This Central Arizona billing study (vendor: Salt River Project) was undertaken to determine if, and how much, inflation was impacting consumer electric bills. These factors were thought to be germane:

UTILITY SIDE:
1. Multiple and ever changing rate schedules.
2. Customer requested schedule changes.
3. Actual meter change-outs.
4. Winter/summer base price differences.
5. Fuel adjustments.
6. Demand, time-of-day and demand PLUS time-of-day metering.

CUSTOMER SIDE:
1. Use habits or new equipments.
2. Travel impacts.
3. Weather.
4. Illness and/or comfort decisions.

Searching carefully though these variables it was decided to select a single customer with continuous residence over a large time frame.

Selection:
A. Retired couple (no children home).
B. Readily available sequential billing data (same vendor).

Method used was to take the actual billed amount each month (all taxes included) divided by the number of kilowatt hours consumed.
This is believed to level out most of the variables, anomalies and suspected obfuscations.

Bottom line observations:
Over this study's full eight year span, the cost per kilowatt/hour remained remarkably stable.
Assuming a modest three percent inflation rate, the cost should have ended up around $0.10/kwh.
In the examined data set, the 1998 costs look very much like the 1991 costs.