Yes, commercial solar can be worth installing if your business is closed at weekends. The decision depends on how much generation you can use during the working week, what happens to the weekend surplus and the full cost of the installation. A five-day working week doesn’t rule solar out, and it doesn’t automatically make a battery necessary.
For an office, workshop or warehouse, the useful starting point is the electricity meter data. A large roof tells you where panels might fit. It doesn’t tell you how much of their output will reduce your bills.
Your building may be closed, but is its electricity use near zero?
Refrigeration, servers, security systems and essential ventilation may keep running after everyone leaves. Other premises have very little daytime demand on Saturdays and Sundays. Those two situations need different designs, even if the businesses spend the same amount on electricity each year.
Ask your supplier or metering provider for 12 months of half-hourly consumption data, where available, and mark bank holidays, shutdowns and unusual trading periods. The Carbon Trust’s energy-monitoring guidance explains that access to supplier data depends on the meter and contract. If the data isn’t available, bills and operating hours can support an initial assessment, with monitoring used to resolve gaps.
An installer can then compare expected solar output with demand over the same time intervals. Check both the proportion of solar used on site and the proportion of your electricity demand it covers: these are different measures. Matching annual generation to annual consumption does not mean the building will be self-sufficient.
Our commercial solar design service starts with this operating profile, alongside the roof, electrical supply and connection constraints.
What happens to solar electricity at the weekend?
Solar generation first helps meet the demand present on site. When output exceeds that demand, the remaining energy needs somewhere to go. It can charge a suitably configured battery with available space, or be exported within the agreed connection limit. Where neither is possible, the system may reduce output, known as curtailment.
Exported electricity can still have value
Weekend surplus isn’t automatically wasted. An eligible installation with the right metering and an export agreement can receive payment for electricity sent to the grid. However, exporting a unit and avoiding the purchase of a unit are separate transactions. Use the relevant import and export prices in the business case.
Ofgem’s Smart Export Guarantee guidance covers eligible solar installations in Great Britain up to 5MW. Applications go to a participating supplier, which sets the tariff and contract terms. Eligibility, certification and metering requirements still need checking; an advertised household export offer should not be assumed available to a commercial site.
An export limit changes the calculation
A roof might accommodate more panels than the local network will allow to export at once. That matters particularly when weekday machinery is switched off and weekend demand drops.
National Grid Electricity Distribution’s guidance on customer limitation schemes explains how controls keep a connection within its agreed limits, alongside the applicable generation connection requirements. An export limiter does not remove the need for the relevant DNO application and approval.
Ask the proposal to show predicted curtailment as well as generation. A forecast that assumes unrestricted export when the connection is limited can overstate the financial benefit.
A simple example: the same solar output, different value
Consider a hypothetical site with no battery. In one half-hour period, its solar system delivers 10kWh of AC electricity after conversion losses. On a working day, the building uses 8kWh in that interval. Assuming generation and demand overlap within the period, it uses 8kWh of solar and exports the remaining 2kWh.
On a closed Saturday, suppose the same solar output meets only 1kWh of demand. That leaves 9kWh for export. With illustrative prices of 25p/kWh for avoided imports and 8p/kWh for export, the working-day benefit is £2.16: £2 of avoided imports plus 16p of export income. Saturday’s benefit is 97p: 25p plus 72p.
These are invented rates for explaining the calculation, not a current tariff offer or Sunergy savings forecast. The example assumes sufficient export capacity, no curtailment and no battery losses. It excludes installation, finance, maintenance, tax and fixed charges. Real modelling needs the site’s contract prices and year-round data, with finer analysis where loads fluctuate sharply.
Why a battery isn’t an automatic weekend solution
A battery can move some surplus into a period when the business needs it. But it has finite capacity. If it fills on Saturday and the site barely uses electricity overnight, there may be little room left for Sunday’s generation.
For a separate illustrative storage example, suppose controls allow a battery to accept 100kWh of surplus AC electricity. At an assumed 90% AC-to-AC round-trip efficiency, that would return about 90kWh to site loads. It would not absorb an unlimited weekend’s surplus. Actual results depend on available usable capacity, charge and discharge power, reserve settings, standby consumption and the selected equipment.
The financial comparison should subtract export income forgone when charging, allow for losses and battery costs, and count only benefits that the proposed operating schedule can actually deliver. Don’t count the same stored energy twice for different purposes.
Our commercial battery storage assessments consider those limits. You can also see our Grant UK battery storage project, which integrated 278kWh of storage with an existing 300kW solar array. That is a project example, not a recommended size for another business.
Compare designs before filling the roof
Ask for a smaller solar-only option and a larger option with their predicted on-site use, exports and curtailment shown separately. Where storage looks promising, compare solar plus battery against the equivalent solar-only design so the battery’s extra cost and benefit are clear.
A higher self-consumption percentage doesn’t automatically identify the best investment: a smaller array may use nearly everything it generates yet deliver less overall benefit. Equally, adding panels just because there is space can increase exposure to low export prices or curtailment.
Include planned changes such as new machinery, EV charging or longer opening hours, but keep uncertain future demand separate from today’s figures. Don’t run unnecessary equipment simply to use solar; moving an existing flexible task into daylight is a different proposition.
Get a proposal based on your working week
Send us a recent bill, your site postcode, usual opening hours and any available half-hourly data. Tell us about weekend loads and regular shutdowns, plus whether you own or lease the building.
Sunergy Renewables is based in Nuneaton and supports commercial solar and battery projects across Warwickshire, Leicester, Leicestershire and the wider Midlands. Ask us to assess your commercial site and we’ll help establish whether solar alone or solar with storage fits the way your business operates.
