Why solar panels are not worth it: five honest cases

Almost everything written about domestic solar is written by somebody who benefits from you buying it. That makes the cases where it does not pay strangely hard to find, even though they are common and easy to identify.

Here are five, with the arithmetic that makes each one real rather than rhetorical. If one of them describes your house, the honest answer is that your money is better spent elsewhere, and no amount of specification changes that.

One: the roof faces the wrong way

A predominantly north facing pitch receives substantially less usable energy across the year than a south facing one. In our model a due north roof produces around two thirds of the south facing output. The panels still work. They just produce less of what you paid for.

Run the numbers on the same 4kW system priced at £7,100, the government cost data’s 2025/26 median for small installations. South facing, it generates about 3,400 kilowatt hours a year in our model; due north, nearer 2,200. For a household self consuming half, at the current capped import rate of 26.11p and a 12p export rate:

• South: about £650 a year, payback around 11 years.
• North: about £420 a year, payback around 17 years.

Same installed cost, same scaffolding, same certification, and the north facing version pushes payback out past the point where the inverter is likely to need replacing, which resets part of the clock. If your only viable pitch faces north, this is the case where the answer is simply no.

Two: heavy shading you cannot remove

A tree you do not own. A taller building to the south. A large chimney in the middle of the array area.

Shading is worse than it looks because of how strings behave. On a plain string inverter, shading one panel affects the whole string, not just that panel. Optimisers and microinverters mitigate this, at extra cost, which pushes up the price of the very installation whose output is already compromised: you pay more to lose less, which is sometimes worth it and sometimes just a smaller loss.

Get shading assessed properly rather than eyeballed. MCS certified installers are required to include a shading assessment in their standard generation estimate, so ask to see it, and ask whether it was measured on site or assumed from a photograph. An installer who will not show the assessment is not the one to buy from, and a shaded quote without per panel electronics is usually a quote that was never surveyed.

Three: the house is empty all day and will stay that way

Solar saves you money mainly by displacing electricity you would have bought. If nobody is home during generating hours, and you are not adding storage, most of your generation is exported at a rate well below what you pay to import: export tariffs like Octopus Outgoing pay 12p per kilowatt hour against a capped import rate more than twice that.

The system still earns something. The worked example in our worth-it guide shows the size of the effect: dropping self consumption from a half to a quarter cuts the annual saving from about £650 to about £530 on the same 4kW system and stretches payback past 13 years. The marketing assumed a self consumption rate that does not describe you.

This one is fixable: a battery, a solar diverter for hot water, or timers on big appliances all raise self consumption. But then you must judge the installation including the cost of the fix, not without it. A battery that adds thousands to the project has to earn its own payback, not borrow the panels’.

Four: you are moving soon

Payback for domestic solar is measured in years. If you expect to move well inside that window, you are not buying an energy investment. You are buying whatever the panels add to your sale price, which is far less certain, not guaranteed to match what you spent, and not something any installer can promise you.

There is nothing wrong with installing solar for reasons other than return. Just do it knowing that is the decision you are making.

Five: the finance costs more than the panels save

This one catches people because the monthly figures are presented so reassuringly.

If a system is bought with borrowed money, the interest is part of the cost. An illustration, using round numbers rather than any particular lender: borrow £7,100 over ten years at 10% APR and the repayments run close to £94 a month, which is roughly £11,260 repaid in total. The £4,100 of interest, spread over the decade, consumes most of a £650 annual saving by itself. The installation may be perfectly good. The deal is not, and the same system bought with savings would have paid back in about 11 years while the financed version struggles to pay back at all inside the agreement.

Two checks:

• Compare the total repayable, not the monthly payment, against the cash price.
• Model the saving and the finance cost side by side across the same period. Our calculator takes a deposit and a term precisely so borrowed and outright purchases can be compared honestly.

If a salesperson resists showing you the cash price next to the financed price, that is the answer.

What to do instead

If one of the five applies, the money usually goes further on reducing demand rather than generating supply. Insulation, draughtproofing and heating controls have no orientation requirement, no inverter to replace and no export rate to worry about.

And if none of them applies, then the case for solar on your house is probably strong, which you can confirm by putting your own consumption, your own tariff and your own roof into the ROI calculator, and then changing the assumption you trust least to see whether the answer survives. A yes that survives its weakest assumption is a real yes.