Our Solis system, comprising solar panels and battery, was installed in June 2023, so we’ve now had a full year’s usage. That makes it worth checking on the experience: what was it like using the system, and how much electricity did it generate?

On the good side: the system reached the “fit and forget” stage reasonably rapidly. There was a certain amount of flailing around required to understand the electrity tariffs from our supplier, Octopus Energy, both for import (we’re buying electricity from the grid) and export (we’re selling excess electricity to the grid), followed by some experimentation to see what was likely to work best. But given that I started from a position of total ignorance, I don’t think the amount of hassle was unreasonable.

I’ve ended up settling on a plan called “Agile Octopus” for import, which varies the price considerably according to the time of day. The system seems quite good at avoiding importing energy in peak times, which means that the agile plan gives a reasonable import price: I’ve been paying around £0.165 / kWh (including 5% VAT). Since the import price varies between £0.156 and £0.31, I’d say the system is doing a good job here.

For export, however, I’ve settled on a plan called “Outgoing Octopus 12M Fixed”, which yields £0.15 per kWh: they have an agile plan, but that was yielding less revenue. The overall effect is that I’m only paying around 10% more for importing electricity than I am receiving when I export it.

In terms of how I use electricity, therefore, I’m now left with very little work. The car is set to charge at 00:30, when import tariffs are guaranteed to be around their lowest. The solar system’s 9.6 kWh battery does a good job of smoothing out everything else, so I’ve now stopped worrying about things like when’s the best time of day to put on the dishwasher, which was confusing, anyway, because it varies so much according to the seasons and according to whether the car needed charging.

The Solis system gives pretty good maxi-geeky graphs of everything it’s been doing. But to be honest, I hardly bother to look at them any more.

So much for the usability. But that leaves the elephant in the room: how much electricity are the panels generating, compared to what was expected when our installer did their estimates? Here, I’m afraid, the results are less favourable.

In the course of the year, the system yielded 5,259 kWh – that’s just 77% of what was predicted in our installer’s quotation. Now obviously, you expect there to be much variability according to the weather: last month, for example, the system reached its best ever yield of 885 kWh, which was 96% of the estimate. Still, I think I was hoping for closer to 85-90% than the 77% I got. 

In terms of value, that was £866 knocked off my electricity bill for a system that cost £22,520 to install. The payback is going to be more like 20 years than the expected 13, bearing in mind that energy prices have come down enormously from when the system was installed.

I certainly don’t regret installing the system. It was the right thing to do my bit for the environment and I never expected giant savings. However, I won’t pretend that I’m not mildly disappointed that the numbers don’t look a bit better.

Of course, things could easily change. The weather’s been pretty poor in London over the last year, so a sunnier year could yield a lot more electricity. And sadly, there’s likely to be another spike in energy prices at some point in the system’s lifetime, in which case it will look like a sounder investment. We’ll just have to wait and see, and attempt to feel virtuous in the mean time. (Of course, I haven’t computed the carbon footprint of getting the system installed – that’s another conversation in itself).

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