ᐅ Combination of air-to-air heat pump, air-to-water heat pump, solar thermal system, and photovoltaic system with storage

Hello everyone,

I hope I’m in the right subforum.

About my project:
My wife and I plan to build a new house (expected start spring 2021) with a KfW55 energy standard. The usable floor area will be approximately 209m² (2250 sq ft) plus a basement.

Our builder includes heating and domestic hot water via an air-to-water heat pump and an air-to-air heat pump, both with a fresh air system including a heat exchanger. Additionally, we decided on a 6 kWp photovoltaic system with a 6.5 kWh battery storage (available as a "spring offer" for about €10,000).

Since I’m generally someone who tries to avoid unnecessary costs (in this case electricity costs for hot water), I’ve been considering having a solar thermal system installed as well. Without the photovoltaic system, I expect savings of around €200 per year (about 800 kWh/year for hot water). If our household grows in the future, the savings would naturally increase.

In our last conversation with the architect, he was convinced that it would make more financial sense to increase the photovoltaic system to 8 kWp (additional cost approximately €5,000) instead of installing the solar thermal system. He couldn’t provide a price for the solar thermal system because it’s not listed in the price catalog, but I assume it would be a similar amount.

Now to my questions:
a) Does anyone have experience with similar energy system combinations?
b) Are there resources or services where one can have such calculations done?

Thank you in advance and best regards,
Kevin

KevinHoehne schrieb:

Without a photovoltaic system, I expect savings of about €200 per year (800 kWh/year for hot water). If the household grows at some point, the savings will increase accordingly.

A photovoltaic system is almost always cost-effective. Your price is reasonable.
I would also have estimated the solar thermal system at around €5,000. That means it produces cubic meters of hot water in the summer that you don’t need, and in winter it sits idle.
If you really save €200 a year, the investment would already have paid off after 25 years. LOL

Increasing capacity from 6 kWp to 8 kWp should cost around €1,500. An extra €5,000 is a complete rip-off.

I, and practically everyone here, prefer photovoltaic systems. Unlike solar thermal, you get paid for excess energy in the summer. For that reason, a photovoltaic system usually pays for itself after about 10 years.

Forget the sanitary installation if you don’t need it for meeting any subsidy requirements, etc. You can efficiently heat the water with an air-to-water heat pump. In summer, the electricity for this will come from the roof.

Also, don’t forget a shading concept. Modern houses tend to turn into a sauna in summer.

An air-to-air heat pump can then be installed for air cooling in the summer (in addition to the main heat source).

Great, thank you all. I have now decided on the 8 kWp system.

KevinHoehne schrieb:

Heating and domestic hot water are provided by an air-to-water heat pump and an air-to-air heat pump, including a fresh air system with a heat exchanger.

I was taken aback here. You are getting both an air-to-water heat pump and an air-to-air heat pump? I hope you meant controlled mechanical ventilation and not an air-to-air heat pump. Using both together doesn’t make sense, and generally, an air-to-air heat pump is impractical unless you are building a “true” passive house.

Hi,

yes, of course, a mechanical ventilation system with heat recovery will be installed. In addition to the heat exchanger, it includes an integrated air-to-air heat pump for warming or reheating the air. The exhaust air from this system is also used to produce domestic hot water via an air-to-water heat pump.

Regards
Kevin