| Work Detail |
Researchers from the German Frauhofer ISE institute have analyzed the performance of a residential heat pump connected to a rooftop photovoltaic system featuring battery storage and have found that this combination significantly improves the performance of the heat pump while significantly increasing the self-consumption rate of the solar field.
A group of researchers from the Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) in Germany investigated the performance of smart grid-ready heat pumps (HPs) combined with rooftop solar power generation and storage. batteries in single-family homes and found that both photovoltaic arrays and batteries can significantly improve the performance of heat pumps.
The grid operator can switch off smart heat pumps during periods of highest grid load. They also offer the advantage of maximizing photovoltaic self-consumption by adjusting their operation depending on the available solar energy.
“Smart grid-ready mode is activated when the battery is fully charged or charging at full power and there is still excess PV available,” explain the scientists, noting that smart grid-ready HPs can adjust their operation depending on the network. “On the contrary, the disconnection condition is met when the instantaneous PV power remains lower than the total building demand for at least 10 min.”
Specifically, the academics analyzed the performance of a PV-HP system using 1-minute resolution field data from a semi-detached single-family house built in 1960 in Freiburg, southern Germany. The house has an annual heating demand of 84.3 kWh/m²a and a heated living area of ??256 m2.
The analysis looked at how the smart control used in the solar plus storage system can affect the performance of the heat pump. They took into account key performance indicators (KPIs) such as self-consumption rate, solar fraction, seasonal performance factor and heating curve. “It may be useful to evaluate the performance of the heat pump only for the electricity consumed from the grid,” they explained. “This approach is based on the assumption that the electricity generated by home PV units and batteries is effectively free to homeowners.”
The proposed system configuration includes a 13.9 kW geothermal heat pump for heating and domestic hot water (DHW), a 12.3 kW south-facing photovoltaic system with an inclination angle of 30 degrees, a 12 kW and a DC coupled battery with a capacity of 11.7 kWh.
The analysis showed that the PV-HP system was capable of achieving an average self-consumption rate of 42.9% throughout the year, reaching the highest peaks in winter. “On the contrary, a high photovoltaic surplus leads to lower self-consumption in summer, normally during the hours of maximum sunlight,” the research team explained. “A greater battery capacity would help maximize self-consumption; However, this also means that most of the battery capacity would remain unused during the winter months with limited PV surplus.”
The scientists also found that the solar plus storage system was able to cover about 36% of the heat pumps electricity demand. “Due to the higher sump temperatures, the HP efficiency decreases by 5.7% in DHW mode and 4.0% in heating mode,” they also specified. “The results showed that when considering the photovoltaic electricity supplied to the heat pump, the seasonal performance factor increased from 4.2 to 5.2. When the combined PV and battery supply to the heat pump was considered, the seasonal performance factor increased to 6.7”.
However, they also noted that smart control can negatively impact heat pump efficiency due to increased supply temperatures. “Long-term evaluation at the system level, taking into account the effect of storage losses and considering economic performance can better evaluate the effect of intelligent control on the system,” they concluded.
Their conclusions are available in the study “ Analysis of the performance and operation of a photovoltaic-battery heat pump system based on field measurement data ” field), published in Solar Energy Advances . |
