Rate Setting

August 25, 2024 Regulation

Utility rate setting converts an approved revenue requirement into customer-class allocations and tariff charges using forecast billing determinants.

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Rate setting is the process of establishing the charges a regulated utility may collect for specified services. In traditional ratemaking, the process moves from approved cost and investment to a revenue requirement, allocates that requirement among services or customer classes, and converts each allocation into tariff charges.

Rate setting is broader than calculating an allowed return. The same total revenue requirement can produce very different customer bills depending on cost allocation, billing determinants, fixed charges, demand charges, usage rates, seasons, and adjustment mechanisms.

Key Takeaways

Revenue requirement determines how much approved annual revenue is needed; rate design determines how it is collected.
Cost allocation assigns the requirement among functions, services, or customer classes.
Billing determinants translate allocated revenue into charges per customer, kilowatt-hour, kilowatt, gallon, therm, or another unit.
A lower volumetric rate can be offset by a higher fixed or demand charge.
Affordability, conservation, revenue stability, gradualism, and cost causation can point toward different designs.

Four Main Stages

Stage	Core question	Typical output
Determine revenue requirement	How much approved revenue is needed?	Annual currency amount
Allocate cost	Which function, service, or customer class causes or benefits from the cost?	Class or service revenue allocation
Design rates	Which billing components should recover the allocation?	Fixed, demand, usage, seasonal, or other charges
Implement and reconcile	How will rates update, true up, or respond to variances?	Tariff, rider, tracker, formula, or reconciliation process

Rate-Design Formula

For one billing component, a simplified rate is:

\text{Rate} = \frac{\text{Allocated Revenue Requirement}}{\text{Forecast Billing Determinant}}

The billing determinant must match the charge. A customer charge uses customer-months; an energy charge may use kilowatt-hours; a demand charge may use billed kilowatts. Forecast error can cause over- or under-collection.

Worked Example

Assume a utility has an approved $245 million annual revenue requirement allocated as follows:

Customer class	Allocation	Class requirement
Residential	`55%`	`$134.75 million`
Commercial	`30%`	`$73.50 million`
Industrial	`15%`	`$36.75 million`

Suppose the residential design assigns 35% of the residential requirement to a fixed customer charge and 65% to an energy charge. The utility forecasts 500,000 residential customers, or 6 million customer-months, and 2.5 billion residential kilowatt-hours.

\text{Monthly Customer Charge} = \frac{\$134.75\text{m} \times 35\%}{6\text{m customer-months}} \approx \$7.86

\text{Energy Charge} = \frac{\$134.75\text{m} \times 65\%}{2.5\text{bn kWh}} \approx \$0.0350\text{/kWh}

These are simplified base charges. Taxes, fuel adjustments, transmission riders, efficiency programs, minimum bills, seasonal tiers, and other tariff components can change the final customer bill.

Common Rate Structures

Structure	How it charges	Main analytical tradeoff
Fixed customer charge	Amount per account or billing period	Revenue stability versus bill impact on low-use customers
Volumetric rate	Charge per unit consumed	Conservation signal versus sales and weather volatility
Demand charge	Charge based on peak or billed demand	Capacity cost signal versus customer complexity
Inclining block	Higher unit price at higher use tiers	Conservation and affordability design versus cost-causation debate
Declining block	Lower unit price at higher use tiers	Large-use economics versus conservation concern
Time-of-use	Price varies by time period	Peak-cost signal versus metering and customer-response uncertainty
Seasonal rate	Price changes by season	Reflects seasonal cost and demand but can increase bill volatility
Rider or tracker	Separate adjustment for a defined cost	Timely recovery but less review of the full base-rate relationship

Cost Causation and Policy

Cost-of-service studies attempt to connect costs with the customers, functions, or usage patterns that cause them. But rate design also involves policy choices. A commission may consider gradual changes, low-income impacts, economic development, distributed generation, conservation, electrification, reliability, or simplicity.

Those objectives can conflict. Recovering more fixed network cost through a customer charge stabilizes revenue but weakens the price signal for conservation and raises the minimum bill. Recovering more through usage charges strengthens the consumption signal but increases weather and volume risk.

How to Review a Tariff Change

Compare the old and new revenue requirement.
Separate the total company increase from each customer class’s allocation.
Identify every changed fixed, demand, usage, and rider component.
Recalculate rates using the approved billing determinants.
Test representative bills at low, average, and high usage.
Check seasonal, time-of-use, minimum-bill, and demand-ratchet effects.
Identify true-ups, refunds, caps, decoupling, and performance adjustments.

The Wisconsin Public Service Commission describes rate setting as balancing cost recovery, revenue stability, affordability, and other objectives. FERC’s electric transmission formula-rate guide illustrates how approved annual cost inputs can update under a formula and protocols. The controlling tariff and commission order remain necessary for a specific rate.

Risks and Limitations

Forecast billing determinants can be stale before rates take effect.
Average-rate comparisons can hide fixed-charge and class-allocation changes.
A customer bill may include costs approved by several regulators or mechanisms.
Rate design can shift costs among customer classes without changing total revenue.
Complex tariffs can make customer response and revenue forecasting difficult.
A headline percentage increase may not describe the effect on a specific usage profile.

Rate Case: A proceeding in which rate evidence and proposed changes are reviewed.
Revenue Requirement: The annual amount allocated and recovered through rates.
Cost of Service: The cost evidence supporting traditional rate setting.
Rate Base: The approved investment amount used in the return component.
Public Utility Commission (PUC): A state-level body that may approve utility rates.

FAQs

Is rate setting just the revenue requirement calculation?

No. It also includes cost allocation, selection of billing determinants, tariff design, implementation, and adjustment mechanisms.

Why can customers see different percentage changes?

Customer-class allocations, fixed charges, usage, demand, tiers, seasons, and riders can change differently even when all customers are served under one overall revenue requirement.

Does a lower energy rate always mean a lower bill?

No. A higher fixed charge, demand charge, rider, or minimum bill can offset a lower per-unit energy rate.

This material is educational and is not legal, regulatory, accounting, rate-design, or investment advice.

Rate Schedule

Rate-of-Return Regulation