You can get a useful first estimate of how much solar power a site can generate and the impact it will have on the client’s energy bill from a roof plan and an annual electricity bill. Adding a battery may save the client more money, but working out how much requires a more detailed calculation.
In this guide, we look at how commercial solar calculators work and the type of tool you need to produce a credible solar-and-battery forecast.
What is a commercial solar calculator?
Commercial solar calculators estimate savings, export income, and investment returns for a site using data about its electricity use and tariff, plus the size and design of the proposed solar and battery system.
There are two types of calculators available - quick and detailed.
- Quick: Many solar installer and EPC sites feature quick calculators to help potential clients get a rough idea of whether solar could reduce their electricity bills. They’re there to help companies decide whether their site has potential by using the available roof area, annual electricity use, and an approximate electricity price.
- Detailed: When out on appointments, installer and EPC reps use more complex project calculators. These take into account electricity use and solar production throughout the day, then applies the site’s actual tariff, export agreement, equipment limits, and grid connection limits.
What information does a commercial solar calculator need?
The detailed commercial solar panel calculators installers and EPCs use ask the following three questions:
1. When does the site use electricity?
Ideally, you should use 12 months of half-hourly or quarter-hourly electricity data, as this shows how much electricity the site uses and when it uses it.
That matters because a business may use a lot of electricity over the year without using much at the times its solar panels generate the most power.
A full year’s data shows you how electricity use changes between seasons, weekdays, weekends, working shifts, and periods of high demand.
If the client indicates they’re going to change the way they use electricity on site by, for example, adding new machinery or extending operating hours, try to factor those changes in. Past meter readings will not show changes that have not happened yet.
2. When will the solar system generate electricity?
You also need the calculator to estimate the amount of electricity the system you’re proposing will generate at different times of the day and year.
The actual figure depends on the location, system size, direction and angle of the roofing and its shadings. You also need to include the proposed panels, inverter, and expected system losses.
The calculator uses this information to build a generation profile for the project.
3. How much solar electricity will the site use or export, and what is it worth?
Use the client’s actual bills and current tariff to find out what they pay for grid electricity and how much they might receive for electricity they send back to the grid.
Your commercial solar PV calculator should then compare the solar generation profile with the site’s electricity use during each period. Solar electricity used on site saves the client from buying that electricity from the grid, while any surplus can be sent through the export meter to earn the agreed export price.
You’ll also need to include how much power the inverter can deliver and how much the site is allowed to send to the grid. If the solar system generates more power than the site can use or export, it may have to reduce its output.
Finally, your commercial solar cost calculator must apply the correct price to each use and avoid counting the same electricity as both an on-site saving and export income.
How should a commercial solar calculator work out solar savings?
A commercial solar power calculator should start by working out how much the site would pay for grid electricity without the proposed solar system, then repeat the calculation with it in place using the same electricity-use data and tariff.
During each period, businesses can use the solar electricity generated to supply the site and send any surplus to the grid. The system may also have to reduce its output if the site cannot use or export all the electricity it could generate.
For each period, the calculator should work out the financial result. Solar used on site saves the client money because they’re buying less electricity from the grid, while solar sent through the meter can earn the agreed export price. Any output the system has to reduce produces no saving or export income.
The calculator should then add the results from every period together to estimate the client’s annual savings and export income.
Avoid using calculators that:
- Value all solar electricity at one price: This could overstate the client’s return because electricity used on site may save more than exported electricity earns.
- Assume the client will use a fixed percentage on site: Check when the business uses electricity against when the panels will generate power. Otherwise, you risk inflating the likely on-site savings.
- Leave out the site’s export limit: This could show the client exporting more electricity and earning more income than their grid connection permits.
- Count the same electricity as both a saving and export income: Check that electricity used on site is kept separate in the workings out from electricity sent to the grid.
Commercial solar + battery calculators: introduction
Battery storage is becoming more common but it’s still an extra option on most commercial solar projects. Across Europe, batteries are expected to feature in around only 20% of commercial solar projects and 10% of industrial projects in 2026.
Not adding a battery controlled by the right software risks:
- Leaving money on the table: The client may often end up selling spare solar electricity back to the grid for too low a price or have to reduce solar generation because the site can’t use or export it. A battery can store some of that electricity for later and may also earn extra income.
- Not delivering the maximum client savings possible: Without a battery, the client only benefits from solar while the panels are generating. A battery lets them use more of that electricity later instead of buying it from the grid.
If you’re up against a competitor offering solar and battery storage while you offer solar only, their proposal gives the client a choice that yours doesn’t. They can compare the cost, annual savings, income, and payback of both options.
Solar alone may still offer a shorter payback period, but solar plus battery can produce greater annual or lifetime returns. Giving the client both calculations helps them choose the option with the strongest overall business case.
Fixed schedule vs responsive schedule commercial solar + battery calculators
There are two types of control software for commercial battery installations: fixed and responsive.
With fixed software, the battery charges and discharges at preset times or when set conditions are met. With responsive software, it optimises when the battery charges and discharges so it saves or earns more, depending on the site’s electricity use, solar generation, import and export prices, and available trading opportunities.
When choosing software for your solar + battery projects, responsive control can save or earn the client more by charging and discharging the battery at the times that offer the best financial return. Be careful to choose responsive software that:
- Checks how much electricity the site is using, how much solar power is available, what grid electricity costs, what exports earn, and how much charge is left in the battery
- Stays within the limits of the battery, inverter, and grid connection
- Works out which use of the battery will save or earn the client the most money at that time
- Doesn’t count the same stored electricity more than once
- Comes with a calculator that reflects how the software will actually run the battery after installation
Using a responsive commercial solar + battery calculator for quotes and in client meetings
The most effective calculators when producing quotes or presenting in meetings are ones whose results stand up to questioning and scrutiny.
The reports they produce separate estimates such as:
- Solar electricity used on site
- Solar export income
- Savings from storing solar for later
- Savings from charging when grid electricity is cheaper
- Savings from reducing peak grid use
- Trading or flexibility income, where available
Clients should be able to compare their existing site, solar only, and solar plus battery, seeing with each option their annual savings, income, project cost, ongoing charges, and payback.
For sales representatives working for installers and EPCs, responsive commercial solar + battery calculators:
- Let you change the battery size, tariff, export price, site demand, or expected trading income during the meeting
- Update the savings, income, and payback figures immediately
- Help you answer “what if?” questions without going away and rebuilding the proposal
- Produce a detailed report showing the figures and assumptions behind each result
- Give the client’s finance team evidence they can examine, question, and use when seeking capex approval
Model the battery case with GridVolt’s free simulator
GridVolt’s free simulator is built for commercial battery projects, including batteries installed alongside solar. It doesn’t replace the software you use to design and quote the solar installation. Instead, it uses your solar generation figures and site data to show what adding a battery and responsive control software could contribute to the client’s savings, income, and payback.
The simulator models the same battery uses that GridVolt’s live software can deliver after installation. Energy Manager controls clients’ batteries, storing solar and cheaper grid electricity to use when grid electricity costs more. Our linked GridTrade platform uses available battery capacity to earn additional trading income for suitable sites.
Our responsive software replans every 15 minutes, or 96 times a day, to reflect changes in site electricity use, expected solar generation, weather, and battery charge. And our free commercial solar + battery simulator, available only to installers and EPCs, uses the same software to model the savings, income, and payback a proposed system could deliver.
Request free access to GridVolt’s commercial solar and battery simulator. If you want to get in touch, fill out the form on the right or visit our contact page.
Commercial solar calculator FAQs
How accurate is a commercial solar calculator?
Use a quick commercial solar calculator to give your client a useful if imprecise first estimate. Factor in their available roof area, annual electricity use, and an approximate electricity price.
For an actual quote or proposal, you need a detailed calculator that compares a client’s solar generation with their electricity use throughout the day and year. You should also include the actual tariff, export price, system design, inverter limits, and grid connection limits.
Can you use an annual electricity bill in a commercial solar calculator?
An annual bill is enough to check whether a site may have potential for solar, but it does not show when a business uses electricity. This is important because two companies may use the same amount of electricity over a year but benefit from very different savings from a solar installation. For example, a business that uses most of its electricity during daylight hours may use more solar on site, while one that mainly operates at night may export more.
Use half-hourly or quarter-hourly electricity data for a detailed calculation.
What information do you need for a commercial solar calculation?
At a minimum, you’ll need information about:
- The site’s electricity use
- The client’s current tariff
- The available roof area
- The roof’s direction, angle, and shading
- The proposed panels and inverter
- The site’s agreed export limit
- The price the client will receive for exported electricity
You should also include any planned changes to the client’s electricity use, such as new machinery, EV charging, or longer operating hours.
How does a commercial solar calculator estimate savings?
The calculator compares what the client would pay without solar with what they’re likely to pay after installing it. Solar electricity used on site reduces the amount the client needs to buy from the grid. If the setup is right, surplus electricity they send through the export meter may earn export income.
Use a more detailed calculator to work out savings for each period before you add the results together. This makes the end figure more accurate because you’re not treating all solar electricity as though it has the same financial value.
Should a commercial solar calculator include export income?
If they have a suitable site, yes but you need to use the client’s expected export price and only apply it to electricity that is likely to pass through the export meter. Your calculator should first work out how much solar electricity the site will use and then apply the export price to any surplus the site is allowed to send to the grid.
It should not assume that all unused solar electricity can be exported or count the same electricity as both a saving and export income.
How does a commercial solar calculator work out payback?
Simple payback shows how long it may take for the project’s savings and income to equal its initial cost. The calculator should include the cost of the solar system, expected annual bill savings, export income, and any ongoing charges. With a more detailed proposal, aim to also show annual cash flow and lifetime return.
Can a commercial solar calculator compare different system sizes?
A detailed calculator should let you compare different panel and inverter sizes using the same site data and tariff. This helps you see whether adding more panels increases on-site savings, export income, or the amount of solar generation the site cannot use or export.
The largest system does not automatically offer the best return. The right size depends on the client’s electricity use, available roof space, export limit, project cost, and financial priorities.