Hello,
I need to determine how much money a solar array will save one of my
customers over the next thirty years.

I'd like to know the formula to calculate this.

Inputing: 17 Cents per kWh.
21,128 kWh's per year
a 5% increase in the cost of electricity per year. (17cents
per kWh increasing by 5% every year).
over 30 years.

Help Please! Thanks.