Where indicated, some cost values on the California DG Stats site can be displayed on either a real or nominal basis. Real values are calculated using a Consumer Price Index (CPI) for California, found on the California Department of Finance
site.
The default setting is to display cost-per-watt (CPW) data on a
real basis, i.e. adjusted for inflation (the exact calculation is described below).
However, you can also view CPW data on a
nominal basis, i.e. not adjusted for inflation.
Months with No Data
The spreadsheet specified above provides exact California CPI data for every other month and interpolates between the surrounding months for each month without data. For example, data in the spreadsheet is provided for February and April, but not for March. The CPI for March = [(February + April) / 2].
Normalization
In all cases, dollars are normalized to the current month, so that ${today} = [(CPI{currentMonth} / CPI{Month}) * ${Month}]. For example, assuming the current month is April 2017 the listed CPI is '261.851'. Current dollars are multiplied by CPI{currentMonth} / CPI{Month} , which in this case is (261.851 / 261.851 = 1). In other words, for today's dollars, $1 = $1.
The listed CPI in August 2015 is 251.253. To find the value of an August 2015 dollar in today's dollars, one would take CPI{currentMonth} / CPI{Month} = (261.851 / 251.253) = 1.04218. In other words, one August 2015 dollar = $1.04218 in April 2017.
Treatment of Quarters and Years
For the purposes of calculation on this site, quarterly values are based on the average CPI for 3 months in each quarter and annual values are based on the average CPI for 12 months in each year.