How Do I Calculate the Right Solar System Size?
To calculate the right solar system size for your home, divide your average daily electricity consumption (in kWh) by your location’s peak sun hours, then multiply by 1.25 to account for system losses. For most Australian households using 15 to 25 kWh per day, this calculation points to a system between 6.6 kW and 10 kW.
That is the short answer. However, getting your Solar System Size right involves a few more practical steps that make the difference between a system that pays for itself quickly and one that either misses the mark or overspends your budget. This step-by-step guide walks you through every factor clearly, with real Australian examples throughout.
Step 1: Find Your Daily Electricity Consumption
The foundation of every solar sizing calculation is understanding how much electricity your household actually uses. Without this number, every other calculation is just guesswork.
How to Read Your Electricity Bill
Your electricity bill is the most accurate source of your consumption data. Look for a section labelled “Average Daily Usage” or “Average Daily Consumption” measured in kilowatt-hours (kWh). Most Australian electricity bills display this figure clearly.
If your bill shows a quarterly or monthly total instead of a daily average, simply divide the total kWh by the number of days in the billing period. For example, if your bill covers 90 days and shows 1,800 kWh used, your average daily consumption is 20 kWh.
On average, Australian homes use 11 to 23 kWh per day. However, your actual usage depends on household size, appliances, climate control habits, and whether you work from home. Therefore, use a full year of bills rather than a single quarter to find your truest average. Summer bills will be higher in states like Queensland due to air conditioning, while Victoria households often see higher winter consumption from electric heating.
What If You Do Not Have a Recent Bill?
If you are a new homeowner or do not have recent bills available, your electricity retailer can provide 12 months of historical consumption data on request. Alternatively, a rough estimate based on household size works as a starting point:
A single person or couple typically uses around 8 to 12 kWh per day. A family of three to four people generally uses 15 to 22 kWh per day. A larger household of five or more people with ducted air conditioning often consumes 25 to 35 kWh per day.
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