Offices: Commercial Solar PV

Why commercial solar PV suits offices

Offices are one of the cleanest fits for commercial solar PV in the UK, and the reason is timing. An office building draws most of its power between roughly 08:00 and 18:00, Monday to Friday, and that is exactly when a rooftop array is generating. The demand curve and the generation curve sit almost on top of one another. That alignment means a well-sized office system consumes the bulk of what it produces on site, without needing a battery to shift power into the evening.

The load itself is stable and predictable. In most offices, IT equipment, HVAC and lighting make up 60 to 80 per cent of total consumption, and that baseload runs steadily through the working day. Servers, comms racks, air conditioning, LED lighting and small power at every desk add up to a flat, dependable draw that solar can offset hour by hour. There are no wild spikes to design around, which makes the yield modelling straightforward and the payback dependable.

There is a property angle too. Solar lifts an office building's EPC rating, and for landlords and owner-occupiers that matters for MEES compliance and for asset value. A better EPC keeps a building lettable under Minimum Energy Efficiency Standards and typically supports a higher valuation. For finance directors and estates managers already fielding Scope 2 and ESG questions from clients and investors, an on-site array is visible, measurable evidence of action rather than a line in a sustainability statement.

The one wrinkle particular to offices is tenure. Office space is often multi-let or leased, so the economics have to account for who pays the electricity bill and who owns the roof. That is a solvable problem, usually through a green-lease addendum or a service-charge recovery route, but it needs deciding at the design stage rather than after the panels are up. We cover how funding fits multi-let buildings further down, and the options in full on our grants and funding routes page.

The office load profile and self-consumption

Self-consumption is the number that decides whether commercial solar pays. It is the share of the electricity your panels generate that you use on site rather than exporting to the grid. Every unit you self-consume displaces a unit you would otherwise buy at 25 to 45p per kWh; every unit you export earns only the Smart Export Guarantee rate, roughly 4 to 15p per kWh. The whole design goal is to keep self-consumption high.

Offices do this naturally. A daytime-occupied building with 09:00 to 18:00 hours typically achieves 55 to 75 per cent self-consumption from a PV-only system, no battery required, because the array generates while the building is full of people and running its systems. The baseload matters here: because IT, HVAC and lighting run continuously through the day, there is always a floor of demand soaking up generation even in the quieter mid-morning and mid-afternoon hours.

The limit for offices is weekends and evenings. An office sits largely empty on Saturday and Sunday and after hours, so on a bright weekend a meaningful slice of generation has nowhere to go on site and is exported at the lower SEG rate. This is why office self-consumption tops out lower than a 24/7 factory. It is also why the design target for an office is usually annual generation equal to 60 to 85 per cent of consumption rather than covering 100 per cent of the roof: oversizing simply pushes more low-value export.

Battery storage can lift office self-consumption from 55 to 75 per cent up to 80 to 95 per cent by capturing surplus daytime generation and releasing it in the early morning and early evening shoulders, and it is usually worth modelling above 100 kWp or where there is significant out-of-hours load such as server rooms or extended shift working. For a standard nine-to-five office, though, the PV-only case often stands on its own, and we design every system to be battery-ready so storage can be added later without rework. You can compare both cases for your building using our savings calculator.

System sizing for offices

Commercial PV is sized from your annual energy spend and the half-hourly shape of your consumption, not from roof area alone. The rule of thumb is that 1 kWp of panels needs about 5 to 6 square metres of unshaded roof and generates roughly 900 to 1,000 kWh a year in the UK. From there, the design target is annual generation equal to 60 to 85 per cent of what you currently use, which maximises self-consumption while avoiding excessive low-value export.

For UK offices, that lands most systems in the 30 to 150 kW range, using somewhere between 55 and 275 panels and occupying 200 to 900 square metres of roof. At the smaller end, a modest suburban office block or converted unit might take a 30 to 40 kW array on 200 square metres of roof. At the larger end, a headquarters or business-park building with a big flat or shallow-pitch roof can carry 150 kW comfortably. A typical office system generates 27,000 to 138,000 kWh a year and saves 6 to 31 tonnes of CO2 over the same period, which feeds directly into Scope 2 reporting.

The physical work is shaped by the roof. Flat commercial roofs use ballasted or fixed mounting on the existing membrane; pitched roofs use appropriate fixed systems. Roof condition and remaining warranty life are checked first, because there is no sense mounting a 25-year asset on a roof with five years left in it. Where the roof is sound, non-penetrative approaches are preferred to preserve the existing roof warranty. Shading from parapets, plant, lift-overrun structures and neighbouring buildings is modelled properly rather than eyeballed, because a small amount of shading on the wrong string can cost a disproportionate amount of yield.

A worked cost and payback example

Office systems typically carry a project value of £30,000 to £150,000 fully installed, and the typical payback for an office is around 7 years. That payback sits slightly above the sector-wide 5 to 8 year range precisely because of the weekend and evening gaps in demand discussed above; a building with heavier out-of-hours load lands lower.

Take a mid-sized example. A 60 kW office array is a realistic middle-of-the-range project. Here is how the headline numbers stack up before and after the main tax levers.

Item	Figure
System size	60 kW, roughly 110 panels
Indicative installed cost	£54,000 to £66,000
Annual generation	around 54,000 to 60,000 kWh
Typical annual saving	£11,000 to £14,000
Effective net cost after 100% AIA	roughly three-quarters of headline
Simple payback	around 7 years
Panel performance warranty	25 years

The tax treatment materially improves that picture. 100% Annual Investment Allowance lets a profitable limited company deduct the entire capex from its taxable profit in the year of purchase, an effective saving of roughly 25 per cent for a company paying corporation tax. On top of that, VAT is reclaimable for VAT-registered businesses, because commercial solar is not a 0 per cent-rated supply the way domestic installs are; the input VAT is recovered through the normal return. Between the two, the net cost a profitable, VAT-registered office business actually carries is well below the headline number.

After payback, the arithmetic keeps working. The panels carry a 25-year performance warranty, so a system that clears its cost in around 7 years then delivers 15 to 20 years of near-free power. Every time grid electricity prices rise, the value of that self-generated power rises with them, which is why we describe an array as a hedge rather than just a cost saving. For the full per-kWp breakdown across the size range, see our real-world UK pricing guide.

Planning, compliance and grid connection

Most commercial rooftop PV on an office falls under Permitted Development, specifically Class A of Part 14 of the GPDO 2015, subject to size and siting limits, so no planning application is needed. The main exception for offices is the frontage: a conservation-area building or a street-facing array may need planning permission, and installing on the rear or a set-back roof plane often avoids the issue entirely. Listed office buildings need Listed Building Consent for visible arrays. We confirm the planning route as part of the feasibility study and handle any application that is required.

Two compliance points are specific to offices and worth flagging early:

• Buildings insurance. Some office insurers require the PV system to be integrated with the building's fire-alarm and detection system. This is a design item to raise with your insurer at the outset, not an afterthought, and correct MCS certification means most insurers continue cover without difficulty.
• Roof warranty and structure first. Before any design work, we assess roof condition, remaining warranty life and structural loading for the additional dead load and wind uplift. On an office this comes ahead of everything else, because it determines whether a non-penetrative mount is viable and whether any strengthening is needed.
• EPC re-assessment. Once the system is live, a fresh EPC captures the rating uplift, which is what turns the install into a MEES and asset-value benefit rather than just an energy saving.

On grid connection, the size of the office system dictates the route. Small systems, roughly under 50 kW or 3.68 kW per phase, can often use the faster G98/G99 fast-track. Most office arrays in the 30 to 150 kW range need a full G99 application to your Distribution Network Operator, and where export needs limiting to secure a connection quickly, a G100 export-limitation scheme is used to avoid costly network reinforcement. DNO timescales run from around 4 to 12 weeks for smaller connections upward, so the application goes in early, usually before the site survey, because it is frequently the longest item on the critical path.

Funding routes that fit offices

Offices have a wider than usual set of funding options because the multi-let and leasehold structures common to the sector open up routes a single owner-occupier would not consider. The three core commercial routes apply, and the tenure structure often decides which fits best.

• Cash purchase with 100% AIA. For an owner-occupied office run by a profitable company, buying outright and expensing the capex in year one under 100% Annual Investment Allowance is usually the lowest lifetime-cost route. VAT is reclaimed in the normal way, and the company owns a 25-year asset outright.
• Asset finance. Spreading the cost over 5 to 7 years is typically cash-flow positive from month one, because the monthly finance payment is less than the electricity bill saving it replaces. You own the system at the end. This suits offices reluctant to commit six figures of capital to a single project.
• Power Purchase Agreement (PPA). A PPA needs zero capex: a funder installs and owns the system, and you buy the power it generates at a fixed rate below grid price. For a leased office, a PPA can be structured to transfer with the building on sale, and for a multi-let building it can sit cleanly alongside a service-charge arrangement.

Beyond the funding structure, the main financial levers for an office are the Smart Export Guarantee, which pays for the surplus that offices inevitably export at weekends, and the tax reliefs already covered. Offices without round-the-clock demand export a meaningful share of generation, so a competitive SEG tariff is a genuine part of the economics rather than a rounding error. Some combined authorities and Growth Hubs also run periodic SME decarbonisation grants worth checking before you commit to a route. We model cash, asset finance and PPA side by side on every proposal, with the IRR for each, so the office board sees a defensible comparison rather than a single pushed option. Start that process with a free no-obligation quote.

A representative office project

To make the numbers concrete, here is a representative scenario for an unnamed office. It is illustrative, built from typical figures for the sector rather than a named client.

A 40-person professional-services firm occupies a converted office and showroom of roughly 900 square metres, and pays in the region of £22,000 a year for electricity. The business is fielding sustainability questions from its larger corporate clients and wants both a real bill reduction and something demonstrable to point to. Its consumption is a textbook office profile: steady IT and HVAC baseload through the working day, tailing off in the evenings and near-empty at weekends.

Modelling from the firm's half-hourly meter data points to a 60 kW system of around 110 panels on the pitched roof, generating roughly 55,000 kWh a year. With a daytime-weighted load that self-consumes most of what it produces, the array delivers an annual saving in the order of £13,500 and a simple payback around the 6 to 7 year mark. The firm self-funds and claims 100% AIA, cutting the effective net cost by roughly a quarter. The EPC lifts from C to B, which supports MEES compliance and the building's valuation, and a small lobby display shows live generation to visiting clients as visible proof of the commitment. The figures here are representative; the only way to size and cost your own building accurately is a desk feasibility from your actual meter data.

Common questions about commercial solar for offices

How much roof do we need for an office solar system?

As a rule of thumb, 1 kWp of PV needs about 5 to 6 square metres of unshaded roof and generates roughly 900 to 1,000 kWh a year in the UK. A typical office system of 30 to 150 kW therefore occupies 200 to 900 square metres. A 250 square metre office roof supports around 30 to 40 kWp. We size from your half-hourly meter data rather than roof area alone, targeting annual generation equal to 60 to 85 per cent of your consumption, and we model shading from parapets, plant and neighbouring buildings properly rather than assuming a clear roof.

Will solar work if our office is empty at weekends?

Yes, and the modelling accounts for it. A daytime-occupied office achieves 55 to 75 per cent self-consumption from a PV-only system because generation and the working-day load line up. Weekend and evening generation is exported to the grid under the Smart Export Guarantee at roughly 4 to 15p per kWh, so it still earns money, just less than the 25 to 45p you save on power used on site. Where weekend or out-of-hours export is significant, we model battery storage, which can lift self-consumption to 80 to 95 per cent, so you can compare a PV-only design against PV-plus-battery.

How does solar affect our EPC rating and MEES compliance?

Installing solar reduces a building's assessed energy use, which lifts its EPC rating; a fresh EPC assessment after commissioning captures the improvement. That matters under Minimum Energy Efficiency Standards, which set the rating a commercial property must meet to remain lettable, and a better EPC typically supports a higher asset value. For landlords and owner-occupiers this is often as valuable as the bill saving itself, and it is one of the reasons offices with lighter weekend use still make a strong overall case for PV.

We lease our office, or it is multi-let. Can we still install solar?

Often, yes, but the structure needs deciding at the design stage. Multi-let and leased offices need a route to allocate the cost and the benefit fairly, usually a green-lease addendum or a service-charge recovery arrangement. A Power Purchase Agreement fits leased buildings well because it needs no capital from the occupier and can transfer with the building on sale. The right approach depends on your lease terms and expected tenure, both of which we factor into the proposal rather than treating solar as a simple owner-occupier install.

Do we need planning permission for solar on an office?

Usually not. Most commercial rooftop PV falls under Permitted Development, Class A Part 14, so no planning application is required. The exceptions relevant to offices are conservation-area or street-facing arrays, which may need planning permission, and listed buildings, which need Listed Building Consent for visible panels. Rear-roof or set-back installs frequently sidestep frontage issues altogether. We confirm the planning route as part of the feasibility study and handle any application that turns out to be needed.

What is the payback on office solar, honestly?

For a typical UK office the simple payback is around 7 years, which sits at the upper end of the 5 to 8 year commercial range because offices sit empty at weekends and export more of their generation than a 24/7 building. Offices with heavy out-of-hours load, such as sites with server rooms or extended shift working, land lower. The panels carry a 25-year performance warranty, so after payback the system delivers 15 to 20 years of near-free power, and 100% Annual Investment Allowance plus reclaimable VAT bring the effective net cost down for a profitable, VAT-registered business. Warehouses and industrial units, with more continuous demand, often pay back a year or two faster; you can compare the two on our solar for warehouses and industrial units page.