German researchers have simulated the seasonal performance of PVT panels in salt water-to-water heat pumps for heating private houses. They compared them to air and ground source heat pumps with solar electricity and air and gas heating systems.
Researchers compared six reference systems to two PVT heat pump systems using seasonal coefficient of performance (SCOP) and carbon dioxide emissions as metrics.
The first PVT heat pump system uses an uncovered PVT collector with fins on the back, which increases energy from the sun and ambient air. The power of this system is 340 W and the electrical efficiency is 17.5%. It has an open-circuit voltage of 48.0 V and a short-circuit voltage of 9.45 A. Another PVT heat pump system uses a standard uncovered PVT collector with a power of 300 W, an electrical efficiency of 18.3%, an open-circuit voltage of 39.9 V and a short-circuit voltage of 9, 77 A.
On the heat pump side, the simulated systems use either a saltwater-to-water heat pump, where the PVT collector is the only heat source, or a borehole heat exchanger (BHE) as an additional source. The heat output of the heat collection water heat pump is 9.1 kW and the coefficient of performance (COP) is 4.13 at a source temperature of 0 C and an output water temperature of 35 C (B0/W35). Both systems have a 560-liter buffer-operated hot water storage tank, and a simulated geothermal heat pump uses a 70-meter-deep BHE.
The reference systems are powered by solar panels or the grid and include air and ground source heat pumps and gas condensing boilers, either independently or combined with solar collectors. The PV modules of the reference systems have similar performance data to the finned PVT collector. The thermal heating power of the air heat pump is 7.4 kW and COP 3.5 in A2/W35. The depth of the BHE of the reference ground source heat pump is 110 meters and the nominal heating power of the gas boiler is 15 kW, the water volume is 7.3 liters and the efficiency is 96.59%. The area of the solar heating system is 15 square meters.
Research shows that using PVT with fins as the sole source of heat for heat pumps gives a SCOP of 3.49 for 20 square meter PVT collectors and 3.80 for 30 square meter. In contrast, standard PVT systems have 8-14% lower performance and require larger areas to achieve comparable results. The researchers note that connecting PVT heat pump systems to a 70-meter depth BHE produces SCOP values in excess of 4.0, regardless of the specific PVT collection technology.
In comparison, the Air Heat Pump produces a SCOP of 3.29 when combined with a 20 m2 solar system, and a SCOP of 3.82 with a 30 m2 solar installation. Academics claim that a direct comparison of PVT heat pump systems with air source heat pumps shows that PVT heat pump systems are a competitive alternative to these reference systems.
A ground source heat pump combined with a 110 meter deep BHE produces a SCOP value of 4.24, which increases to 4.87 when combined with a 30 m2 photovoltaic system. Therefore, the researchers emphasize that the combination of PVT with BHE opens up the possibility of shortening the BHE length by about 35% without affecting the efficiency of the system.
Finally, the study states that using PVT as the sole source of heat pump systems can reduce carbon dioxide emissions by up to 57% compared to gas condensing boilers. Combining PVT with smaller BHE heat pump systems could reduce carbon dioxide emissions by up to 63%. Air source heat pumps combined with solar energy can reduce emissions by 52% and geothermal heat pumps with a 110 meter BHE can reduce emissions by 63% compared to a reference gas boiler.