In France it is, and has been successfully for more than 33 years [1]
That is, assuming that grid scale storage is in fact viable.
France's nuclear fleet has an all-in cost of 7c/kWh, which is roughly the same as the cost of solar or wind power in France, but without the need for storage or smart grids that doubles the cost of solar/wind. (For all this remember that France has about a third of the insolation of California or Arizona per year, or maybe half at best in some places.)
I don't think that is correct. This is a table of average insolation for different cities around the world derived from NASA's Surface meteorology and Solar Energy data set: http://stalix.com/isolation.pdf
Los Angeles gets 5.4 kWh/m^2/day. San Francisco gets 4.9. Lyon, Paris, and Toulouse get 3.7, 3.3, and 3.7 respectively.
So you don't have power outages on windless nights.
> backup fossil fuel
In practice this means fossil fuels become the baseload power source.
False. In the immediate future, synthetic anhydrous ammonia will displace it. Extracting NG will be too expensive to compete, because the only cost of ammonia will be capex. The more you make, the less it costs.
The previous poster talked about using fossil (or any other means) to supply the mismatch between the supply and demand at the times where such a mismatch might exist. This is completely unrelated to baseload, it could in fact be larger than baseload. Note that such a mismatch would also exist for nuclear (dependent on overprovisioning). However it would in general be only needed of short periods of time.
Because if your baseload is your minimum power consumption (which generally occurs at night) and you have a windless night (therefore your renewables are generating 0 power), your "gas peakers" will have to provide the entire baseload amount of power.
China is building solar in Chile, at their antipodes, and a transmission line back to China with only 50% loss, for solar energy through the night.
As the name baseload power implies, it would have to be providing power all the time and that's not what is needed.
It is one of the main reason why investing in fossil fuel energy when countries turn to wind power is fairly good choice. The plant has lower costs in terms of fuels, when it burn fuel it does so when the market price is at the highest possible, and it get paid regardless from the government. The government are also locked into continuing this scheme as the alternative is to not have the reserve energy when needed which makes voters very angry.
Burning fossil fuels when the price is lowest and without any government subsidies is just something people with too much fossil fuel can afford to do.