Most people start with how big a system they need. Your bill is the better starting point. Here is how to read a commercial bill line by line, and what each line tells you about whether solar or a battery is worth the trouble.
Most people ask us how big a system they need. It's the wrong first question, and it's the one that gets you a quote instead of an answer.
The right first question is what you're actually paying for right now. Your bill already says. The trouble is it says it in a format designed by people who bill for a living, across two pages, in units that don't match how you think about your building.
So here's how to read it yourself, line by line, and what each line tells you about whether solar or a battery is worth the trouble on your site.
Send us your latest electricity bill and we'll analyse it for you. It's free, there's no obligation, and we'll tell you if solar or batteries aren't the right fit.
Send us your bill →Pull out your most recent bill. Most commercial bills carry five or six kinds of charge, and they behave completely differently.
What it costs just to be connected. A fixed daily amount, whether you use power or not. On the bill it's the supply charge, sometimes the service availability charge. If you're closed for three weeks over Christmas you still pay it. Solar generally doesn't remove this one.
What you used. Cents for every unit of electricity you pulled from the grid. On a commercial bill this is usually split by time of day, so the same unit costs you different amounts at different hours. This is the line solar hits hardest, because solar reduces how much you buy.
What you used at your busiest moment. This one surprises people. On many commercial tariffs you're charged for your single highest rate of draw in the month, measured over a half hour, and then billed on that number for the whole month. On the bill it's the demand charge, or capacity charge. One hot Tuesday afternoon when everything ran at once can set it. Solar helps only if the sun is up at that moment. A battery helps whenever it happens.
What it costs to get the power to you. Poles, wires and substations, passed through from the network company. On the bill these are network or distribution charges, and on a lot of commercial accounts they're a bigger share than the electricity itself.
The scheme and market charges. Small line items covering various regulatory and market costs. You can't do much about these and they're rarely worth the attention.
Metering. A fixed charge for the meter. Small, and it doesn't move.
The useful exercise is to add up what share of your total each of these represents. On a lot of commercial sites the actual electricity is well under half the bill, and almost everybody is surprised by that.
Solar does one thing: it makes power on your roof so you buy less from the grid during daylight.
That means it works on the "what you used" line, during the day, in proportion to how much of your load runs while the sun is up. A bakery that does most of its work before 7am gets less out of a roof than a cold store that runs hard through the afternoon. Same roof, same system, very different outcome.
It generally doesn't remove the connection charge. It only reduces your busiest-moment charge if your busiest moment happens in daylight. And it does nothing about the network charges that are calculated on your demand rather than your usage.
This is why two businesses on the same street with the same roof can get very different answers, and why anyone who quotes you a system size before looking at your bill is guessing. If capital is the thing standing in the way rather than the arithmetic, our note on the capital barrier in commercial solar covers the other half of that conversation.
A battery stores power you've already got, from the roof or from the grid when it's cheap, and releases it when power is expensive or when your draw spikes.
So it works on two lines solar can't reach on its own: the expensive hours after the sun has gone, and the busiest-moment charge, by flattening the spike that sets it. On sites where that charge is a large share of the bill, the battery can be doing more work than the solar. We pulled that apart line by line in what a battery actually does to a commercial bill.
Whether that stacks up depends on the size of that charge on your bill, your tariff, and how spiky your load actually is. All three are visible in your billing data. None of them are guessable from your address.
We hear this constantly, and it's almost always one of five things.
The system is too small for the load. Common on sites that grew after the system went in, or that added refrigeration, machinery or EV charging.
Most of the load is outside daylight. The solar is working fine. It just isn't on when you are.
The demand charge was never addressed. Solar reduced the usage line and left the busiest-moment line untouched, so the total didn't move nearly as much as expected.
Something has failed quietly. A string down, an inverter fault, soiled panels, a tripped breaker nobody noticed. Systems don't announce this. If nobody's watching the generation data, it can run at half output for a year.
The export is worth less than it used to be. What you're paid for power you send back to the grid, the feed-in tariff, has fallen a long way. A system designed around generous export economics behaves differently now.
Your bill plus your generation data tells you which one it is, usually within an hour of looking.
You don't need a site visit to get a real answer. You need the data.
The minimum: one recent bill, both pages, including the summary and the itemised charges. Most people send page one only and page two is where the useful detail lives.
Better: twelve months of bills, so seasonal swing is visible. A single summer bill makes a site look worse than it is, and a single winter bill makes it look better.
Best: your interval data, which is the half-hourly record of what the site actually drew. Your retailer will give it to you if you ask, usually as a spreadsheet, usually within a few days. It costs nothing to request and it's the difference between an estimate and a proper answer, because it shows exactly when your busiest moments happen and whether the sun is up when they do.
If you already have solar: add whatever your monitoring portal will export. Even a screenshot of the last twelve months of generation is enough to spot a system running under.
Whether you send it to us or to somebody else, the analysis is only as good as what it's willing to tell you.
Ask which line of the bill each part of the recommendation attacks. A good answer names the line.
Ask what share of your load runs in daylight, and how they worked it out. If the answer isn't from your own data, it's an assumption dressed as a finding.
Ask what the recommendation would be if you did nothing about the demand charge. If the numbers barely change, the demand charge wasn't the problem. If they collapse, the solar was never the main event.
Ask what the result would be in a bad year. Weather varies, and a model built on an average year quietly assumes you'll get one.
And ask what they'd say if the answer were no. Not every site suits solar. Shaded roofs, short leases, structurally unfit roofs, sites about to be sold, loads that run almost entirely at night. Somebody who has never once said "not this site" isn't analysing, they're selling.
Your bill is a record of exactly how your building uses energy, written in a format that hides it. Read it line by line and most of the decision makes itself: you can see what you're paying for the connection, what you're paying for the power, and what you're paying for your busiest half hour. Solar deals with the second. A battery deals with the third. If neither of those is where your money is going, neither is worth buying.
Nobody can tell you which one applies to your site from the street. It's in the bill.
We'll show you:
It's free, there's no obligation, and we'll tell you if solar or batteries aren't the right fit.
Send us your bill →Your bill already has most of the answers. Let's take a look.
How many bills do you need?
One is enough to start. Twelve months is better, because it shows the seasonal swing. Interval data from your retailer is better again, because it shows exactly when your site draws hardest.
What does it cost?
Nothing, and there's no obligation attached to it. If the answer is that your site doesn't suit solar, that's what you'll be told.
Do you need to visit the site?
Not to tell you whether it's worth looking at. A site assessment comes later, once the numbers say there's something there, and it's what confirms the roof, the switchboard and the connection.
We're a tenant, not the owner. Is there any point?
Yes, and the length of your lease matters more than most people expect. Worth knowing where you stand before you talk to the landlord.
What's interval data and how do I get it?
It's the half-hourly record of what your site drew, held by your retailer. Ring them or email them and ask for your interval or NMI data for the last twelve months. Most will send a spreadsheet within a few days.
Our bill is on a different retailer every year. Does that matter?
No. The charges have the same shape whoever issues them, and switching history doesn't change what your building does.
Charge names, tariff structures and demand measurement intervals vary between networks and retailers, so this describes how commercial bills generally work rather than what applies at your site. Figures in an assessment are estimates based on your bill and stated assumptions, and actual savings vary.
Discover how easy it is to transform your business with energy-efficient solutions. Whether you're ready to start or just exploring your options, we'll guide you every step of the way.