Photovoltaic-thermal hybrid collector performance for direct trigeneration in a European building retrofit case study

Abstract

This article compares the annual energetic, exergetic and economic performance of a combined (hybrid) photovoltaic-thermal collector system (PVT) to that of a system with separate solar thermal and photovoltaic collectors. Furthermore, energy saving potentials through refurbishment of the building envelope are investigated. The analysis is based on simulations with an experimentally validated PVT model. The major novelty of the study is that the water based PVT collectors are also used for long wave radiative cooling. Three different residential case study buildings from Central to Southern European climate zones are investigated. Their heat, cooling and electricity demand, as well as their renewable supply, are determined along with savings through the envelope measures. In general, the performance of the PVT system varies strongly with the boundary conditions of the demand profile, climate situation and energy price levels. The results demonstrate that PVT collectors used for heat (primary DHW) and electricity offer approximately 6–7 percentage points higher exergetic efficiency than thermal and PV collectors equally sharing the available surface area. Raising the temperature level for cooling by 4K increases the amount of renewable cooling by a factor 2–4. The analysis shows that the economic performance of the trigeneration PVT system is only better than separate generation if the additional electricity and cooling generate enough benefit to compensate the loss of heat gains. Especially in the Portuguese location of Almada, with high electricity price levels and high enough cooling demand, the application of PVT in a trigeneration system is recommendable from an exergetic and economic point of view.