We need commercially viable.
Waves....no-one can build a useful sized commercially viable power station yet.
Solar panels need "light" not heat. They actually work best in full sun on a cold day.
Thermal solar, reflectors to a central heat source use heat, but once again, not horribly viable, though there have been some interesting pilot sized plants.
People keep talking about Electicity like its transportable.
You really need to be within 500km of a power source , and you still get 10% total system loss. ( part of that is transmission loss ).
You can use a DC link, which has less loss over longer distance, but then you can't use it along the way.
A DC transmission line loses around 3.5% per 1000km. It works better underwater, because conductivity is better in the cold.
The conversion at the end is expensive.
If you had a big solar farm at Perth, you could ship the solar energy to Melbourne at prime time, but if you wanted to ship to Adelaide too, you'd need a separate link. New Zealand probably feasible too.
Of course Victoria's government didn't realise this when they promised Alcoa Portland years of cheap power, at the opposite end of the state to where the power stations were.
They were also kind of left trying to come up with a reason they were spending millions on transmission lines...."ohhh uh....we're uh...building a national grid link to South Australia " true story.
If they hadn't needed to get electricity to Portland in huge chunks, we probably wouldn't be connected to S.A.
