Path-Q Solar
How does a partial solar offset change the system's payback period?
Answer
A partial offset can shorten or lengthen payback depending on which electricity use is offset and how additional generation is valued. A smaller system may have strong value if it offsets high-value on-site consumption, while a larger system may have lower marginal value if more output is exported or compensated at a lower rate.
Key points
- Payback is based on the value of avoided and exported electricity, not simply the percentage of annual consumption covered.
- Time-of-use pricing, demand patterns, storage, and export rules affect the value of generation.
- A partial system may reduce upfront cost and unused production risk.
- Increasing offset can provide more savings but may have diminishing returns.
What it depends on
- Annual consumption and hourly usage pattern
- System size, orientation, shading, and production
- On-site consumption and export compensation
- Electricity rates and future rate assumptions
Risks and trade-offs
- A percentage-offset estimate can conceal low-value exported energy.
- Future consumption changes can make the selected system size less suitable.
- Underestimating degradation or overestimating bill savings can lengthen actual payback.
Information you may need
- At least one year of interval or detailed usage data if available
- Production estimates for multiple system sizes
- Export and billing assumptions
- Planned changes in occupancy, appliances, or electrification
Your next step
What to do next
Compare several system sizes using the same assumptions and calculate payback from actual bill reduction rather than annual kilowatt-hours alone.
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