1. Roof age and condition
Solar PV systems are 25+ year assets. Installing on a roof with less than 15-20 years of remaining life means you'll need to remove and reinstall during the PPA term, adding cost and disruption.
- Ideal: roof installed within last 10 years, in good condition, with manufacturer warranty still active
- Acceptable: 10-20 year old roof in sound condition, no significant repairs needed
- Problematic: roof over 20 years old, signs of degradation, recent leaks, or asbestos-containing material
- Workaround: if your roof needs replacement, we can sequence: roof refurbishment first, then solar, or include refurbishment in the PPA financial structure
2. Roof orientation and pitch
South-facing is optimal in the UK, but solar PV works well across a wide range of orientations:
- South-facing (180° azimuth): ~100% of peak yield
- South-East or South-West: ~95-98% of peak yield
- East or West: ~80-85% of peak yield (still economically viable)
- East-West "shed" arrangement on flat roofs gives ~85-90% with better daily generation curve (morning + evening, not just midday peak)
- North-facing: typically not economic except for special use cases
Pitch is less important than orientation. UK commercial roofs work well from 5° (low-pitch industrial) up to 35° (typical pitched roof). Flat roofs (0-5°) use ballasted or tilted mounting frames.
3. Available unshaded roof area
For meaningful PPA economics, you need a minimum usable roof area:
- 500 m²+, minimum for institutional funder interest
- 1,000-3,000 m², sweet spot for most commercial PPAs (200-600 kWp systems)
- 3,000-10,000 m², large systems with strong economies of scale (600-2,000 kWp)
- 10,000+ m², utility-scale rooftop installations on warehouses and large industrial roofs
"Usable" area excludes shaded zones (around skylights, rooftop plant, adjacent buildings), roof obstructions (vents, parapets, walkways), and structural exclusion zones. Typical usable area is 60-80% of total roof footprint.
4. Shading assessment
Shading is critical because it disproportionately reduces solar output. Sources to consider:
- Adjacent buildings, taller buildings or trees to the south, east, or west
- Rooftop plant, air conditioning units, chimneys, masts, water tanks
- Parapets and overhangs, particularly on flat roofs near edges
- Skylights and roof lights, usually small impact, panels routed around them
- Future development, planned construction nearby that might shade the roof
Modern microinverter and DC optimiser technology mitigates shading impacts compared to older string inverter systems. Even partially shaded roofs can be viable with the right system design.
5. Structural capacity
Solar PV adds approximately 12-18 kg per m² of roof load. Most commercial roofs designed in the last 30-40 years easily handle this, but specific situations need structural assessment:
- Lightweight modern construction, some warehouses and lighter-frame buildings need engineering analysis
- Snow loading regions, solar can affect snow accumulation patterns and combined loading
- Wind exposure, coastal sites and exposed elevated locations have higher wind uplift considerations
- Older industrial buildings, pre-1980s steel-frame buildings can be assessed but sometimes need strengthening
A structural survey by a qualified engineer is included in our assessment process, typically completed within 2-3 weeks.
6. Electrical infrastructure and grid connection
Your existing electrical infrastructure determines what size system can be installed and how:
- Existing supply size, what's your incoming electrical capacity in kVA?
- Distribution arrangement, single distribution board or multiple sub-mains?
- Available space for inverters, typically in a plant room or dedicated cabinet
- DNO capacity, does your local distribution network have headroom for solar export?
The G99 grid connection application is the most variable timeline step in our project plan. Some DNO regions have weeks; others have months of waiting. We submit applications early in the project to manage this risk.
7. Electricity consumption profile
The strongest PPA economics come from high self-consumption, using solar generation directly on-site rather than exporting to the grid. Assess:
- Daytime vs nighttime usage, what proportion of your electricity is used 8am-6pm Mon-Fri?
- Seasonal variation, does demand peak in summer (cooling-driven) or winter (heating-driven)?
- Production schedule, 5-day operation? 7-day? 24/7?
- Plant downtime, extended shutdowns affecting summer production?
- Future demand growth, expanding operations? Adding EV charging or heat pumps?
The ideal site profile: continuous daytime electrical demand year-round, growing over the PPA term, with limited summer downtime. Examples include cold storage, 24/7 manufacturing, data centres, and continuous-process industries.
Quick self-assessment scorecard
Score your roof on each factor:
- 5+ "yes" or "ideal" answers, your roof is a strong solar candidate. Get a free assessment.
- 3-4 "yes" answers, likely viable with some considerations. Worth a free assessment.
- 1-2 "yes" answers, solar may not be the right fit, but a brief conversation can confirm.
What we do in a free site assessment
- Roof survey and structural review
- Solar production modelling for your specific site (irradiance, orientation, shading)
- Electrical infrastructure assessment
- DNO grid connection capacity check
- Consumption analysis from your 12-month electricity invoices
- Indicative PPA rate and system sizing
- Projected annual savings and carbon impact
Typically completed within 2-3 weeks of initial enquiry. No obligation.