In short
- Four parts of your bill decide whether solar pays: energy charges, your time-of-use split, demand charges and the fixed daily charge.
- Solar only cuts the power you use while the sun is up, so the number that matters most is your daytime use.
- Your bill gives you totals. Interval data from your retailer shows when you use power, half-hour by half-hour.
A commercial electricity bill can run to several pages, but only a few lines decide whether solar will save you money. The key question is how much of your power you use in daylight, because that is the only part solar can replace. This guide shows you where to find it on your bill, and what to ask for when the bill doesn't show it.
| Quick facts | Reading a business power bill |
|---|---|
| Lines solar can cut | Energy charges used in daylight, and sometimes the demand charge |
| Lines solar can't cut | The fixed daily charge, and most of your night-time use |
| Most useful extra file | Interval data: your meter's reading every 15 or 30 minutes |
| Who to ask for it | Your electricity retailer (or your network) |
| How long they have | Usually within 10 business days of a complete request |
| Your meter's ID | The NMI, printed on your bill |
What are the main parts of a business electricity bill?
Most business bills split the cost into four groups. Names vary between retailers, so look for these ideas rather than exact words.
| Part of the bill | What it charges for | Can solar cut it? |
|---|---|---|
| Energy charges (c/kWh) | The total power you use | Yes, for the power you use while solar is making it |
| Time-of-use split | Different rates for peak, shoulder and off-peak hours | Shows how much of your use falls in daylight |
| Demand or capacity charge ($/kW or $/kVA) | Your busiest half-hour | Only if that peak falls in strong sun |
| Fixed daily charge ($/day) | Being connected | No |
Your bill may also list network charges, environmental charges and metering charges. Many of these are worked out per kWh, so they fall when your grid use falls. Others are fixed.
In plain words: solar lowers the energy part of your bill. It doesn't lower the fixed part.
Where do I find my usage on the bill?
Look for a usage table, often on page two. It lists the kWh used in each rate period across the bill period.
- On a flat tariff you get one figure for the whole period. It tells you how much you use, but not when.
- On a time-of-use tariff you get separate figures for peak, shoulder and off-peak. This is a rough guide to how much falls in daylight, but the windows don't match the sun. A peak window that runs into the evening includes hours when solar makes very little.
Write down three numbers: total kWh for the period, the number of days in the period, and the rate you pay per kWh in each window. Total kWh divided by days gives your average daily use.
What is interval data and how do I get it?
Interval data is your meter's reading for every 15 or 30 minutes, usually for the past year. It shows exactly when your site uses power: when it starts up, when it peaks, and what runs overnight and at weekends.
It's the single most useful file for sizing solar. A bill tells you that you used 30,000 kWh last month. Interval data tells you how much of that was used between 9am and 4pm on a weekday.
To get it:
- Find your NMI. This is the National Meter Identifier, the ID for your connection point. It's printed on your bill, usually on the first or second page, and is 10 characters long, often printed with an 11th check digit. It stays with the property if the meter is replaced.
- Ask your retailer for your interval data. Ask for it as a file, not a printout. Your network can also provide it. Under the national rules, retailers and networks must make reasonable efforts to send it within 10 business days of a complete request.
- Ask for 12 months if they have it. A full year shows the seasons, so summer air conditioning or a winter shift pattern isn't missed.
Most commercial sites already have an interval or smart meter, so the data usually exists. Western Australia sits outside the national rules, so check with your retailer there.
How do I split day from night use?
With interval data, add up the readings between roughly 9am and 4pm and compare them with your total. That share is your daytime use, and it is the ceiling on what solar can replace.
Here is a worked example with made-up figures. These are example figures, not our prices or a real site.
A Melbourne food business uses about 1,000 kWh a working day. Its interval data shows:
- 9am to 4pm: about 450 kWh, or 45% of the day
- 4pm to 9am: about 550 kWh, mostly refrigeration and an evening clean-down
- Weekends: about 300 kWh a day, nearly all refrigeration
On the Australian Government's YourHome guide, Melbourne makes about 3.6 kWh a day for each kW of panels. So:
- A 100kW system makes about 360 kWh a day on average. On working days the site could use almost all of it, because its daytime use is higher.
- At weekends daytime use drops, so some of the output is spare and goes to the grid, usually for a small credit.
- The overnight 550 kWh is untouched by solar, whatever its size. Only a battery could shift solar into those hours, and it rarely pays on night-time use alone. See commercial solar batteries.
In plain words: the size that pays best is the one your daytime use can actually soak up.
Without interval data, a time-of-use bill gives a rough answer. Treat the shoulder and peak figures as an upper limit on daytime use, not the real figure.
How do I find the demand charge?
Look for a line called demand, capacity, maximum demand or peak demand, charged per kW or kVA. The bill usually shows the rate and the peak reading, but not when the peak happened.
Interval data answers that. If your peak falls around midday on sunny days, solar may lower it. If it falls at a 6am start-up or in a 3pm to 9pm window, solar mostly won't. We explain this in demand charges.
What should I send for a solar proposal?
| Send | Why |
|---|---|
| One recent bill, every page | Shows your tariff, rates, NMI, demand charge and retailer |
| Any known plans (optional) | A new freezer room, extra shift or EV fleet changes your daytime load |
That's all we need. Using the NMI on your bill, the team gets your interval data for you.
If you send a recent bill, the team gets your interval data and an accredited installer prepares a costed proposal for your site. It's free, and there's no obligation.
For how size, output and payback come together, see commercial solar cost.