A good commercial solar system is designed around how your site uses power, not just how many panels fit on the roof. Here is how we approach it, step by step.

1. Start with your electricity data

Most business sites have a half-hourly meter. It records how much electricity you use in every half hour of the year. If your meter number (MPAN) starts with “00”, you have one.

Twelve months of this data shows when you use power: weekdays, weekends, summer and winter. We lay a model of the solar output over it to see how much you would use on site and how much would be exported. Power you use yourself is usually worth far more than power you export, so this is where the savings come from.

Your supplier can usually send you the data. Ask for “half-hourly consumption data” for the last 12 months.

2. Check the roof before anything else

The roof has to carry the system safely for 25 years or more.

  • Structure. Panels and frames add weight, but wind uplift is often the bigger issue. A structural engineer checks the roof can take both.
  • Roof life. If the roof will need replacing in the next 10 to 15 years, fix it first. Taking panels off and putting them back later is expensive.
  • Flat roofs. Panels are either weighed down with ballast or fixed through the roof. Ballast has to be designed so the array can’t lift, slide or tip in high winds.
  • Fibre cement roofs. These are fragile and may contain asbestos. They need a survey and safe working methods.

One recent survey of 575 commercial roofs found around a third needed some repair work before solar could go on. So it is worth checking early.

3. Orientation: south or east-west?

  • South-facing, tilted panels give the most output per panel.
  • East-west panels give roughly 80 to 85% of the output of due south per panel. But on a flat roof, low east-west rows fit more panels in the same space and catch less wind, so they need less ballast.
  • East-west also spreads generation through the day, morning and afternoon. That often matches a business’s use better than a big midday peak.

We model both and pick what suits your roof and your load.

4. How much will it make?

A well-placed south-facing system near Exeter makes around 1,050 kWh per kWp a year, compared with under 900 in Manchester. We model your site with tools such as PVGIS, allowing for shading from trees, parapets and plant on the roof.

5. Inverters

Inverters turn the panels’ direct current (DC) into the alternating current (AC) your site uses.

  • Commercial roofs mostly use string inverters, from about 30kW to over 100kW each.
  • Very large ground-mount sites may use central inverters.
  • Designers usually fit a little more panel capacity than inverter capacity, often around 1.25 to 1.4 times, because panels rarely hit full output in UK weather.
  • Optimisers or microinverters can help where parts of the roof are shaded.

6. The grid connection

  • Anything bigger than a small home system needs approval from your network operator under G99 before it is connected. In the South West, that is NGED.
  • If the local network is busy, the operator may set an export limit. A G100 export limitation system then caps what can be sent to the grid.
  • An export limit doesn’t stop you using the power on site. But it can change the best system size, and it’s where a battery can help.

7. Should you add a battery?

A battery can make sense if:

  • you have an export limit and would otherwise waste solar,
  • you are on a time-of-use tariff and can use stored power at peak times, or
  • you want to cut peak demand charges by lowering your site’s maximum import.

Batteries add cost, so we only recommend one when the numbers work.

8. Planning

In England, many rooftop systems on business buildings are permitted development. The old 1MW cap was removed in December 2023.

  • Systems over 50kW need prior approval from the local planning authority on design, appearance and glare. The local planning authority has 56 days to decide.
  • Panels must sit within height limits and at least 1 metre from the roof edge.
  • Listed buildings and scheduled monuments are excluded, and conservation areas need more care.
  • Ground-mounted systems beyond a very small size need full planning permission.

Our in-house Chartered Town Planner handles this for you. See our fixed fees.

What we do

We take your bills or half-hourly data, check the roof, the grid and planning, and design a system around how you actually use power. Installs are delivered with certified partner installers. Get a quote →

Related: What every installer should include · Commercial solar payback · Getting paid for exported power

Sources

Facts last checked 8 October 2026. This is general guidance, not design or legal advice.