KOSTAL Pressebereich


Using photovoltaics, energy storage and heat pumps for your own energy transition

How do you bring a two-family house with energy technology from the 1980s up to modern standards? The Wiedmer family from Inzlingen in Germany's southwestern corner, near the Swiss city of Basel, has successfully implemented its own energy transition following the "KOSTAL dual power" principle.

With KOSTAL dual power, two KOSTAL inverters from the PLENTICORE plus series work together to make optimum use of self-generated solar power. This means that even during transitional seasons with low solar irradiation, a good level of self-generation is possible. We spoke to Mr Wiedmer about the challenges he faced when switching from gas heating to renewable energy and the benefits of his 17.54-kilowatt peak solar power system used in combination with a 12.8-kilowatt hour energy storage unit and a 9.54-kilowatt air-water heat pump.
Using photovoltaics, energy storage and heat pumps for your own energy transition

Editorial team: Mr Wiedmer, what motivated you to invest in renewable energies? 

Siegbert Wiedmer: My motivation, of course, was to use the new heating system to improve the future energy balance of the building – especially with regard to the CO2 taxes we can expect to have to pay in the future. Furthermore, we were looking for an investment that would also yield a "profit". Our "profit" is the costs that will no longer be incurred in the future because with the new heating system we won't buy in any gas and we'll buy much less electricity. Thanks to renewable energy, we also won't be faced with any CO2 taxes.

Editorial team: Together with your wife, in 2021 you converted your home to a supply of electricity and heat delivered by renewable energies using photovoltaics, an energy storage unit and a heat pump. The decision to make this change will certainly have been a long while in the making. Can you explain it in a little more detail? 

Siegbert Wiedmer: The initial spark came from our electrician. He had already installed many photovoltaic systems with KOSTAL components, including some combined with heat pumps, and had only good things to report. After our initial conversations, I looked into the topic in more depth, read about other people’s experiences and even took part in a webinar. After that, the decision was obvious.

Editorial team: Right from the start, you designed your solar system with an energy storage unit and heat pump for high self-consumption. What role does the Renewable Energies Act subsidy play for you in terms of the economic viability of your solar system?

Siegbert Wiedmer: The Renewable Energies Act subsidy obviously has a role to play in a system of this power class. Especially in the months between April and September, because during this time we don't consume all the electricity we generate ourselves. Our system sometimes supplies over 100 kilowatt hours for several days. However, the motivation for switching to renewable energy was the ability to consume the power we generate as two households.

Using photovoltaics, energy storage and heat pumps for your own energy transition
Using photovoltaics, energy storage and heat pumps for your own energy transition

Editorial team: Energy storage units are vitally important to a high degree of self-sufficiency. What has your own experience been here?

Siegbert Wiedmer: It was clear to me that we would definitely need a storage unit. This is the only way we can consume a lot of the electricity ourselves. This has also been demonstrated in practice over the past few months – we've already enjoyed four months of 99 % self-sufficiency over the eight months of PV operation.

Editorial team: Why did you choose the KOSTAL inverter, BYD storage unit and heat pump? With KOSTAL you can choose from a wide range of compatible storage systems.

Siegbert Wiedmer: In tests, KOSTAL proved to me the very high level of efficiency of the BYD storage unit. I also know from our installer that KOSTAL inverters work perfectly in combination with heat pumps and storage units.

Editorial team: You have just under 13 kilowatt hours of storage capacity. What are your experiences of this?

Siegbert Wiedmer: In the months between May and September, the storage unit is easily sufficient. In the other months, the capacity is sufficient on very good sunny days. When the sky is overcast and the heat pump is running, we only draw from the grid what the solar system does not supply.

Editorial team: Do you use the KOSTAL Solar App and if so, what do you think of it?

Siegbert Wiedmer: Yes, of course. It's clearly laid out and reliably provides me with data that is relevant to me and that I need for efficient system operation.

Using photovoltaics, energy storage and heat pumps for your own energy transition

Editorial team: You have taken a step towards self-supply with green electricity and renewable heat. Many people are still wondering whether PV, a storage unit and a heat pump will be able to keep their homes warm in winter. Do you have any tips, advice or recommendations for people who are still undecided? 

Siegbert Wiedmer: In general, I recommend that anyone thinking about switching to a renewable heating system should start planning early and not wait until their old heating system breaks down. The technical implementation takes some time, especially in an existing building. 

Mr Wiedmer, thank you very much for talking to us.

Facts & figures:

Building: Two-family house with 240 square metres of living space

Residents: Five adults, one child

Year of construction: Before 1980

Living space: 240 square metres split over two homes

Photovoltaics: Self-consumption system with 17.6 kilowatt peak. East-west

Inverters: Two PLENTICOREs in a device network – known at KOSTAL as dual power for short – with 10 kW and 5.5 kW

Energy storage unit: BYD, 12.8 kilowatt hours

*KOSTAL dual power: The energy of the second PLENTICORE inverter can also be stored as AC using the "smart AC link" function. This means that all the PV generator output is available to charge the battery during transitional seasons. Nevertheless, all inverters supply the house grid. Only when the energy from the photovoltaic system is no longer sufficient does the inverter connected to the energy storage unit draw energy from this unit – and it draws exactly the amount required, so that no energy has to be drawn from the public grid. Domestic consumers such as heat pumps can be easily integrated into the KOSTAL dual power system. All the customer needs to do is install the KOSTAL Smart Energy Meter so that it can "see" (measure) the demand of all consumers – including the heat pump.

Energy management: KOSTAL Smart Energy Meter (KSEM) in combination with two PLENTICORE plus inverters

Work cascade: 1. Cover domestic consumption; 2. Charge energy storage unit; 3. Feed into the grid

Heat pump: WPL 20 A air-water heat pump from Stiebel Eltron with a rated output of 9.54 kW. The calculated annual performance factor (APF) for heating and hot water was 3.6. The value actually observed from July to December 2021 was 3.57. Panel radiators are used in the building. The residents describe the heating performance in the winter months as very good.