Rate growth and panel degradation

The first year’s savings come from this year’s rates and new panels. The 25-year number has to guess how both change, and these two settings are that guess.

Utility rate increase

In Price & settings, under Calculation, Utility rate increase, % per year sets how fast electricity prices rise in the forecast. The starting value is 3.4% a year — Cali-Graf recommends 3.4%. You can type 0 to 15%; to use your own value in every new calculation, set it in Settings under Calculations — see Set defaults for new calculations.

A higher number makes every future year’s bill — and so the savings — bigger. Pick a number you can explain to the customer — future rates are a forecast, not a fact.

Panel degradation

Panels make a little less power each year. Cali-Graf takes the yearly loss from the panel’s datasheet — you can see it in the panel’s details under Warranty and degradation, as Degradation after year 1. If the datasheet doesn’t give it, the forecast uses 0.5% a year. There’s nothing to set.

How they show up

The result’s 25-year savings and the savings page of the proposal add up 25 years of bills with solar against bills without it, each year with rates grown and production degraded. The first year isn’t affected.