How big a solar system can my roof take?

Roof area is rarely the binding constraint. The right size is determined by your half-hourly demand profile — the point at which self-consumption falls below ~70% is usually where it stops being worth adding more panels.

Do I need battery storage with solar?

Not for the project to pay back. Add storage when your evening import is expensive (peak/red-band tariffs) or when DNO export limits cap the system size. Many commercial sites do better with solar-only first, battery later.

What if my roof needs replacing in 10 years?

We use mounting systems that can be lifted and re-laid as one operation when the roof is replaced. This is planned for at design stage if your roof age is known.

What's the realistic payback on UK commercial solar today?

Most well-designed rooftop systems pay back in 3–6 years at current import tariffs. Lower payback (3–4 years) is typical for sites with high daytime demand and import tariffs above 25p/kWh. Longer payback (5–6 years) is typical for offices with lower daytime load.

Can I get solar with zero capital outlay?

Yes — via a Power Purchase Agreement (PPA) or Energy-as-a-Service (EaaS). You pay only for the energy delivered at a fixed unit rate below grid. The third party owns and maintains the asset.

How does solar affect my balance sheet?

CAPEX adds a tangible asset and depreciation schedule. Asset finance can be structured on or off balance sheet depending on lease terms. PPA and EaaS are pure operating expense — no asset, no liability.

How long does installation take?

Typical commercial rooftop installs run 4–10 weeks depending on system size and access. Internal disruption is near-zero; most works happen on the roof and at the inverter/cable interface.

How much maintenance does solar need?

Minimal. Annual visual inspection, inverter firmware checks and string-level monitoring catch 99% of issues. Cleaning is rarely cost-justified in UK rainfall conditions.

What happens at end of life?

Panels carry 25-year linear warranties at ~87% of nameplate. End-of-life recycling is funded by the original sale via manufacturer take-back schemes; 95%+ of panel mass is recyclable.

Solution · Commercial Solar PV

Commercial Solar PV — how it actually pays back.

A practical guide for energy, finance and operations leaders weighing rooftop or ground-mount solar on UK commercial sites.

3–6 yrs

Typical payback

25+ yrs

System lifetime

20–40%

Import reduction

In short

Commercial solar PV pays back when the system is sized against your real half-hourly demand — not your annual kWh total. On UK commercial sites, well-designed rooftop arrays typically deliver 3–6 year payback, 25+ years of generation, and a 20–40% reduction in grid imports. The risk is buying generic capacity that exports cheaply instead of offsetting expensive import.

Jump to what matters to you:Energy Director → How it works CFO → Commercial impact Operations → Operational impact

Definition

What Commercial Solar PV actually is

It is

On-site photovoltaic generation — panels, inverters and balance-of-system — sized to a building's daytime demand profile and connected behind the meter so every generated kWh displaces an imported one.

It is not

A generic 'put solar on the roof' commodity. The economics live or die on how the system matches your half-hourly load, your tariff structure, and your roof or land constraints.

kWp (kilowatt-peak): The rated DC capacity of the PV array under standard test conditions. A 100 kWp system typically generates around 85–95 MWh per year in the UK.
Half-hourly (HH) data: Your supplier's record of grid imports in 30-minute intervals. The single most useful input for sizing solar correctly.
Self-consumption ratio: The share of generated energy used on-site rather than exported. Higher = better project economics.
MPAN: Meter Point Administration Number — the unique ID for your electricity supply point.
DNO: Distribution Network Operator — the regional grid operator who must approve any generation connection.
Module degradation: Linear performance loss over time. Modern Tier-1 modules degrade ~0.4–0.5% per year, with 25-year warranties at ~87% of nameplate.

Mechanics

How it works

Six checkpoints from data to commissioning. Scroll to step through each one.

Step 1 of 5

Half-hourly demand analysis

Step 01
Half-hourly demand analysis
We pull 12 months of HH data from your supplier and overlay it with site-specific solar yield modelling. This tells us the maximum system size that achieves high self-consumption — the number that drives payback.
Step 02
Structural and electrical survey
Roof load-bearing capacity, condition, pitch, orientation, shading, cable runs, inverter location, MPAN headroom and DNO connection envelope are all assessed before a single panel is specified.
Step 03
System design and DNO application
We design to a target self-consumption ratio (typically 70–90% for commercial sites) and submit the G99 or G98 application to your DNO. Connection terms shape the final sizing.
Step 04
Procurement and installation
Tier-1 panels and inverters, sourced against your timeline and the project's funding model. Installation is sequenced around your operational calendar — out-of-hours, weekends or staged areas as needed.
Step 05
Commissioning and monitoring
Every system is handed over with live performance monitoring at string level. Year-1 generation is benchmarked against the design — variance triggers immediate investigation.

For the CFO

Commercial impact

Solar PV produces a known commodity — kWh — at a fixed unit cost for 25+ years. That predictability is the financial story. The CFO question is not 'is solar good?' but 'is this specific system, sized this specifically way, on this specific tariff, NPV-positive?'

01
Payback windows of 3–6 years are achievable on UK commercial rooftops with current panel pricing and grid tariffs above 20p/kWh.
02
Levelised cost of energy (LCoE) from a well-designed rooftop system sits at 4–7p/kWh over 25 years — a fraction of grid import.
03
Generation is inflation-hedged: every grid tariff rise increases the value of every self-consumed kWh.

For operations

Operational impact

The biggest operational worry is the wrong one. Most directors fear disruption during installation; in practice, well-sequenced commercial solar installs cause near-zero downtime. The real operational question is what happens in years 3–25.

01
Rooftop installs on commercial buildings are typically completed in 4–10 weeks with zero internal access disruption.
02
Roof penetrations are minimised through ballasted or rail-clamped mounting systems where possible.
03
Inverter MTBF is ~15 years; expect one inverter replacement over a 25-year system life.

The honest list

Risks — and how we de-risk them

Risk 01

System sized to roof area, not demand

We size against half-hourly demand data, not nameplate roof capacity. Oversized systems export at <5p/kWh and destroy payback.

Risk 02

Roof structure can't carry the array

Independent structural survey before design lock. Ballasted systems, lightweight modules and reinforced fixings used where loading is marginal.

Risk 03

DNO refuses or curtails the connection

Pre-application capacity check with the DNO before committing design. Battery storage, export limitation or phased connection used to land an approval.

Risk 04

Tariff falls and undermines payback

Sensitivity modelling at 15p, 20p, 25p and 30p/kWh import scenarios. Payback survives historical lows; current tariffs offer significant headroom.

Risk 05

Tenure too short to recover capital

Asset Finance (lease-to-own) or PPA structures align cost to the lease period. EaaS removes the asset from the tenant entirely.

Risk 06

Underperformance hidden until year 3+

String-level monitoring with alerting on day one. Annual performance reports against design. Ongoing O&M contract for response SLAs.

Funding

How it gets paid for

Four ways to fund the same physical asset. Pick the one that matches your balance sheet and your time horizon.

Option 01

CAPEX (outright purchase)

Capital outlay

100% upfront

Asset ownership

You

Best when

Cash-rich balance sheet, long tenure, want maximum lifetime IRR.

Option 02

Asset Finance / lease

Capital outlay

Deposit + monthly

Asset ownership

You at term end

Best when

Want CAPEX off operating budget but still own the asset; finance rate < projected savings.

Option 03

Power Purchase Agreement (PPA)

Capital outlay

Zero

Asset ownership

Third party

Best when

Want a fixed unit rate below grid with no capital, no O&M, no risk.

Option 04

Energy-as-a-Service (EaaS)

Capital outlay

Zero

Asset ownership

Nuvolt

Best when

Want solar + storage + EV bundled, fully managed, single fixed unit rate.

The signature curve

A day in the life of a well-sized array

Generation rises with the sun, demand sits underneath it. The shaded area is self-consumption — the only kWh that earn full retail value.

Solar generation

Site demand

Self-consumed kWh

Compared

How this stacks up against the alternatives

Solar PV is one of several ways to reduce grid spend. Here's an honest comparison.

	Solar PV	Behind-the-meter battery only	Better grid tariff	Do nothing
Reduces import cost	Yes — 20–40%	Small — arbitrage only	Yes — variable	No
Reduces Scope 2 carbon	Yes — directly	No — energy still imported	Only via grid mix	No
Inflation hedge	Strong (25 yrs)	Partial	No — re-prices	No
Capital required	£ or zero (PPA/EaaS)	££	Zero	Zero
Operational disruption	Low	Very low	None	None
Typical payback	3–6 yrs	5–10 yrs	Immediate but ongoing	n/a