ᐅ Pellet-Solar Combination – Issues During Summer?

Hello everyone,

I am currently in discussions with the first heating installers. The centerpiece will be a pellet heating system (15 kW) — either ETA or KWB. Since I’ve only heard good things about solar combination systems, I want to implement this as well. I expect to almost completely save on pellet consumption during the summer, as solar should be sufficient for domestic hot water preparation.

After talking with the heating installer, I am now a bit uncertain. He mentioned problems with such a combination because in summer, too much heat is generated (since very little water from the buffer tank is used), and the glycol in the solar panels can partially evaporate due to overheating. Instead, he would prefer to use photovoltaic panels and support the heating with an electric heating element. This issue is new to me, and I couldn’t find much information about it online either.

What do you think? Maybe one of you has experience with either of these heating technologies.

Best regards,
XxTankerxX

XxTankerxX schrieb:

He, on the other hand, would rather use photovoltaic panels instead of solar thermal and implement heating support with an electric heating element.

I would ALWAYS prefer photovoltaic systems over solar thermal for exactly the reason that the sun shines in summer, and you don’t really know what to do with the energy. You can’t take continuous showers that often.

How about photovoltaic combined with a domestic hot water heat pump or something similar?

Solar thermal systems are beneficial if you have them for free (or receive them at no cost). Otherwise, photovoltaic systems are preferable because you can use the electricity (from the sun) for other purposes as well.

But yes, of course, a 5m² (54ft²) solar thermal system typically covers the hot water needs of an average household from March to October in our climate.

The glycol can evaporate occasionally, but it mostly remains within the system. Since this does not happen suddenly, the system does not suffer any damage.

nordanney schrieb:

I would ALWAYS prefer photovoltaic systems over solar thermal for exactly the reason that the sun shines in summer and you often don’t know what to do with the excess energy. You can’t shower continuously that often.
How about photovoltaic combined with a domestic hot water heat pump or something similar?

Domestic hot water heat pump? But aren’t the costs much higher than with a simple electric heating element?

Mycraft schrieb:

Yes, of course, a 5 sqm (54 sq ft) solar thermal system typically covers the hot water needs of an average household from March to October in our region.

That was my thought, yes.

Mycraft schrieb:

The glycol can evaporate occasionally, but it mostly stays within the system and since it doesn’t happen suddenly, the system doesn’t suffer damage from it.

If you plan to cover the house’s own consumption with photovoltaic anyway, wouldn’t it make more sense to rely on an electric heating element during summer?
How many kilowatts peak (kWp) of photovoltaic would you recommend for a 170 m2 (1830 sq ft) single-family home (+ basement) if it’s only meant to cover the household’s own electricity demand?

XxTankerxX schrieb:

How many kWp of photovoltaic capacity would you recommend for a 170 m2 (1830 square feet) single-family home (+ basement) if it should only cover self-consumption?

No small photovoltaic system just for self-consumption. As large as possible. Anything less is uneconomical. So around 10-15 kW peak.

XxTankerxX schrieb:

Domestic hot water heat pump? Aren’t the costs much higher than for an electric heating rod?

Yes, the initial investment is higher. But in operation, definitely not.

This is a small heat pump installed indoors that provides the heating. Maybe around 1 kW power input – producing 4 to 5 kW of heat output (the electric heating rod is 4 to 5 times less efficient).

Just look up “domestic hot water heat pump.”

Your electric heating rod is also known as an electric immersion heater or instantaneous water heater in other regions. That might make its effectiveness clearer to you (though it’s cheap to buy).

nordanney schrieb:

No small photovoltaic system just for personal use. As large as possible. Anything else is uneconomical. So 10-15 kWpeak

Yes, upfront costs are high. In operation, clearly no.
This is a very small heat pump installed indoors that performs its work there. Maybe 1 kW output – from that, you get 4-5 kW of heating capacity (the electric heating element is 4-5 times less efficient).
Just google domestic hot water heat pump.

Your electric heating element is also called an instantaneous water heater by others. That might help you understand how efficient it is (even if it’s cheap to buy).

Thanks for the information. I really have zero knowledge about heating systems.
How much does a small heat pump usually cost?