The following is based on figures provided in an article titled "Should I
quit the grid?" written by Andrew Reddaway, printed in the magazine ReNew,
which is published by the Alternative Technology Association.
Reading 'between the lines' the article suggests that a 4kW solar installation
is large enough to generate more power than many households' annual
electricity consumption (and I would agree with this; especially for those
people who were aware of, and cared about, their energy consumption).
Mr Reddaway goes on to estimate that to go off the grid a 10kW solar system
together with about 65 kWh of battery storage would be required at a total cost
of about $55,000; this apparently does not include a back-up diesel generator
which would also be needed.
The higher capacity solar system is needed to generate sufficient power
during winter, when many days will be cloudy and all will be short.
High solar feed-in tariffs, 2018
In at least some Australian states the payment per kilowatt-hour on offer for the excess electricity that a householder feeds into the grid has risen very substantially.
For example, on 2018/12/19
Solar Choice was showing that a number of retailers in South Australia were offering 16¢ to 23¢/kWh; up from 6-8¢/kWh a few years earlier.
One of my properties has 6.7 kW of solar panels and exports an average of about 25 kWh/day (9,300 kWh/year) into the grid.
At the 20¢/kWh my retailer is offering this is worth $1,850/year to me; a substantial amount.
A solar power system in southern Australia can be expected to have a capacity
factor of about 18%.
This means that a 4kW system will generate about 6300 kWh each year
(4 × 0.18 × 24 × 365) and a
10kW system will generate about 15,800 kWh each year
(10 × 0.18 × 24 × 365).
So, this off-grid home would generate about 15,800 kWh of power each year, but
consume only about 6300 kWh.
The difference, 9500 kWh of potential generation, would be wasted.
If this house, with its annual consumption of 6300 kWh and 10kW of solar power
stayed on the grid, that excess 9500 kWh would be fed into the grid.
If the house was to remain on the grid it could displace 9500 kWh of
reduce the nation's emissions by 5-10 tonnes of carbon dioxide each year
(see CO2 released per kWh) and produce an
income for the householder of $760/year (if the electricity was sold for
$0.08/kWh to an energy retailer such as Diamond Energy).