SolarGridCheck.co.uk

Grid Viability Assessment Tool

Commercial Solar

100kW Solar System Cost UK (2026)

£60,000–£120,000 installed. 3–5 year payback. Save £18,000–£24,000 per year on electricity bills.

Calculate Your ROIView Cost Breakdown

100kW Solar System: Key Facts

A 100kW commercial solar system costs £60,000 to £120,000 installed in the UK in 2026. It generates approximately 95,000 kWh per year, saving £18,000–£24,000 annually on electricity bills at current commercial rates. Payback is typically 3–5 years, with systems lasting 25+ years. You need approximately 600–700m² of roof space (around 200–250 panels). Systems over 50kW require a G99 grid connection application.

How Much Does a 100kW Solar System Cost?

A 100kW commercial solar system costs £60,000–£120,000 in 2026. The wide range reflects panel quality, inverter type, roof complexity, and grid connection costs. Here is a full breakdown by component:

Component% of TotalCost Range
Solar panels (200–250 panels)40–50%£24,000 – £50,000
Inverters & electrical20–30%£12,000 – £30,000
Mounting & installation labour20–30%£12,000 – £25,000
Grid connection (G99)2–10%£2,000 – £10,000
Total100%£60,000 – £120,000

Grid connection costs vary significantly depending on your local DNO and available capacity at the nearest substation. Use our commercial solar calculator for a tailored estimate based on your location.

100kW Solar System Output & Savings

A 100kW solar system in the UK generates approximately 95,000 kWh per year based on average UK irradiance (~950 kWh/kWp). With commercial electricity at 25p/kWh and 60–75% self-consumption, annual savings are substantial.

Investment

System Cost (mid-range):£90,000
Tax Relief (ECA 25%):-£22,500
Net Investment:£67,500

Annual Returns

Generation:95,000 kWh
Self-Consumption (70%):66,500 kWh
Bill Savings (@ 25p/kWh):£16,625
Export Income (@ 15p/kWh):£4,275
Total Annual Benefit:£20,900
3.2 years
Payback Period
31%
Annual ROI
£500k+
25-Year Savings

Based on South England irradiance (~950 kWh/kWp), 70% self-consumption, grid rate 25p/kWh, SEG rate 15p/kWh. Enhanced Capital Allowances provide 25% tax relief on full system cost.

100kW Solar Panel System: Space & Specifications

A 100kW solar panel system requires approximately 600–700m² of unobstructed roof space and uses 200–250 panels depending on wattage. Each kW of solar capacity needs roughly 6–7m² of roof area. Here is a comparison of common panel options:

SpecificationStandard (400W)Premium (500W)
Panels needed250 panels200 panels
Roof area~700m²~600m²
Panel typeMonocrystalline PERCMonocrystalline TOPCon/HJT
Efficiency20–21%22–23%
Cost premiumStandard+15–25%
Best forLarge roofs, budget-focusedLimited roof space, max output

A typical warehouse with 1,000m² of roof can fit a 100–140kW system. Panel count varies by module wattage, roof obstructions, and whether flat or pitched mounting is used. Flat roof installations require additional spacing between rows to avoid shading.

How to Finance a 100kW Solar System

CapEx (Buy Outright)

Pay £60k–£120k upfront. Own the system and all the savings from day one.

  • ✓ Highest long-term ROI (15–25%)
  • ✓ Full asset ownership
  • ✓ 100% tax relief via ECA
  • ✗ High capital outlay

Asset Finance (Loan)

Spread the cost over 5–7 years. Savings typically exceed monthly repayments.

  • ✓ Cashflow positive from month 1
  • ✓ 100% tax deductible
  • ✓ Own the asset at term end
  • • Medium ROI
Most Popular

PPA (Zero Upfront)

£0 upfront. A fund installs the system; you buy power at 30–50% below grid price. Read the full PPA guide →

  • ✓ Zero capital expenditure
  • ✓ Immediate bill reduction
  • ✓ Fully maintained & insured
  • ✓ 100kW+ systems eligible

100kW Solar System: Grid Connection Requirements

All solar systems over 16A per phase (approximately 3.68kW single-phase or 11kW three-phase) require a grid connection application. A 100kW system requires a G99 application to the local Distribution Network Operator (DNO), which is the main timeline factor in any commercial solar project.

G99 Application Required

Systems over 50kW must apply under G99 (not G98). Your installer handles the application, but it's submitted to the DNO for assessment.

DNO Approval: 45–65 Working Days

The DNO assesses whether the local grid can accommodate 100kW of generation. Approval timelines vary by DNO and local grid capacity.

Grid Reinforcement (If Required)

If the local grid is constrained, the DNO may require reinforcement works at additional cost (£5,000–£50,000+). This is increasingly common in areas with high solar penetration.

No Planning Permission Needed

Rooftop solar on commercial buildings is permitted development — no planning application required regardless of system size.

For a detailed walkthrough of the G99 process including costs, timelines, and common pitfalls, read our G99 Application Guide.

Is a 100kW Solar System Worth It?

A 100kW solar system is one of the best investments a UK commercial property can make in 2026. Here is how it compares to leaving your money in a savings account:

100kW Solar Investment

Investment:£90,000
Annual Return:£20,900 (23% ROI)
Payback:3.2 years
25-Year Total Return:£500,000+
Lifespan:25–30+ years

£90k in Savings Account

Investment:£90,000
Annual Return (4.5%):£4,050
Real Return (after inflation):~1.5%
25-Year Total Return:~£101,000
Energy costs meanwhile:Rising 5–8%/year
3–5 yrs
Payback Period
15–25%
Annual ROI
25+ yrs
System Lifespan
£500k+
Lifetime Savings

Calculate Your 100kW Solar ROI

Use our free commercial solar calculator to get an instant estimate for your property.

Get Free Quote

100kW Solar System FAQs

Frequently Asked Questions

A 100kW solar system uses approximately 200–250 panels rated at 400–500W each. Using modern 500W monocrystalline panels, you need around 200 panels. With standard 400W panels, you need approximately 250 panels. The exact number depends on the wattage of the panels chosen.
A 100kW solar system requires approximately 600–700m² of unobstructed roof space. This is roughly equivalent to a 25m × 25m area. Each kW of solar requires about 6–7m² of roof space, accounting for panel size and spacing between rows.
No — rooftop solar on commercial buildings is permitted development in the UK, regardless of system size. You do not need planning permission for a 100kW rooftop system. However, you will need a G99 grid connection application (required for all systems over 16A per phase) and building regulations compliance.
A 100kW system costs £60,000–£120,000 vs £33,000–£60,000 for 50kW, but delivers better per-kW economics. The 100kW system generates ~95,000 kWh/year (vs ~47,500 kWh for 50kW) and typically achieves a faster payback due to lower per-kW installation costs at scale.
Annual maintenance for a 100kW commercial solar system costs £500–£1,500 per year, covering panel cleaning (1–2 times annually), inverter monitoring, and periodic electrical inspections. Most systems include remote monitoring as standard. Inverters may need replacement after 10–15 years at £3,000–£8,000.
Yes. A 50–200kWh battery system paired with 100kW solar costs an additional £20,000–£80,000 and can increase self-consumption from 60–75% to 80–95%. Battery storage is particularly valuable for businesses with evening energy use or time-of-use tariffs, and typically pays back in 4–6 years.
A 100kW commercial solar installation takes 2–4 weeks on-site. However, the full project timeline is 3–6 months from decision to operation. The main delay is the G99 grid connection application, which takes 45–65 working days for DNO approval.
A 100kW solar system has a lifespan of 25–30+ years. Solar panels typically come with 25-year performance warranties guaranteeing at least 80% of original output. Inverters last 10–15 years and may need one replacement. Total lifetime savings for a 100kW system exceed £500,000.

Related Resources