Power bills look complicated because they combine several different kinds of charge, measured in different units. Once you can see which line is which, you can check whether the bill is right, compare plans properly, and work out what solar or a battery would actually save you.
Every bill is laid out a little differently, and names vary between countries and retailers, but nearly all of them are made of the same few parts.
1. The supply charge: cents per day
The daily supply charge (also called a fixed charge, service charge or standing charge) is what you pay just to be connected, whether you use any power or not. It's shown in cents (or pence) per day.
supply cost = daily rate × days in the billing period
Supply charges have risen a lot in many places, and solar can't reduce them. A home that makes all its own power on paper can still have a bill, and this line is why. When comparing plans, check the supply charge as well as the usage rates: a cheap usage rate can hide an expensive daily charge.
2. Usage charges: cents per kWh
This is the part you control: the kilowatt-hours you bought from the grid, multiplied by the price per kWh. (If kW vs kWh is still blurry, watch the three-minute explainer.) There are two common ways to charge for it.
Flat rate (single rate)
One price per kWh, any time of day. Simple, and fine for households that use most of their power in the evening or can't shift their use.
Time of use
Different prices at different times, usually:
- Peak: the expensive hours, often late afternoon and evening;
- Off-peak: overnight, the cheapest;
- Shoulder: the bits in between, sometimes including the middle of the day.
Time-of-use tariffs reward you for moving use out of the peak. They suit homes with solar (which covers the daytime), a battery (which covers the evening peak), or an EV charged at off-peak times. They can cost more for a household that uses most of its power at peak times and can't change that. Some retailers now also offer a free or very cheap window in the middle of the day, when there's plenty of solar on the grid.
Your bill should split your usage into these periods. Check that the hours match your plan.
3. Demand charges: kW, not kWh
Some tariffs add a demand charge, based on the highest kilowatts you drew at once during a set window, usually in the late afternoon or evening. It's priced in dollars per kW per day or per month.
This is where kW and kWh really matter. Using 10 kWh across an evening is cheap on a demand tariff; using it all at once (oven, kettle, air conditioner and EV charger together) sets a high peak, and you pay for that peak for the whole month. If your bill has a demand charge, spreading big loads out can save more than using less energy.
4. Solar exports: the feed-in tariff
If you have solar, the bill also shows the kWh you exported to the grid and what you were paid for them: the feed-in tariff, a credit per kWh.
What's important is how small that credit usually is compared with the price of buying power:
- Australia: feed-in tariffs are now mostly set by retailers, typically somewhere between 0 and 10 cents per kWh, against usage rates often above 30 cents. Some states set a minimum: Tasmania's regulator, for example. In others, such as New South Wales and Victoria, rates are set by retailers, often with a higher rate for the first few kWh each day.
- United Kingdom: exports are paid under the Smart Export Guarantee. Rates are set by suppliers and vary widely, from a few pence to much more on some time-of-use export tariffs.
- United States: it depends on your state and utility. Some still offer net metering, where an exported kWh offsets an imported one at close to full price. Others, including California's current system, credit exports at a much lower rate.
That gap is why using your own solar is worth far more than exporting it. A kWh you use yourself saves the full usage rate. A kWh you export earns the feed-in tariff. It's the whole basis of the battery payback sum.
5. Everything else
- Discounts and credits: pay-on-time discounts, government rebates, concessions.
- Tax: GST (Australia), VAT (UK) or sales tax, depending on where you are. Check whether the rates on your plan include it.
- Meter readings: "A" means actual and "E" or "Est" means estimated. If most readings are estimates, the bill can drift a long way from reality.
A worked example
A 91-day quarterly bill for a home with solar in Australia, on a flat rate:
Line | Amount | Rate | Cost |
|---|---|---|---|
Supply charge | 91 days | 110c per day | $100.10 |
Usage (bought from the grid) | 1,200 kWh | 32c per kWh | $384.00 |
Solar exports | 900 kWh | 5c per kWh | −$45.00 |
Total | $439.10 |
Now the useful questions:
- Average daily use from the grid: 1,200 ÷ 91 = 13.2 kWh a day. That's the number for sizing solar or a battery.
- Average daily export: 900 ÷ 91 = 9.9 kWh a day of spare solar.
- What if those exports had been stored and used in the evening? Each kWh would save 32c instead of earning 5c, so 27c more. Over the quarter that's 900 × 0.27 = $243, if a battery could shift all of it. In practice it's less, because of winter and battery losses; our battery guide does that sum properly.
- How much of the bill can't be avoided? The $100 supply charge, about a quarter of the total.
Checking and comparing plans
- Note your daily supply charge, usage rates and feed-in tariff from your current bill.
- Use a year of usage if you can. Your retailer's app or online account often has it, split by time of day.
- Put the same usage through any plan you're considering. In Australia, the government comparison sites, Energy Made Easy and Victorian Energy Compare, do this for you. In the UK and US, use your regulator's or state's comparison tools where they exist.
- Be wary of comparing on the headline discount alone. A big discount off high rates can still cost more than a plain plan with lower ones.