Variant 1: The checklist lead
The 5 Questions to Ask Before You Trust a Solar Quote
Get three solar quotes for the same roof and the savings figures can vary wildly.
One installer might say you will save £600 a year. Another £1,100. A third quotes a number so precise, down to the pound, that it sounds like the work has already been done.
In most cases, it has not. The savings figure on a UK solar quote is usually the part of the document with the shakiest foundations underneath it.
Producing a genuinely accurate savings estimate for a specific home takes work that a lot of installers skip, especially the ones quoting over the phone. Before you commit to a system that will sit on your roof for the next 25 years, it is worth knowing which questions separate a real estimate from a guess.
Why the same roof gets very different numbers
Five things determine what you will actually save with solar:
- Roof orientation and shading. South-facing with no shade is the gold standard. East-west splits, chimney shadows, and neighbouring trees all change the maths.
- Your postcode. Sunlight hours in Cornwall are not sunlight hours in Aberdeen. A proper estimate uses local irradiance data rather than a national average.
- Your actual electricity usage pattern. Not just how much you use, but when. Solar generates during the day. If your household is empty from 9 to 5, your self-consumption rate, and your savings, drops sharply unless you add a battery.
- Battery vs no battery. A battery lets you use evening electricity from solar generated during the day. It changes both the upfront cost and the savings profile.
- Your tariff and export rate. What you pay per imported unit, and what you are paid per exported unit, can shift annual savings by hundreds of pounds.
A quote that ignores three of these is closer to a guess than an estimate.
Already thinking your roof might qualify? The personalised check takes 90 seconds and uses your actual details, not an industry average.
The precision problem
If an installer quotes you a savings figure after a five-minute phone call, or after looking at your roof on Google Maps, ask them which of the five factors above they actually verified.
Often the answer comes back as: a couple of them, with assumptions for the rest.
That gap is how the same roof can produce a £400 to £1,400 swing in annual savings across three quotes. The roof never changed. The assumptions underneath each quote did.
It is also why "homeowners save an average of £X per year" claims in solar advertising are difficult to use. An average reflects what happened across a sample of homes that probably looks nothing like yours. Different roofs, different usage, different tariffs, different system sizes.
The number worth paying attention to is the one calculated from your inputs.
What an honest solar check actually involves
A proper assessment does three things a phone quote cannot:
- Surveys your real roof rather than a satellite approximation
- Uses your previous electricity consumption rather than a generic profile
- Spells out the assumptions behind the savings figure so you can stress-test them
Project Solar UK is one of the installers who works this way. Brendan Johnson, a Project Solar customer, specifically praised them for doing an actual survey instead of relying on Google Maps or a phone quote, and for basing the recommendation on his previous consumption rather than handing him an off-the-shelf number.
Worth knowing the company behind that approach has been installing since 2010, holds MCS certification, has completed installations on more than 50,000 UK homes, and has over 6,000 reviews on Trustpilot.
Project Solar is also the installer recommended by Kevin McCloud, the Grand Designs presenter. For homeowners who want to know a company has been scrutinised before they trust it with their roof, that endorsement is worth noting.
The 5 questions to ask any solar installer
Before you sign anything, ask:
- "How are you calculating my annual savings, and what assumptions are you using for my tariff, export rate, and self-consumption?"
- "Are you doing a physical roof survey, or estimating from satellite imagery?"
- "Are you basing my system size on my actual previous electricity consumption, or a generic household profile?"
- "What is the warranty on the panels, the inverter, and the workmanship, and is it backed by the manufacturer or just the installer?"
- "What happens to my quote if I add or remove a battery, and how does that change my payback period?"
If you have not had a quote yet, or if the one you have does not answer all five clearly, the fastest next step is a check calculated for your specific home rather than another round of assumptions.
"I had a quote from two other companies before Project Solar came out. The figures were completely different. The difference was that Project Solar actually looked at the house."
(Trustpilot review, 5 stars. Placeholder in this style: swap in a real approved Trustpilot quote before launch.)
See a personalised estimate for your home
Everything in this article comes down to one thing: the savings number worth trusting is the one calculated from your roof, your usage, your postcode. That is what the check below produces.
The personalised check uses your postcode, roof, and usage pattern to calculate an estimate for your home specifically. Not a national average, not a figure padded for margin. It is available for UK homeowners and takes about 90 seconds.
The check gives you a personalised estimate, not a final figure. Final figures come after a proper roof survey, which is how Project Solar works.
Final figures confirmed after a full survey. Savings vary based on roof, usage, tariff, and system specification.