How to read a solar installer's quote

Two quotes for the same roof can differ by thousands of pounds, and the cheapest is not always the better buy. The detail that decides it sits in the line items, not the headline total. Read a solar quote the way an installer would and the differences stop looking random. Here's what to check, and the warning signs that should make you slow down.

Start with the numbers that let you compare

A quote you can't compare is a quote you can't trust. Three figures make it comparable:

• System size in kWp, plus the panel count, wattage and brand. Capacity drives output, so this is the anchor for everything else.
• Expected annual generation in kWh, calculated by the MCS standard method for your location and roof. A quote with no generation estimate can't be lined up against another.
• Price per kWp, which you work out by dividing the total by the size. It's the only fair way to compare a 3 kWp job against a 5 kWp one. The typical bands are in how much solar costs.

The hardware lines

Panels carry two separate warranties: a product warranty against faults, often 10 to 25 years, and a performance warranty guaranteeing output stays above a set level, usually around 87% at year 25. The inverter is the component most likely to need replacing first, typically after 10 to 15 years, so check its brand and warranty. If a battery is on the cards now or later, a hybrid inverter avoids paying for a second one down the line.

If the quote includes a battery, it should state the usable capacity in kWh, the chemistry (lithium iron phosphate is the common home choice), the warranty in years or cycles, and whether it provides backup in a power cut, which most do not unless specified. The trade-offs are in do I need a battery.

The lines people skip

A compliant install involves more than panels on a roof. Look for the MCS certification, which you need for SEG export payments, and membership of a consumer code such as RECC or HIES, which backs your deposit and workmanship. There should be a DNO application (a G98 or G99 notice to your network operator) so the grid connection is approved. Scaffolding and access for steep or multi-face roofs belong in the quote, not as a surprise later.

Red flags

• No generation estimate. Without an expected annual kWh, you're buying blind.
• Pressure or "today only" pricing. A fair price is still fair next week. Discounts that expire tonight are a sales tactic, not a deal.
• A large deposit. Anything much above 25% upfront is worth questioning, and your deposit should be protected through a consumer code.
• Vague hardware. "Premium panels" with no brand or wattage tells you nothing you can check.
• An oversized battery. A pack far bigger than your daily usage rarely cycles, so you'd be paying for capacity that never earns.

What a strong quote looks like

The good ones read like a spec sheet, not a sales flyer. Expect named panel and inverter models with wattages and warranty terms, the system size and MCS-estimated annual generation, a clear scaffolding and access plan, the DNO notification, and a line for the consumer-code membership that protects your deposit. If there's a battery, its usable capacity, chemistry, cycle warranty and backup status should all be stated. A quote that gives you those is one you can hold up against a rival line for line.

The finance small print

Many installers offer finance, and the headline monthly figure can hide the real cost. Check the APR, the total repayable, and the term, then compare paying cash against borrowing over the system's life. A loan can still make sense if it lets you fit a system that pays back faster than the interest costs, but the comparison should be on total cost, not the monthly number. Payback and the long-run picture are in is solar worth it.

The questions to ask

Find out who actually does the install, since some firms subcontract it. Ask whether the workmanship warranty is insurance-backed, so it survives if the company folds. Ask what happens if the system underperforms its generation estimate. Then compare on price per kWp and the 25-year picture, not the deposit or the headline discount. Treat a quote that comes in far below the others with the same caution as one far above: it usually means a corner is being cut somewhere in the hardware, the access plan, or the cover. Whether the whole thing is worth doing is the prior question, answered in is solar worth it.