Even with storage (batteries, hydro pumping or alternatives) solar and wind are still cheaper than fossil fuels, generally by a 25% to 50% margin.
Depends on the fuel. If I eventually go with a back-up whole house generator, propane has less maintenance issues but isn't as energy dense as, say, diesel. I would look at a 500 gallon tank, and not factoring in delivery charges, that's around $1,600 US. That just under $2,450 AU. Note: I'm spit balling fuel cost here. It goes up in winter. How long that 500 gallons last depends, of course, on how much it runs and that depends on the size of the generator and demand. Highest energy density is coal.
The pay-back time here is longer than what you cite for Australia. A full off-grid system with battery storage is expensive enough that at one time
Mother Earth News suggested it rolling it over into the mortgage when building a home. I'm aware of a local hunting camp far enough from the grid that the owner didn't want to pay aid in construction to run a power line back there, and had to opt for both conventional generator and solar. Saw some specifics on it when it came up for sale, but unless someone was using propane for heating and cooking, the installation was kind of anemic. Maybe sufficient for a hunting camp, though.
Very few of the residential / commercial accounts we serve generates more power than it uses. I think the grand total is two, from what saw earlier this year. Both are commercial accounts with low overall usage and large roof area. Large solar fields connect to transmission lines and we're distribution, so other than how they're connected (based on when we ran great big diesel generators for peaking), can't say how they stack up. I do recall a residential customer who, when told there was a 20 -30 year payback, replied "I'll just double it." Doesn't work that way, of course. if you have to build a transmission line to serve one, the price around four or five years ago was roughly $1,000,000 US per mile.
