I'm trying to figure out how to setup an equation for figuring out what the future value of a utility's usage rate will be over time. For example I want to know how much electricity in dollars a light bulb will consume over its life time taking into account real inflation costs on an electrical rate. Given that Inflation = 4%, Time=10 years, Electrical rate = .11/kilowatt hr, Lamp hrs=10,000, Lamp power usage/hr = 23w

(10,000 hours x $0.11 per Kwh x 23W)/1000= $25.30 worth of consumed electricity over its life time, but I can figure out how to apply the rising cost of the electrical rate due to inflation over the bulb's 10 year life.

I have tried using the formula I=PeRT as well as I=PRT and can't seem to find a solution. Can anyone shed some light on this problem?

Thanks