Here's my 2 cents worth. I installed a Pentair variable speed pump around three years ago. I don't think I have saved one dime. Running at low speed, with longer pump run time it is very quiet, and uses little energy or $. But, here's some of the dirty little secrets they don't tell you. 1. At low speeds, the skimmers are virtually useless, because there is not enough flow over the weirs to suck anything off the surface, so be prepared to spend lots of time manually skimming for debris, 2. if you have solar, you will certainly be running during peak electric rate hours, and you will need to crank up the pump speed to maintain flow through the panels and prevent air being sucked in through the air relief valve on the roof.
I would not replace a pump solely to save money, because you may well be disappointed. In California, replacement pumps must be of a variable speed type, supposedly to reduce electric use. For some folks, it may work. For others, like me, it affords no economies whatever. You can spend hours doing calculations, messing with the pump speeds, and find your electric bill unchanged. Good luck.