Is the solar system on the roof worthwhile?

We have just decided on a system.

Our structural conditions are fairly favorable. A south-facing roof without significant shading. The size is such that a generator output of 9.9 kWp can be achieved without the use of expensive high-performance modules. Under such conditions, the price is about €1100-1200 per installed kWp. With one installed kWp, you generate about 900-1000 kWh per year depending on the location. For simplicity, assume 1000 kWh (kWp) about €120 feed-in tariff if you do not consume anything yourself. Or about €1100/year for our system. This feed-in tariff is legally fixed for 20 years. These are the guaranteed revenues.

Depending on the consumption profile, you can use about 20-25% of the generated energy yourself. In that case, you don’t pay about 25 ct/kWh but only the tax. So you save about 20 ct in expenses instead of 12 ct in income. If we now simply calculate with €1200 income per year, the system is paid off after 10 years. In reality, due to insurance costs, replacement parts (inverter) and (lost) interest, this will not quite add up. But in 13-15 years you are definitely through. Overall, you end up with about 4-6% ROI. That’s not bad. But calculate it concretely for your conditions.

I basically understand how to calculate it. However, there are a few pieces of information that are not quite so transparent to me: the annual yield. How do I calculate it depending on roof orientation, roof pitch, and possibly shading? And what are the ongoing costs?

The investment costs of a solar system are relatively transparent. The feed-in tariff and the saved electricity costs are also not so problematic. The self-consumption rate is probably somewhere between 20% and 35%.

The annual yield. How do I calculate it depending on roof orientation, roof pitch, and possibly shading? And what are the ongoing costs?

Using PVGIS. Google it. The solar installer does this as well, as they calculate the amortization of the system. It’s interesting when their expected yield is higher than what PVGIS would suggest. Ongoing costs ... many will have insurance. You can also get a maintenance contract or occasionally consider cleaning. If you want to kill your returns, have your tax advisor do the paperwork. But otherwise ...

The rate for self-consumption is probably somewhere between 20% and 35%.

I consider that too optimistic for most households.

I consider that too optimistic for most households.

Of course, it largely depends on the size of the generator and the existing consumers.

I consider that too optimistic for most households.

What do you consider realistic then? I have no idea. My assumption was based on statements I have received on the topic so far.