"How many solar panels do I need for my business?" is the most common pre-quote question UK business owners ask before formally engaging with commercial solar installers. The honest answer: approximately 1 panel per 525 kWh of annual electricity demand, but the precise count depends on your self-consumption ratio (24/7 operations need more panels than weekday-only offices) and your available roof area. This page covers the calculation methodology, sizing tables by business type, worked examples, and the common sizing mistakes to avoid. For our interactive calculator see payback calculator; for cost-by-system-size see how much do commercial solar panels cost.
The simple 4-step calculation
Sizing UK commercial solar panel count is a 4-step calculation any business owner can do in 10 minutes with their last 12 months of electricity bills.
- Find your annual electricity demand in kWh. Add up the kWh from your last 12 months of electricity bills (commercial meters above 100,000 kWh/year typically have detailed half-hourly data via supplier portal — request access).
- Set your self-consumption target. Most UK commercial sites optimal at 60-85% of annual demand. 60% for weekday-only offices; 70% for typical SME industrial; 80% for 24/7 baseload; 85% for cold storage / continuous manufacturing.
- Calculate system size in kW. Target kWh ÷ 950 (UK average kWh per kWp annual yield) = system size in kW. Example: 100,000 kWh × 0.70 self-consumption target = 70,000 kWh ÷ 950 = 73.7 kW system.
- Calculate panel count. System size kW × 1.85 = panel count (modern 540W panels). Example: 73.7 kW × 1.85 = 136 panels. Or use 425W modules: × 2.35 = 173 panels.
UK commercial solar panel sizing table — by annual demand
Below is the panel-count sizing table for typical UK commercial annual electricity demands. Use this as a starting point; site survey will refine based on roof orientation, shading, and electrical infrastructure.
| Annual demand | Panels needed | System size | Typical fit |
|---|---|---|---|
| 10,000 kWh/year | 20-25 panels | 10-12 kW | Very small office, single retail unit, café |
| 25,000 kWh/year | 45-55 panels | 25-30 kW | Small office (10-20 staff), salon, dental practice |
| 50,000 kWh/year | 90-105 panels | 50-55 kW | SME office (20-40 staff), small restaurant, light industrial |
| 100,000 kWh/year | 180-205 panels | 100-110 kW | Medium office, small warehouse, mid-size hotel |
| 250,000 kWh/year | 450-510 panels | 250-275 kW | Medium warehouse, manufacturing, larger hotel |
| 500,000 kWh/year | 900-1,020 panels | 500-550 kW | Large warehouse, factory, cold storage, hospital wing |
| 1,000,000 kWh/year | 1,800-2,040 panels | 1-1.1 MW | Major industrial, data centre, regional distribution centre |
Worked example 1: 40-staff Manchester office
Real-world worked example for typical UK SME. Site: 40-staff insurance brokerage in Manchester, 700 sqm two-storey office, three-phase 200A supply, 9am-5.30pm Mon-Fri operations, annual demand 52,000 kWh. Self-consumption target: 65% (weekday-only office) = 33,800 kWh target solar generation. System size: 33,800 ÷ 950 = 35.6 kW. Panel count: 35.6 × 1.85 = 66 panels (at 540W). Or 84 panels at 425W. Roof area needed: 66 × 2.8 = 185 sqm. Available pitched roof area 280 sqm — comfortable fit. Annual generation: 35.6 kW × 950 kWh/kWp = 33,800 kWh. Year-one savings: 65% self-consumption = 21,970 kWh × 26p saved = £5,712 + 35% export at SEG = 11,830 kWh × 8p = £946 → total £6,658/year. Capex: £33,800 turnkey (£950/kW). Payback: 5.1 years gross, 3.8 years net of AIA.
Worked example 2: 250-cow Birmingham dairy farm
Real-world worked example for UK agricultural. Site: 250-cow dairy farm near Birmingham, milking parlour + bulk milk tank + grain store, single-phase 60A supply (limit 17 kW per phase) + planned upgrade to three-phase 200A, annual demand 95,000 kWh. Self-consumption target: 75% (cow milking parlour cooling + water heating + vacuum pumps + refrigeration baseload) = 71,250 kWh. System size: 71,250 ÷ 950 = 75 kW (requires three-phase upgrade — £8,000 one-time cost). Panel count: 75 × 1.85 = 139 panels (at 540W). Roof area: 139 × 2.8 = 390 sqm. Available milking parlour + grain store roof: 520 sqm — comfortable. Capex: £71,250 turnkey + £8,000 three-phase upgrade = £79,250. Year-one savings: £13,800. Payback: 5.7 years gross, 4.3 years net of AIA. DEFRA Farming Investment Fund potentially adds 30% grant, reducing net capex further.
Worked example 3: 5,000 sqm West Midlands warehouse
Real-world worked example for UK distribution. Site: 5,000 sqm distribution warehouse in West Midlands, 45 staff + 18 forklifts + chilled distribution baseload, three-phase 800A supply, 6am-10pm Mon-Sat operations, annual demand 480,000 kWh. Self-consumption target: 85% (forklift charging + lighting + chilled refrigeration) = 408,000 kWh. System size: 408,000 ÷ 950 = 429 kW (round to 425 kW for inverter configuration). Panel count: 425 × 1.85 = 786 panels (at 540W). Roof area: 786 × 2.8 = 2,200 sqm. Available steel-portal sandwich-panel roof: 4,500 sqm — substantial headroom. Capex: £361,250 turnkey (£850/kW for 100-500 kW band). Year-one savings: £87,000. Payback: 4.2 years gross, 3.1 years net of AIA + IETF Phase 3 eligibility for combined-measure decarbonisation bid.
What if my available roof area is the binding constraint?
For some UK commercial sites the available roof area is smaller than the panel count optimal for demand. Three options. (1) Size to roof area constraint: install maximum panels the roof can support, accept that solar covers a smaller percentage of annual demand. Common for offices with small flat roofs. (2) Ground-mount adjacent to building: install additional capacity in adjacent yard or low-use field area. Common for industrial sites with available yard space. Solar carports over car parks particularly effective. (3) Solar canopies + ground-mount combined with rooftop: for major industrial or holiday park sites with multiple usable areas. Requires planning permission for ground-mount above 50 kW (typical 8-12 week determination). See holiday parks for ground-mount + carport examples.
What if I have more roof area than I need?
For some UK commercial sites the available roof area is much larger than the panel count optimal for demand. Don't over-install solar. Excess generation above what you can self-consume exports at low SEG rates (4-15p/kWh) rather than self-consumes at high retail tariffs (24-32p/kWh) — a 13-25p/kWh value loss per excess kWh. Better strategies: (1) Right-size to demand and use remaining roof area for future expansion or alternative uses. (2) Add battery storage to time-shift excess generation to evening/overnight self-consumption (lifts self-consumption from 70% to 90%+). (3) Plan for known future demand growth (electric vehicle charging, heat pump replacement, business expansion) — size for current demand + 30% growth headroom.
How many solar panels by business sector
Common UK commercial sector sizing examples:
- Small office (10-30 staff): 45-110 panels (25-60 kW) — see offices
- Medium office (30-60 staff): 110-205 panels (60-110 kW)
- Restaurant or café: 30-100 panels (15-55 kW) — see hospitality solar
- Pub (food-led): 55-185 panels (30-100 kW) — see pubs sector
- Hotel (50-100 rooms): 90-370 panels (50-200 kW) — see hotels
- Small warehouse (3,500-8,000 sqm): 460-925 panels (250-500 kW)
- Large warehouse (8,000-15,000 sqm): 925-1,850 panels (500 kW-1 MW)
- Factory / manufacturing: 460-9,250 panels (250 kW-5 MW)
- Cold storage: 460-1,850 panels (250 kW-1 MW)
- Care home (50-150 beds): 55-275 panels (30-150 kW) — see care homes
- School / academy: 90-560 panels (50-300 kW) — see schools
- Dairy farm (200-400 cows): 185-465 panels (100-250 kW)
- Intensive poultry shed: 460-1,850 panels per multi-shed site
The 3 common sizing mistakes UK businesses make
Mistake 1: Sizing to roof area, not demand. "We have a big roof so we want a big system." Wrong approach — over-sized systems waste capex on low-value SEG export rather than high-value self-consumption. Always size to demand, then check roof area can accommodate. Mistake 2: Assuming 100% self-consumption. "We'll consume everything the panels make." Wrong — UK commercial solar self-consumption is typically 55-90% depending on load profile. Always model self-consumption against half-hourly demand data, not theoretical 100%. Mistake 3: Single-phase capacity ceiling. "We'll install 50 kW on our existing supply." Most UK commercial sites with single-phase supply can only host 17 kW max (single-phase ceiling). Larger systems require £3-15k three-phase upgrade — must be priced into the project, not surfaced as change order during install.
Get a site-specific panel count + sizing
The sizing formulas on this page give you a defensible starting point but your specific site will vary based on roof orientation, pitch, shading, structural capacity, and electrical infrastructure. For a free site-specific sizing report within 5 working days, submit our quote form with your annual electricity spend and postcode. We deliver: PVSyst yield model accounting for your actual roof, specific panel count + system size recommendation, AIA-adjusted capex + payback projection, and finance route comparison. No call required, no obligation.
How many solar panels do I need — common questions
How many solar panels does my business need?
A general rule for UK businesses in 2026: install approximately 1 panel per 525 kWh of annual electricity demand (assuming 540W panels and 950 kWh/kWp UK average yield with 65-85% self-consumption). A business using 50,000 kWh/year typically needs 90-100 panels (50 kW system). A business using 200,000 kWh/year typically needs 360-400 panels (200 kW). The exact count depends on three factors: your annual demand, your roof area, and your self-consumption ratio (24/7 operations can size larger; weekday-only office should size smaller).
How do I calculate how many solar panels I need for my business?
Four-step calculation. (1) Find annual electricity demand in kWh from your last 12 months of bills (commercial meters usually have half-hourly data via supplier portal). (2) Target solar to cover 60-85% of annual demand (60% for weekday-only office, 85% for 24/7 baseload operations like cold storage). (3) Divide target kWh by 950 (UK average yield per kWp) to get system size in kW. (4) Multiply system kW by 1.85 (modern 540W panels need ~1.85 panels per kW). Example: 100,000 kWh demand × 70% = 70,000 kWh target / 950 = 73.7 kW system × 1.85 = ~137 panels.
How many solar panels does a typical UK office need?
A typical UK office building installs 50-300 panels (30-160 kW system) depending on staff count and floor area. Small office (10-30 staff, 250-700 sqm): 45-110 panels (25-60 kW). Medium office (30-60 staff, 700-1,500 sqm): 110-205 panels (60-110 kW). Large office (60-150 staff, 1,500-4,000 sqm): 205-560 panels (110-300 kW). Offices typically achieve 55-70% self-consumption (weekday daytime only) so sizing usually targets 60-75% of annual demand. See offices sector.
How many solar panels does a typical UK warehouse need?
A typical UK warehouse installs 460-3,700 panels (250 kW-2 MW) depending on warehouse size and electrical demand. Medium warehouse (3,500-8,000 sqm): 460-925 panels (250-500 kW). Large warehouse (8,000-15,000 sqm): 925-1,850 panels (500 kW-1 MW). Very large distribution centre (15,000-40,000 sqm): 1,850-3,700 panels (1-2 MW). Warehouses typically achieve 65-80% self-consumption (forklift charging + lighting + refrigeration baseload) so sizing usually targets 70-85% of annual demand. See warehouses sector + Warehouses Birmingham as example city page.
Do I need a panel per kWh of usage?
Not directly — panels generate variable kWh based on UK regional yield (typically 950 kWh/kWp per year on south-facing arrays). A modern 540W commercial panel rates as 0.54 kWp and generates approximately 510-540 kWh per year in average UK conditions. Roughly: 1 panel generates ~525 kWh/year. To cover 100,000 kWh annual demand at 80% self-consumption you need 80,000 kWh of solar = ~152 panels at 540W. But sizing-to-demand only works if you can self-consume the generation — over-sized systems waste capex on lower-value SEG export rather than higher-value avoided grid import.
How much roof space do I need per solar panel?
Modern 540W commercial solar panels require approximately 2.8-3.0 sqm of roof area per panel including standard array spacing for maintenance access. For UK commercial solar: ~5-6 sqm of unshaded roof area per kW of installed capacity (south-facing pitched roofs at the lower end, east-west flat roofs at the higher end due to lower packing density). Practical examples: 50 kW system needs 280-300 sqm roof; 100 kW needs 560-600 sqm; 250 kW needs 1,400-1,500 sqm; 500 kW needs 2,800-3,000 sqm. Most UK commercial buildings have ample roof area — structural capacity and shading are typically the binding constraints, not raw area.
Should I install more panels than I need to maximise generation?
Generally no for UK commercial sites in 2026. Over-sizing (installing more solar than your annual demand can self-consume) means excess generation exports at low SEG rates (4-15p/kWh) rather than self-consumes at high commercial retail tariffs (24-32p/kWh) — a 13-25p/kWh value loss per excess kWh. The optimal sizing for UK commercial is 60-85% of annual demand. Two exceptions where over-sizing makes sense: (1) battery storage to time-shift excess for later self-consumption, (2) planned future expansion within 1-3 years of install. Better strategy: size to current demand + 20-30% growth headroom rather than full over-size.