ᐅ Switching from Gas to Solar / Photovoltaics with or without a Heat Pump

Hello everyone,

We have a semi-detached house that we fully renovated in 2014. We installed underfloor heating, new pipes, electrical wiring, etc. The only thing we didn’t replace was the old gas heating system.
Due to climate change and rising energy costs (reasons you all know very well), we are now considering replacing the heating system.

What is important to us?
- Becoming less dependent on gas and electricity
- Subsidies through a loan

• What is currently state-of-the-art and commonly installed?
• Solar thermal and/or photovoltaic systems with or without a heat pump?
• With or without electricity storage?

Unfortunately, I don’t have a clear overview yet of what would be best for us.

I hope you can help guide me in the right direction.

I haven’t had this combination for long yet, but based on my very low consumption values, I suspect it works quite well. 😉

Ground-source heat pump + photovoltaic system + battery storage

My amateur recommendation (based only on my own experience!):

- Photovoltaics should be as large as possible (ideally covering the entire roof, up to about 30 kWp)

- Size the battery storage according to your consumption* (*in summer, between 6:00 PM and 8:00 AM).
If you can bridge this period with the battery, the number of charging cycles stays reasonable, and you optimize self-consumption.

- Heat pump: We have an AI ground-source heat pump to achieve high efficiency and “passive cooling.” However, there are experts who can provide more detailed information on this.
I’m not sure what subsidies are currently available, but I suspect that especially refurbishment of existing buildings will have to be massively supported in the future.

I would also recommend a photovoltaic system combined with a heat pump. However, a ground-source heat pump is significantly more expensive and therefore more suitable for larger houses. An air-to-water heat pump usually requires an outdoor unit and is not quite as efficient. For a house built to current standards, though, this difference is not very significant.

I currently consider battery storage to be too expensive. However, if electricity prices remain high—which I doubt—the balance will increasingly shift towards storage solutions.

If the energy storage system is your future electric car, with bidirectional charging capability, even better.
I would also consider a heat pump combined with a large photovoltaic system as a top choice.
I hope the underfloor heating is designed for 30°C (86°F), since it has already been renovated.

Regarding battery storage, the question is what exactly is meant by "high electricity prices." I still have a rough estimate of 40c/kWh from storage in mind (does this still apply?). At this rate, there is currently price parity with cheap new contracts. I find it rather unlikely that prices will drop back to 30c/kWh within the next 2-5 years. Accordingly, the risk of losing a lot of money on battery storage is limited.

Aside from the fact that electricity currently comes not only to a large extent from Russian gas but also from Russian coal. Expanding wind and photovoltaic energy will certainly reduce that share but will require expensive grid-level storage solutions for balancing.

Semi-detached house, renovated in 2014, suggests a relatively moderate heating energy demand. How much gas do you use annually?
With that figure, you can roughly estimate the heat pump capacity.

Solar thermal systems are never worthwhile. Instead, cover the roof fully with photovoltaic panels. Also consider east, west, and north-facing roofs up to 25° pitch, garages, carports, south-facing walls... The more, the better, more cost-effective, and more environmentally friendly.
Storage systems become economically viable at around 60 cents per kWh electricity price. So, it largely depends on your forecast whether you want to invest in one. With a heat pump, I would only add a storage system once your photovoltaic setup exceeds 20 kWp. If the PV system is smaller, the heat pump won’t leave enough surplus energy for the storage. An electric car reduces the storage efficiency even further, since from October to February it practically won’t see any kWh at all...

I can’t think of any loan-based subsidies (e.g., through KfW). However, Bafa offers 35-40% funding including everything for replacing a gas heating system with a heat pump.