ᐅ Photovoltaic system for water heating and grid feed-in

The BWWP only costs a "few euros" extra but saves about half the electricity for domestic hot water compared to an electric tankless water heater. Tankless water heaters definitely do not fall under renewable energy systems, even if they are powered by photovoltaic panels. I know this because we currently have two of them and need to switch to meet the KfW Standard 100. Photovoltaics are far from sufficient for regular self-consumption in winter, let alone for heating. They are more suitable for spring and autumn. With my 7.28 kWp (kilowatt-peak) system, I sometimes only generate 1-2 kWh per day in winter (for comparison: on sunny summer days, it’s 45-48 kWh per day!), and I have a south-facing setup. That is not nearly enough.

I also don’t fully understand the logic of why a BWWP costing 700-1000 euros should be considered uneconomical, while a 15,000-euro air-source heat pump for heating is not. Especially since the BWWP operates at room temperature, around +20°C (68°F), whereas the air-to-water heat pump has to work with outdoor temperatures (we’ve had -15°C (5°F) last winter).

In-roof (building-integrated) photovoltaics are more expensive; stay below 10 kWp (kilowatt-peak)! (As far as I know, there is a small system regulation up to 10 kWp, but you should double-check that.)

Lexmaul79 schrieb:


But why are 30% of a 10 kW system 3,000 kWh?

Now you’ve confused me a bit.
A 10 kWp system produces roughly 10,000 kWh per year, as far as I know (of course depending on the region, around 8,700–9,300 kWh).
So 30% of that would be about 3,000 kWh.
Am I making a mistake in my reasoning?

Yes, because a 10 kW system delivers 10 kW at peak output – this has nothing to do with the annual energy production.

That means that overall, less energy will be fed back into the grid over the year, since the winter months produce little yield, right?

Lexmaul79 schrieb:
Yes, because a 10 kW system can deliver 10 kW at peak – this has nothing to do with the annual output.

Ah – OK.
Then it is indeed a misconception on my part.
My system has been running since September last year. So I still have about 3 months (mid-summer) left to see how large the difference is between the rated capacity and the actual output. Let’s see.

And how are you doing now with your system?