Buying Solar Panels: How Many Will You Need?

Here’s what you need to know when it comes to buying the right and right number of solar panels for your home in 2025 — and discover the biggest mistake to avoid.

Clarifying Units Of Measurement

It’s first worth briefly explaining a few relevant terms many people still get confused – Watt (W) and Watt-hour (Wh), and kilowatt (kW) and kilowatt-hour (kWh).

• Watt¹ is a measure of instantaneous power.
• Watt-hour is a measure of energy generated or consumed over time.
• There are 1,000 Watts in a kilowatt.
• There are 1,000 Watt-hours in a kilowatt-hour. When you look at your electricity bill, you’ll see you are charged in kilowatt-hours for mains grid consumption.

To use round numbers for the sake of simplicity, a 500-Watt (500 W) solar panel (its power rating or capacity) operating under ideal conditions for 4 hours generates 2 kilowatt-hours (2 kWh) of electrical energy:

4 (hours) x 500 (W) = 2,000 Watt-hours (Wh) or 2 kilowatt-hours (2 kWh).

How Much Solar Panel Capacity Do You Need?

How many solar panels, or how much capacity you’ll need to keep your electricity right bills down all year round is probably more than you think.

The typical Australian household consumes about 16-20 kilowatt-hours of electricity per day. Using the example of 500-Watt solar panels each producing 2 kWh of energy a day would mean 10 panels should be enough.

But it isn’t.

Those 10 solar panels might produce enough electricity to power through the middle of a sunny summer’s day. But then there’s winter, overcast days, mornings and evenings to consider; along with other factors impacting efficiency. A system should be sized to get you through winter, and not just an average day.

You will very rarely hear anyone complain of having too many solar panels — but you’ll often hear system owners wishing they had more; and this is the biggest mistake people make. SolarQuotes founder Finn Peacock’s advice is completely fill your north, west and east-facing roof with panels if you can. 

Fill ‘er up! The rooftop of Finn’s house.

A good installer will evaluate your household energy consumption profile and recommend a system size suited to your needs and circumstances.

What To Do With Surplus Solar Energy

The goal is to catch as many of the sun’s rays as possible — particularly in the early mornings, late afternoons and evenings, and especially during winter. And you do that with a large system, which means you’ll likely have surplus solar energy at other times.

Any surplus solar power generated by your panels is usually automatically diverted/exported to the mains grid by your solar inverter, and you will receive a credit for that on your electricity bill if you’re on the right energy retailer plan. This is called a feed-in tariff.

But generally speaking, feed-in tariff rates aren’t anywhere near as generous as they were during the early days of Australia’s rooftop solar revolution when systems were much more expensive. Think of feed-in tariffs as a nice bonus, rather than as the primary reason for installing a system. The real value of a solar system is from self-consumption to avoid paying for mains grid electricity.

There are other things you can do with surplus solar power to maximise its value, among them:

• Get a home battery to store energy for use in the mornings, evenings and other times when the sun isn’t shining. And with a national federal government battery rebate on the way, it’s a good time to consider this.
• If you have electric hot water system, move your water heating to the middle of the day using a timer (or a PV diverter). If you have a gas service, consider replacing it with an electric one at the end of its life (or better still, a hot water heat pump) and doing the same. Basically, use a hot water system as a battery.
• Make your next car an electric vehicle, get a home EV charger and enjoy super-cheap top-ups courtesy of your solar system.

A hot water heat pump system

You can also have your inverter set so it won’t export surplus if it really bothers you. But if you’re using all the solar energy you can, don’t fret too much about “wasting” surplus. It’s a bit like having full rainwater tanks that overflow when there’s more rain; and you don’t even get any feed-in tariffs for that spilled water.

Which Solar Panels Are Best To Buy?

For most households, panel specifications such as efficiency, temperature-coefficient and degradation aren’t something to spend too much time worrying about if you simply buy a good brand — but view the video above or this solar panel guide for more detail on those aspects if you want to learn more².

“Good” doesn’t mean expensive these days, with the better budget brands offering very affordable high-performing panels with 25-year warranties. In fact, Finn recently posted about why premium solar panels are dead.

To help you choose and to whittle down any choices you may already have, Finn has put the solar panel brands he trusts on this chart; with the cheaper panels to the left, more expensive to the right.

While good solar panels are important, so too is installation; so be sure to get them well-installed by an appropriately qualified local who’ll be there for you in the unlikely event you need to claim on warranty. And there’s more to a good system than just the panels. On that note, learn everything you need to know about buying a solar power system here.