Evaluation of Photovoltaic System Offer with Storage

Hello everyone.
The storage costs 5800€.

How can I best determine when it approximately pays off?

That depends on the cycles you manage or need, and also on the electricity prices.

Here is an example for 200 cycles per year and 10 years of use:
5800€ / (9kWhx200C/y * 10y) = 0.32€/kWh, + lost feed-in tariff of 0.08€/kWh, makes 40ct/kWh from the storage
Currently, electricity can easily be bought again for 30ct/kWh, therefore an amortization period of about 11 years.

For 150 cycles per year:
5800€ / (9kWhx150C/y * 10y) = 0.43€/kWh, + lost feed-in tariff of 0.08€/kWh, makes 51ct/kWh from the storage
Currently, electricity can easily be bought again for 30ct/kWh, therefore an amortization period of about 14 years.

There are also conversion losses and so on of a few percent.

And now you actually have to consider that the 5800€ also need to be interest-bearing and that the electricity price will increase.
At the moment, I would simply assume that this balances out. But of course, this is just a guess.

That depends on the cycles you manage or need, and also on the electricity prices.

Here is an example for 200 cycles per year and 10 years of usage:
5800€ / (9kWhx200C/y * 10y) = 0.32€/kWh, + lost feed-in tariff of 0.08€/kWh, makes 40ct/kWh from the storage
Currently you can easily get electricity again for 30ct/kWh, therefore a payback period of about 11 years.

At 150 cycles per year:
5800€ / (9kWhx150C/y * 10y) = 0.43€/kWh, + lost feed-in tariff of 0.08€/kWh, makes 51ct/kWh from the storage
Currently you can easily get electricity again for 30ct/kWh, therefore a payback period of about 14 years.

There are also conversion losses and the like of a few percent.

And now you actually have to take into account that the 5800€ also have to be interest-bearing and that the electricity price will rise.
At the moment, I would simply guess that this balances out. But of course, this is only a guess.

Sorry, my head is working a bit slowly right now. How do you get from the ct/kWh to the payback period?
Then it’s a bet on the durability of the storage?!

The calculation also confuses me, with useful life and additional amortization. I would calculate differently here: Assumption: 150 cycles per year at 10 kWh -> 1500 kWh per year from the storage Network electricity costs 30c, feed-in tariff 8c Charging and discharging losses not considered

The storage then saves 1500 kWh * (30c-8c) = €330 per year, so it pays off after 17.6 years At 200 cycles we get €440/year or 13.2 years. The storage is worthwhile if it is still usable after amortization.

The durability of the storage is the big question. After 10 years, capacity loss is certainly to be expected. On the other hand, the storage does not suddenly fail on the key date (although that can basically happen). And storage systems today are often advertised with 10,000 cycles, that would last forever. The calculation is more of a rough estimate. Interest is not considered, the electricity price is constant and the cycles per year as well. For example, if electricity prices are around 40c/kWh, then even at 150 cycles the amortization time is 12 years. On the other hand, if you believe our Greens and their stories about cheap green electricity, clearly below 30c/kWh, a storage system would definitely not be economical.

Sorry my head is working a bit slowly right now. How do you get from the Ct/kWh to the payback period?

Sorry, maybe I should have written it out. I rearranged the formula and used the 30ct/kWh that you pay when you buy the electricity instead of taking it from the storage: 5800€ / (9kWhx150Z/a * 0.3€/kWh) But now that you ask again, I realize that I didn’t take into account that you also miss out on feed-in compensation. So you actually save only 0.22ct/kWh when you take electricity from the storage instead of buying it. And correctly end up at: 5800€ / (9kWhx150Z/a * 0.22€/kWh) = 19.5 years

Then it’s a bet on the durability of the storage?!

Yes, and on the development of electricity prices. But as you often read, such a storage system is apparently associated with many emotions. The feeling of using your own electricity (which often isn’t really the case, because the consumer may be on a different phase than the generation), the feeling of giving others less of the "own" electricity, etc., seems for many not to be outweighed by reason.

Currently, you can easily get electricity again for 30ct/kWh.

But at most the dirty kind. It is likely that people who want to invest money in photovoltaics & storage not only focus on savings but also on clean energy, and therefore would not buy non-green electricity.
If you value genuine green electricity without certificate trading, you are more likely looking at prices from 40 ct upwards.

Netzstrom kostet 30c,

100% green electricity currently available for at least 24.66 cents. Contracted two weeks ago. Even from the municipal utilities and not some mailbox electricity company.