Path-Q Solar
What battery degradation should I include in a long-term solar storage estimate?
Answer
Include a decline in usable energy capacity over time and account for both calendar aging and cycling. Use the specific battery warranty’s capacity-retention terms and operating assumptions when available, rather than applying one generic percentage to every system.
Key points
- Model usable capacity by year, not just initial nameplate capacity.
- Consider cycle depth, temperature, time, charging limits, and operating controls.
- Distinguish capacity degradation from inverter or control-equipment replacement.
- Include the warranty’s retention threshold, throughput limits, and remedy.
What it depends on
- Battery chemistry and design
- Expected cycles and depth of discharge
- Temperature and installation conditions
- Manufacturer warranty and replacement assumptions
Risks and trade-offs
- Optimistic degradation assumptions overstate future backup and savings.
- Conservative assumptions may make a system appear less attractive than its warranted performance.
- Warranty capacity retention does not necessarily guarantee a specific economic output.
Information you may need
- Manufacturer degradation and warranty documents
- Expected annual throughput and operating profile
- Usable capacity and reserve settings
- Long-term replacement and service assumptions
Your next step
What to do next
Request a year-by-year capacity forecast based on the quoted battery’s warranty and expected cycling, and run the economics using both base and conservative cases.
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SQ00359