Abstract
We investigate solar combined heat and power (S-CHP) systems based on hybrid photovoltaic-thermal (PVT) collectors for the simultaneous provision of domestic hot water (DHW), space heating (SH) and power to single-family homes. The systems include PVT collectors with a polycarbonate flat-box structure design, a water storage tank, an auxiliary heater and a battery storage subsystem. A methodology is developed for modelling the energetic and economic performance of such PVT-based S-CHP systems, which is used to optimally size and operate systems for covering the energy demands of single-family reference households at three selected locations: Athens (Greece), London (UK) and Zaragoza (Spain). The results show that optimised systems are capable of covering ∼65% of the annual household electricity demands in Athens, London and Zaragoza when employing 14.0, 17.0 and 12.4 m2 collector array areas respectively, while also covering a significant fraction of the thermal energy demands in Athens (∼60%) and Zaragoza (∼45%); even in London, almost 30% of the reference household’s thermal demand is covered by such a system. A corresponding economic analysis reveals that, despite the suitability of Athens’ weather conditions for implementing such solar-energy systems, the payback time (PBT) of the optimised S-CHP system in Athens is 15.6 years in contrast to the 11.6 years predicted for Zaragoza, due to the lower electricity prices in Greece. On the other hand, the high carbon emission factor of the electricity grid in Greece makes these systems particularly promising at this location. Specifically, the investigated systems have the potential to displace 3.87, 1.65 and 1.54 tons of CO2 per year in Athens, London and Zaragoza, when substituting the conventional means for household energy provision (i.e. grid electricity and gas-fired boilers). Furthermore, it is demonstrated that the optimised systems outperform benchmark equivalent systems comprising conventional sheet-and-tube PVT collectors in all studied cases, by covering similar or slightly (up to 3%) higher fractions of the household electrical and thermal demands with 9–11% lower PBTs, and that PV-only solutions displace 3.56, 1.21, 1.22 tCO2/year (up to ∼20–25% lower) for the same area. Overall, the results suggest that the newly proposed polymeric flat-box PVT collector designs are an improved economic proposition over their conventional equivalents, but that the cost of this technology still remains high relative to PV and that if decarbonisation is a desirable goal, especially in high population-density regions with space restrictions, it is important to consider how to promote this technology.
Highlights
The utilisation of solar energy is a key enabler of the transition to a clean and sustainable energy future [1,2]
The outputs returned by the model at each half-hourly time-step include the temperatures of the different layers of the PVT collector, the collector water outlet temperature, the water temperatures at each node in the storage tank, the state of charge (SOC) of the batteries, the electrical and thermal energy generated by the complete solar combined heat and power (S-CHP) system, the electrical and thermal energy demands of the household covered by the system, the energy, cost and CO2 emissions savings, the levelised production cost (LPC) and the payback time (PBT) of the system
The system performance indicators are evaluated for the case of Zaragoza, which was selected amongst the locations of interest here as it is an intermediate case between those of Athens and London
Summary
The utilisation of solar energy is a key enabler of the transition to a clean and sustainable energy future [1,2]. Of particular interest are the limited conversion efficiencies experienced at elevated operation temperatures and the greater thermal cycling experienced (passively) in response to external weather conditions, both of which act to damage the PV cells. This has motivated important research into cooling techniques for the thermal regulation of PV modules [3], which has led to the proposal of hybrid photovoltaic-thermal (PVT) collectors, comprising a PV module typically laminated on top of a thermal absorber for heat removal, that are capable of generating both electrical and thermal outputs from the same collector area [4]. Abbreviations (monthly) battery self-discharge rate domestic hot water feed-in tariff fuel saving International Energy Agency poly-crystalline silicon polycarbonate payback time photovoltaic photovoltaic-thermal system photovoltaic-thermal water system renewable heat incentive seasonal energy efficiency ratio space heating solar thermal transparent insulating cover life cycle cost levelised production cost net present value solar combined heat and power state of charge (radiant) underfloor heating Symbols
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