ᐅ Cost-effectiveness Analysis of Heat Pump / Ice Storage / Photovoltaic Systems
Created on: 28 Oct 2025 09:36
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NorbT
Hello everyone,
I have a detached house (built in 2018) with underfloor heating that runs on gas. I am considering a personal "energy transition" in the future. My question is whether and when it makes sense financially.
Currently, I pay about 5,000 € per year for gas (11,600 kWh/year) and electricity (3,600 kWh/year) with the local utility. About two years ago, I got a quote for a photovoltaic system (22.62 kWp, east/west orientation) including a battery storage (9.6 kWh). At that time, the system cost around 25,000 €. Do you have experience with when such a system becomes cost-effective? I would like to do the calculations myself (using Excel).
The main challenge is probably replacing the heating, or more precisely, the gas consumption. Has anyone had experience with ice storage systems? Are there better alternatives?
Thank you very much for your help!
I have a detached house (built in 2018) with underfloor heating that runs on gas. I am considering a personal "energy transition" in the future. My question is whether and when it makes sense financially.
Currently, I pay about 5,000 € per year for gas (11,600 kWh/year) and electricity (3,600 kWh/year) with the local utility. About two years ago, I got a quote for a photovoltaic system (22.62 kWp, east/west orientation) including a battery storage (9.6 kWh). At that time, the system cost around 25,000 €. Do you have experience with when such a system becomes cost-effective? I would like to do the calculations myself (using Excel).
The main challenge is probably replacing the heating, or more precisely, the gas consumption. Has anyone had experience with ice storage systems? Are there better alternatives?
Thank you very much for your help!
N
nordanney28 Oct 2025 10:20NorbT schrieb:
Have you already created a corresponding analysis?In my personal situation, the break-even point for my photovoltaic system is about 6 to 7 years (just a 10 kWp system without storage).A
ajokr202528 Oct 2025 15:40NorbT schrieb:
I dug up my bill from last year again. I pay 38.59 Ct/kWh, is it 36.1 Ct/kWh for you as described above? My gas price is 13.88 Ct/kWh. I’m probably 2 to 4 Ct/kWh higher... which provider do you use? With that, I can hardly reach more than €3,000 per year. You probably didn’t include fixed charges in the kWh prices. But even then, it won’t add up to €2,000.
The ice storage sounds good in theory. However, to store around 11,600 kWh of gas consumption over the summer, you will probably need a very large storage system. You can store photovoltaic electricity in battery storage, but not from summer to winter because the standby losses are too high.
If you have space in your garden, you’re probably better off building a DIY horizontal ground collector (also known as a trench collector). Although it can’t store heat, it does not have to process freezing outdoor air to generate heat during winter.
To get back to cost-effectiveness:
11,600 kWh of gas corresponds to about 10,000 kWh of heat demand after subtracting chimney losses. A good heat pump would then consume 2,500 kWh of electricity, which would cost you about €965 if you don’t find a cheaper electricity supplier. So, the energy cost is already lower than gas. Before seriously switching, have a heat meter installed in the heating circuit—it measures actual consumption more accurately than the gas meter before the chimney.
With photovoltaic systems, you can save some energy during transitional seasons and definitely for domestic hot water in summer.
The investment costs, of course, come on top, but you can depreciate those for your internal cost calculation over 20 years of service life. At a €40,000 quote minus 55% subsidy, that adds roughly €900 per year. Therefore, switching only really pays off when the old system breaks down or when the gas supplier shuts down their network.
Hello,
Regarding the gas and electricity prices the original poster is paying: they are absurdly high and can easily be reduced by about one-third each. Please consider switching providers. This is usually done every 12 months!
The problem is that the original poster does not receive a 55% subsidy, but only 35%, because the gas heating system is less than 20 years old. The offers you will receive already include the 55% subsidy, meaning they are roughly twice as expensive as they should be. This makes it very difficult to achieve any economic viability. And if you honestly factor in financing costs of at least 5% (which is rather low), the calculation basically fails immediately...
This might change in the coming years if any government actually enforces a significant increase in gas prices. However, I don’t expect that to happen.
I’m facing the same issue here with a gas heating system in a house built in 2026. Realistic offers are currently not available. I had hoped subsidies would end and prices would return to realistic levels, but unfortunately, I was mistaken.
On the topic of photovoltaics – yes, absolutely do it as soon as possible. Feed-in tariffs probably won’t last much longer. €25,000 for a 22 kWp system including storage was a very, very good price two years ago. It should be slightly cheaper now, but likely not under €20,000. A 22 kWp system also sounds like a great size. We are completely self-sufficient for about eight months of the year with 18 kWp, including an electric car!
Best regards,
Andreas
Regarding the gas and electricity prices the original poster is paying: they are absurdly high and can easily be reduced by about one-third each. Please consider switching providers. This is usually done every 12 months!
ajokr2025 schrieb:
With an offer price of €40,000 minus 55% subsidy, that adds another 900 euros per year on top.
The problem is that the original poster does not receive a 55% subsidy, but only 35%, because the gas heating system is less than 20 years old. The offers you will receive already include the 55% subsidy, meaning they are roughly twice as expensive as they should be. This makes it very difficult to achieve any economic viability. And if you honestly factor in financing costs of at least 5% (which is rather low), the calculation basically fails immediately...
This might change in the coming years if any government actually enforces a significant increase in gas prices. However, I don’t expect that to happen.
I’m facing the same issue here with a gas heating system in a house built in 2026. Realistic offers are currently not available. I had hoped subsidies would end and prices would return to realistic levels, but unfortunately, I was mistaken.
On the topic of photovoltaics – yes, absolutely do it as soon as possible. Feed-in tariffs probably won’t last much longer. €25,000 for a 22 kWp system including storage was a very, very good price two years ago. It should be slightly cheaper now, but likely not under €20,000. A 22 kWp system also sounds like a great size. We are completely self-sufficient for about eight months of the year with 18 kWp, including an electric car!
Best regards,
Andreas
A
ajokr202528 Oct 2025 16:22andimann schrieb:
The problem is that the original poster only receives 35% funding instead of 55% because the gas heating system is less than 20 years old. Yes, early replacement of the gas boiler is not cost-effective.
Regarding the photovoltaic system: I was recently offered €1400 per kWp (kilowatt peak), €510 per kWh (kilowatt hour) for the battery storage, and €1500 for installation.
However, it was made clear to me that my roof rafters are not suitable for photovoltaic panels. Therefore, I only went for a small balcony solar system, with a total investment of €500 for self-installation.
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