How Commercial Solar PV Systems Work: A Buyer's Guide

What a commercial solar PV system actually is

Strip away the jargon and commercial solar PV systems do one thing: they turn daylight falling on your roof or land into electricity your business uses during the working day. Every unit you generate and consume on site is a unit you no longer buy from the grid at 25p to 45p per kWh, roughly double the rate UK businesses paid three years ago. That is the whole economic case in one sentence.

The physical system is more mature than most buyers expect, installed on tens of thousands of UK commercial roofs. There is no moving machinery to wear out, the panels carry a 25-year performance warranty, and once commissioned it runs quietly in the background for two and a half decades. This is bankable engineering, not a gamble.

This guide covers how the parts fit together, why self-consumption decides your payback, how the system connects to the grid, what it costs, and how businesses fund it. If you are a finance director or estates manager signing off the capex, it should give you enough to interrogate any quote you are handed.

The components, and what each one does

A commercial PV system has four core parts and a handful of supporting elements. Understanding them helps you read a proposal properly.

• Panels (modules). Monocrystalline silicon panels sit on the roof or on a ground frame and produce direct current (DC) when light hits them. Modern panels generate usefully in diffuse and overcast light, not only direct sun, which matters in the UK climate. As a rule of thumb, 1 kWp of panels occupies roughly 5 to 6 sqm of roof and produces about 900 to 1,000 kWh a year here.
• Mounting system. How the panels attach to the building. Non-penetrative clip-fix mounting suits standing-seam and trapezoidal metal roofs common on warehouses and industrial units, and it preserves the existing roof warranty. Pitched and flat roofs use ballasted or fixed systems sized for wind uplift.
• Inverter. Converts the DC from the panels into the alternating current (AC) your building and the grid use. Inverter sizing relative to panel capacity is one of the design decisions that actually affects yield, so it is worth asking about.
• Metering and monitoring. A generation meter records what the system produces, and an export meter records surplus sent to the grid. Monitoring software lets you see live and historic output, which is how you verify the system is performing as modelled.

Larger sites often already have a three-phase or high-voltage supply, which simplifies connecting bigger inverters. Battery storage is an optional fifth component, covered further down.

Self-consumption is the number that decides your payback

Most buyers fixate on roof area or panel count. The figure that actually drives the economics of commercial solar PV systems is self-consumption: the share of what you generate that you use on site rather than exporting.

The reason is simple. A unit you consume on site is worth the full 25p to 45p you would otherwise pay the grid. A unit you export earns you the Smart Export Guarantee rate, roughly 4p to 15p per kWh. Same electron, three to ten times the value depending on where it goes. So a well-designed system is sized to match your consumption shape, not to fill every square metre of roof.

This is why building type matters so much. A factory with a steady daytime process load consumes 80% or more of what it generates, which is why manufacturing sites reach the best paybacks in the sector, around 5 years. An office with 09:00 to 18:00 occupancy typically self-consumes 55% to 75% without a battery. A retail unit or school with lighter weekend use sits lower and exports more.

The design target for a UK commercial system is usually annual generation equal to 60% to 85% of current consumption. That maximises self-consumption while avoiding a large surplus sold cheaply to the grid. A serious installer sizes this from your half-hourly meter data, not from a per-square-metre estimate. If a quote does not mention your consumption shape, treat it with caution. You can compare real figures on our cost and payback guide.

Rooftop, ground-mount or solar carport

Where the array goes depends on your roof, your land and your demand. Most commercial buildings start with the roof because it is space you already own and it keeps the generation close to the load.

Option	Best for	Typical cost	Watch-outs
Rooftop	The default for warehouses, factories, offices, retail	Lowest per kWp; uses existing structure	Roof condition, remaining warranty life, structural loading, asbestos on pre-2000 roofs
Ground-mount	Sites with spare land where roof area is short of demand	Higher; needs frame, groundworks, cabling	Usually needs full planning above permitted-development thresholds
Solar carport	Car parks at retail, hospitality and offices; adds EV-charging canopy	Highest per kWp; structural canopy cost	Best justified where it also shelters vehicles or supports EV charging

Roof and ground-mount are frequently combined on manufacturing and agricultural sites where the roof alone cannot meet demand. Whichever route you take, the feasibility study confirms structural loading and the planning position before design is finalised. Sector-specific detail sits on the relevant pages, for example warehouses and industrial units and agricultural buildings.

PV only, or PV plus battery

Battery storage stores surplus daytime generation for use in the evening, at weekends or overnight. Whether it earns its keep depends entirely on your demand profile.

For a business that consumes most of its generation during the working day, such as an office or a single-shift factory, PV alone already delivers high self-consumption and a battery adds cost without adding much saving. For a hotel, restaurant or refrigerated site with strong evening, weekend or overnight load, a battery makes clear sense. It typically lifts self-consumption from 55% to 75% up to 80% to 95%, and adds around 25% to 40% to annual savings, at the cost of a longer payback.

Configuration	Self-consumption	Best fit	Effect on payback
PV only	55% to 75%	Daytime-occupied offices, single-shift sites, most warehouses	Shortest payback
PV plus battery	80% to 95%	Hotels, restaurants, refrigerated retail, 24/7 sites	Longer payback, higher total saving

Storage is usually worth modelling above 100 kWp or wherever significant load falls outside generation hours. The sensible default is to design every system to be battery-ready, so you can add storage later if tariffs or your demand change without re-engineering the array. Hospitality economics are covered on the hospitality and leisure page.

How the system connects to the grid

A commercial installation has to be approved by your Distribution Network Operator (DNO). This is often the longest part of the whole project and the single biggest lever on your timeline, so it should be handled first, not last.

Small commercial systems, roughly under 50 kW, can sometimes use the faster G98 or G99 fast-track. Most commercial systems need a full G99 application to the DNO. For larger systems, export limitation (G100) is often used to cap what the array can push to the grid, which speeds up the connection and avoids expensive network reinforcement. Timescales run from 4 to 12 weeks for small connections up to 6 to 18 months for large ones, and above 1 MW the DNO may require reinforcement works.

The practical takeaway: a good installer submits the DNO application early, often before the site survey. Rural sites in particular can hit network capacity limits, so the grid question is worth raising in the very first conversation.

What commercial solar PV systems cost

Pricing scales with size. Larger systems cost less per kWp because the fixed costs of design, scaffolding and connection are spread across more capacity.

System size	Typical price per kWp	Example real-terms cost
Under 100 kW	£900 to £1,300	50 kW office: £45,000 to £60,000
100 to 250 kW	£750 to £950	250 kW warehouse: £190,000 to £240,000
Above 500 kW	£600 to £800	1 MW factory: £600,000 to £750,000

Those are headline capex figures. The effective net cost for a profitable company is lower, because of the tax treatment covered below. Set against the outlay, a well-sized system commonly cuts total grid electricity costs by 30% to 60%, and that saving grows in real terms every time grid prices rise. Full worked examples sit on the cost and payback guide, and you can run your own numbers on the savings calculator.

The tax relief and funding that changes the maths

Two levers turn the headline price into a far better net figure, and several funding routes remove the need for upfront capex.

• 100% Annual Investment Allowance. Solar PV qualifies as plant and machinery, so a profitable company can deduct the full capex from taxable profit in the year of installation, up to the £1m AIA cap. For most commercial installs that means the whole cost is expensed in year one, an effective saving of roughly 25% for a limited company paying corporation tax.
• VAT is reclaimable. For a VAT-registered business, the VAT on a commercial installation is recoverable through the normal return. Note this is different from the domestic 0% relief, which does not apply to commercial work.
• Smart Export Guarantee. MCS-certified systems earn 4p to 15p per kWh for surplus exported to the grid. For buildings that export a meaningful share, offices, retail and schools, a competitive SEG tariff is a real part of the return.
• Sector grants. Energy-intensive manufacturers may access the Industrial Energy Transformation Fund. Public bodies use Salix and the Public Sector Decarbonisation Scheme. Some combined authorities run regional SME decarbonisation grants.

On funding, most businesses do not pay upfront at all. Asset finance spreads the cost over 5 to 7 years and is usually cash-flow positive from month one, because the finance payment is less than the bill saving it replaces, and you own the system at the end. A Power Purchase Agreement needs zero capex: a funder installs and owns the system, and you buy the power at a fixed rate below grid. A serious quote models cash, finance and PPA side by side with the IRR for each. See the full picture on the grants and funding page.

Accreditations to look for, and why they matter

Commercial PV is an engineering and finance exercise, not just a wiring job, so accreditation is your main protection against a poor install. Look for MCS commercial certification (which also unlocks the Smart Export Guarantee), NICEIC registration, RECC and TrustMark, an IWA insurance-backed workmanship warranty on top of the 25-year panel performance warranty, and ISO 9001, 14001 and 45001. A generalist electrical contractor can fit panels, but rarely designs for optimal self-consumption or navigates G99 and grant processes, which is where most of the value is won or lost.

From enquiry to commissioned system

A typical project runs from signed contract to a working system in 8 to 20 weeks. The physical install is only 1 to 6 weeks of that; the critical path is usually the DNO connection. The order of events is: desk feasibility from your meter data, site and structural survey, DNO application (submitted early), fixed-price proposal with the PVSyst yield model shared, installation, commissioning, and EPC re-assessment to capture the rating uplift for MEES compliance.

Because the proposal is built from your real consumption data and a shared yield model, the generation and payback figures are verifiable by any third party rather than sales estimates. If you want to see how the numbers land for your building, request a free desk feasibility, or read the frequently asked questions for the detail behind any of the points above.