Pellet-solar combination - Issue in summer?

If photovoltaics, then as much as possible. If solar thermal, then 4-5 sqm, and if your gut feeling doesn’t let you decide, just install both. You also see that occasionally on new roofs (even though it is rather the exception).

You can then use the excess electricity in summer for an air conditioner.

What does a small heat pump cost approximately?

It should cost around €2,000 (+/- depending on installation). Whether Buderus, Wolf or Vaillant.

What do you think about it?

The man thinks ahead. Once the hot water tank is heated through by the pellet system, the maintenance energy or reheating for consumption in summer is manageable. Of course, a heating rod does not have the same efficiency as a heat pump, is absolutely right about that. However, using the heating rod with surplus energy from the roof has its charm. With a feed-in tariff well below 8 ct per kWh, which you can expect, and a 3-4 times higher purchase price, this will be cost-neutral to positive financially. In addition, it feels good to consume your own climate-friendly electricity. Many of us still receive a feed-in tariff at a level that makes every sqm of photovoltaic roof area a "no-brainer." That is slowly changing. Economically, self-consumption optimization is on the rise, as feed-in orientation is becoming less and less worthwhile.

Solar thermal now 13 years on the roof (old house), still tight, no pressure loss or refilling of glycol. Unfortunately, the roof is too small and too old for worthwhile photovoltaics and in at most 15 years "there will be an excavator going through the house anyway" :cool:. However, the new house has as much photovoltaics as possible installed.

But 15KW is quite something, how big is the property or is a pool supposed to be heated too? ;)

And as the predecessors already described: Now fill the roof fully with photovoltaics and optimize self-consumption (just not necessarily with "force" in the form of a battery). There were never any "limits" anyway, only small hurdles. So if 30KWp fits: Do it!

A heat pump probably provides a baseline noise for electricity consumption, just like deep freezers and other continuous consumers. But heat pump + pellet? High temperature + low temperature is simply not an optimal combo. The production costs of self-generated photovoltaic electricity are currently mostly (if you only consider the amortization period/feed-in tariff period of 25 years) above the feed-in tariff. But the nice thing is that the system does not dissolve into thin air after 25 years, but will probably still have an efficiency of over 90% (from 100% at the beginning) :)

The man thinks along. Once the hot water tank has been heated through with the pellet system, the maintenance energy or reheating for consumption in summer is manageable. Of course, a heating element does not have the same efficiency as a heat pump, is absolutely right about that. However, using the heating element with surplus energy from the roof does have its charm. With a feed-in tariff significantly below 8 cents per kWh, which you can expect, and a 3-4 times higher purchase price, this will have a cost-neutral to positive effect. Additionally, it feels good to consume your own climate-friendly electricity.
Many of us still receive a feed-in tariff at a level that makes every sqm of photovoltaic roof area a "no-brainer." That is slowly changing. Economically, self-consumption optimization is on the rise, as feed-in orientation is becoming less and less worthwhile.

Thank you very much for your detailed explanation.
The heating and/or building services technician told me that there are now intelligent controls that use the surplus energy for the heating element aka flow heater, and the rest is then completely used for the house – after 1-2 nights I no longer find the concept so bad. With this, I could probably dimension the buffer tank much smaller than with solar. This could also bring hygienic advantages in the long run (regarding legionella, etc.).

For this reason, I no longer understand the motto "Photovoltaics as much as possible" because, as you already said, the feed-in tariff is currently so low, and I wonder if it wouldn’t be cheaper to size everything (panel area, inverter, etc.) so that self-consumption (+ a small buffer for the future) is covered. Am I wrong here?

What is this actually about? Renovation, refurbishment, or new construction? In the case of new construction, I couldn't quite understand the focus on the pellet heating system.