Is there anyone on the forum whose housing company has decided to install solar panels on their apartment building’s roof? The idealists in our building are pushing for quite a large package which includes heat recovery, geothermal heating, and solar panels. A cost/profitability study has been commissioned from the builder for this entire package, and the payback period with an electricity price of 6c was somewhere in the 15+ year range. The question would be whether it was/is profitable in apartment buildings.
Monthly price of exchange electricity, i.e., spot electricity 
Why was the 6c price used? Is the assumption that the price of electricity would rise 2-3 times?
When panels produce a good amount of electricity, the price is never 6c/kWh.
That’s not a bad estimate at all. For energy consumed by oneself, it saves on transmission costs and taxes, meaning its value is over 6c. For energy sold, it’s less than that, so the average might settle around those figures.
5 Likes
The housing company board had, as I understood it, specified at least the interest rate, and calculations were made with a few different prices, the cheapest of which was 6c/kWh.
What kind of company is it? Will it still be in habitable condition in 15 years, or will it be demolished then?
Built in 2005, a 7-story building with about 100 doors in Helsinki. With a flat roof, and it will probably last 20 years before renovation. Roughly speaking. Electricity consumption is roughly 35 tons and heat about 85 tons. If I recall correctly off the top of my head.
This sounds quite reasonable, as electricity is used in ground source heating and transmission fees are saved. It was a really good investment for the rental property.
2 Likes
Real dividends seem to be a thing of the past. The increasing prevalence of solar power systems has eroded the profitability of small installations, and the margin charged by the electricity company is the final blow. Are there any experiences of having to pay for the electricity you’ve sold? This significantly alters the payback calculation..
1 Like
Everything is relative; we aim to use as much electricity as possible ourselves. Even in summer, automation directs electricity to the heating element of the bathroom floor heating system to keep the spaces dry. With a battery, one could use one’s own production even more precisely, but the acquisition costs are still too high to get anything for our consumption. The biggest savings in summer come from transmission fees and electricity tax. And by the way, most electricity companies do not charge a margin on sold electricity if you also buy the electricity you use from them, and some don’t even when you don’t buy 
1 Like
And also, the turnkey prices of those systems have dropped quite a bit. I just asked for offers, and an 8kWp system can now be had for around 5k€. Wasn’t it just talked about that those data center investments would also raise electricity prices?
1 Like
Exactly. If someone gets solar panels with the idea of selling as much as possible to the grid, then the starting point is completely wrong. The ideal situation is to have a hot water tank and an electric car, into which you can pump as much “free” energy from the sky as possible from spring to autumn. In this case, the savings primarily come from not having to pay taxes and electricity transmission fees.
10 Likes
Cheap electricity on a summer day, the electricity seller’s margin, and occasionally negative prices are nothing new nor a problem for a properly sized and configured system.
At current prices, a solar power plant investment yields roughly the same return as the stock market after taxes.
1 Like
Has anyone installed backup batteries with solar panels, or even without panels, and charges the battery during cheap spot market electricity? It seems there are companies offering these services, similar to solar panels. So, are there any reliable and reasonably priced companies?
1 Like
I had an Emaldo Power Store installed in March; it has a 15kWh battery and an 11kW inverter, costing just under 10k including installation. Emaldo has not yet been approved for the reserve market (it seems quite difficult to get in), but the contract stated they would pay a fixed compensation of 150€/month until then, which they have paid. The panels on the roof are an 8kWp system, and my electricity bills have been really small as I’ve been able to consume grid electricity during cheaper hours and use the batteries when prices are high. I’ve charged 3 electric cars mainly from solar power during the summer and still managed to charge the batteries with it.
Here is the price/consumption data:
April consumption 407kWh 8.26€ average price 1.53c solar production 760kWh
May consumption 305kWh 5.50€ average price 1.30c solar production 945kWh
June consumption 139kWh 4.39€ average price 0.54c solar production 897kWh
July consumption 222kWh 10.79€ average price 2.15c solar production 1009kWh
August consumption 488kWh 20.57€ average price 2.71c solar production 788kWh
September consumption 766kWh 21.41€ average price 1.79c solar production 411kWh
October consumption 891kWh 21.91€ average price 1.96 solar production 148kWh
Sales to the electricity grid have been 1059kWh at an average price of 5.35c, yielding 56.62€.
5 Likes
At current prices, a solar power plant investment yields roughly the same return as the stock market after taxes.
I really wonder about this. System sellers say the same in their sales pitches.
If savings are 5%/year, then it takes 20 years for the system to just pay for itself, meaning at that point there has been no return yet! Returns only start coming after those 20 years, if the system is still in good condition. In my opinion, that cannot be called a return if there is no return for the first 20 years, and after that, one might start getting 5% if nothing has gone into system maintenance during those 20 years.
11 Likes