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Free tools can help you estimate how much energy you'll get from a plug-in solar panel – and how long it'll take to earn your money back. But can you trust them?
Senior Contributing Editor
Senior Contributing Editor
October 7, 2026, 9:46 am ET
Now that plug-in solar has landed in both the US and the UK, people are wondering how much power they can get — and how much money they can save — from such systems. After all, if you’re going to drop upwards of $700, it’s a good idea to know in advance how long it’ll take to earn your money back.
Also: How I boosted my portable solar panels’ power by up to 30% – 11 expert-approved tips
There are a lot of calculators out there that give all sorts of estimates, but I was curious about what I’d get from a real-world test. I mean, calculators (especially ones by solar panel manufacturers) might be nudged to make a system seem better than it is. So, I took a solar panel and put it out in the UK sun for a year.
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Of course, there was a little bit more to the experiment than throwing a panel out in the garden for a year. I started with a Renogy ShadowFlux 200W solar panel, one of the best-performing rigid panels that I have.
I connected this panel to several different power stations over the year, as I didn’t want to dedicate just one to the job. I used this setup and a separate power meter to monitor how much power I collected over the year.
I set the panel up in three different spots (one at ground level and two on commercial building rooftops), and it was out for a total of 49 weeks throughout the year. The gaps were because I wasn’t responsible for fitting the panel onto the commercial rooftops and had to get people more competent than me to do it. This requirement took the panel out of action for a few days between each move.
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The panel’s orientation was set to due south (180 degrees) and its azimuth angle to 40 degrees, close to the optimal settings for my location (optimal would have been 185 degrees and an azimuth of 39 degrees). I chose spots that would provide the least possible obstruction and the best possible view of the horizon. The panel was up from October 2025 to September 2026.
Bottom line: I did the best I could to optimize solar power collection.
Over the year, the 200W panel collected 204 kWh (this figure is scaled up to 52 weeks from the actual 49 weeks the panel was harvesting power).
The best months were May, June, and July, when the panel gathered 29, 28, and 27 kWh, respectively. The panel averaged 0.56 kWh per day, with the worst month (December) dropping to 0.13 kWh per day and the best month (May) delivering 0.94 kWh a day.
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When these figures are scaled up to an average 800W plug-in solar system, I’d have collected 816 kWh a year, or an average of 2.2 kWh a day. At UK prices per kWh, that’s just under $300 worth of power (assuming you use all of it, because otherwise it’s pushed back into the grid and you get nothing for it).
This year was an exceptionally good for UK sunshine, with lower cloud cover and higher temperatures than average. According to the UK’s Met Office, Wales saw 1,608 hours of sunshine for the test period, up 14% from the 1991 to 2020 average of 1,408 hours. Sunshine is good for solar panels, but higher temperatures overall reduce their efficiency.
This test aimed to explore how accurate online calculators are. The answer? They’re pretty accurate. EcoFlow offers ballpark estimates for the US and UK that turned out to align well with my results (within about 10% to 15%).
Also: Is plug-in solar legal in your state? How to check before setting one up at home
Meanwhile, the European Union’s Photovoltaic Geographic Information System (PVGIS), a calculator that lets you input locations and tweak variables, was uncannily accurate. PVGIS estimated an average of 200 kWh a year for a 200W solar panel in my location.
Oh, and good news for all you folks outside the EU — this calculator works worldwide. So, unlike me, you don’t have to put a panel out for a year to see how much power you’d collect.
In short, you can run an online calculator estimate against the fact that an 800W plug-in/balcony solar system will cost about $1,449 to $2,229 and get an idea of how long it will take to make your money back.
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