Commercial solar is usually bought the wrong way round: three installers are invited to quote, each one measures the roof, each one proposes the biggest system that fits, and the owner is left comparing three different projects at three different prices. None of them has asked how much electricity the building actually uses, whether the grid will accept the system, or whether the roof can take it. Settle those first, and the quotes become comparable.
1. What the building uses, hour by hour
Solar on a business pays through the electricity you stop buying, so the first fact is when you use it. A workshop that runs weekdays from eight to five is a perfect match for solar. An office closed at weekends exports two days in seven. A dairy farm has a morning and evening peak that the panels miss.
Your electricity supplier, or your smart or half-hourly meter, can give you the usage in half-hour steps for the last year. Ask for it before you ask anyone to quote. It tells you the size of system that the building can actually use, which is often smaller than the roof could hold and almost always smaller than the first quote proposes.
2. Whether the roof can take it
Farm and industrial roofs are often older than the panels will be. Three questions:
- What is it made of? Asbestos cement sheet is common on farm buildings built before the mid-1980s. Panels can sometimes be fitted over it, but drilling it is a specialist job and some installers will not touch it. Know before they visit.
- Can the structure carry the weight? Panels and their rails add 12 to 20 kg per square metre. On a purlin roof that was sized for sheeting and snow, a structural check is not a formality.
- How long has the roof got? Panels last twenty-five years. If the roof does not, the panels come off and go back on at your expense, mid-life.
3. Whether the grid will accept it
Any system above a modest size needs the network operator’s permission before it is connected, through an application that can take weeks and can come back with a limit or a charge. On a rural supply the answer is sometimes “a smaller system, or pay to reinforce the line”. Finding that out after three installers have quoted a large system wastes everyone’s time. The application can be made before any installer is chosen, and it costs nothing to ask.
4. Who owns the roof, and who pays the bill
If the building is leased, the landlord’s consent is needed for the installation and the lease will say what happens to the panels at the end of the term. If the business pays the electricity bill but a different company owns the building, the savings and the asset sit in different places, and the arrangement wants writing down. These are solicitor’s questions, but they are best asked before the quotes, not after.
5. One specification, so the quotes compare
With the usage, the roof and the grid answer in hand, you can write one page that says what you want: the system size, the roof areas to use, the connection limit, the standard of equipment, the warranty terms and the paperwork you expect at handover. Every installer quotes against it. Then the quotes differ only in price and in the quality of what is offered, which is a comparison you can actually make.
Money, briefly
Capital allowances can make a real difference to the after-tax cost of a solar system on a business, and the rules change with the Budget. Ask your accountant before you sign, not after. Most roof-mounted commercial systems do not need planning permission, with conditions on size and on listed or protected buildings; check with the local authority if you are near any of the limits.
What to do next
Request the half-hourly data from your supplier this week. When it arrives, add up a typical weekday between nine and four. That figure, in kWh, is the first honest estimate of what a system here could usefully produce in a day, and it sets the size. The five steps above are what stage 1 and stage 2 of Project Support do for you, ending in the specification the installers quote against.