Evaluation of Photovoltaic System Offer with Storage

And ask photovoltaic owners about the actual yield in August 2023 and the forecasts for it.

Yield expectation (without considering partial shading until 12 o'clock): 3,307 kWh
Yield 2021: 2,701 kWh
Yield 2022: 3,174 kWh
Yield 2023: 2,844 kWh

And now? This is neither dramatic nor surprising. This year had comparatively bad weather. August is not as good as one might think based on the summer weather anyway. Because in August it is often very hot and heat reduces the performance of the modules. In addition, the sun is already lower.

My best month so far was May 2022 with 4,002 kWh.

Nice that you provide concrete numbers. Thank you!

You have a large feed-in system and not a 10 kWp system. Your system is, as you yourself write, significantly below the yield forecast.

And that’s what I meant, forecasts are one thing, results another.

My system has 7.2 kWp, the inverter has 6 kW, and the system usually delivers realistic 4.5 - 5 kWp output. Sometimes, like in May, just under 6 kW. But it’s not like you think I install a 10 kWp system and then also get 10 kW output when the sun is shining. Of course, that’s not the case.

But even if you have 8 kW output from the roof, where to put it? A normal household simply cannot consume that. A storage system would be full in roughly 2 hours. Feeding in with small systems also makes little sense.

With my system of 7.2 kWp and 10 kW storage, I still feed 2500 kWh into the grid. That brings me 200 euros per year. You can forget about that. Without my storage, I would feed somewhere around 4500 kWh. That doesn’t make much difference either.

My system is clearly too small to charge an electric car.

Especially since the car would have to be at home to charge during the day, which it wouldn’t be. I rarely drive at night anyway.

What would help us further would be a storage solution from the grid operator. I feed in during summer and withdraw the electricity in winter. That way, even with a smaller system, I would be self-sufficient and it would be cost-neutral. But we are miles away from that.

Your system is, as you yourself write, significantly below the yield forecast.

Where did I write that? In the so far worst year 18% below forecast in a rainy month. Additionally, the note that the forecast is not realistic because it does not take into account an existing shading. I don't find that bad. And yet in good months I am even above the forecast. Now in September 2023: forecast: 2,362 kWh, yield: 2,637 kWh.

What would help us further would be a storage solution from the grid operators. I feed in electricity in summer and withdraw it in winter. That way I would be self-sufficient even with a smaller system and it would be cost-neutral. However, we are miles away from that.

Why do you think? Because that is pure selfish illusion. For that to work, yield and demand would have to be balanced across the broad mass and the entire year. In practice, in summer EVERYONE wants to feed in and in winter EVERYONE wants to withdraw. Where is the grid operator supposed to put the electricity in summer and where is he supposed to get it from in winter? "In a storage solution," is probably your answer. Well, that doesn’t seem to exist because it is not profitable – just like a battery in your house that would last until winter would be unprofitable.

Boy, boy, you are contradicting yourself right now. First storage is great & indispensable, now you're basically talking trash.

No idea what kind of data you're throwing around ... don't understand your mumbling.

Now to the numbers: My system, currently still 6.5 KWp ;-) has produced exactly 18205 KWh in almost 2 years (exactly 21.10.2021 - today). Of that, I was able to consume 8072 KWh myself (brine-water heat pump, one electric car since 11.2021, another since 02.2023), overall I have consumed 17729 KWh, fed in 6681 KWh. Drew 9657 KWh.

August 2023 with 780 KWh was actually not the best month, that was June with 1087 KWh. In summer there is enough anyway, so no problem. Winter is critical (P.S. I am forced to have a small battery with just under 4 KWh capacity due to KfW40+, but I am glad to have it. At "normal" prices this battery just doesn’t pay off.

I still feed 2500 kWh into the grid with my system of 7.2 kWP and a 10 kW storage. Brings me 200 euros a year.
Can forget it. Without my storage, I would feed in about 4500 kWh somewhere. Doesn't make much difference either.

This is simply because your storage is too large for the system. With 4500 kWh feed-in, the system comfortably pays for itself. Plus the energy consumption savings.

I fed in 18,830 kWh last year. That makes 1,750€ remuneration. Plus 1,120€ energy consumption savings.

With 4500 kWh fed in, the system pays off comfortably.

4500 x €0.08 per kWh is €360 feed-in tariff per year for me. €7200 feed-in tariff in 20 years. That doesn’t pay off comfortably.

In my case, however, the battery saves me 2000 kWh less grid consumption, which means €800 savings per year. It pays off after 6 years.

I also don’t know where the problem is. Photovoltaic systems in Germany are heavily subsidized. The batteries as well. Modules with 430 heat pump cost €100, 10 kW battery already €4000. Man, photovoltaics have never been that cheap.

Whatever. For me, I made a very simple calculation. I have €10,000 in my account. Until last year, I had an electricity bill of €1800. My system cost €10,000. Now I pay only €60 for electricity. That’s €1200 savings per year.
That makes €24,000 savings in 20 years. Plus, currently, €3200 feed-in tariff.

No financing costs, only €40 insurance for the system per year. The battery and the modules have 10 and 20 years warranty, respectively.
What else should I calculate? For me, that’s fine and I am satisfied.