Path-Q Solar

How should I estimate solar savings when my utility charges different rates by time of day?

Answer

Estimate savings by matching hourly or interval electricity use with hourly solar production and applying the applicable rate to each period. Solar generation is usually worth more when it offsets consumption during expensive periods than when it is exported or offsets cheaper periods.

Key points

  • Use interval usage data if available rather than multiplying annual solar production by one average rate.
  • Model direct consumption, exports, storage charging and discharging, and any remaining grid purchases separately.
  • Include fixed charges and export-credit rules because solar may not eliminate them.

What it depends on

  • The utility's time-of-use periods and prices
  • Hourly household load and solar-production profiles
  • Export compensation, battery behavior, and system size
  • Seasonal changes in both usage and rate periods

Risks and trade-offs

  • A system that produces heavily during low-price periods may save less than its annual energy output suggests.
  • Changing usage to consume more solar can improve savings but may reduce convenience.
  • Battery storage can shift energy into expensive periods but adds cost, losses, and replacement considerations.

Information you may need

  • Current tariff, including time periods, prices, fixed charges, and export rules
  • Interval consumption data or a reasonable hourly load estimate
  • Hourly production estimates and any planned battery dispatch strategy

Your next step

What to do next

Create an hourly or monthly time-of-use model using the actual tariff and compare solar-only and solar-plus-storage cases.

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