Commercial Solar Installers for UK Businesses

How a commercial rooftop solar project runs

A non-domestic rooftop project is a sequence of gates, and each one can stop the job. The order matters, because a design signed off before the structural and network checks is a design that gets rebuilt.

Survey comes first: roof construction, covering, age, penetrations, access and the route from array to switchroom. The MCS solar PV installation standard requires that PV systems “should not adversely affect the weather tightness or structural integrity of the building to which they are fitted”, and that this is maintained for the life of the system (MIS 3002, clause 5.9.1). The same standard requires that where an existing roof covering is under warranty, the warranty provider is consulted, and where a warranty may be invalidated the contractor must notify the customer in writing and obtain explicit written agreement before proceeding. MIS 3002 is explicit that a clause buried in standard terms and conditions does not satisfy that requirement. The domestic sequence, from survey to MCS certificate, is laid out step by step in our guide to the solar PV installation process.

Design follows. Under the MCS method the estimated annual output is calculated as kWp multiplied by a location-specific kWh/kWp figure and a shade factor, with the location figure taken from postcode zones that MIS 3002 confirms “are the same as the SAP postcode zones”. St Albans AL postcodes fall in zone 1. If shading is present and the MCS shading methodology has been used, the standard requires the quotation to carry a note saying the factor “will yield results within 10% of the actual energy estimate stated for most systems”. Ask to see that wording; its absence tells you how the estimate was produced.

Then come the grid application, the export metering arrangements and commissioning. Both the network application and the metering have their own thresholds and timescales, and both are covered in detail further down this page.

What a commercial array costs, and what actually drives the price

We do not publish a price per kWp on this page, because a credible commercial figure depends on variables that only a site survey settles. Anyone quoting a flat rate before seeing your roof is quoting a guess. What we can set out honestly is what moves the number, so you can read competing quotations against each other.

The cost drivers that matter most on a commercial roof are structural rather than electrical. A standing-seam or single-ply membrane roof, a shallow deck with limited spare load capacity, a long cable run to a distant switchroom, restricted crane or scaffold access, or a roof covering still inside its warranty period will each move the figure more than the choice of panel. Fire performance is a design input too: MIS 3002 reproduces the Approved Document B (2019 edition) classification table, under which a Broof-rated solar kit “can be installed anywhere and in any amount of roof covering” while lower-rated kits are restricted by distance to the relevant boundary.

On the regulatory side, the grid outcome is the biggest single unknown. Where the network operator identifies that reinforcement is needed, the EREC G99 small-generation procedures state that installation must not proceed “until the DNO has established if it is necessary to upgrade the network, and whether such work may be chargeable to the Generator”. A quotation that does not name who carries that risk is incomplete.

• Roof type, deck capacity and existing covering warranty
• Distance and route from array to the point of connection
• Access, edge protection and whether work must be phased around trading hours
• Fire classification of the mounting kit against boundary distances (Approved Document B, 2019 edition)
• Whether the network operator requires reinforcement, and who pays for it
• Whether an export limitation scheme is needed to stay inside a lower application route

The tax position: AIA and the 50% first-year allowance, not Full Expensing

This is the single most commonly misstated fact in UK commercial solar marketing, so take it from HMRC directly. The Capital Allowances Manual states that “all capital expenditure on the provision of solar panels is specifically designated as special rate” (CA22335), a designation that has applied since 1 April 2012 for corporation tax and 6 April 2012 for income tax.

That designation decides which reliefs are available. Full expensing is, in HMRC's own description, “a 100% first-year allowance for main rate expenditure”, sitting alongside “a 50% first-year allowance for special rate expenditure”. Because solar is special rate, a solar array does not qualify for full expensing. A company can claim the 50% first-year allowance instead, and both allowances are restricted to companies, to assets bought from 1 April 2023, and to plant that is new and unused and not a car.

The Annual Investment Allowance is the other route and is open to unincorporated businesses as well as companies. HMRC confirms that the AIA “may be claimed on long-life assets, integral features and other special rate expenditure, as well as on general plant and machinery” (CA23084), and that “the AIA amount is £1 million”. For most single-site rooftop projects the AIA is the simpler and more valuable claim.

One scheme you may still see referenced does not exist any more. The first-year allowance and first-year tax credit for products on the Energy Technology List and Water Technology List “will both end with effect from 1 April 2020 for companies and 6 April 2020 for unincorporated businesses”. Any quotation that offers you Enhanced Capital Allowances on an Energy Technology List product is working from guidance that is more than six years out of date. Confirm the treatment of your own expenditure with your accountant before you commit; this page states the rules, not advice on your tax position.

Business rates: onsite generation plant sits outside the rateable value until 2035

Adding generating plant to a commercial building would normally risk increasing its rateable value. In England it does not, for now. The Valuation for Rating (Plant and Machinery) (England) (Amendment) Regulations 2022 created a category of “excepted renewables plant and machinery” covering “plant and machinery used or intended to be used for the generation, storage, transformation or transmission of power” where the technology relied upon is mainly or exclusively from a listed set that includes photovoltaics and solar power. The regulations apply the exception “in relation to any day before 1st April 2035”.

The explanatory memorandum to those regulations puts the window plainly: the instrument “will implement an exemption from non-domestic rates for plant and machinery used in connection with renewable generation and also plant and machinery used for storage at Electric Vehicle Charging Points” and “the exemption will apply from 1 April 2022 until 31 March 2035”. It also records that the exemption “will be implemented by the Valuation Office Agency (VOA) who will automatically remove the eligible items from rateable values”, so it is not something a ratepayer applies for.

Two practical points. The instrument's territorial application is England, so Scotland and Wales need checking separately. And the exclusion is written with an end date, which means the position for any project commissioned late in the window should be confirmed against the regulations as they stand at the time rather than against this page.

Planning: the permitted development right for non-domestic roofs

Rooftop solar on a commercial building in England is usually permitted development under Class J of Part 14 of Schedule 2 to the General Permitted Development Order 2015. Class J covers “the installation, alteration or replacement of—(a) microgeneration solar thermal equipment on a building; (b) microgeneration solar PV equipment on a building; or (c) other solar PV equipment on the roof of a building, other than a dwellinghouse or a block of flats”.

The split between J(b) and J(c) is the 50 kW line, and it is worth understanding because it is not written in Class J itself. Part 14 defines microgeneration by reference to section 82(6) of the Energy Act 2004, which caps microgeneration at 50 kilowatts for electricity generation. A rooftop array at or below that capacity is J(b). Above it, the array is J(c) — and J(c) carries an extra condition: “Class J(c) development is permitted subject to the condition that before beginning the development the developer must apply to the local planning authority for a determination as to whether the prior approval of the authority will be required as to the design or external appearance of the development”. Confirm the current wording with your local planning authority before you rely on it.

The old megawatt ceiling has gone. Article 6 of the Town and Country Planning (General Permitted Development etc.) (England) (Amendment) (No. 2) Order 2023, which “comes into force on 21st December 2023”, omitted paragraph J.3 — the paragraph that had read “development is not permitted by Class J(c) if the capacity of the solar PV equipment installed (together with any solar PV equipment installed under Class J(b)) to generate electricity exceeds 1 megawatt”. Rooftop capacity on a non-domestic building is no longer capped by that limit.

The dimensional and heritage limits in J.1 still apply, and they are the ones that catch real projects.

• Pitched roof: equipment must not protrude more than 0.2 metres beyond the plane of the roof slope
• Flat roof: the highest part must not be more than 1 metre above the highest part of the roof
• Equipment must not be installed within 1 metre of the external edge of the roof
• Not permitted on a scheduled monument, or on a listed building or within its curtilage
• Separate restrictions apply on article 2(3) land, and stand-alone solar in the curtilage falls under Class K instead

Grid connection: G98, G99 and the 16 A per phase line

The threshold that decides your network application is current per phase, not kilowatts. ENA Engineering Recommendation G99 Issue 2, published 10 March 2025, states that it “applies to all Power Generating Modules which are not in the scope of EREC G98, 'Requirements for the connection of Fully Type Tested Micro-generators (up to and including 16 A per phase) in parallel with public Low Voltage Distribution Networks on or after 27 April 2019', or which would be in the scope of EREC G98 but are not suitable for type testing or which are designed to work in island mode”. Sixteen amps per phase is 3.68 kW on a single phase and 11.04 kW across three, which is why almost every commercial array is a G99 job and why the figure of 50 kW sometimes quoted as the G99 trigger is simply wrong.

G99 also defines the module classes. A Type A module is “a Power Generating Module with a Connection Point below 110 kV and a Registered Capacity of 0.8 kW or greater but less than 1 MW”, so the overwhelming majority of commercial rooftop projects are Type A. For those, G99 says the generator “should apply to the local DNO for connection using the DNO's Standard Application Form”, after which “the DNO will assess whether any Distribution Network studies are required and whether there is a requirement to witness the commissioning tests”, and permanent energisation is sanctioned only on successful completion of commissioning tests.

Below Type A there are three Small Generation Installation routes that can shorten the process, each defined by intrinsic design capacity, registered capacity and whether an EREC G100 export limitation scheme is fitted. For SGI-2 and SGI-3, G99 states that the DNO “will provide the results of the assessment within 10 working days of receiving the application”, and that the planned commissioning date on the form “shall be between 10 working days and 3 months from the date that the application is submitted”, with commissioning confirmed “no later than 28 days after commissioning”. If the DNO decides further analysis is needed, the SGI route ends and the standard application process takes over.

• EREC G98: all individual and aggregate registered capacities 16 A per phase or less, no export limitation scheme required
• EREC G99 SGI-1: individual intrinsic design capacity up to 32 A, registered capacities and aggregate 16 A or less
• EREC G99 SGI-2: aggregate registered capacity up to 32 A with a G100 scheme limiting export to 16 A per phase
• EREC G99 SGI-3: aggregate registered capacity up to 60 A with a G100 scheme limiting export to 32 A per phase
• Standard G99: everything above, assessed on the DNO's own application form and timescales

What happens to the power: self-consumption, export and the SEG above 50 kW

On a commercial site the economics are driven by self-consumption, because a self-consumed unit displaces the full delivered import price while an exported unit earns whatever the export tariff pays. The displaced import price includes the Climate Change Levy, which HMRC sets at £0.00801 per kWh of electricity from 1 April 2026, up from £0.00775 from 1 April 2025. DESNZ describes the levy as “an energy tax payable on supplies of electricity, gas, liquified petroleum gas and solid fuels to businesses and public sector organisations” — a charge on supply, and therefore not one that falls on units you generate and consume on site.

Export runs through the Smart Export Guarantee. Ofgem's generator guidance confirms the SEG requires licensed suppliers to offer export tariffs to “anaerobic digestion (AD), hydro, onshore wind, and solar photovoltaic (PV) generators with a total installed capacity up to 5MW”. Metering is a hard eligibility condition: “that meter must be capable of taking half-hourly measurements and have an export MPAN”, and “an export meter must be located at the point where the installation connects to the distribution network”.

The certification requirement changes at 50 kW, and this is the part most pages get wrong. Ofgem's summary table sets out that for micro-CHP, solar PV and wind at 50 kW or less, both installation certification and installer certification are required; for the same technologies above 50 kW up to 5 MW, installation certification is required but installer certification is not. For installations above 50 kW, Ofgem states that “SEG licensees have discretion in how they satisfy themselves that the installation is suitably certified”. So an MCS certificate is the standard evidence below 50 kW, and above it the supplier sets the bar — which makes the export route something to agree with a named SEG licensee before you design the system, not after.

Procurement and compliance checks a business buyer should run

Two of the schemes a domestic buyer leans on do not reach a commercial buyer, and knowing that changes what you should be asking for in a contract.

MCS has a ceiling. The MCS solar PV installation standard specifies requirements for contractors undertaking solar PV systems “supplying permanent buildings and normally connected in parallel to the electricity distribution network up to a maximum DC output of 50kWp” (MIS 3002). Below that figure an MCS certificate is meaningful and, as above, is what the SEG expects. Above it the standard does not apply, so an installer's MCS certification tells you about their competence on smaller systems rather than certifying the array you are buying.

The consumer code has a ceiling too, and it is lower. The Renewable Energy Consumer Code (version 9, published 1 July 2026) sets out standards “for domestic consumers (referred to as Consumers in this Code)”, and defines a Consumer as “an individual or individuals acting for purposes that are wholly or mainly outside that individual's trade, business, craft or profession”. A trading business is not a Consumer under the Code. RECC does recognise a “micro-business consumer” — broadly, annual electricity consumption of not more than 55,000 kWh, or fewer than 10 full-time-equivalent employees and turnover or balance sheet total not exceeding £1.5 million — but RECC states that “micro-business consumers are not permitted to use the RECC complaints process” and instead routes them to independent arbitration through CEDR Solve, with each party paying a flat fee of £200 plus VAT. Above the micro-business thresholds there is no consumer-code route at all: your protection is the contract you signed.

That is the argument for doing the commercial diligence properly rather than relying on logos.

• Ask which named scheme covers the system you are buying, and what happens if the capacity exceeds 50 kWp
• Ask who submits and tracks the network application, and who carries any reinforcement cost the DNO identifies
• Ask whether the generation estimate used the MCS methodology and the MCS shading methodology, and for the required wording in writing
• Ask for the roof covering warranty position in writing before works start, as MIS 3002 requires
• Ask for the commissioning documentation set, including the PV array test report and verification certificate
• Check the contract terms carefully, because no consumer code applies above the micro-business thresholds

The buildings commercial solar suits, and how to start

The sites that work best are the ones where generation and consumption overlap: single-storey industrial and warehouse units with large uninterrupted roof planes, offices with daytime load, agricultural buildings, retail and trade counters, schools and academies, and care and hospitality premises with steady daytime demand. The common factor is daytime electrical load on the same meter as the roof, because that is what converts generation into displaced import at the prices quoted above.

SOLA UK installs solar PV, battery storage and EV charging for commercial and domestic customers from our St Albans base, and we have completed more than 700 installations company-wide. On the equipment side we fit AIKO 485W all-black panels, SigEnergy battery systems and the Tesla Powerwall 3 at 13.5 kWh and 11.5 kW continuous output. Battery storage on a commercial site is a separate sizing exercise from the array and is covered on our battery storage page.

One VAT point to close on, because it is often misread. The zero rate for energy-saving materials applies to residential accommodation and to buildings used solely for a relevant charitable purpose, and HMRC's Notice 708/6 is explicit that “the standard rate applies to the installation of energy-saving materials in hospitals, prisons or similar institutions, hotels or inns or similar establishments”. Solar on ordinary business premises is standard-rated at 20%, which a VAT-registered business can normally recover. The domestic zero rate runs to 31 March 2027, after which those installations revert to the reduced rate of 5%.

If you want a design and a figure for your own roof, call 0800 470 0922 or use the quote form on this page. We will tell you which application route your site falls into and what the survey needs to establish before anyone quotes a price.