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We like to talk about solar panel generation in perfect conditions; a clear, cool, sunny day. But what about solar panel on a rainy day? Let's use my real world data to take a look.
What does a sunny day look like?
What does a sunny day look like?
Let's start with a sunny day. On a clear, sunny day, solar generation looks like a smooth curve - an example of one of my clearest days is below. It starts gradually as the sun comes up, gets more intense towards midday and then decreases as the day draws to an end. There were a few clouds towards the end of the day but overall pretty clear.
On this sunny July day I generated just under 50kWh from my 7kWp system. That compares to my typical usage of 8-10kWh so I exported about 40kWh. On that day I exported £4.34 and saved £2.17 compared to what it would have cost to buy the electricity that I used. A total value of around £6.50.
How does this compare to a rainy day?
How does this compare to a rainy day?
Solar panel generation on a rainy day unsurprisingly varies with how rainy the day is, and more importantly, how cloudy.
Let's look at a rainy summer day so that it's a fair comparison (in terms of length of day) to the sunny day above.
A week or so later, still in July of the same year we had a rainy day. You can see the difference on the chart below. The generation is much more scattered and bitty. The first half of the day was gloomier than after lunch, which you can also see though the different peaks. Overall generation was around 18kWh, vs almost 50kWh a few weeks earlier.
Importantly however, even on this rainy day my generation of 18kWh was still almost double my typical daily usage. There points in the year when solar panel generation does not exceed electricity usage (see my guide of a complete year of ups and downs or my evolving data) but even a couple of hours of modest weather on an otherwise cloudy and rainy day is enough to cover all of my usage and even sell some back. Splendid!
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