How many solar panels do I actually need?
3kW? 6.6kW? 10kW? 20kW?! What does that even mean and how many panels are needed for those sizes? How many solar panels do I really need? If you’ve ever been scratching your head after asking yourself these questions, allow me to break it all down for you!
First Things First: Understanding Your Usage
Understanding what appliances use the most energy in your home, when you use them and how often you use them is the key to understanding your energy needs. Here’s a short list of some items that might be adding up on your energy bills:
- Some electric water heaters use up 4kWh an hour and represent about 30% of an average Aussie electricity bill. (You can sort that with a Apricus heat pump, read more on heat pumps here)
- Some Microwaves use over 1,000 Watts when in use.
- Household appliances account for approximately 46% of home electricity usage.
- Heating and cooling accounts for 50% of the average home’s total energy consumption! (You can also reduce that without freezing or breaking the bank with a reverse cycle system, I did a separate write up about that here).
Understanding your daily usage is a good starting point to knowing where you stand with your daily usage. The best way to get an average idea of your usage is note all the wattages of your appliances and how long they run for each day, then you can use the following formula:
(wattage x hours used per day) ÷ 1,000 = Daily kilowatt-hour consumption
(kWh is a measurement of energy usage over time, whereas kW is a measurement of power). You can also see your average daily usage on your bill.
System Sizes Explained
When you hear us, or other solar installers talk about a 6.6kW solar system, what we’re referring to is the system size.Â
Solar panels come in an assortment of different capacities and physical sizes, so instead of saying a system is 15 panels of REA 440W panels, we say that is a 6.6kW system, because 15 x 440 watt panels = 6.6kW.Â
But what does that actually mean?
Well, it means, that at maximum sun exposure (also called “full sun”), your system is capable of producing 6.6kWh of energy per hour!  Of course, your house isn’t always in full sun during the day, The peak times for generation are usually around 9am to 4pm in the arvo during the summer but you get a shorter window in the winter. For a real-world example, a customer of ours with a standard 6.6kW system facing north makes about 34kWh a day on average in Summer and about 10kWh a day in the Winter, although there are multiple other factors to consider when going solar…
Things to Consider:
Your Energy Requirements:
You need to look at your current usage, a 6.6kW system might be what any other cheap installer offers you – which sometimes is appropriate, but any real company worth their salt will look at your current energy requirements when installing solar, your main goal should be total energy independence, using the grid as a backup in times of increased usage or during the night. It’s not worth putting up a 6.6kW system on your roof if you’re using 50kWh a day!
Physical Roof Capabilities:
Another consideration to look at when installing solar is what you can actually fit on your roof. We’ve had a few clients that have wanted the massive 13.2kW system, but unfortunately, they don’t have the actual roof space to accommodate the sheer number of panels. Our talented designers can usually overcome issues like difficult roof layouts with a large number of ridges & valleys using Enphase microinverters, but we can’t make extra roof space.
Seasonal Generation:
One mistake I see a lot of people make when planning for solar is just looking at peak generation during summer and not really thinking about the differences in generation throughout the seasons. For example, a 6.6kW system with a good roof design can generate up to 35.3kWh a day in January but we have seen that figure drop to 9.83kWh a day in June! In the winter you typically use more energy to heat the home, so this is something worth factoring in.
When You Use Your Energy:
If you work away from home during the day or use a lot of energy during the night, you’d want to maximise your savings by using the power you generated during the day with a solar battery, like a Tesla Powerwall 2 or SonnenBatterie and avoid those peak usage tariffs!
Future Usage:
I’ve got a saying when it comes to solar panels “Panels on the roof is like money in the bank, you can never have too much!”. If you over-size your system thinking about potential future usage, it may work to your benefit. As internal combustion cars phase out and EV ownership ramps up it could be a smart pay to ensure that you can charge your car and keep your bills low. Another thing to consider is how much of your home will be electrified, getting off the gas and getting a reverse cycle air conditioner? Maybe you’re looking at getting a heat pump for your hot water service or doing a kitchen reno and fitting an electric stovetop? With modern solar panels designed to last 25+ years with the warranty to back them up, it can save you money to think forward towards the future!
Quick Reference Guide:
System size and daily generation:
Below I’ve listed a rough guide on what a small, medium and large PV system generates in a day. Comparing this to your home’s daily usage can be a great starting point.
Also remember, your usage may be during the night at which point it might be worth looking at battery, this would be a bit different to just your PV as you’ll need to look at battery storage vs your overnight use and plan a system that can charge that battery too, for example, the Tesla Powerwall 2 has 13.5kWh of capacity, so you will need a system that can generate an extra 13.5kWh of whatever is used throughout the day. We have found this is usually enough to cover most people’s energy use overnight, but again, it’s best to check your own usage and think about the future. Secondly, these system sizes are what is generally considered small, medium and large but our system designers can tailor a system size to suit your specific needs goals (given the roof space).
Figures are based on an average between summer generation and winter generation modelled off jobs we’ve installed in the past.
- 6.6kW (15 x 440W panels) = 21kWh per day
- 8.36kW (19 x 440W panels) = 25.5kWh per day
- 13.2kW (30 x 440W panels) = 50.9kWh per day
