This is the most important number in a solar quote and it is usually buried.
Why it matters
A unit of electricity you use in the house saves you the full import price, currently about 26.32p.
A unit you export earns you the export rate, currently around 12p to 13p per kWh on a flat tariff.
So a unit used is worth roughly twice a unit exported.
That means two households with identical systems on identical roofs can get very different financial results, purely from when they use electricity.
Prices last reviewed 4 Nov 2026.
What a typical household exports
Without a battery, a typical UK household uses well under half of what it generates and exports the rest.
The reason is timing. Solar generates in the middle of the day. Most households use most of their electricity in the morning before work and in the evening after it. The generation and the demand do not line up.
With a battery the picture changes substantially, because the battery holds the midday surplus for the evening.
How to shift the ratio
In rough order of how much difference each makes:
1. Fit a battery The largest single change. It moves midday generation to the evening. See solar batteries.
2. Add a big electrical load that runs across the year. A heat pump or an electric car uses far more electricity than anything else in a house and transforms the ratio. See solar and a heat pump together and EV charging.
3. Move flexible use into daylight Washing machine, dishwasher, tumble dryer. Most have delay timers. This is free and it works.
4. Divert surplus to hot water A solar diverter sends surplus that would otherwise be exported into an immersion heater. Relatively cheap, and it turns a half-value export into a full-value saving on whatever fuel heats your water. Worth asking about if you have a hot water cylinder.
5. Size the system to your usage rather than filling the roof, if none of the above applies. Though note that the marginal panels are cheap, so this is less clear-cut than it sounds. See comparing system sizes.
Exporting is not a failure
Worth saying, because the above can read as though export is waste.
It is not. You are paid for it, the electricity is used by somebody, and the marginal panels that mostly export were the cheap ones. A system that exports a lot can still be a good system.
The point is simply that a savings figure assuming high self-consumption, for a house that is empty all day with no battery, is wrong. Know which situation you are in.
What to ask
- What self-consumption percentage does your savings figure assume?
- What is the figure based on: my actual usage pattern, or a standard assumption?
- What would the savings look like at ten percentage points lower?
- How much would a battery change it, and is that worth the battery’s cost?
- Would a solar diverter to the hot water cylinder be worthwhile here?
If an installer cannot answer the first question, the savings figure in the quote is not something you can rely on.