ᐅ Solar panel system for the entire roof or is it better to undersize it?
Created on: 2 May 2024 22:12
A
Alec_Trevelyan
To qualify for the KfW subsidy, the developer has sized the photovoltaic system at 6 kWp. However, according to the electrician, it is possible to install up to 10 kWp, and I have been offered to expand the system for an additional cost.
But I have made the following calculation, and it doesn’t make much sense to me:
- The additional cost would be: 4 kWp * €1000/kWp = €4000
- 4 kWp would produce about 4000 kWh/year. Based on values I have read in this forum, the self-consumption would be: 4000 kWh * 20% = 800 kWh.
- 800 kWh * €0.30/kWh (according to Check24) = €240 per year
This would mean a payback time of 4000 / 240 = 16 years.
And these are all very optimistic figures. Have I missed anything? I actually don’t find this a very sensible investment. That’s why I wonder why the mantra is always “you should ALWAYS max out your roof.” I think it is most optimal if the photovoltaic system is slightly undersized, so that the most energy can be used for self-consumption.
But I have made the following calculation, and it doesn’t make much sense to me:
- The additional cost would be: 4 kWp * €1000/kWp = €4000
- 4 kWp would produce about 4000 kWh/year. Based on values I have read in this forum, the self-consumption would be: 4000 kWh * 20% = 800 kWh.
- 800 kWh * €0.30/kWh (according to Check24) = €240 per year
This would mean a payback time of 4000 / 240 = 16 years.
And these are all very optimistic figures. Have I missed anything? I actually don’t find this a very sensible investment. That’s why I wonder why the mantra is always “you should ALWAYS max out your roof.” I think it is most optimal if the photovoltaic system is slightly undersized, so that the most energy can be used for self-consumption.
Zaba123 schrieb:
That might be theoretically correct, but you’re not calculating that over 20 years without photovoltaic panels, due to your higher grid consumption, you are missing out on monthly savings of x€ that could, for example, be invested in ETFs with a 7% return.That’s exactly what you consider in a proper calculation.For me, it’s not about pros and cons or squeezing out the last penny. I enjoy my photovoltaic system as well as electromobility.That’s exactly what I’m saying too. It’s purely a decision made for enjoyment. I don’t enjoy it. If the original poster enjoys it: fill the roof. If not, then don’t.H
hanghaus20233 May 2024 17:24I would definitely size the inverter as a hybrid from the start and for 10 kWp (kilowatt peak). Eventually, the storage system and the additional 4 kWp will be added, so if you wait, you'll have to buy a new one. I recommend going full-size right away.
As of today, I would stick to the old rule of thumb of 10 kWp and avoid fully covering the roof. In the Netherlands, since last summer, it has become very clear how spot electricity prices develop when a significant amount of solar capacity is added. At times when you have full output, everyone else also has their peak production – resulting in very low spot prices on the electricity market.
You can benefit from this with variable electricity rates if you have large controllable loads. My own system delivers a maximum of just over 5 kW; for the remaining kW, I would prefer to be compensated in the future, for example when charging an electric car. Just a thought…
You can benefit from this with variable electricity rates if you have large controllable loads. My own system delivers a maximum of just over 5 kW; for the remaining kW, I would prefer to be compensated in the future, for example when charging an electric car. Just a thought…
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