How Much Solar Do I Need for My House?
Let's walk through sizing with a real-world example. Take the Jacksons — a family of four in Wollongong. They use about 22 kWh a day. Someone's usually home. They want to know what size system fits.
We'll follow their logic step by step. Then you can run the same numbers for your own place.
Step 1: Find Your Daily Usage
Your bill shows average daily usage in kWh. That's the number that matters. Not the dollar figure — the energy number.
The Jacksons use 22 kWh per day. Slightly above average for Australia (most households fall between 15 and 25 kWh).
Know yours? It's usually on page one of your bill, labelled "average daily consumption" or something similar. Not sure? An uploaded bill can tell you in seconds.
Step 2: Estimate How Much You Use During the Day
Solar only generates while the sun's up. The portion of your usage that falls during daylight is your daytime usage percentage. This is the single most important number in sizing.
The Jacksons have someone home most days — working from home, running appliances, cooking dinner prep. About 40% of their 22 kWh daily total happens during daylight. That's roughly 9 kWh they could cover directly with solar. The other 60% is evenings and overnight.
Quick rule of thumb: if the house is occupied during the day, figure 30–50% daytime usage. Empty on weekdays? More like 10–20%. The lower that number, the more solar gets exported.
Step 3: Match System Size to Daytime Usage
The Jacksons need to cover about 9 kWh of daytime usage. In Wollongong, 1 kW of solar generates roughly 3.5–4 kWh per day averaged across the year (more in summer, less in winter). A 6.6 kW system would produce about 23–26 kWh per day total.
Most of their daytime usage — that 9 kWh — gets covered directly. The rest of the generation, around 14–17 kWh, gets exported. Export earns the feed-in tariff, but the real money is in that 9 kWh of self-consumption.
A 6.6 kW system looks like a solid fit for the Jacksons. Could they go smaller? A 5 kW system would still cover their daytime needs and export less. Bigger? An 8 kW system would export more and stretch the payback.
Step 4: Check Your Roof
Each panel is roughly 1.7m by 1m and produces about 400–500 watts. A 6.6 kW system needs around 14–17 panels, which is about 30–35 square metres of usable roof space. The Jacksons have a north-facing section of about 40 square metres with no shade. They're fine.
If your roof is shaded, smaller, or mostly east-west facing, it can still work but the numbers shift. East-west arrays actually have an upside — they produce a flatter generation curve through the day, which can match usage patterns better than pure north-facing.
Step 5: Consider the Future
The Jacksons are planning an EV next year and thinking about a battery down the track. That changes things. An EV adds roughly 10–15 kWh of charging per day — which they could do during daylight if they schedule it right. That extra daytime load makes a bigger system worth considering, maybe 8 kW instead of 6.6 kW.
Sizing for the future is a balancing act. Oversizing for an EV you might not buy adds cost today. But installing a slightly larger system upfront is cheaper than adding panels later. No perfect answer here — it depends how certain those plans are.
Quick Sizing Reference
- 3–5 kW — Small homes, low usage (under 15 kWh/day), limited roof space
- 6.6 kW — The sweet spot for most. Suits 15–25 kWh/day with moderate daytime occupancy
- 8–10 kW — Bigger homes, higher usage, EV charging, or battery plans
- 10 kW+ — High usage, multiple EVs, or home-office/commercial needs
These are rough starting points. Your actual size depends on your usage, roof, and plans. System size should follow usage, not roof maximum — bigger isn't always better if most of the power gets exported. A payback calculator using your real bill data will give a much more precise answer.
Find the right system size for your home
Upload your electricity bill and we'll recommend a system size based on your actual usage data.
Frequently Asked Questions
Common questions about solar system sizing
How much solar do I need for a 4-bedroom house?
A 4-bedroom home using 20–30 kWh per day might start looking at 6.6kW to 8kW systems. But the right size depends on your usage, roof space, and budget — not the number of bedrooms.
What size solar system do I need for my usage?
As a rough guide, 1kW of solar generates about 3.5 to 4.5 kWh per day on average in a good location. If you use 24 kWh per day, a 6.6kW system would cover most of your daytime needs. Rough guide only — your mileage will vary.
Can a solar system be too big?
Yes. A system that generates way more than your daytime usage exports most of its power at the feed-in tariff rate, which is much lower than retail. That stretches the payback. Oversizing can still make sense if you plan to add a battery or EV charger later.
Can a solar system be too small?
An undersized system may not make a real dent in your bill. If savings are too small, the payback drags because you're still buying a lot from the grid. The system should match your usage.
Does roof size limit solar system size?
Absolutely. A typical panel is about 1.7m by 1m and produces roughly 400–500W. A 6.6kW system needs about 30–35 square metres of usable roof space. Complex roof shapes, skylights, and obstructions eat into that area.
Related guides
This guide is for informational purposes only. System sizing recommendations are estimates and should be confirmed with a qualified solar installer.