Hanging house in the Southwest Palatinate - Our House Construction 2.0

Back then we mostly used over 60% ourselves, and that without storage.

A colleague is currently annoying me regularly with screenshots of his self-sufficiency, so I calculated it again.

Total consumption 2022 with heat pump and e-car: 8.7 MWh
Grid consumption 2022: 6.1 MWh

If I now assume being self-sufficient for the entire period from March through November, I would save a maximum of €1048 per year.

Probably significantly less, since 1. the storage rarely gets completely full during the transitional period, is never empty in summer, and I did not account for missed savings.

For you, that would only take 8 years to get the money back. If you include interest, longer. So you might as well join now – the money for the garage door never comes back ;)

For me it doesn’t pay off because I would also need a new inverter. Unfortunately.

[A COLLEAGUE is currently regularly annoying me with screenshots of his self-sufficiency, so I recalculated it again.

Total consumption 2022 with heat pump and e-car: 8.7 MWh
Grid consumption 2022: 6.1 MWh

If I now assume being self-sufficient for the entire period from March through November, then I would save a maximum of €1048 per year.

Rather significantly less, since 1. the storage system is rarely fully charged during transitional periods, never empty in summer, and I didn’t account for missed savings.

For you, that would be only 8 years until the money is back. If you factor in interest, longer. So you might as well do it right away — the money for the garage door never comes back ;)

For me, it doesn’t pay off because I would also need a new inverter. Unfortunately.

That roughly matches our calculation. We have now assumed €7800 for the storage alone — he gave us a good €2000 discount, which I should probably also allocate proportionally to the storage.

If I now assume 200 charge cycles per year for the storage (is that realistic?), I get 12.8 kW * 200 = 2560 kWh grid consumption saved. Calculated with the current electricity price, that is 2560 × €0.4 = €1024 savings per year.
€7800 / €1024 = about 7.6 years until the storage pays off.
It has a 10-year warranty.

This is based on the assumption that electricity won’t be cheaper than €0.4. If it gets more expensive, that would support the amortization.
For simplicity, I have ignored losses. That definitely should be considered—where are those approximately?]

Hello,

Your calculation is not quite right.

If I now assume 200 charge cycles per year for the storage (is that realistic?), I get 12.8 kW * 200 = 2560 kWh saved grid consumption. Calculated with the current electricity price, that would be 2560 x €0.4 = €1024 savings per year.
€7800 / €1024 = about 7.6 years until the storage pays for itself.
It has a 10-year warranty.

The assumption here is that electricity will not get cheaper than €0.4. If it got more expensive, that would favor the amortization.
For simplicity, I have neglected losses. That would certainly have to be considered, where are they approximately?

You can roughly estimate charging/discharging losses at 5% per direction. So for your 2560 kWh, you actually had to use 2816 kWh for which you get no feed-in tariff. So you forgo €0.075 times 2816 = €211. And you save 2560 kWh times €0.33 = €844. So in total not €1024 savings but only €633. And now calculate interest on your €7800 purchase price for the storage with 3% (you can almost get that in a daily savings account), which is another €234 less.
That leaves savings of €400 and an investment of €7800. Your ROI is therefore not 7.6 years but 19.5 years!
And that only if the storage holds its full capacity that long. That is rather unlikely...

In forums dealing with photovoltaic systems, it is also usually the opinion that storage is not economically worthwhile and that you should rather fill the roof with panels for the money saved.

Best regards,

Andreas

Hello, what roof orientation do you have? Gable roof? We also decided on a full roof and against an attic two years ago. And in hindsight, unfortunately, we have a hip roof. Our main orientation is east-west. Did you also have a quote made for a complete coverage of the roof?

Hi,

Your calculation doesn’t quite add up.

You can roughly assume charging/discharging losses of 5% per direction. So, for your 2560 kWh, you previously used 2816 kWh for which you don’t get any feed-in tariff. So you forego 7.5 cents times 2816 = 211 euros. And you save 2560 kWh times 0.33 cents = 844 euros. So in total, it’s not a saving of 1024 € but only 633 €. And now calculate the interest on your 7800 € purchase price for the storage at 3% (you could almost get that with a savings account), that’s another 234 euros less.
That leaves a saving of 400 euros and an investment of 7800 euros. So your ROI is not 7.6 years but 19.5 years!
And that only if the storage lasts at full capacity that long. That is rather unlikely...

In forums dealing with photovoltaic systems, the prevailing opinion is usually that storage is not economically worthwhile and that you should rather fill the roof with panels for the money saved.

Best regards,

Andreas

Do I really have to deduct it twice? So the lost feed-in tariff of 0.08€ currently, that’s true, you have to offset that.
But then only assuming a saving of 33 cents would be doubling up, right, or am I missing something? If I were to draw electricity from the grid instead of from the storage, I would pay 40ct, not 33?

I’ve also read the forums you mean, but often very different prices were quoted than 7.8k for 12.8kW storage.

Hello, what roof orientation (gable roof, right?) do you have?
Two years ago, we also decided for a full roof coverage and against the attic. And in hindsight, unfortunately, we have a hip roof. Our main orientation is east-west.
Did you also get an offer for a complete coverage of the roof?

No, we do not have a gable roof. The coverage is currently planned as shown with the offered system: