There is no useful single price for a domestic solar installation, because four site facts move the cost more than the hardware does: roof height and access, roof covering and condition, the cable route to the consumer unit, and whether the board can take another circuit. A calculator knows none of those, which is why calculator outputs and real quotes routinely disagree.
What is the cost of installing solar panels made of?
Panels, mounting system and fixings, inverter, DC and AC cabling, isolation and protection, a generation meter where required, scaffolding, labour, commissioning and certification, and making good. On many quotes scaffolding is a significant line on its own, and on a three storey terrace or a steep roof it can be the difference between two quotes that look otherwise identical. Batteries, bird protection, a new consumer unit and any roof repair are separate items and should be listed separately rather than folded into a total.
The four site facts that move a solar system price most
Access decides scaffolding. Covering decides the fixing method and the risk: slate and clay need care and skill, concrete tile is straightforward, and an old or brittle covering may need work first. The cable route decides how much of the house gets disturbed, and a run from roof to a consumer unit at the other end of the property is real money. Finally the existing board decides whether you are adding a circuit or upgrading the installation, and the second is a different job.
Why a solar panel cost calculator UK sites offer disagrees with quotes
A calculator assumes an unshaded roof at an assumed pitch and orientation, an average price per kilowatt and a self consumption fraction it cannot know. Change the self consumption assumption and the payback moves by years without a single number on the installation changing. Use a calculator to decide whether the idea is worth pursuing, and use three surveyed quotes to decide what it costs.
What makes a price high for a good reason
A genuinely higher quote often buys a better inverter, a longer workmanship warranty, in house crews rather than subcontractors, roof work included, or a proper structural and electrical assessment rather than an assumption. Ask what the extra is for and get the answer in writing. A higher price with no stated difference is just a higher price, and a much lower one usually has something missing from the scope.
Other questions people ask
Is scaffolding included in solar quotes?
Sometimes, and that is one of the biggest reasons two quotes differ. Ask explicitly whether scaffolding, its licence if it stands on a pavement, and making good after removal are inside the price.
Does the roof need work first?
It depends on the covering's remaining life. Fixing a twenty five year array to a roof with under ten years left means taking the array off again later. Have the roof assessed before the array is designed, and price the two together.
Why is a small system not proportionally cheaper?
Because scaffolding, survey, commissioning, certification and the inverter barely change with size. The fixed part of the job is a larger share of a small system, so cost per kilowatt is higher.
Can I trust an online solar savings calculator?
For a rough order of magnitude, yes. For a decision between installers, no. It cannot see shading, roof condition, the cable route or your consumer unit, and those are what move the price.