Electric Cost of Service

The Purpose of a Cost of Service Study

The electric cost of service study is the analytical foundation of utility rate-making. It answers two fundamental questions: How much revenue does the utility need to cover its costs and provide an adequate financial return? And how should that revenue requirement be allocated among different classes of customers — residential, commercial, industrial, and others — based on how each class uses the electric system? Without a cost of service study, rates are set by tradition or rough approximation. With a well-constructed study, rates reflect the actual costs of serving each customer class.

Step 1: Developing the Revenue Requirement

The revenue requirement is the total amount of money the utility needs to collect from customers in a given year. Under the utility method — the industry standard — the revenue requirement has three components: operation and maintenance expenses (the costs of running the system), depreciation expense (the recovery of capital investment), and a return on rate base (compensation for the capital invested, measured as a percentage return on net plant in service). For cooperatives and municipal utilities, the "return" component typically takes the form of debt service requirements and contributions to operating reserves rather than a traditional equity return — but the economic concept is the same.

Step 2: Functionalization of Costs

Once the revenue requirement is determined, costs must be functionalized — assigned to the major functional categories: production (generating or purchasing power), transmission (moving power from generators to substations), distribution (delivering power from substations to customers), and customer (billing, metering, and customer service). Each function has different cost drivers and allocates differently among customer classes.

Step 3: Classification and Allocation to Customer Classes

Within each function, costs are classified by their relationship to three basic cost components: demand (costs driven by peak capacity requirements), energy (costs that vary with kilowatt-hours consumed), and customer (costs that exist regardless of usage). Demand costs are allocated based on each class's contribution to system peak demand. Energy costs are allocated based on each class's share of total consumption. Customer costs are allocated based on the number of customers or equivalent meters in each class.

Translating the Study into Rates

The cost of service study tells you what each customer class should pay in aggregate. Rate design determines the specific rate structure — how those costs are recovered through energy charges, demand charges, customer charges, and other rate elements. The rate design phase involves both technical analysis and policy judgments, balancing cost-based pricing with simplicity, customer impact, and broader utility objectives. The cost of service study is the foundation; rate design is how that foundation becomes the bills your customers receive.