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Understanding and Analyzing Utility Rates

Considering just the acquisition costs of installing a grid-tied solar-electric system is only half of the equation. It is necessary to estimate how much return on investment a system will bring. It may occur that owners of a grid-tied system will at some point be asked to make a choice regarding new rate plans. Making informed decisions requires an understanding of utility rate structures, and these structures have become increasingly complicated. Below are files that contain my efforts to come to a thorough understanding of these rates and to model them accurately.

The basic premise is the assumption that the rate of return on energy generated equals the cost of buying the same energy. This ignores the effect that the consumption of energy has on the process. I feel this is acceptable because if a system is sized appropriately these effects are inconsequential.

Treatise on the basics of the subject HTML

Applying Spreadsheet tools for analyzing Utility Rates HTML

Below are spreadsheets that I have developed to model these PG&E rate plans. They are based on a simulated 4 kW grid-tied system installed in zip code 93422. They model the generated energy and value it at the rate buying the same energy would cost.

I make no claim as to accuracy of these models. They are based on my best knowledge of how this is to be accomplished.

PG&E E-1 Rate Study XLS Spreadsheet

PG&E E-6 Rate Study XLS Spreadsheet

PG&E TOU-C Rate Study XLS Spreadsheet

PG&E TOU-D Rate Study XLS Spreadsheet

Below is the comparative results of the study as of 5/3/21. As you can see, there is little difference between the four plans as far as dollar value of solar harvest.

If I find any errors in my process these results might change.

Calculated value of energy generated in simulated 4 kW system over 1 year.  Does not factor in consumption patterns.
Rate Plan Total Diff Description
E-6 $1,900 100% TOU and Tiered. Summer: Off, Part-Peak, Peak. Winter: Off, Peak.  Account for Weekends and holidays.
TOU-C $1,912 101% TOU and Tiered. Summer: Off, Peak. Winter: Off, Peak. 
TOU-D $1,914 101% TOU and Tiered. Summer: Off, Peak. Winter: Off, Peak.  Account for Weekends and holidays.
E-1 $1,939 102% 3 Tiers

PG&E Tariff Page Web Link

Note: Miller Solar takes no responsibility for the results of the use of any data provided on this site. All critique and suggestions are welcome.