On kWh costs, don't forget that when you reduce use, you reduce the last kWh first. Meaning, in a tiered pricing model, you reduce your most expensive electricity first.

So, the price you would use to calculate savings is not your average price / kWh. You should use your max price / kWh.

That's also why if/when you install solar panels on your roof, you recover your investment faster if you don't quite cover your entire electrical needs.