Exploitation of PV electricity in a single-family house- with battery and heat pump

Results achieved

The main results of the project can be summarized as follows:

We have built a functioning advanced energy system which combines solar PV, battery, heat pump and heat storage in a home.

We have demonstrated state-of-the art within IoT (control through the Internet) for the home's energy management.

In order to optimize the utilization of solar electricity production, we have conducted experi-ments to raise the temperature of both heat pump vessels during periods of the day so that it could absorb more solar energy. Also, attempts have been made to show in which periods the heat pump could be switched off.

The storage potential of the heat pump by raising the temperature 10 degrees C is approx. 5 kWh, and with the included efficiency from the heat pump this corresponds to approx. 2 kWh of electricity. In addition, there is a storage potential in the concrete floor of approx. 45 kWh - equivalent to 15 - 20 kWh of solar cell electricity.

Total efficiency of charging and discharging the battery system varies from 66% to 77% month by month depending on load. Charging and discharging at low power results in high losses. The efficiency can therefore be increased by raising the power limit for charging / discharging (and ensuring that inverter idling is avoided).

The same amount of energy (primary electricity) can be stored in the tested battery as in the heat storage system of the heat pump system.

Storage in an electrically heated water heater is still (one of the) most economical storage options, as there is also a need for hot water in the summer.

Storage in thermal storage using floor heating works well during the heating season, but it is required that the mixing circuits are switched off and the room thermostats are opened com-pletely. Therefore, there is a need for more intelligent coupling between the housing temperature control and the heat pump control system. In a newly started EUDP project (OPSYS2) this chal-lenge will be addressed.

In the project, a user-friendly spreadsheet has been prepared for calculating energy flows and the economic saving of the various storage measures. Through the use of the calculator with current consumption and prices for electricity, solar cells, batteries and heat pumps, the project can be assessed – concerning as well energy as economy.

The largest savings are obtained from the PV plant itself, by displacing grid electricity. There is a further saving by investing in battery and / or heat storage up to a certain limit, which can typically double the self-consumption of PV power.

If you already have a heat pump with thermal buffer, this is a good storage option as it is only a matter of changing the control to make its electricity consumption flexible.

A simple design tool for combined battery storage and thermal storage has been developed.

The main practical experience is:

It is not easy for an advisor / installer to design a system with PV, batteries and / or heat pumps, as it is often difficult to make different components communicate.

Therefore:

Select components from the same company - or components that can communicate for sure. The system should be integrated, tested and installed by the same installer.

Select components from companies with technical customer support.

Choose a battery inverter that is relatively small compared to the PV system. Alternatively, the relatively small base load must be purchased from the electrical grid.

The project shows that the consumption pattern is of paramount importance when planning a control and storage system, and that energy losses are substantial if care is not taken in the design phase. Other important results are that ordinary concrete floor heating systems can store a large amount of energy without major fluctuation in room temperature.

The project shows opportunities – such as using the battery-storage for external energy – (e.g. wind power or hydro) – and barriers such as efficiency and noise, difficulties for users.

Also, the economic perspective is considered – mainly in the spreadsheet (calculation pro-gramme) for evaluation of energy storage in connection with solar PV systems. As a consumer or RE-installer / dealer, it is of great value to be able to test different scenarios before deciding on a specific plant size and structure. For example, a light building and a heavy building will have different options for integrating thermal energy storage.