Economic efficiency of a 10-kWp system vs. a 5-kWp system

Hello,

has anyone ever conducted (or had conducted) profitability calculations for a 10-kWp system compared to a smaller one (e.g., a 5-kWp system) and compared them? What were the results?

Here is my calculation:

A 10-kWp system does not cost twice as much as a 5-kWp system, for example €13,300 instead of €7,600 (1340 €/kWp instead of 1530 €/kWp)*. That would be an argument that a larger system is more cost-effective.

On the other hand, with a 10-kWp system I can only use about 20% of the generated electricity myself, with a 5-kWp system about 30%.* (Using it yourself saves 23.99 cents/kWh, feeding in only brings 12.2 cents/kWh) That would be an argument that a smaller system is more cost-effective.

The question is which effect predominates.

I compare two 5-kWp systems with one 10-kWp system. In both variants, I have 7000 kWh per year.

Two 5-kWp systems cost €1900 more.
Yearly they bring
70%*7000 kWh*12.12 cents/kWh + 30%*7000 kWh*23.99 cents/kWh
=
€597.80 + €503.79
=
€1101.59

The 10-kWp system brings annually
80%*7000 kWh*12.12 cents/kWh + 20%*7000 kWh*23.99 cents/kWh
=
€689.74 + €335.86
= €1025.60
So the balance differs by €76. That means the additional cost of the two 5-kWp systems pays off again in 25 years.

This leads me to the conclusion that the profitability of the two variants is quite similar and it is more a matter of preference how much money one wants to invest. Tendingly, a larger system probably amortizes a little earlier. If one wants to retrofit a battery storage in x years, the larger variant with 10 kWp also seems more sensible to me.

Have you conducted similar calculations and come to similar results?

Both systems were definitely purchased at prices that are too high [emoji4]

Don’t get lost in these details. At the latest when you add the tax factor, you’ll go crazy.
(by the way, self-consumption does not save 23.99 cents. It costs 4 cents VAT for the first 5 years and you give up the feed-in tariff if you consume the kWh yourself)

10 kWp, if it fits and the money is available.

Right, you seem to ignore taxes and depreciation.

In the end, I have 5.4kWp (no more fit), but I would say that the larger system would not have meant excessive additional financial effort.

If I had had more space, I would have chosen a larger one.

This is the general statement nowadays. Since the system pays for itself after about 12 years and then produces "free" electricity, you at least fully equip the roof up to 10 kWp. Beyond that, one can discuss what is sensible and what is not.

Here is an updated invoice again.

The average electricity price over the next 20 years has now been calculated at 0.36 cents/kWh, which corresponds to an increase of 3% per year. In addition, the return is considered as a key figure:


5-kWp system
============

Cost: 7600 €

Annual yield:
70%*3500 kWh*12.2Cent/kWh + 30 %*3500kWh*36 Cent/kWh
=
€298.90 + €378
=
€676.80

Return = €676.80 / €7600 = 8.9%

10-kWp system
=============
Cost: 13300 €

Annual yield:
80%*7000 kWh*12.2Cent/kWh + 20 %*7000kWh*36 Cent/kWh
=
€683.20 + €504.00
= €1187.20

Return = €1187.20 / €13300 = 8.9%

This leads me to the conclusion that the profitability of both options is quite similar and it is more a matter of preference how much money one wants to invest. If one wants to retrofit a battery storage system in x years, the larger variant with 10 kWp appears more reasonable to me.

Have you conducted similar calculations and come to similar results?

What I don’t understand is why you assume 30% for self-consumption with the small system and 20% with the large system?

No matter how big the system is, the proportional self-consumption is the same, right?! Unless the system is so undersized that you inherently end up with a higher share.

As many have already written here, the bigger the system (up to 10kwp), the faster the system pays off. Especially if you get to €1100 per kwp or below. You might not be able to achieve this with a “small” 5.7kwp.