Editor SolarHow to estimate home energy use from your electricity bill
Learn to read the kWh on your bill, work out daily use and average power, and check it by adding up your appliances before sizing a solar system.
Why start with consumption
Every solar sizing starts with a simple question: how much energy does the home use? Without that number you cannot choose panels, an inverter or batteries. The good news is that the answer arrives every month, printed on your electricity bill.
In this article you turn the number on the bill into daily consumption and average power, and then check the result by adding up the appliances in the home.
Where to find consumption on the bill
Look for the consumption in kWh field, usually labelled “energy used” or “billed consumption”. Ignore the amount of money: it changes with tariffs, taxes and surcharges, but the kWh do not.
- 1Gather 12 months
Consumption changes with the seasons. Add up the last 12 months and divide by 12 to get an average that represents the whole year.
- 2Confirm the unit
Use the consumption in kWh for the period of about 30 days, not the total cost and not the meter’s running total.
- 3Add what is coming
A new air conditioner, an electric car or more people at home change consumption. Include what you already plan to install.
From the bill to the day and to average power
Dividing the daily energy by 24 hours gives the home’s average power: 10 kWh ÷ 24 h ≈ 0.42 kW, or about 417 W running all the time. It is an average: at night the home uses far less, and in the early evening far more.
The average of the four seasons is (360 + 300 + 250 + 310) ÷ 4 ≈ 305 kWh per month, close to the 300 kWh used as the example.
Checking it against the appliances
To find out where the energy goes, add up the appliances. The rule is the same for all of them: energy = power × time of use. A 1,000 W air conditioner running for 4 hours uses 4,000 Wh, or 4 kWh.
What weighs most on the bill
With the calculator’s starting values, the six appliances add up to about 7 kWh per day, or 209 kWh per month: roughly 70% of a 300 kWh bill. The rest comes from appliances the list leaves out.
Common mistakes and the next step
Do
- Use the 12-month average, not just the most expensive month
- Add what you plan to install over the coming years
- Use the average power of the refrigerator and other appliances that switch on and off by themselves
- Compare the appliance total with the bill: the gap shows what was left out
Avoid
- Mix up kW (power) with kWh (energy)
- Use the amount in money as if it were consumption
- Use only summer, or only winter, for the whole year
- Forget the minimum charge the utility applies
With daily consumption in hand, the next step is to find out how many solar panels cover that energy. The diagram below shows the energy path from the grid to the appliances: use it as a starting point to draw your own home.
Draw it in Editor Solar
This is Editor Solar itself, already loaded with the diagram from this article. Move the equipment, edit labels, connect new parts and export to PNG, SVG or PDF. It is free and runs right in your browser.
Try it: Add your own appliances to the board and write each one’s power and daily hours of use. Add up the energy and compare it with the consumption on your bill.
Ready-made templates: see all diagram templates