System analysis of a PV/T hybrid solar window

Abstract: A building-integrated multifunctional PV/T solar window was suggested and developed by Andreas Fieber. The solar window is constructed of PV cells laminated on solar absorbers placed in a window behind the glazing. To reduce the costs of solar electricity, tiltable reflectors have been introduced in the construction to focus radiation onto the solar cells. The reflectors make it possible to control the amount of radiation transmitted into the building. The insulated reflectors also reduce the thermal losses through the window. Fieber discusses the architectural implications of the solar window. The effects on the light distribution are discussed together with effects on the building if different strategies of controlling the reflectors are used. Following this, long term measurements on the energy output from the solar window were performed. A model for simulation of the electric and hot water production was developed and calibrated against the measured values. The model can perform yearly energy simulations where different features such as shading of the cells or effects of the glazing can be included or excluded. The simulation can be run with the reflectors in an active, upright, position or in a passive, horizontal, position. The simulation program was calibrated against measurements on a prototype solar window placed in Lund in the south of Sweden and against a solar window built into a single family house, Solgården, in Älvkarleö in the central part of Sweden. The results from the simulation show that the solar window produces about 35% more electric energy per unit cell area than a vertical flat PV module.
When the solar collector is placed in the window a complex interaction takes place. On the positive side is the reduction of the thermal losses due to the insulated reflectors. On the negative side is the blocking of solar radiation that would otherwise heat the building passively. This might result in an increase of auxiliary energy need compared to a standard solar energy system. However, this might be accepted if the price of the PV/T hybrid is less than the total price of the individual components. To investigate the sum of such complex interaction a system analysis has to be performed. Results from simulations using TRNSYS show that the system with individual solar energy components annually uses 1100 kWh less auxiliary energy than the system with a solar window. However, the solar window system annually uses 600 kWh less auxiliary energy than a system with no active solar energy system.