Red Flags in Solar Quotes: What Dodgy Installers Don't Want You to Know

Most solar installers in the UK are honest professionals doing a solid job. But a minority rely on inflated promises, vague paperwork, and pressure tactics to close sales at inflated prices. This guide walks you through the ten most common red flags in solar quotes so you can spot the dodgy ones before you sign anything.

1. Inflated Generation Claims

This is the single most common trick in a dodgy solar quote. The installer promises your system will generate an eye-catching number of kilowatt-hours per year, making the payback period look shorter and the return on investment look better.

Here is the reality. The MCS tables — the industry standard used by every legitimate installer — show that a well-installed, unshaded, south-facing system in the south of England generates around 900-1,050 kWh per kWp per year. In Scotland and northern England, that drops to 800-950 kWh/kWp. These figures assume optimal conditions. Real-world performance is often slightly lower once you account for partial shading, inverter losses, and panels that aren't perfectly oriented.

If a quote promises 1,200 kWh/kWp or more, they are either incompetent or deliberately inflating the numbers to make the deal look better. Even south-facing roofs in London top out around 1,050 kWh/kWp under ideal conditions.

2. Missing Line Items

A proper solar quote is an itemised document, not a single number on a page. If the quote just says "4kW solar panel system — £7,500 installed," you have no idea what you are actually getting.

A detailed, trustworthy quote should break out each of the following as separate line items:

• Solar panels — brand, model, wattage per panel, and number of panels
• Inverter — brand, model, and capacity (or microinverters if applicable)
• Mounting system — type and brand (roof hooks, rails, clamps)
• Scaffolding — often subcontracted, but should still be listed
• Consumer unit upgrade — if needed for the additional circuit
• DNO notification — the installer should handle this as part of the job
• Commissioning and testing — the final checks before handover
• MCS certification — confirming the installation will be MCS-registered

If an installer won't provide a breakdown, they're either hiding the quality of components they plan to use, or padding the margin somewhere. Either way, ask for the detail. If they refuse, walk away.

3. No MCS Certification Number

The Microgeneration Certification Scheme exists to ensure solar installations meet quality and safety standards. Every legitimate solar installer in the UK should be MCS-certified, and that certification number should appear on their quote and contract.

Why this matters so much:

• No MCS = no SEG payments. You cannot register for the Smart Export Guarantee without an MCS certificate for your installation.
• No MCS = no grant eligibility. Schemes like ECO4 and local authority grants require MCS-certified installations.
• No MCS = limited recourse. If something goes wrong, MCS provides a complaints and arbitration process. Without it, your only option is the courts.

Verify any installer's MCS status yourself at mcscertified.com/find-an-installer before agreeing to anything. It takes thirty seconds and could save you thousands.

4. Pressure Tactics

"This price is only valid if you sign today." "We've got one installation slot left this month." "The government incentive is about to change." These lines have one purpose: to stop you from getting competing quotes and doing your due diligence.

Legitimate solar installers know their work stands up to comparison. They are happy for you to take a week, get three quotes, and make an informed decision. If an installer makes you feel rushed, pressured, or anxious about missing out, that tells you everything you need to know about how they do business.

The Consumer Contracts Regulations give you a 14-day cooling-off period for contracts signed away from the trader's premises (including your own home). But it is far better to avoid signing under pressure in the first place.

5. Comparing Different System Sizes

This one catches people out regularly. You get three quotes, and the prices look wildly different. But when you look closely, one company has quoted a 4kW system with 10 panels, another has quoted 3.6kW with 9 panels, and the third has quoted 4.5kW with 10 higher-wattage panels. You are not comparing like with like.

To make a fair comparison, check these three things across every quote:

1. Number of panels and wattage per panel — 10 x 400W panels is a 4kW system. 9 x 400W panels is 3.6kW. That 10% difference in system size means a 10% difference in generation.
2. Total system capacity in kWp — this is the number to compare directly.
3. Inverter capacity — a 3.6kW inverter paired with 4kW of panels will clip output on the sunniest days. Check the inverter matches the array size.

If one quote is significantly cheaper, check whether they have simply quoted a smaller system. Cost per kWp installed is a much more useful comparison metric than the total price.

6. VAT Errors (or Deliberate Overcharging)

Since April 2022, residential solar panel installations in the UK carry 0% VAT. This applies to the panels, inverter, battery storage, and the installation labour — the entire job.

If a quote includes a line for 20% VAT, one of two things is happening: the installer has made a genuine administrative error (which still doesn't inspire confidence in their attention to detail), or they are knowingly adding 20% to the price and pocketing it.

On a £7,000 system, bogus VAT would add £1,400 to the price. That is not a rounding error.

7. Warranty Smoke and Mirrors

"25-year warranty" is a phrase that appears in a lot of solar quotes. It sounds brilliant. But what does it actually cover?

Most solar panels come with two separate warranties:

• Product warranty — covers manufacturing defects and hardware failure. Typically 10-15 years for mainstream panels, up to 25 years for premium brands.
• Performance guarantee — promises the panels will still produce a certain percentage of their rated output after 25 or 30 years (usually 80-85%). This only covers gradual degradation, not breakdowns.

If a quote says "25-year warranty" without specifying which type, ask. A 25-year performance guarantee with a 10-year product warranty means that if a panel fails in year 12 due to a manufacturing defect, you may not be covered.

Also check the inverter warranty separately. Standard inverter warranties are 5-10 years, with extensions available to 15-20 years on some brands. Since an inverter replacement can cost £800-£1,500, this matters.

And don't forget the workmanship warranty from the installer — covering roof penetrations, wiring, and mounting. This is separate from the manufacturer warranties and typically lasts 5-10 years.

8. Unrealistic Payback Claims

Some installers quote payback periods of 3-4 years for a standard residential system. In 2026, this is not realistic for a typical UK home.

A fair calculation for a standard 4kW residential system in 2026 looks like this:

• System cost: approximately £6,000-£8,000
• Annual generation: around 3,400-4,200 kWh
• Self-consumption savings plus SEG export income: roughly £800-£1,200 per year depending on your usage patterns and tariff

That gives a realistic payback period of 6-9 years. Still an excellent return — far better than a savings account — but not the 3-4 years some installers promise.

If a quote claims payback under 5 years, ask them to show their working. Check what electricity price they have assumed (some use inflated future prices), what self-consumption rate they have used (70%+ is optimistic unless you work from home), and whether they have included maintenance costs.

9. No Site Survey

Anyone who provides a binding quote without visiting your property is guessing. Satellite images and Google Street View can give a rough idea of roof orientation and size, but they cannot tell an installer:

• Whether your roof structure can support the weight of panels
• What shading your roof receives from trees, chimneys, or neighbouring buildings at different times of day and year
• The condition of your roof tiles and whether any need replacing before installation
• The cable run distance from the roof to your consumer unit
• Whether your consumer unit needs upgrading
• Access requirements for scaffolding

A preliminary remote assessment to check basic feasibility is reasonable. But the final quote should only come after someone has physically been on your property, ideally looked at the roof from the loft space, and checked the electrical setup. If an installer wants you to commit based on a desk-based estimate alone, they are either cutting corners or setting you up for "additional costs" on installation day.

10. Full Payment Demanded Upfront

Standard payment terms in the UK solar industry are straightforward: a deposit of 10-20% when you sign the contract, with the balance payable on completion once you are satisfied the system is working correctly.

If an installer demands 100% payment before they start work, you have zero leverage if something goes wrong. They have your money, and you have a half-finished roof.

What a Good Quote Looks Like

After reading ten red flags, it is worth remembering what a proper quote includes:

• Itemised components with exact makes, models, and quantities
• Realistic generation estimates based on your roof's orientation, pitch, and location
• Clear payment terms with a reasonable deposit and balance on completion
• MCS certification number and confirmation the installation will be MCS-registered
• Warranty breakdown covering panels, inverter, and workmanship separately
• 0% VAT correctly applied
• A site survey completed before the final quote is issued
• No pressure to sign immediately

Get at least three quotes, compare them on a like-for-like basis, verify the MCS certification of each installer, and take your time. A good solar installation will serve you well for 25 years or more. Spending an extra week choosing the right installer is time well invested.

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