This year, solar panels have gained popularity as Europe plunged into an energy crisis. In this thread, let’s consider acquiring solar panels as an investment and examine how profitable they actually are. Or are they not at all?
I’m not much of an expert on the subject, and my own panels have only been installed for less than half a year. Hopefully, this thread will still provide some benefit to readers. In this first post, I’ll share my own experiences and present the data collected so far for others to see. My perspective will certainly emphasize living in a detached house, as heating consumes electricity differently than, for example, in a terraced house.
First, a few words about solar panels. Panels and systems are compared using the kWp value (peak kilowatt), which describes the panels’ power under certain standard conditions. You can think of it as the maximum power of the panels, even if it’s not exactly accurate. Close enough. The higher the kWp value, the more electricity the system can potentially produce.
In addition to the panels, a solar panel system includes an inverter, which converts the electrical energy from the panels into a suitable form to be fed into the property’s electrical grid. The inverter is the most expensive single component of the system and must be sized large enough to handle the power produced by the panels. For example, my system is 4.32 kWp, and the inverter is 6 kW. Many inverters offer real-time monitoring, which is a nice feature. Of course, some systems also include a battery bank to enable the storage of produced electricity, so that excess production can be used for one’s own consumption, e.g., at night.
What then is the “correct” size for the system? I can’t answer properly; someone wiser might do it better. However, I will try to clarify the matter through my own system. For a small-scale producer, electricity production is tax-free, even the sale of surplus production. However, if the panels were acquired for income generation, rather than for personal consumption, taxes must be paid (more information from the Tax Administration’s website). If I recall correctly, the limit was at least 100 kW with Helen, so quite a lot of panels would need to be acquired to exceed that.
Unfortunately, panels usually produce the most when one’s own consumption is at its lowest. So, it might not make sense to size the system such that there is no overproduction at all. In the summer, most of the production goes for sale, but in spring and autumn, a completely different amount goes for personal use. I’ll show some of my own charts on this below.
Now to my own experiences. My system was acquired in March 2022, and its size is indeed the previously mentioned 4.32 kWp (12 * 360 W panels), costing 8900€. Here’s my first piece of advice for those considering panels: research prices at least superficially beforehand. I didn’t do that and was just excited about the panels, which led to me overpaying. I estimate that the same system could have been obtained for up to 2000€ less. The panels have a 25-year production guarantee (meaning they will still produce >80% of their nominal power then) and the inverter has a 10-year guarantee.
You can get a household deduction for panel installation. In my case, the installing company stated the labor cost as 3625€, of which 40% is 1450€. With a deductible of 100€, 1350€ can be deducted from the price of the panels after the deduction (more information from the Tax Administration’s website).
The surplus can be sold back at the spot price, or at least in Helen’s case, it can be “stored” in a virtual battery, in which case 13 c/kWh is credited (8/2022, as prices may change). I made an agreement to sell at the spot price. There is no transmission fee to pay for the transmission of sold electricity in Caruna’s network.
We live in Lohja, and our detached house has a steep roof, with all panels on one slope facing roughly southeast. There are no shading trees in front, so on a sunny day, the production profile looks approximately like this:
Then to the actual data. I have calculated the panel yields once a month and drawn some charts. For calculating the portion used for personal consumption, I have used the current 6.96 c/kWh contract (plus transmission ~7 c/kWh and tax ~3 c/kWh), which may be something completely different next year. The sold portion has been calculated directly from spot prices.
Let’s start with April, which was the first full month with the panels. April was reasonably sunny, although there was a week of snowfall in the early part. A total of 525.8 kWh of electricity was produced, of which 272.4 kWh went for personal use. The average price of sold electricity was 12 c/kWh.
May was also very sunny, and production amounted to 583.1 kWh, with 232.05 kWh for personal use. In May, the outdoor temperature was still relatively low, which slightly increases the efficiency of the panels (~5-10%). The average price of sold electricity rose, being already 17 c/kWh in May.
In June, electricity production was very good, 677 kWh (only 203.9 kWh for personal consumption). The average price of sold electricity was the same 17 c/kWh as in May.
July’s electricity production was roughly at the same level as in May. However, spot prices continued to rise, and the average price of sold electricity was already 26 c/kWh.
In summary:
Sellers heavily touted that the payback period would easily be less than 10 years. And this was before Russia invaded Ukraine and prices started to skyrocket even in the summer. Of course, with the increased prices, we are clearly closer to that claim, but many things they said were quite a load of nonsense.
It would be nice to hear forum members’ thoughts, experiences, and tips on the topic. Many were interested in panels when it was discussed in the Coffee Room. Hopefully, this introductory post wasn’t too confusing 
EDIT: corrected the columns in the last image.
EDIT2: added a note about the transmission and tax portion when buying electricity
