A rooftop array produces a kilowatt hour and it goes one of two places. Used in the house, it avoids buying one at the import price. Sent to the grid, it earns the feed-in tariff. Those two prices are rarely close, and the gap between them is what actually determines the value of the system.
At a 30 cent import price and a 5 cent feed-in tariff, a kilowatt hour used on site is worth six times one exported. Not six per cent more. Six times.
What the share is worth
Take 8,000 kilowatt hours of annual generation against 6,000 of household use. At 35 per cent self-consumption, the self-consumption calculator puts the value at $1,100 a year: 2,800 kWh used on site worth $840, and 5,200 kWh exported worth $260. Averaged across everything generated, that is 14 cents a kilowatt hour.
Lift the share to 75 per cent and the value becomes $1,900: 6,000 kWh used on site worth $1,800, and only 2,000 exported. The average value per kilowatt hour generated nearly doubles, to 24 cents. The panels did not change, the weather did not change, and the system is worth about 73 per cent more.
Which is why shifting load matters more than adding panels on most houses. Running the dishwasher, the pool pump, the washing machine or the car charger during the day is not a marginal efficiency, it is the difference between selling at 5 cents and not buying at 30.
There is a ceiling, and it is the house
Self-consumption cannot exceed what the household actually uses. Ask the calculator for 100 per cent on these figures and it reports 75 per cent, capped by household use, because 8,000 kilowatt hours of generation cannot be consumed by a house that only uses 6,000.
That ceiling is worth finding before sizing an array. Past it, every additional panel is selling at the feed-in tariff, and the economics of those extra panels are a completely different and much weaker calculation than the first ones. The related question of how much inverter to put behind the panels is in the DC to AC ratio calculator.
Where a battery comes in
A battery exists to move energy across that gap, so its value is set by the same spread. A 10 kilowatt hour battery cycled once a day, charging at an 18 cent off-peak price and discharging against a 45 cent peak, at 88 per cent round-trip efficiency, saves $895.91 a year on the battery arbitrage calculator.
The efficiency loss is easy to overlook: delivering 10 kilowatt hours means buying 11.36, so the effective cost of stored energy is 20 cents rather than 18. At $9,000 installed that is a ten year simple payback, or 3,667 cycles, which is worth holding against the warranty cycle count rather than the warranty years.
Every price on both pages is a field, because tariffs, feed-in rates and battery prices move constantly and differ by network. The structure is what lasts: value follows the spread between what you pay for a kilowatt hour and what you are paid for one.