Cost per kW: the benchmark to hold your quote against

Where these numbers come from, and why it matters

Most published cost ranges are collected from installers, from comparison sites that sell leads, or from nowhere in particular. This series is different in three ways that matter.

It is prices paid, not prices advertised. The Department for Energy Security and Net Zero derives it from the MCS Installation Database — records of installations that actually happened.

It is large. The 0–4 kW band alone covers 158,512 installations in 2025/26.

It is published under the Open Government Licence, so we can republish it here with attribution rather than describing it second-hand.

The one caveat worth stating: it covers MCS-certified installations. Work outside MCS is not in it — see MCS versus non-MCS for why that distinction matters beyond the price.

Bigger systems cost less per kW

This is the single most actionable fact in the dataset, and quotes almost never explain it.

A solar installation has a large fixed component: scaffolding, the survey, the visit, the inverter, the DNO paperwork, the certification. It has a variable component: the panels themselves and the rails they sit on.

So as the system grows, the fixed cost spreads:

• 0–4 kW — £1,595/kW median
• 4–10 kW — £1,546/kW median
• 10–50 kW — £1,204/kW median

What that means when you are quoted. If your installer says another four panels adds £1,200, that is £300 per panel against a system average of perhaps £600 — because you are paying the marginal cost, not the average. Filling a suitable roof is usually better value per pound than a modest array, provided you can use or export the extra output.

The corollary: a small system is expensive per kW and always will be. That is not the installer overcharging. It is arithmetic.

Regional variation

Source: Solar photovoltaic (PV) cost data, Department for Energy Security and Net Zero, release 2025-26, published 28 May 2026. OGL v3.0. Derived by the department from the MCS Installation Database — prices paid, not prices advertised.

Two things to notice. The spread is modest — the difference between the cheapest and dearest regions is smaller than the difference between a median and a mean quote in the same street. And it does not track sunshine at all: it tracks labour and access costs, which is why London sits at the top.

Do not use this to justify a quote from a distant installer. Travel, and the ability to come back when something fails, are worth more than a few percent.

Domestic against non-domestic

Source: Solar photovoltaic (PV) cost data, Department for Energy Security and Net Zero, release 2025-26, published 28 May 2026. OGL v3.0. Derived by the department from the MCS Installation Database — prices paid, not prices advertised.

Domestic installations cost more per kW than non-domestic ones of the same size, which is what you would expect: smaller jobs, harder access, more visits per kW installed, and a consumer rather than a procurement department at the other end of the negotiation.

How to use the benchmark on your own quote

1. Get the capacity right. Use the kWp of the array — panels multiplied by their rating. Not the inverter’s kW, which may be smaller. Our figures are on the Total Installed Capacity basis, so array capacity is the right comparison.

2. Strip out what is not solar. A battery, an EV charger, a re-roof or a consumer unit upgrade are separate products. If a quote will not itemise them, that alone is a finding — see what a good quote looks like.

3. Divide, and compare with the right band. A 5 kWp system belongs against the 4–10 kW figures, not the 0–4 kW ones.

4. Ask what the difference buys. Above the mean is not automatically bad.

What the benchmark cannot tell you

Whether the installation is any good. The series records price. A cheap installation by a firm that disappears is not a bargain — see checking an installer and what happens when one goes bust.

Whether the system suits your house. The right size depends on your consumption and your roof, not on the price per kW.

What you will save. That is self-consumption and generation, and it is a different calculation entirely.

The figure to write down

Before you speak to anyone: £1,595 per kW for a system up to 4 kW, £1,546 per kW between 4 and 10 kW, both medians for 2025/26.

Take your quote, divide, and see where you land. It is the cheapest ten seconds of due diligence available to you, and the one thing no installer expects you to have done.