Path-Q Solar

How should I calculate solar savings when my electricity bill includes substantial non-energy charges?

Answer

Separate the bill into charges that solar can avoid, reduce, or shift and charges that remain regardless of solar production. Calculate savings only from the affected components, while modeling any demand, fixed, minimum, or export-related charges separately.

Key points

  • Classify energy charges, demand charges, fixed customer charges, taxes, riders, minimum charges, and other line items.
  • Determine whether each component changes with imported energy, peak demand, exports, or system size.
  • Do not assume that reducing kilowatt-hours eliminates the entire bill.
  • Use actual bills and the applicable rate structure rather than a single average cost per kilowatt-hour.

What it depends on

  • Detailed bill line items
  • Applicable tariff and rate structure
  • Interval load and production timing
  • Export compensation and demand-charge treatment

Risks and trade-offs

  • Treating fixed charges as avoidable overstates savings and understates payback.
  • A system may reduce energy charges but have little effect on demand or minimum charges.
  • Rate changes or changes in usage can alter the value of the system.

Information you may need

  • Recent detailed electricity bills
  • Applicable tariff or rate schedule
  • Interval usage if available
  • Solar production and export assumptions

Your next step

What to do next

Create a line-by-line bill model that labels each charge as fixed, usage-based, demand-based, export-related, or uncertain, then verify the uncertain categories with the utility or qualified adviser.

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