You will find a great many cost and payback figures for solar, batteries and charge points online. We are not adding to them.
A cost or payback number is only meaningful against a specific roof, a specific consumption pattern, a specific tariff and a specific date. A published average, quoted back to you as though it were a forecast for your property, is not information: it is decoration.
What we will tell you is which variables actually move the number, so that when you do get a quotation you can interrogate it.
The six things that move the number
- Usable roof area after obstacles, shading and access are taken into account. Not the area of the roof: the area you can actually put panels on.
- How much of the generation you would use yourself rather than export. Two identical arrays on two identical roofs return quite different numbers if one household is out all day and the other is not.
- Your tariff, and whether it rewards export, off-peak import, or both.
- Whether the roof, the consumer unit or the incoming supply need work first. Any of these can be a substantial line of its own, and none of them appear in a headline price.
- Which permissions, prior approvals or connection applications apply. Each one has a time cost and some have a fee.
- What happens to the assumption if you change vehicle, work pattern or occupancy. A payback figure is a forecast about your life, not only about your roof.
One item almost no quotation carries, and should: the exact inverter and battery model, so you can check whether they work with a supplier controlled tariff. Does your inverter talk to your energy supplier sets out why that decides which tariffs you can reach.
What a good quotation looks like
The test is not the total. It is whether the total can be taken apart.
A quotation that separates hardware, access, electrical work and any enabling work lets you see what you are paying for and compare two proposals honestly. One that gives a single figure for the job does not, and two single figures from two firms cannot be meaningfully compared at all, because you cannot see which of them has included the scaffold, the consumer unit or the roof repair, and which has left it to be discovered later.
Ask for the access cost separately. It is often the largest single line after the hardware, and it behaves differently to everything else: it is priced per visit rather than per panel, which is why fitting a smaller array now can cost more overall than fitting a bigger one.
Where a figure genuinely cannot be known
Where a figure depends on your property and we cannot know it, we will say so rather than publish an average and call it an estimate. That is the same reason we sometimes tell people their property is not ready to proceed.
For how those assumptions are put together and taken apart for solar specifically, read understanding solar panel costs, savings and payback without misleading claims.
