Consultation for photovoltaic systems

I suspect you have to divide the "Entladen" value by the capacity (not the "Geladen" value).

At a purchase price of 27ct minus 11ct feed-in tariff, that equals 693 * 0.16 about 110€.

Minus 130 x 0.11€ = 14.3 € loss due to storage losses. That makes just under 300,- € savings per year through the 8 kWh battery (if you can also charge it in the winter). If it runs flawlessly for 20 years, that amounts to 7200,- € (neglecting degradation and inflation). That would be a very, very good value.
What did it cost including installation?

I suspect you have to divide the "Discharge" value by the capacity (not the "Charge" value)

Why?

Addendum: In the above-mentioned 4 months, I extracted 693 kWh from the batteries. With a purchase price of 27ct minus 11ct feed-in tariff, that corresponds to 693 * 0.16 about 110€. With a feed-in tariff for a new system registered today of 7.25ct, that would be 693 * 0.1975 about 137€

There is a small calculation error; the lost feed-in tariff must of course be calculated from the charged value. Therefore new: Replaced purchased electricity with own: 693 kWh at 27ct = 187.11€ Lost feed-in tariff from charged electricity: 920 kWh at 11ct = 101.20€ That leaves 85.91€ For a new registration today, the feed-in tariff would be 7.25ct - that would correspond to 66.7€ That would leave 120.41€ Conclusion: Profitability still strongly depends on the subsidy.

Minus 130 x €0.11 = €14.3 loss due to storage losses. That makes not quite €300 savings per year through the 8 kWh battery (if you can fill it even in winter). If it runs faultlessly for 20 years, that is €7200 (if you neglect degradation and inflation). That would be a very, very good value. What did it cost including installation?

Since I did a kind of offset deal, it is not so easy to say. The system is premium and costs about €9000 gross and can do more than it does for me, but I still have a few stupid things planned with it.

Why?

For one, because otherwise, as correctly pointed out, you have more full cycles than days. Theoretically, this could work if you also discharge the battery during the day, but I find that hard to believe. On the other hand, most of the system losses occur outside the battery (in the inverter), meaning electricity lost in the inverter never even reaches the battery and therefore has nothing to do with its charging/discharging cycles. At least that’s what I suspect as a non-professional ;)

Otherwise, I calculated with my numbers from post #38 (period January 1 to September 15):

Battery charge = 1,181 kWh Battery discharge = 943 kWh Battery gross capacity = 9.8 kWh Battery net capacity = 9.3 kWh (according to data sheet)

Results in 943 / 9.3 = 101 full cycles in the mentioned period. Since the depth of discharge at night increases toward winter, I forecast 160-170 cycles per year for us. We receive just under 9 cents feed-in tariff, so the difference to the purchase price can be reasonably assumed to be 20 cents. That results in €189 “savings” until mid-September, and a forecast of €260-280 for the entire year. To be completely accurate, VAT on self-consumption should still be considered here, so €153 until mid-September and €210-225 forecast for the entire year. And now taking into account the lost 20% system loss, approximately €130 until mid-September and €180-200 for the entire year remain.

We paid €6,500, minus €2,000 direct subsidy, so ‘net’ €4,500. With luck and no repairs, that will be a break-even game over 20 years...

That would theoretically work if you also drain the battery during the day, but I can't really believe that.

There are many days when the battery is discharged intermittently. During the transition period in spring, this is likely to be even more pronounced.