The headline question asks about the difference between singular and plural energy saving, but I'll just say straight away that the rest of the sentence isn't well-constructed. It would be more "correct" to say something like..
the energy saving(s) [ratio] of A compared to B
In OP's exact context, energy saving(s) is effectively a noun phrase being used adjectivally (i.e. - the ratio under consideration is calculated from the two different values of energy saving(s) for A and B).
I've put [ratio] in square brackets in my rephrasing because it's superfluous verbiage. I'd also point out that if A uses 3 units of energy where B uses 4, that means A saves 25% relative to B (not 0.25%).
Turning to the general case of singular/plural energy savings, you might like to look at Pluralization of savings and costs as asked previously on ELU. In OP's context I think either form is valid, and it's really stretching a point to suggest they actually mean different things.
But I do think there's a potential tiny difference based on the fact that plural savings is more associated with money put by for the future (i.e. - not spent). So you could say that using the plural places more emphasis on the reduced monetary cost for whoever pays the electricity bill, if they use A rather than B.
Conversely, if saving is given in the singular, this slightly places the emphasis on the total amount of energy that's not used, if people in general adopt A instead of B.
Thus there's (not much, but some) justification for saying that savings is more likely in an appeal to people's financial self-interest, as opposed to saving the planetary ecology (by us all using less energy).