Can someone help me with math? I feel dumb that I can't figure this out because I'm normally pretty good with math. But I suppose it's not the actual math I'm having a problem with, it's figuring out the right equation to use. I'm making a spreadsheet to compare several systems and trying to figure out the 1, 5, 10, 15, 20, 25, 30 year savings and right now for the system I'm thinking about, my formula puts me at +$85,712 in 30 years. Maybe that's correct... but it doesn't feel like it. Especially because the same formula puts the number at +$35,235 at 20 years, which seems more correct to me, but I can't figure out what's going wrong. So here are my numbers. Production: The .995 is a 0.5% decrease in efficiency each year. 11213 kWh * .995^30 * 30 = 289,425 kWh Consumption: This is based on my current average year kWh comsumption 10236 kWh * 30 = 307,080 kWh Difference: Production - Consumption 289,425 - 307,080 = -17,655 kWh S
