pv magazine talks to Tim Riedel, who owns a 24 kW rooftop solar system and a 12.86 kW air source heat pump, about the return on investment of air source heat pumps and the savings that households can achieve by combining them with solar energy.
Although there is plenty of simulation data on the ROI of heat pumps and their symbiotic relationship with rooftop electricity, field statistics are more difficult to obtain. Tim Riedel, a sustainable development consultant at Berlin-based Planetgroups, has shared information about the heat pump and solar power system installed in his detached house in Germany.
On February 24, 2022, Riedel installed an air source heat pump system in its listed building from 1796, which consisted of an external heat pump unit with a heating power of up to 12.86 kW, a 170 liter hot water storage tank and a smaller indoor unit for heating water in the basement of the property.
“From May to October, the main heat pump is not in operation at all, we only use the small one to heat the water,” Riedel said. pv magazine. “In the long term, it is more cost-effective, because a small heat pump is more efficient at heating water. Then the bigger one won’t have as many starts, which will extend its life.
The heat pump system cost 31,000 euros ($34,260), including installation services. It was entitled to a subsidy of 10,500 euros from the German heat pump discount system, when the price dropped to 20,500 euros.
Riedel reports that his property used 20,000 kWh of gas in 2021, while the heat pump used 4,009 kWh of electricity from April 1, 2022 to March 31, 2023. According to Riedel, the heat pump saved him 1,595 euros per year in payback. For 13 years based on current gas and electricity prices.
“This investment result does not even take into account the fact that a new gas heating system would also cost money,” Riedel stated. “Only the payback period for the additional costs of the heat pump compared to the gas heating system would be much shorter.”
The Riedel family also has a 24 kW solar power system installed on the roof of the barn, which further maximizes the annual electricity savings. The system was installed in 2020 and has 325 W solar modules from the German manufacturer Heckert Solar. It produces 19,000 kWh of electricity per year and its total cost was 26,000 euros, including installation on the flat roof of the barn.
According to Riedel, the solar power system on the roof produced 1,433 kWh of the electricity used by the heat pump. At the price of self-consumption electricity of €0.07/kWh, the solar electricity and heat pump system produced annual savings of €2,256 compared to gas heating.
The Riedel family installed the heat pump system without any modernization or insulation. Their 18th-century house uses traditional radiators, and they replaced one with a larger one. An intelligent thermostat controls the system remotely to guarantee efficient heating.
Considering its annual heating output of about 20,000 kWh and electricity consumption of 4,009 kWh, the seasonal coefficient of performance (SCOP) of the heat pump system is 5. According to the technical form, the coefficient of performance (COP) is 2.98 at outside temperature. Source at 7 C and 4.14 at 2 C. The SCOP reported in the technical form is 4.53.
“This 5:1 ratio (heating power/electricity consumption) is not only due to the heat pump. It’s also because of how we use it with the smart meter,” Riedel said. “We also had temperature control before (installing the heat pump system), but this meter is just a little bit smarter.”
