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The size of system you need depends on 5 main factors:
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\n\nYour daytime energy consumption
\n\tYour local Feed In Tariff
\n\tYour local network rules
\n\tThe size and layout of your roof
\n\tWhether you have a 3 phase or single phase supply to your house
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The key point to realise is that the ideal solar system size no longer hinges on the size of your current power bill.
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10 years ago it was different. Then solar cost about $2,500 per panel. Determining the right system size required an engineer like Finn Peacock from SolarQuotes or a really good installer to calculate what will maximise self-consumption and minimise surplus returned to the grid. You had to consider every panel you added really carefully.
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Today the cost of solar is closer to $200 per panel (90% cheaper).
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According to Finn, the #1 regret he hears from solar owners who have experienced the bill busting value of solar is that they wish they had bought more panels. There are two reasons for this:
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Bigger systems are much cheaper per panel than smaller systems.
\n\tMost Australian postcodes get a good price for selling their surplus solar back to the grid.
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So, if solar stacks up even if most of your solar energy is returned back to the grid, what is the right size for your home?
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According to Finn it’s simple:
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“For most people the ‘sweet spot’ is simply a 6.6kW system with a 5kW inverter.”
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Without going into detail - this size is where you get maximum kW for your money. If you have a high daytime consumption your payback will be spectacular. If you have low daytime consumption, but a reasonable Feed In tariff (10-16c per kWh) you payback will still be good - thanks to the low cost of panels these days.
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Of course if you have a huge daytime consumption, a large roof and a 3 phase supply, you can go much bigger. Often you’ll be allowed to add up to 30kW of panels.
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A note about self-consumption
\n\nThe benefits of solar are about three times (2-3x) greater when you self consume solar. A typical household can work on these approximate rates for energy:
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Consume from the grid
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\n\nYOU PAY
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\n\n30 Cents / kWh
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\n\nReturn excess to the grid
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\n\nYOU ARE PAID
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\n\n10 Cents / kWh
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\n\nYour system makes energy in the day. The more time at home during the day - the larger the system.
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\n\nHouseholds which benefit the most from solar include:
\n\nWeekend homebodies, families with children and retirees
\n\tHouseholds with large appliances (pool, heating/cooling)
\n\tHome offices
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Pro Tip: The average AUS rate of self-consumption is 30%. Most systems we finance are cash-flow positive from day 1 down to a self consumption rate of 20%.
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\nRead Finn’s 7 Mistakes Solar eBook here for more details on this.