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Schematic design of the optimised glazed PVT collector.
© Fraunhofer ISE

Overview of efficiency-enhancing measures in pneumatic drive and handling technology (compressed air).
© EnEffAH project consortium

Exergy yield of a glazed PVT collector relative to the operating temperature.
© Fraunhofer ISE

Technologically optimised hybrid collector

Previous systems where the PV modules are bonded to solar absorbers in glazed collector housings have not achieved satisfactory outputs. The additional glass pane creates higher cell temperatures, which limits the electricity yield. In addition, the solar thermal yield also reduces, whereby heat is lost as a result of the poor heat transfer from the cells to the heat transfer fluid and because there is no selective coating on the absorber.

With a newly developed PVT collector, researchers from Fraunhofer ISE have now been able to reduce optical losses and considerably increase the thermal conduction and thus the efficiency: crystalline solar cells are directly laminated to the metal absorber with an ethyl vinyl acetate (EVA) film. The collector is furnished with a glass pane with a double-sided antireflective coating, which increases the transmission. A polymer film with a suitably matched refractive index covers the module absorber composite and reduces the reflection (Fig. 1). The new collector was created as part of the PVTcol project in collaboration with industry. In the PVTmax follow-up project funded by the Deutsche Bundesstiftung Umwelt (DBU), researchers are working on further improving the thermal efficiency and preventing the PV laminate from being destroyed through increased stagnation temperatures.

Dreieich pilot system with PVT collector, borehole thermal energy storage and heat pump

In a project funded by the German Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, the ISFH investigated a new heat supply system with a heat pump and borehole heat exchanger. With this combination, the unglazed PV module is cooled, the electrical efficiency is improved (by around 10 % when cooled from 60 to 40 °C) and the surplus solar heat from the collector is routed to the borehole heat exchanger where it is stored. For the heat pump, an increase in the temperature of the heat source of around 10 K enables the heat pump COP to increase by around 1.5. The system therefore achieves greater yields in the PV area and savings with the heat pump. With this innovative energy concept, a pilot system in Dreieich in the German state of Hesse (Fig. 2) provides complete solar coverage of the energy requirement. In the system, which was designed for a larger house, arrays with and without cooling are located next to each other for comparison purposes. The 280-m2 single-family home with surface heating is equipped with a 39-m² PVT collector surface area, two PV reference modules without cooling (= 3.2 m2) and a 12-kW heat pump connected with three 75-m borehole heat exchangers.

In the two measured operating years, the heat pump achieved a very good COP of 4.2 in relation to the heat flow to loads and taking into account the storage losses and the pump’s electricity consumption. Per year and square metre, the collectors produced a thermal yield of around 450 kWh. The PVT collector regenerates the heat source using the solar thermal yields in summer. Calculations based on measurements and simulations have shown that this regeneration prevents the long-term cooling of the borehole heat exchangers and increases the temperature T*WP on average by 4.3 K. The researchers have been able to simulate a very precise model of the heat source comprising the borehole heat exchanger and PVT collector. Comparison measurements across two years have shown that the combined system supplies a PV yield that is up to 4 % higher, whereby up to 10 % is possible with special installation situations or under different climatic conditions. 10 % electricity savings are achieved when using the heat pump.

Kümmersbruck pilot system produces electricity and heats an indoor swimming pool

With this PVT system, the heat from the photovoltaic module warms air via a special absorber system for an indoor swimming pool in Kümmersbruck, Bavaria. The system was developed by the University of Applied Sciences Amberg-Weiden and the Grammer Solar company, and was funded by the Bavarian State Ministry of Economic Affairs, Infrastructure, Transport and Technology. With a photovoltaic module area of approximately 130 m2, it supplies an electrical output of approximately 16 kWpeak. An airflow system cools the rear side, whereby the waste heat of around 50 kWpeak reduces the ventilation heating requirements for the indoor swimming pool. The PV energy yield was over 5 % greater than that of a non-cooled comparison system. The system is designed to optimise the photovoltaic yield in preference to the solar thermal yield. Such hybrid collectors can supply large volumes of air at a relatively low temperature level. They work best of all when they supply loads such as drying facilities and indoor swimming pools throughout the year or pre-heat air for process heat systems.


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Project BiSolar-WP
ISFH GmbH Hameln

Project BiSolar-WP

Project PVTcol
Fraunhofer ISE

Pilot system Kümmersbruck
Institut für Energietechnik IfE GmbH

Pilot system Kümmersbruck
Grammer Solar GmbH