Question 1

Fixing solar to a flat roof will wreck the waterproofing.

Accepted Answer

A ballasted, penetration-free system never pierces the membrane — it sits on slip-sheets and is held by weight. The waterproofing guarantee stays intact. Concede: a mechanical fixing done badly WILL leak, which is why it is sealed to the manufacturer’s specification when it is used at all.

Question 2

Flat roofs are bad for solar because the panels lie flat.

Accepted Answer

The panels do not lie flat — they sit on a frame at 10 to 15 degrees. A flat roof needs more area per kWp, but it lets you orient the array freely and, with an east-west layout, fit more capacity than a pitched roof of the same building.

Question 3

Commercial solar qualifies for full expensing (100% first-year relief).

Accepted Answer

It does not — solar PV is special-rate plant and machinery, so it is excluded from that allowance and from the 50% first-year allowance. The correct route is the Annual Investment Allowance (AIA). This is the single most common tax error in solar marketing — check with your accountant.

Question 4

You can get solar panels completely free on a commercial roof.

Accepted Answer

There is no general grant that makes commercial solar free of charge. A power purchase agreement gives you no-upfront-cost solar, but the funder owns the asset and you buy the power — it is a financing arrangement, not a giveaway.

Question 5

A flat roof can always take an array — just add ballast.

Accepted Answer

Concede the opposite: ballast is dead load, and not every deck can carry it. A structural engineer checks residual capacity first; weak decks need a lightweight system or strengthening, and some cannot take solar at all.

Question 6

Solar only pays if you export a lot to the grid.

Accepted Answer

The reverse — the money is in self-consumption, using the power on site. Export under the Smart Export Guarantee pays less than you pay for grid power, so a high daytime load, not high export, is what makes a commercial system pay.

Myth	The fact
Fixing solar to a flat roof will wreck the waterproofing.	A ballasted, penetration-free system never pierces the membrane — it sits on slip-sheets and is held by weight. The waterproofing guarantee stays intact. Concede: a mechanical fixing done badly WILL leak, which is why it is sealed to the manufacturer’s specification when it is used at all.
Flat roofs are bad for solar because the panels lie flat.	The panels do not lie flat — they sit on a frame at 10 to 15 degrees. A flat roof needs more area per kWp, but it lets you orient the array freely and, with an east-west layout, fit more capacity than a pitched roof of the same building.
Commercial solar qualifies for full expensing (100% first-year relief).	It does not — solar PV is special-rate plant and machinery, so it is excluded from that allowance and from the 50% first-year allowance. The correct route is the Annual Investment Allowance (AIA). This is the single most common tax error in solar marketing — check with your accountant.
You can get solar panels completely free on a commercial roof.	There is no general grant that makes commercial solar free of charge. A power purchase agreement gives you no-upfront-cost solar, but the funder owns the asset and you buy the power — it is a financing arrangement, not a giveaway.
A flat roof can always take an array — just add ballast.	Concede the opposite: ballast is dead load, and not every deck can carry it. A structural engineer checks residual capacity first; weak decks need a lightweight system or strengthening, and some cannot take solar at all.
Solar only pays if you export a lot to the grid.	The reverse — the money is in self-consumption, using the power on site. Export under the Smart Export Guarantee pays less than you pay for grid power, so a high daytime load, not high export, is what makes a commercial system pay.

Flat-roof solar: myths vs facts

Why we bother correcting these

Get the facts for your own roof

Commercial Solar Across the UK