ᐅ How large should the photovoltaic system be?

We received a quote from the electrician for a 10 kWp photovoltaic system. However, I am wondering whether investing in a 10 kWp system is really cost-effective or if a smaller system might be sufficient. Our four-person household consumes around 4,500 kWh in our rented apartment without a heat pump. In our planned single-family house (140 m² (1,507 sq ft), KfW 55 standard), there will be an air-to-water heat pump and possibly an electric car in the future. I am not familiar with the energy consumption of heat pumps, but wouldn’t 8 kWp or even less be enough? We do not want to feed electricity back to the grid, and the feed-in tariff is not a reason for us to choose a larger system.

MeinHaus45 schrieb:

We use about 4,500 kWh with 4 people in our rental apartment without a heat pump.

Quick calculation: add 1,000 kWh more for a house compared to an apartment (outdoor lighting, more rooms, etc.).
For a heat pump, you can also estimate around 2,500 kWh. So in total, you will likely reach about 8,000 kWh.

MeinHaus45 schrieb:

We don’t want to feed electricity back to the grid, and the feed-in tariff is not a reason for us to buy a larger system.

Why is that? There is basically no reason not to feed electricity back to the grid.
With a reliable solar installer, the price difference between an 8 kWp and a 10 kWp system is about 1,500 – 2,000 euros.
And you can expect some return on investment.

Only a €2000 difference between 8kWp and 10kWp? I have researched that you can get an 8kWp system with storage and installation for €16,000. The offer for a 10kWp system with a 6kW storage is €25,000.

We are building a KfW Efficiency House 55 EE, using an air-source heat pump. Instead of a battery storage system, we installed a slightly larger photovoltaic system. Therefore, we clearly recommend opting for a larger system. What roof areas and orientations are available? We installed 13.68 kWp on southeast and southwest exposures. The forecast predicts 1006 kWh/kWp for us.
Many users in another forum advocate for full roof coverage, but I don’t agree with that. We could have installed another 13.68 kWp on northeast and northwest exposures, but the expected yield was below 700 kWh/kWp.

Photovoltaic system as large as possible.
Exclude storage, feed excess energy back into the grid.

Your offer is too expensive; get additional quotes.

MeinHaus45 schrieb:

The offer for a 10 kWp system with a 6 kWh battery is 25,000€

That is (unfortunately common) price gouging; it can be done much cheaper.

Hausbau 55 schrieb:

We installed SE and SW facing panels with 13.68 kWp. The forecast predicts 1006 kWh/kWp for us.
Many users in the other forum advocate for full roof coverage, but I don’t agree. We could have installed another 13.68 kWp on NE and NW with a yield forecast below 700 kWh/kWp.

What extra costs would the north-facing panels have caused?
Usually the yield is lower, but additional costs are also lower, often about the same scale.