Collector Versus PV Module The conversion efficiency of PVT collectors is higher than the same size and identical PV technology modules [30] due to the additional thermal output. However, the final energy performance usually depends on the application or the PVT operation mean temperature and on the classical efficiency versus heat quality dilemma. The period conversion efficiencies determined for the testing period are shown in Figure 16. Apart from the coldest month peaks, due to low resource and ambient energy collection, the rest of the winter months show higher PVT values with a significantly greater thermal side contribution. However, for the high irradiation and hot month of August, the PV influence on efficiency is larger than the electrical one. In annual terms, the PV converts 13.9% of incident solar energy, while PVT reaches 37%. 0 1 2 3 4 5 0.00 0.33 0.66 0.99 1.32 1.65 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec SSR (pu) RES, SCR and SF (pu) RES SSR SCR SF ↑ 0.77 ↑ 1.36 0.0 0.1 0.2 0.3 0.4 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Efficiency (pu) Effpv Effpvt Figure 16. Monthly average daily PV module and PVT collector conversion efficiency. Additionally, in the dually driven DX-saHP tested solution, the PVT collector is not required to operate at high temperatures to offer valuable heat and as a result, the electrical output is not reduced. Figure 17 evidences that the PVT extracted heat reduces from almost 1 to 3.7 ◦ C the average temperature of the PVT collector absorber versus PV module backsheet. Due to the cooling, the electrical PR of the PVT collector is improved for almost all the months, except January and December, affected by heavy collector front layer condensation and icing. However, according to datasheet values, the temperature reduction of 1 K should be traduced in a 0.43% increase in the PR, but the obtained PR results are not in consonance, which might suggest an optimum cooling during high irradiation periods. Finally, the year base result concludes with a PR increase of 4.5%, achieved not only by the HP active cooling but also by better natural convection. Energies 2022,15, 3205 18 of 23 Energies 2022, 15, x FOR PEER REVIEW 18 of 23 Figure 16. Monthly average daily PV module and PVT collector conversion efficiency. Additionally, in the dually driven DX-saHP tested solution, the PVT collector is not required to operate at high temperatures to offer valuable heat and as a result, the electrical output is not reduced. Figure 17 evidences that the PVT extracted heat reduces from almost 1 to 3.7 °C the average temperature of the PVT collector absorber versus PV module backsheet. Due to the cooling, the electrical PR of the PVT collector is improved for almost all the months, except January and December, affected by heavy collector front layer condensation and icing. However, according to datasheet values, the temperature reduction of 1 K should be traduced in a 0.43% increase in the PR, but the obtained PR results are not in consonance, which might suggest an optimum cooling during high irradiation periods. Finally, the year base result concludes with a PR increase of 4.5%, achieved not only by the HP active cooling but also by better natural convection. Figure 17. Monthly average daily PR and operation temperature relation between PVT and PVT. 3.4.3. Heat Pump The KPI selected to determine the HP operation is the PF, the conventional and the boosted. Figure 18 shows the PF oscillation between 2.3 and 3.4, in accordance with datasheet ranges. However, when the net grid imported energy is considered the PF is significantly improved. Even for the winter solstice, the obtained values are similar, during the summer period it reaches median values between 20 and 30. For the calculations, singular values with null grid consumption are not considered. Figure 18. Monthly median daily PF per month, for common grid absolute and net versions. 3.4.4. Thermal Energy Store 1 10 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec PF (pu) PF PFnet Figure 17. Monthly average daily PR and operation temperature relation between PVT and PVT. 3.4.3. Heat Pump The KPI selected to determine the HP operation is the PF, the conventional and the boosted. Figure 18 shows the PF oscillation between 2.3 and 3.4, in accordance with datasheet ranges. However, when the net grid imported energy is considered the PF is significantly improved. Even for the winter solstice, the obtained values are similar, during the summer period it reaches median values between 20 and 30. For the calculations, singular values with null grid consumption are not considered. Energies 2022, 15, x FOR PEER REVIEW 18 of 23 Figure 16. Monthly average daily PV module and PVT collector conversion efficiency. Additionally, in the dually driven DX-saHP tested solution, the PVT collector is not required to operate at high temperatures to offer valuable heat and as a result, the electrical output is not reduced. Figure 17 evidences that the PVT extracted heat reduces from almost 1 to 3.7 °C the average temperature of the PVT collector absorber versus PV module backsheet. Due to the cooling, the electrical PR of the PVT collector is improved for almost all the months, except January and December, affected by heavy collector front layer condensation and icing. However, according to datasheet values, the temperature reduction of 1 K should be traduced in a 0.43% increase in the PR, but the obtained PR results are not in consonance, which might suggest an optimum cooling during high irradiation periods. Finally, the year base result concludes with a PR increase of 4.5%, achieved not only by the HP active cooling but also by better natural convection. Figure 17. Monthly average daily PR and operation temperature relation between PVT and PVT. 3.4.3. Heat Pump The KPI selected to determine the HP operation is the PF, the conventional and the boosted. Figure 18 shows the PF oscillation between 2.3 and 3.4, in accordance with datasheet ranges. However, when the net grid imported energy is considered the PF is significantly improved. Even for the winter solstice, the obtained values are similar, during the summer period it reaches median values between 20 and 30. For the calculations, singular values with null grid consumption are not considered. Figure 18. Monthly median daily PF per month, for common grid absolute and net versions. 3.4.4. Thermal Energy Store 1 10 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec PF (pu) PF PFnet Figure 18. Monthly median daily PF per month, for common grid absolute and net versions. 3.4.4. Thermal Energy Store The TES operation key temperature evolution indicates the end-user comfort over the testing period. Figure 19 illustrates the TES KPIs. The tank water volume is the representative temperature range ∆TTES50 during almost all the period is below 8 K. However, for some months the minimum day average temperature is reduced beyond desirable values, mainly driven by laxer controller parameterization (April–May), although no critical points are reached. The November–January period evidences the already previously commented lower TES state of charge, with the minimum for December. For this scenario, the average DHW load temperature is 39.3 ◦C. The end-user gathered experience after the experimentation period concludes comfort levels have overall been achieved in terms of DHW service temperature even in hard winter times. Only a couple of days with punctual low TES temperature information shown at HP display have been reported, mainly during the beginning of the testing period. However, the gas boiler that was left as a potential backup has not been connected. Energies 2022,15, 3205 19 of 23 Energies 2022, 15, x FOR PEER REVIEW 19 of 23 The TES operation key temperature evolution indicates the end-user comfort over the testing period. Figure 19 illustrates the TES KPIs. The tank water volume is the representative temperature range ∆𝑇 during almost all the period is below 8 K. However, for some months the minimum day average temperature is reduced beyond desirable values, mainly driven by laxer controller parameterization (April–May), although no critical points are reached. The November–January period evidences the already previously commented lower TES state of charge, with the minimum for December. For this scenario, the average DHW load temperature is 39.3 °C. Figure 19. Monthly median daily TES KPIs. The end-user gathered experience after the experimentation period concludes comfort levels have overall been achieved in terms of DHW service temperature even in hard winter times. Only a couple of days with punctual low TES temperature information shown at HP display have been reported, mainly during the beginning of the testing period. However, the gas boiler that was left as a potential backup has not been connected. 4. Conclusions Global energy consumption is estimated to be increased over future decades, up to 50% by 2050. At the same time, it is imperative to reduce greenhouse gas emissions by 45% by 2030, compared to 2010 levels, while reaching net zero emissions by 2050. The last COP26 emphasized the urgency and opportunities of moving to a carbon-neutral economy. In the meantime, EU building stock is responsible for 40% of the energy consumption and 36% of CO2 emissions. However, in the current energy crisis scenario, the European Commission seems to have a clear roadmap toward energy sector decarbonization. Most of those buildings to be decarbonized need to meet electricity and heat demands. In the nZEB scenario, most of the consumed energy would need to be generated locally by means of renewable solutions that nowadays seem not to provide an attractive performance or cost-competitiveness. Solar-based technologies tend to be the most promising ones, but for highly densely populated and restricted areas, the usual PV or ST single approaches may not be efficient enough. The current work is focused on the experimental analysis of the dual use of the solar resource by means of hybrid PVT collectors and their smart combination with direct expansion HPs through predictive control strategies. For that purpose, a solution with several innovations in the collector and in the overall control strategy was developed. A realuse single-family house has been selected for hosting the test at a continental climate (Jablonec nad Nisou, Czeck Republic) for a DHW application over one-year of operation. The sizing of the system has been carried out. The system comprising three PVT collectors and one PV module, dually connected to an inverter DX-saHP with an oversized TES and a predictive control has been properly installed, commissioned and fully accurately 25 30 35 40 45 50 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Temperature (ºC) TES.50,max TES.50,mean TES.50,min TES.100,mean Figure 19. Monthly median daily TES KPIs. 4. Conclusions Global energy consumption is estimated to be increased over future decades, up to 50% by 2050. At the same time, it is imperative to reduce greenhouse gas emissions by 45% by 2030, compared to 2010 levels, while reaching net zero emissions by 2050. The last COP26 emphasized the urgency and opportunities of moving to a carbon-neutral economy. In the meantime, EU building stock is responsible for 40% of the energy consumption and 36% of CO 2 emissions. However, in the current energy crisis scenario, the European Commission seems to have a clear roadmap toward energy sector decarbonization. Most of those buildings to be decarbonized need to meet electricity and heat demands. In the nZEB scenario, most of the consumed energy would need to be generated locally by means of renewable solutions that nowadays seem not to provide an attractive performance or cost-competitiveness. Solar-based technologies tend to be the most promising ones, but for highly densely populated and restricted areas, the usual PV or ST single approaches may not be efficient enough. The current work is focused on the experimental analysis of the dual use of the solar resource by means of hybrid PVT collectors and their smart combination with direct expansion HPs through predictive control strategies. For that purpose, a solution with several innovations in the collector and in the overall control strategy was developed. A real-use single-family house has been selected for hosting the test at a continental climate (Jablonec nad Nisou, Czeck Republic) for a DHW application over one-year of operation. The sizing of the system has been carried out. The system comprising three PVT collectors and one PV module, dually connected to an inverter DX-saHP with an oversized TES and a predictive control has been properly installed, commissioned and fully accurately monitored. The recorded dataset has been postprocessed according to specific internationally recognized procedures for PVT plus HP systems. After one entire year of the experimental campaign the obtained system-level average day KPIs show 83% for RES, 220% for SSR, 41% for SCR and 46% for SF. For the entire period of aggregation, the KPIs are 86% for RES, 204% for SSR, 28.5% for SCR and 25.7% for SF, due to the impact of common summertime high energy resource short HP operation days. The high RES is essentially based on HP performance and enhanced by solar field contribution. The obtained SCR shows good underlying control performance. The obtained SSR and SF results are huge, but somehow artificially boosted due to the summer season’s high solar resource and DX-saHP ambient heat collection. The overall good performance results are endorsed with monthly level analyses, which show the DHW demand is well covered even for the most critical months. For day-based analysis, a detailed intraday performance has been carried out, concluding with the validation of the smart high-level prediction-based controller that handles the operation of the HP during the optimum solar resource and high ambient temperature period without impacting end-user comfort. Energies 2022,15, 3205 20 of 23 The end-user experience after one year of operation was good, with no impact on the DHW usage patterns or comfort levels. Just some punctual remarks were reported at the beginning of the testing period due to the uncertainty caused by not having the TES at maximum temperature. It would be desirable to have a detailed explanation for end-users when these kinds of systems are replacing traditional boilers. As the main outcome, it can be concluded that the proposed solution has provided effective and efficient DHW to a family for one entire year. However, the oversizing of components, mainly for solar collection field and TES, may enhance system capabilities and ensure the end-user comfort, but also makes it difficult to succeed in all the KPIs at the same time. Further simulation and sensitivity analysis might be helpful in order to determine the required trade-off between objectives to achieve. 5. Patents The PVT collector tested in the current work presents different intellectual property rights protection. The overall system control software is also registered. Author Contributions: Conceptualization, A.S., A.J.M. and E.R.; methodology, A.S.; software, A.S. and A.P.; validation, A.S., A.J.M. and A.P.; formal analysis, A.S., A.J.M. and R.F.; investigation, A.S., A.J.M. and R.F.; resources, A.S. and R.F.; data curation, A.S., A.P. and R.F.; writing—original draft preparation, A.S.; writing—review and editing, A.S., R.F. and E.R.; visualization, A.S., R.F. and A.P.; supervision, A.S. and R.F.; project administration, A.S., P.I. and E.R.; funding acquisition, A.S., P.I. and E.R. All authors have read and agreed to the published version of the manuscript. Funding: This research was funded by EIT InnoEnergy, grant number 56_2014_IP127_Handle and the APC was funded by Fundación TECNALIA Research & Innovation. Data Availability Statement: Not applicable. Acknowledgments: We are grateful to Fundación TECNALIA Research & Innovation and Energy Panel S.A organizations for supporting the research activities not covered by funding, especially for their technical support and for enabling the use of their own research infrastructure. To Termosol, Vaclav and Lenka for their hospitality and willingness to host the field demonstrator and be our local support. To the University of the Basque Country UPV/EHU for its access to research resources. And finally, to the IEA SHC Task 60 group for the valuable dissertations on PVT. Conflicts of Interest: The authors declare no conflict of interest. Glossary APVT/PV aperture area of collector or module c-Si crystalline silicon DHW domestic hot water DX-saHP direct expansion solar assisted heat pump EGC grid net consumption EHP heat pump electrical energy EPVac solar field electrical energy output fPVT PV maximum power deviation factor between collector and reference module GPoA global plane of array irradiance HP heat pump H&C space heating/cooling IComp compressor current KPI key performance indicators nZEB nearly zero energy building OECD Organisation for Economic Co-operation and Development PR performance ratio PPV solar field photovoltaic power PPVm reference module photovoltaic power Energies 2022,15, 3205 21 of 23 PPVT collector field photovoltaic power PGrid grid power consumption PGrid,NC grid net power consumption PF performance factor PR performance ratio PRPVT PV performance factor deviation between collector and reference module PV photovoltaic PVT photovoltaic-thermal QHP heat pump heat output QPVT collector field heat output RES renewable energy share SCR self-consumption ratio SF solar fraction SSR self-sufficiency ratio ST solar thermal Tamb ambient temperature TCon condensation temperature TCOut condenser outlet temperature TDis discharge temperature TES thermal energy store TEva evaporation temperature TSuc suction temperature TTES100 upper tank, top height, temperature TTES50 middle tank, half height, temperature TTES50max middle tank maximum day temperature TTES50min middle tank minimum day temperature TTES50 max min middle tank day cycle temperature delta TTES,load tank load temperature TTES,mid tank middle temperature TPV reference module middle backsheet temperature TPVT collector middle absorber backsheet temperature TPVT PV operation temperature deviation between collector and reference module VComp compressor voltage ws wind speed ηPV electrical conversion efficiency ηPVT aggregated, electrical and thermal, conversion efficiency References 1. 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