What size solar system do you actually need
Anyone who gives you a number before asking three questions is guessing. Those questions are how much power you use, when in the day you use it, and how much roof you have facing the right way. Everything else is detail.
Here is how to think about it, including the case for a smaller system than we would like to sell you.
Start with your consumption, not your roof
The single most common sizing mistake is filling the available roof. A bigger system generates more, but the extra generation is only worth full value if you use it. Anything beyond that gets exported at a fraction of the price you pay.
So the starting point is your power bill. Not the dollar figure, the units. Your bill shows kilowatt hours used per month. That number, and the shape of your day, drives everything.
When you use power matters more than how much
| Empty from eight until five | Someone home during the day | |
|---|---|---|
| What happens to generation | Uses almost nothing while the sun is up; most generation gets exported | Consumes its own generation |
| What a unit is worth | Your export rate | What you would have paid for it |
| Does a larger system help? | Not proportionally | Yes, up to your consumption |
| What to look at first | A battery, or shifting loads into daylight | Heat pump, pool pump, hot water on a daytime timer |
Before you spend money on more panels, look at whether you can move existing loads into daylight. Hot water on a timer is the cheapest capacity increase available, and it costs nothing.
Since 11 May 2026 the default export limit for a straightforward residential connection is 10kW. The constraint that produced 6.6kW is gone.
Sources: Electricity Authority.
The three sizes, side by side
- 5kW
- $9,990
- 6.6kW
- $11,990
- 10kW
- $17,490
- 5kW
- 12
- 6.6kW
- 15
- 10kW
- 23
- 5kW
- 6,750 kWh
- 6.6kW
- 8,900 kWh
- 10kW
- 13,500 kWh
- 5kW
- $1,400
- 6.6kW
- $1,900
- 10kW
- $2,700
- 5kW
- 22–25 m²
- 6.6kW
- ~30 m²
- 10kW
- ~45 m²
- 5kW
- 1–2 people, no EV
- 6.6kW
- 3–4 people, the default
- 10kW
- EV, 4+ bedrooms, battery
Indicative pricing only, GST inclusive. Actual pricing depends on your home, roof, power use and electricity plan, and is confirmed in your tailored quote.
Smaller households, low daytime use
Around 5kW. Enough to cover daytime baseload without generating a large surplus you can only export cheaply.
Most family homes
6.6kW upwards. Still a sensible size for many houses, particularly where daytime consumption is moderate.
Higher use, an EV, electric hot water
Towards 10kW. This is where the export limit change matters most, because these are the households that were being throttled.
These are starting points for a conversation, not recommendations. Roof orientation, shading, pitch and your distributor's actual export limit all move these. So does whether you are adding a battery.
We quote what we think is right, not what fills the roof
We look at your consumption, your roof and your actual export limit. If that is smaller than the quote you have in front of you, we will tell you why.
Export is currently worth somewhere between about 5 and 17 cents a unit on standard plans, against 33 to 39 cents for power you buy. The marginal panel on an oversized system is earning a fraction of what the first panel earned.
If your daytime consumption is genuinely low and you are not planning an EV, a smaller system with the money redirected to load shifting or storage often returns more than a larger array.
Sizing for an EV you do not have yet
Reasonable, within limits. An EV is a large, flexible daytime load and it changes the arithmetic more than almost anything else you could add.
The caution is that adding panels later is usually possible but not always cheap, particularly if the inverter has to change too. If an EV is a firm plan within a couple of years, size for it. If it is a maybe, size for now and confirm your system can be extended.
Common questions
General guidance only, not a system design or a quote. Actual generation, savings and payback depend on your roof, shading, consumption, electricity plan and export limit, and are confirmed in your tailored quote. Prices and rates are indicative and change without notice.
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