Path-Q Solar
How should I calculate savings when solar exports are compensated differently from imported electricity?
Answer
Calculate bill savings hour by hour or billing interval: value solar used on site at the avoided import cost and exported solar at the applicable export compensation, then account for demand-charge effects and any fixed or minimum charges that actually change. Unchanged fixed charges cancel in a before-and-after bill comparison. Treat system, operating, and financing costs separately when calculating net cash flow rather than bill savings.
Key points
- Self-consumed generation usually has a different value from exported generation when import and export rates differ.
- Include timing, billing tiers, time-based rates, minimum charges, and any demand components that apply.
- Use actual or modeled production and consumption profiles to determine self-consumption and exports.
- Separate bill savings from incentives, tax effects, financing costs, and maintenance.
What it depends on
- Import tariff and billing structure
- Export compensation rules
- Hourly or interval consumption
- Solar production profile
- Fixed charges and demand-related billing
Risks and trade-offs
- Using an average retail rate can materially overstate savings.
- Future tariff or export-rule changes can alter the result.
- A larger system may produce more energy but a lower value per additional kilowatt-hour.
Information you may need
- Current tariff and export terms
- Interval or monthly usage data
- Solar production estimate
- System cost, financing, and operating assumptions
Your next step
What to do next
Build an interval-based bill-savings model using the applicable tariff and export rules, then add system and financing costs in a separate net-cash-flow analysis and test sensitivity to possible future changes.
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