Whether solar panels are worth it does not have one answer, because it depends on your roof, your habits and your reasons for fitting them. What it does have is a clear set of factors that push the case one way or the other. Run your own situation through them honestly and you can judge a quote without relying on the salesperson's optimism. The how-it-works detail sits in the solar basics guide; this one is about the decision.
The roof comes first
No amount of clever financing rescues a poor roof. A south-facing, unshaded roof at a reasonable pitch is the strong case; east and west roofs still work but generate less; a north-facing or heavily shaded roof rarely justifies the cost. Shading is a particular killer, because even partial shade across part of the array at the wrong time of day can drag the output down disproportionately. Before anything else, be honest about which way your roof faces and what shades it through the day. If the roof is wrong, the rest of the sums do not matter.
Self-consumption makes or breaks the return
As the basics guide stresses, power you use yourself is worth several times what you are paid to export. So the return hinges on how much of your generation you actually consume. A household with someone home during the day, or one willing to shift the washing, dishwasher, hot water and car charging into daylight, captures far more value than one that exports most of its midday output while the house is empty. When you weigh a quote, the assumed self-consumption rate matters as much as the headline generation figure, and an honest installer will discuss it rather than assuming you use everything you make.
Where batteries fit
A battery stores your surplus midday generation for use in the evening, which lifts self-consumption and therefore the value of the system, especially for households out all day. The catch is that batteries are expensive, so they improve the usefulness of solar while often lengthening the overall payback rather than shortening it. Whether to add one is a separate calculation, not an automatic yes. For some homes it transforms the case; for others it is a costly extra that the export payments would have covered more cheaply.
Export payments and the moving goalposts
You are paid for the electricity you export to the grid, which adds a modest income on top of the savings from self-used power. Export rates vary between suppliers and change over time, so treat any figure in a sales projection as a snapshot rather than a guarantee. The same caution applies to the assumed price of the grid electricity you are displacing, since the whole saving scales with how dear that electricity is. Because both numbers move, be wary of glossy payback calculations that present a single confident figure; ask what prices and what self-consumption rate they assumed.
The honest payback picture
A well-sited system with decent self-consumption typically pays for itself over a long but not unreasonable span and then generates free power for many years beyond, since panels last a long time. It is a long-term investment, closer to overpaying your mortgage than to a quick win, and it competes for your money with the cheaper efficiency jobs that pay back far faster. The sensible order is to do the insulation, draught-proofing and heating basics first, since they cost less and return sooner, and then consider solar as the larger, slower-burn step once the easy savings are banked.
Questions to ask before you sign
When you get a quote, ask what generation it predicts for your specific roof orientation and shading, not a generic figure; what self-consumption rate it assumes and why; what electricity price and export rate underpin the payback; whether a battery is included and what the sums look like without it; and what warranties cover the panels and, separately, the inverter, which is the component most likely to need replacing within the system's life. A reputable installer answers these plainly. Vague, pressured or too-good-to-be-true answers are the signal to walk away and get another quote.