It's absolutely a net gain when compared to running gas/coal only. But unfair to say that this produces 0 CO2, like it's often claimed. And this backup CO2 production is very far from negligible.
Similarly, the cost of running gas only should be computed as: cost of gas power plant + cost of gas. And the cost of the renewable option should be computed as : cost of renewable power plan + cost of backup gas power plant + cost of backup gas. You can't magically exclude the backup from the calculation. And suddenly the renewable option sounds way more expensive.
Similarly, the cost of running gas only should be computed as: cost of gas power plant + cost of gas. And the cost of the renewable option should be computed as : cost of renewable power plan + cost of backup gas power plant + cost of backup gas. You can't magically exclude the backup from the calculation. And suddenly the renewable option sounds way more expensive.