Solar pays when you use what you generate

Direction matters, but less dramatically than people expect. A due-south roof is the best case in the UK. East and west roofs typically generate less over the year, though they spread output across the morning and evening, which can suit a household that is out at midday. A north-facing roof is rarely worth panelling.

Shading is harsher than orientation. A chimney, a dormer, a neighbouring tree or a telegraph pole can knock a disproportionate hole in output depending on how the panels are wired. Ask whether the design uses optimisers or microinverters where shade is unavoidable, and ask what that adds to the price.

Usable area is what is left after roof windows, vents, edge setbacks and access. A survey should produce a panel layout drawing, not just a system size. If nobody has looked at your roof properly, the number you have been given is a guess wearing a suit.

Every kilowatt hour you use at the moment it is generated saves you the full import price. Every kilowatt hour you export earns a much lower export rate. So two identical systems on two identical roofs can produce very different returns purely because of who is home and when the washing machine runs.

Before you size a system, find your annual consumption in kilowatt hours from a bill or your smart meter data, and think honestly about your daytime pattern. Working from home, daytime hot water, an EV charged during the day and a heat pump all push self-consumption up. An empty house from eight until six pushes it down.

A bigger array is not automatically better. Beyond a point, extra capacity mostly produces export, and export is worth a fraction of import.

A battery raises self-consumption by storing midday surplus for the evening. That is genuinely useful, and it is also a second large cost with its own lifespan. Adding a battery to a solar quote usually improves the annual saving and worsens the payback, unless your tariff lets you arbitrage cheap overnight electricity as well.

Price the two separately. If an installer will only quote solar and battery as an indivisible bundle, ask them to split it so you can see what each part is buying you.

The Smart Export Guarantee requires larger licensed electricity suppliers to offer a tariff that pays domestic generators for the electricity they export to the grid. It is an obligation to offer something, not a fixed national rate.

Rates, contract lengths and terms differ between suppliers, and you are generally free to take an export tariff from a supplier other than the one that sells you electricity. You will normally need an eligible installation, a suitable smart meter capable of half-hourly export readings, and the relevant certification paperwork.

We do not publish specific export rates here, because they change and a stale rate quietly distorts the whole calculation. Check the current offers yourself and put your own number into the calculator.