Commercial solar means panels on a building you trade from, not a house. This article is about small business systems in East Sussex, on units, workshops, offices, shops and farm buildings. It covers which roofs suit, why your daytime use matters more than your roof size, and how the grid connection works. It also explains the size of job we normally take on, and where we stop.
Key Points
- The value comes from the power you use on site during the working day, not from the size of the roof.
- Steel portal frame roofs, flat roofs and pitched tile roofs all take solar. Each is fixed differently.
- The roof structure has to be checked by a competent person before design. That is an MCS requirement.
- Our normal working range is about 50 kW of inverter capacity. That is our choice, not a limit set by anyone else.
- Panel capacity is measured in kWp DC. Inverter output is measured in kW AC. They are different numbers.
- A three phase supply lets you fit roughly three times more before the fuller grid application applies.
- Under G98 you can install first and tell the network operator within 28 days. Under G99 you apply and wait.
- Ground mounted arrays are an option where the roof is poor, but permitted development limits are small.
- We make no tax claims. Ask your accountant about capital allowances and your rates position.
Common Misconceptions
Fill the roof, it is free money. Roof area is not the driver. Power you use on site is. A system sized past your daytime demand exports the surplus at a lower value.
50 kW is the legal maximum. It is not. It is our normal working range. Separately, MCS MIS 3002 covers solar installations up to 50 kWp DC. MIS 3012 covers battery systems up to 50 kW. Those are certification scopes, not laws, and they are measured differently from our figure.
A 50 kW inverter means 50 kWp of panels. No. DC panel capacity and AC inverter output are different measures, and the array is often larger than the inverter.
We can just install it and tell the network later. Only under G98. Above 16 A per phase you must apply first and wait for the assessment.
Solar will keep the unit running in a power cut. Not by default. Loss of mains protection is required, so the system shuts down with the grid.
Panels on a commercial roof always need planning permission. Usually not, if the installation stays inside the permitted development limits above. A listed building is the common exception.
Real-World Advice
We have no published commercial case study yet. Every project on our showcase pages is a home, from 8 panels in Bexhill up to 33 panels in Hailsham. We are not going to describe a commercial job we cannot show you.
UK-Specific Considerations
Which roofs suit
Steel portal frame. This is the standard modern industrial or agricultural building. The roof is profiled metal sheet on purlins. Panels clamp to the sheet's ribs or bolt to the purlins. There is usually plenty of clear area and no chimneys or dormers in the way.
Flat roof. Panels sit on frames, either weighted down with ballast or fixed through the covering. MCS MIS 3002 has specific rules for both. For a weighted system a structural engineer has to confirm the roof can carry the panels plus the ballast. If the covering is under warranty, the warranty provider should be consulted first.
Pitched tile. The same approach as a house, only larger. MCS defines a pitched roof as one between 10 and 70 degrees.
For every roof type, MIS 3002 says the structure shall be checked by a suitably competent person to carry the load. Where the structure is unusual, or there is any doubt, a qualified structural engineer shall be consulted. That check happens before we quote a firm design.
Why daytime use matters
Solar makes power in the day. If your business runs in the day, you use it as it is made. That is the cheapest unit of electricity you will ever have, because you never buy it.
If your building is empty during the day, the power leaves the building and you are paid an export rate instead. That is worth less than avoiding a purchase. So a shop, a workshop or a surgery is usually a better fit than a building used only in the evening.
This is why we ask for half hourly consumption data before designing anything. It shows when you actually use power, not just how much you use in a year.
Our normal working range
We design small commercial systems up to about 50 kW of inverter capacity. That is our own working range. It is not a legal limit, not a grid limit, and not a rule set by MCS or anyone else. It is the size of job we are set up to do well.
Two measurements get confused here. Panels are rated in kWp DC, which is what the array could make in perfect conditions. The inverter is rated in kW AC, which is what it can pass into the building. A larger panel array can sit behind a smaller inverter where the design and the connection allow it. So a 50 kW inverter does not mean a 50 kWp roof.
Above that range the grid connection work gets much bigger, and that is not the market we target. We will say so rather than take the job.
Single phase and three phase
Most homes have a single phase supply. Most commercial premises have three phase. This changes the design and it changes which grid application you need.
The connection rules use current, not kilowatts. ENA Engineering Recommendation G98 covers generation up to 16 A per phase. G98 states that 16 A per phase corresponds to 3.68 kW on a single phase supply, and 11.04 kW on a three phase supply. Anything larger goes down the G99 route.
So the same 10 kW inverter is a G99 job on a single phase supply and a G98 job on three phase. If your unit is single phase and you want a bigger system, ask about the cost of a three phase supply early.
G98 and G99
G98 is the connect and notify route. The installer fits the system, then tells the network operator. G98 requires that the operator is advised no later than 28 days after commissioning.
G99 is the apply first route. The network operator assesses your site before anything is installed. G99 is explicit that no generating equipment should be installed or commissioned before that assessment is complete. Where the network needs upgrading, you find out at that point, and the work may be chargeable.
Both documents also require loss of mains protection, so a normal system disconnects itself in a power cut. In East Sussex the network operator is UK Power Networks. Applications from installers go through the ENA Connect Direct platform.
Plan for the G99 timescale rather than hoping. It is the part of a commercial job we cannot speed up.
Ground mount
If the roof is the wrong shape, the wrong age or shaded, land can be a better answer. The catch is planning.
In England, a stand alone solar array in the grounds of a commercial building is permitted development only within tight limits. The Planning Portal states the array should be no more than 9 square metres, or 3 m by 3 m. No part should be higher than 4 m, and it should be at least 5 m from the boundary. Only the first stand alone installation is permitted development. Panels should not go within the boundary of a listed building or a scheduled monument.
That is a very small array. Any useful commercial ground mount will therefore need planning permission from your local council. Build that time into the project.
Roof mounted solar and planning
Roof solar on a commercial building is usually permitted development, again within limits. The Planning Portal states panels should project no more than 200 mm from the roof slope or wall. On a flat roof the highest part should be no more than 1 m above the highest part of the roof, excluding the chimney. Equipment must not be within 1 m of the external edge of the roof. It must not go on a listed building or within its grounds. These rules are for England, and Wales may differ.
Commercial battery storage
A battery on a commercial site is optional, and often unnecessary. It earns its place in three cases. You have real demand outside daylight hours. You want to shave a peak. Or you are on a time of use tariff. Note that PAS 63100:2024, the domestic battery fire safety specification, applies to dwellings. Commercial battery work follows the IET Code of Practice for Electrical Energy Storage Systems, and MCS MIS 3012 for systems up to 50 kW. We recommend storage only where your usage pattern supports it.
EV charging
Chargers pair well with commercial solar because vehicles are often parked all day. A charger can be set to take solar first, so a van or a company car soaks up power that would otherwise be exported. Charger loads are large, so the spare capacity in your supply has to be checked alongside the solar design, not after it.
Tax and business rates
We make no tax claims on this site, and we do not give tax advice.
Capital allowances are a real thing. HM Revenue and Customs describes them as a tax relief. They let a business deduct some or all of an item's value from its profits before tax. Whether solar qualifies for a particular allowance, and at what rate, depends on the rules in force and on your business. Those rules change at fiscal events.
Business rates are a separate question. They are charged on most non domestic properties. The Valuation Office sets and reviews the rateable value. Whether adding solar changes your rateable value is a question for them, not for us.
Ask your accountant before you build either into your figures. Treat any installer who quotes you a tax saving as a warning sign.
When This Isn't Right For You
- Your building is used mainly in the evening or at night, and you do not want a battery.
- The roof covering is close to the end of its life and you are not replacing it.
- You have a short lease left and the landlord will not agree to the installation.
- The site needs far more than about 50 kW of inverter capacity. That is beyond our normal range.
Before You Spend Money
- Get your half hourly data from your supplier or meter operator. It is free and it changes the design.
- Find out whether your supply is single phase or three phase, and what capacity it has.
- Check who owns the roof. On a leased unit you will need the landlord's written consent.
- Ask when the roof was last inspected. Panels should not go on a covering near the end of its life.
- Ask any installer to separate kWp DC from kW AC on the quote.
- Ask which grid route applies, G98 or G99, and what the expected timescale is.
- Send the proposal to your accountant before you sign, for the tax position.
Frequently Asked Questions
Q: How big a system can you install?
A: Our normal working range is up to about 50 kW of inverter capacity, in AC terms. The panel array can be larger than that figure. Bigger projects are outside the market we serve.
Q: Do I need permission from the network operator before installing?
A: It depends on the size. Up to 16 A per phase, G98 lets you install and then notify within 28 days. Above that, G99 requires an application and assessment before anything is installed.
Q: Does a three phase supply let me have a bigger system?
A: Yes, before the fuller application applies. G98 gives 3.68 kW on single phase and 11.04 kW on three phase for the same 16 A per phase limit.
Q: Can we put panels in a field instead of on the roof?
A: You can, but expect to apply for planning permission. Permitted development for a stand alone array on commercial land is limited to about 9 square metres in England.
Q: Will solar cut our business rates or our tax bill?
A: We make no claims either way. Capital allowances are set by HMRC and rateable values by the Valuation Office. Ask your accountant.
Summary
Commercial solar in East Sussex works best on a building that is busy in the day. Steel portal frame, flat and pitched tile roofs all suit, once the structure has been checked. Our normal working range is about 50 kW of inverter capacity, which is our own choice rather than a rule. Your supply decides whether you go down the G98 or G99 route, and G99 has to be applied for before work starts. Ground mount is possible but usually needs planning permission. On tax and rates we say nothing, because that is your accountant's job.