Solar panels: common questions

A typical ten or twelve panel array makes around 3,500 to 4,000 units a year in southern England, and around 3,000 in Scotland. For most households that is roughly what they use in a year.

The system size calculator will work out your own roof from your postcode.

Usually yes. East or west makes about 80 per cent of what a south-facing roof makes, which is a smaller penalty than most people expect.

It also spreads generation across morning and evening instead of piling it into midday, so more of it tends to get used in the house.

Barely. Anything from about 20 to 50 degrees is within a few per cent of the best, and almost every British pitched roof is in that range.

A flat roof is the exception: panels laid flat lose about 16 per cent and soil faster, so they are usually tilted on frames.

More than its share of the roof. Panels are wired in a chain, so a shadow on one drags down the others connected to it.

A chimney shadow across five per cent of the array can cost fifteen or twenty per cent of the output while it lies there.

On a shaded roof, genuinely yes — they let each panel work independently instead of being held back by its neighbour.

On an unshaded roof they add cost and more parts on the roof to fail, for very little gain.

It goes back into the grid, and licensed suppliers must offer you a payment for it. The rate is generally well below what you pay to buy electricity.

You will need a smart meter and your installation certificate before a supplier will pay you.

Without a battery, usually between a sixth and a third. Panels generate at midday and households use most electricity morning and evening.

Running the washing machine and dishwasher in the middle of the day shifts this in your favour with no equipment at all.

It roughly doubles how much of your own generation you use, which is a real improvement. Whether it pays depends on the gap between what you pay for electricity and what you are paid for it.

On typical tariffs that comes to a few hundred pounds a year against a cost of several thousand.

Twenty-five to thirty years, losing about half a per cent of their output each year. After two decades a panel is still doing around ninety per cent.

The inverter is the part that needs replacing sooner, usually around year twelve.

In Britain, rarely. Rain does the job provided the roof has enough pitch for water to run off.

Worth a look once a year for moss creeping up the bottom edge, or bird droppings, which are opaque and can affect more than one panel.

Most will. An array adds roughly 12 to 15 kilograms per square metre, which a normal British roof carries comfortably.

Older roofs with thin timbers, or ones already carrying a heavy covering, need somebody to check properly, and your installer has to arrange that check.

No. Waiting a year costs you a year of savings, and panels improve by far less than that in a year.

More in should you wait for better panels?

Yes. Plug-in solar became legal in the UK on 27 August 2026, which opens it up to renters and flats for the first time.

It is much smaller than a roof array and works differently. See plug-in balcony solar.