Path-Q Solar
How do I calculate solar payback when my electricity use may increase later?
Answer
Model payback with time-based consumption scenarios rather than assuming either today's use or immediate future use. Calculate annual net savings for a baseline, likely-growth, and conservative-growth case, then identify when cumulative savings exceed the relevant project cost under each case.
Key points
- Estimate when new loads begin, how much energy they use, and when they operate.
- Separate energy produced, energy used directly, energy stored, and energy exported.
- Include panel degradation, changing consumption, operating costs, financing, and any applicable current bill rules.
- Report a range or scenario results instead of a single precise payback year.
What it depends on
- Current consumption and load profile
- Timing and size of future loads
- System production and degradation
- Electricity prices, bill structure, exports, financing, and project cost
Risks and trade-offs
- Future usage may not occur as expected, reducing the value of early oversizing.
- Higher future consumption can improve self-consumption but may require system or service capacity that is not available.
- Payback is sensitive to assumptions that may change over time.
Information you may need
- Historical and preferably interval electricity use
- Future appliance or electrification plans
- Production, cost, financing, and current bill assumptions
Your next step
What to do next
Build a scenario spreadsheet with current, expected-growth, and delayed-growth cases and compare cumulative cash flow for each.
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Some details may depend on your location, installer, utility, incentives, regulations, or specific property.
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