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New research from the Fraunhofer Institute for Solar Energy Systems (Fraunhofer ISE) in Germany has shown that combining rooftop PV systems with storage batteries and heat pumps can improve the efficiency of heat pumps and reduce dependence on electricity. electrical network.
Researchers at Fraunhofer ISE have studied how residential rooftop photovoltaic systems could be combined with heat pumps and battery storage.
They evaluated the performance of a PV-heat pump-battery system based on a smart-grid (SG)-ready control in a single-family house built in 1960 in Freiburg, Germany.
“It was found that the intelligent control increased the performance of the heat pump by increasing the set temperatures,” researcher Shubham Baraskar told pv magazine . “The SG-Ready control increased the supply temperature by 4.1 Kelvin for hot water preparation, which reduced the seasonal performance factor (SPF) by 5.7%, from 3. 5 to 3.3?. Additionally, for space heating mode, the smart control decreased the SPF by 4%, from 5.0 to 4.8”.
The SPF is a value similar to the coefficient of performance (COP), except that it is calculated over a longer period with variable boundary conditions.
Baraskar and his colleagues explained their findings in “ Analysis of the performance and operation of a photovoltaic-battery heat pump system based on field measurement data. ” field), recently published in Solar Energy Advances . They stated that the main advantage of photovoltaic-heat pump systems consists of their lower grid consumption and lower electricity costs.
The heat pump system is a 13.9 kW geothermal heat pump designed with buffer storage for space heating. It also has an accumulator and a fresh water station to produce domestic hot water (DHW). Both storage units are equipped with auxiliary electric heaters.
The photovoltaic system faces south and has an inclination angle of 30 degrees. It has a power of 12.3 kW and a modular surface of 60 square meters. The battery is DC coupled and has a capacity of 11.7 kWh. The selected house has a heated living area of ??256 m2 and an annual heating demand of 84.3 kWh/m²a.
“The direct current of the photovoltaic and battery units is converted into alternating current by an inverter with a maximum power of 12 kW and a European efficiency of 95%,” explain the researchers, who point out that the SG-ready control is capable of interacting with the electrical grid and adjust system operation accordingly. “During periods of high grid load, the grid operator may switch off heat pump operation to reduce grid stress or may also undergo forced start in the opposite case.”
With the proposed system configuration, the PV energy must initially be used for the house loads, and the surplus is supplied to the battery. Excess energy could only be exported to the grid if the house does not need electricity and the battery is fully charged. If both the photovoltaic system and the battery are not capable of covering the energy demand of the house, you can resort to the electrical grid.
“The SG-Ready mode is activated when the battery is fully charged or is being charged to its maximum power and there is still photovoltaic surplus available,” the academics explain. “Conversely, the deactivation condition is met when the instantaneous PV power remains less than the total building demand for at least 10 minutes.”
Their analysis took into account self-consumption levels, solar fraction, heat pump efficiency, and the impact of the photovoltaic system and battery on heat pump performance efficiency. They used 1-minute high-resolution data from January to December 2022 and found that SG-Ready control increased heat pump supply temperatures by 4.1 K for DHW. They also verified that the system achieved global self-consumption of 42.9% during the year, which translates into economic benefits for the homeowners.
“The electricity demand of the heat pump was covered by 36% with the photovoltaic/battery system, 51% in the domestic hot water mode and 28% in the heating mode,” explained the team. research, which added that higher sump temperatures reduced heat pump efficiency by 5.7% in domestic hot water mode and 4.0% in heating mode.
“A negative effect of smart control on heating was also observed,” Baraskar said. “Due to the SG-Ready control, the heat pump operated in heating above the heating setpoint temperatures. This was because the control probably increased the storage setpoint temperature and operated the heat pump even though the heat was not needed for heating. It should also be taken into account that excessively high storage temperatures can lead to greater storage heat losses.”
The scientists stated that in the future they will investigate other PV/heat pump combinations with different system and control concepts.
“It must be taken into account that these results are specific to the individual systems evaluated and can vary greatly depending on the specifications of the building and the energy system,” they concluded. |
