Solar panels on a commercial roof
Electricity you use on site is worth far more than electricity you export. That decides most commercial solar cases.
What it actually is
Panels are fixed to the roof and wired into your incoming supply. The building uses what it can. The rest goes to the grid.
Electricity you use displaces the grid rate. Electricity you export earns a fraction of it. A warehouse running plant all day does far better than one empty on weekdays.
Rooftop solar is a set of panels fixed to your roof, wired through an inverter into the incoming supply of the building. When the sun is on the roof, the building draws from the panels first and from the grid only for whatever is left. Nothing changes in how you use the building, and nothing switches off when the panels are not producing.
The money is made in one place. Every unit the building uses on site replaces a unit you would have bought at your commercial rate. Every unit you cannot use goes out to the grid and earns you a fraction of that. So the value of an array is not set by how much it generates. It is set by how much of what it generates you consume yourself, hour by hour.
That is why two identical roofs can produce opposite answers. A chilled distribution unit running compressors from six in the morning uses almost everything the roof makes. A solicitor's office that is dark on Fridays and empty in August exports a large share at a low price. The roof is the same. The case is not.
Nothing about a commercial array is speculative any more. The equipment is mature, the installation is routine, and the failure modes are known. The uncertainty sits entirely in your building: what the roof can carry, what the network will allow, and what your load looks like through a working day.
Which buildings it suits, and which it does not
It suits single storey buildings with a wide roof and daytime load. Distribution units, manufacturing, retail parks, cold stores and air conditioned offices are normal cases.
It suits you less if the roof is at the end of its life, if you cannot get the freeholder's authority, or if the building is empty during daylight.
- Distribution and warehousingGood fitWide unobstructed roof, long daytime hours, and forklift charging, chillers or automation drawing power while the sun is up.
- Cold storageGood fitCompressors run hardest on the hottest, brightest days. Generation and demand line up better here than in almost any other building type.
- ManufacturingGood fitSteady weekday load through daylight hours. Watch the roof structure on older industrial sheds and the export limit if the array is large.
- Air conditioned officesGood fitCooling peaks with sunshine. Multi storey offices have less roof per square metre of floor, so the array covers a smaller share of the load.
- Retail parks and supermarketsGood fitLong trading hours, lighting and refrigeration all day, and usually a simple single storey roof.
- Schools and collegesDependsGood weekday load in term time, then the highest generating months fall in the summer holiday. The summer export share decides the case.
- Hotels and residential careDependsLoad is weighted to early morning and evening. Laundry, kitchens and cooling in the middle of the day are what make it work.
- Unheated storage and low occupancy unitsRarelyVery little daytime load to displace, so nearly everything is exported at the low rate.
- Buildings with a roof near end of lifeRarelyNot a no, but a wait. Do the roof first, or do both together, or you will pay to take the array off and put it back.
What it typically costs and saves
- Installed cost
- from £450 to £620 per kWp
- Roof area needed
- 5.5 to 8 square metres per kWp
- Annual yield
- 750 to 1,100 kWh per kWp per year, depending on region
- Share used on site
- 50 to 85 per cent
What drives the variation
- •Size. Cost per kWp falls as the array grows, so a small array on a small roof sits at the top of the range.
- •Roof type and fixing. Standing seam, trapezoidal sheet, membrane and concrete each need a different system, and ballasted flat roof work carries more weight and more labour.
- •Access and working at height. A live warehouse with racking underneath costs more to work over than an empty unit.
- •Distance from the array to the intake, and whether cabling can be run internally.
- •Electrical works. Switchgear upgrades, a new metering position or a network connection charge can be a large single line.
- •Whether the roof needs remedial work first, and whether that is inside or outside the quote.
How this appears on your building
What decides whether it works on your building
Roof condition and remaining life
An array is a twenty five year asset bolted to a covering that may have far less left. A structural and covering survey before design is not optional. If the roof needs replacing inside the next few years, plan the array with the reroof and you save the removal, the scaffolding and a second set of access costs.
Structural capacity
Older industrial roofs were designed for wind and snow, not for added dead load. Lightweight non penetrative systems reduce the loading but need the roof pitch and covering to suit them. A structural engineer's sign off is a normal cost of a commercial project, not a sign of a problem.
Usable area, once plant and rooflights are removed
Gross roof area flatters every early estimate. Take out rooflights, air handling units, walkways, fall protection zones and the shading each of those casts, and the usable figure is often well below the plan area. That is the number your quote should be built on.
Orientation and pitch
South facing gives the biggest annual total. East and west facing gives a flatter curve, with output in the morning and the late afternoon, which often matches an occupied building better and exports less. On a flat roof the installer chooses, so ask which they have assumed and why.
Export headroom at the connection
You can have a perfect roof and no permission to put power onto the network. Export is agreed with the distribution network operator, and in a constrained area the answer can be a limit well below what the roof could produce, or a connection cost that changes the whole case. Ask for this to be checked before design work is paid for.
Your load through the day
This is the one that changes the answer most. Half hourly data from your meter shows exactly how much of the generation you would have used. An annual consumption total cannot tell you that, so any model built on one is a guess wearing a decimal point.
Tenure and authority
If you lease the building you need the freeholder's consent, and the lease may be silent on who owns the array at the end of the term. If you let the building, the tenant gets the bill saving unless you agree otherwise. Settle that before you design anything.
How long it takes and what it disrupts
Before anything happens on the roof
Survey, structural check, network application, design and, on some buildings, planning. This stage takes most of the elapsed time on a commercial project, and almost all of it is administrative rather than physical. The network response is usually the longest single wait.
On site
The physical installation is quick and largely happens above your head. Deliveries, a crane or hoist lift, and scaffold or mansafe access are the parts you will notice. Roof work stops in high wind, so weather moves dates.
The disruptive hour
The only genuine interruption is the electrical tie in at your switchboard, which needs a planned shutdown. It is short and it is scheduled, usually out of hours. Everything else can be done around an operating building.
After commissioning
Expect a commissioning certificate, a network notification, monitoring access, and an operation and maintenance plan. Ask for the monitoring to be handed to you rather than kept by the installer.
What usually goes wrong or gets missed
The array is sized to the roof, not the load
It is easy to fill a roof and it looks impressive on a proposal. If half the output is exported at a fraction of your grid rate, you have paid full price for a low value asset. Size to what the building will actually consume, then decide whether the extra is worth adding.
Export headroom is discovered late
Design fees are spent, then the network answer arrives and the scheme is cut in half. Ask for the connection position in writing before the design fee is committed.
The roof is not surveyed properly
Panels over a roof with five years left mean paying twice. A covering survey costs very little against the price of removing and refitting an array.
A single annual consumption figure is used
Without half hourly data the daytime share is assumed, and the whole saving rests on that assumption. Get the data. It is free from your supplier or your data collector.
Nobody checks the inverter replacement
Panels outlast inverters. If the payback model runs for twenty years and never replaces one, the model is wrong.
Ownership at the end of a lease is left unwritten
If you fund an array on a building you do not own, write down who owns it, who maintains it and what happens on yielding up.
- •The array is sized to the roof rather than the load, so too much is exported at a low rate.
- •Export headroom is discovered late, after design work has been paid for.
- •The roof needs replacing within a few years and the panels have to come off and go back on.
- •A single annual consumption figure is used, so the daytime share is a guess.
What to ask an installer
- 01What usable roof area have you assumed, and does it exclude rooflights, plant and shading?
- 02Has a structural check been done, and by whom?
- 03What is the condition and remaining life of the roof covering?
- 04What export limit have you assumed, and have you had that in writing from the network operator?
- 05Have you modelled this on my half hourly data, or on an annual total?
- 06What share of the output do you expect the building to use itself, and what happens to the case if that is ten points lower?
- 07Does the price include scaffolding, access, electrical works and the network connection charge?
- 08Does the payback model include inverter replacement and any ongoing maintenance?
- 09What warranty covers the panels, the inverter, and the workmanship, and who honours each?
- 10Who owns the monitoring data and how do I get access to it?
How it interacts with other measures
With battery storage
A battery only earns its keep here if a meaningful share of the array is being exported, or your tariff has a real difference between periods. Fit the array, get a year of data, then decide. Buying both at once on the same proposal is how batteries end up half used.
With EV charging
Chargers add daytime load, which raises the share of generation you use yourself. That improves the solar case. Both draw on the same connection though, so plan the capacity once rather than twice.
With LED lighting
Do lighting first. It cuts consumption at a much shorter payback, and it shrinks the array you need. Sizing solar to an un retrofitted lighting load builds a bigger array than the building will need.
With a roof replacement
The single biggest saving available on a solar project is doing it at the same time as a reroof. One set of access costs, one programme, one disruption.
With an EPC rating
On site generation reduces the modelled energy use of the building, so it can move a band. It is rarely the cheapest way to do that, but on a building already having solar for other reasons the rating gain comes free.
Does it move an EPC rating
On site generation reduces the modelled energy use of a building, so it can move an EPC rating.
Ratings matter most if you let the building. Our guide to MEES and the commercial EPC standard sets out the thresholds, the dates and what to do if a building falls short.
Common questions
Is solar worth it on a commercial building in the UK?
It depends almost entirely on how much of the generation your building uses itself. A site with strong weekday daytime load, a sound roof and export headroom usually has a solid case. A building that is empty during daylight usually does not, because exported power earns a fraction of what you pay for grid power.
How much roof do I need?
Between 5.5 and 8 square metres of usable roof per kWp, depending on the panel and the mounting system. Usable is the important word. Rooflights, plant, walkways and shading all come off the plan area first.
Do I need planning permission for commercial solar?
Roof mounted arrays on commercial buildings often fall under permitted development, but there are limits and exceptions, and listed buildings and conservation areas are treated differently. Your installer should confirm the position for your building in writing rather than assume it.
What happens if the network will not let me export?
You can still fit an array with an export limiting device, sized to what the building consumes itself. That is often a better commercial case anyway, because self consumption is where the value is.
Can I put solar on a leased building?
Yes, with the freeholder's consent, and with agreement on who owns the array and what happens at the end of the term. If you are the landlord, the tenant receives the bill saving unless the lease or a side agreement says otherwise.
How long do commercial solar panels last?
Panels are generally warranted for output over twenty five years and degrade slowly. Inverters have a shorter life and should be budgeted for replacement within the life of the array.
Will solar move my EPC rating?
It can. On site generation reduces the modelled energy use of a building, which feeds the non domestic assessment. Lighting and fabric are usually cheaper routes to the same band.
Where these figures come from
Show the provenance
- Installed cost: from £450 to £620 per kWp
- Derived from real commercial installer proposals rather than a published average.
- Roof area needed: 5.5 to 8 square metres per kWp
- UK commercial rooftop market data, 2026.
- Annual yield: 750 to 1,100 kWh per kWp per year, depending on region
- UK regional solar yield data, 2026. Southern England sits at the top of that range and Scotland at the bottom.
- Share used on site: 50 to 85 per cent
- Typical commercial rooftop range. Replaced by your own half hourly data.
Grid electricity is taken at 20 to 27 pence per kWh, from 2026 UK commercial rates.
The figures on this page are modelled ranges for UK commercial buildings, not a quote for yours. Add your building and we will model it on your own roof, load and rating.