Commercial Solar Savings Calculator

How the calculator works

The calculator returns a directional estimate within roughly ±15% of a full PVSyst design study. It uses three live UK assumptions:

• Panel density: 200 Wp installable per m² of usable roof (industry standard for tier-1 monocrystalline).
• Regional irradiance: kWh per kWp per year, calibrated to UK Met Office regional averages. South coast: 1,100. Midlands: 980. Scotland north: 820.
• Tariff structure: 30p/kWh self-consumed (commercial market rate, 2026), 12p/kWh exported (competitive SEG-tier rate as at July 2026).

Install cost is calculated at £900/kWp installed in 2026 — the mid-range for UK commercial solar. Payback is simple (capital ÷ year-1 saving) before AIA tax relief.

What changes the answer

If your real-world numbers diverge from the calculator estimate by more than 20%, it usually comes down to one of these factors:

• Roof orientation and pitch. South-facing 30° pitch maximises yield; east/west orientation sacrifices ~12%.
• Shading from neighbouring buildings, trees, plant rooms, skylights. Major shading can reduce yield 5–25%.
• Self-consumption ratio. A 24/7 industrial site self-consumes 85–90% of generation; a Mon–Fri office self-consumes 55–65%. The calculator dropdown lets you set this.
• Time-of-use tariffs. Half-hourly metered businesses on red/amber/green DUoS bands see different effective tariffs by hour. Solar generation aligned to red-band hours is worth 50p+/kWh.
• System sizing strategy. Sizing to match peak demand maximises self-consumption. Sizing to roof capacity maximises generation but increases export ratio.

From calculator to commissioned system

The calculator gives you the headline figure. From there:

1. Free desk feasibility from your half-hourly meter data — within 5 working days. Pulls real local irradiance, models in PVSyst, returns a precise system size + saving forecast.
2. On-site survey — 1 day, structural + electrical + roof condition assessment.
3. Fixed-price proposal within 5 working days of survey.
4. Permits + DNO — planning where required, G99 grid connection.
5. Install + commission — 2–10 weeks on site depending on size.
6. 25-year output warranty activates on commissioning day.

Want the calculator number validated?

Send us:

• 12 months of half-hourly meter data (request from your supplier — usually free)
• Either a roof drawing or postcode + building outline (from Google Maps)
• Your current electricity unit rate

We return a PVSyst-grade desk feasibility, generation forecast, year-by-year cashflow model, IRR, NPV, and fixed-price quote within 5 working days. No commitment.

Common questions about commercial solar calculations

How accurate is the calculator?

Within roughly ±15% of a full PVSyst design study. The calculator uses real UK regional irradiance data and current commercial tariff assumptions, but cannot account for site-specific shading, roof orientation, or your business's exact daytime consumption pattern.

Why is annual generation lower in Scotland than southern England?

UK irradiance varies from ~820 kWh/m² in northern Scotland to ~1,100 kWh/m² on the south coast — a ~25% range. The calculator applies this regional adjustment automatically.

What does "self-consumption ratio" mean?

The percentage of solar electricity used directly on-site (versus exported to the grid). Higher self-consumption = better economics, because each on-site kWh saves you 30p instead of earning 12p export (as at July 2026).

Can the calculator handle ground-mount or solar carport projects?

The calculator assumes rooftop PV. Ground-mount and solar carport economics differ slightly: higher install cost per kWp, slightly better yield from optimised tilt, no roof-condition risk. For ground-mount or carport feasibility, contact us for a bespoke calculation.

How does the 25-year ROI calculation work?

The calculator multiplies year-1 savings by an inflation factor (1.5%/year energy price growth), applies a 0.5%/year panel degradation factor, and sums 25 years. This produces a conservative cumulative saving — actual returns depend on real grid tariff trajectory.

Ready for the precise number?

The calculator gives you the headline. The next step is a free 5-day desk feasibility — uses your real meter data and produces a PVSyst-grade design.