Path-Q Solar

How should battery degradation affect the capacity I install initially?

Answer

Size the battery for the usable capacity you need near the end of its expected service life, not only when new. Use the manufacturer's warranted end-of-term capacity, expected cycling, operating temperature, and planned reserve rather than assuming a fixed degradation rate.

Key points

  • Distinguish nameplate capacity from usable capacity and warranted remaining capacity.
  • Oversizing can preserve future backup duration but increases upfront cost and may reduce financial payback.
  • A larger system may also operate less efficiently if it is rarely used.

What it depends on

  • Required backup loads and duration
  • Expected daily cycling and seasonal use
  • Manufacturer warranty capacity guarantee and test conditions
  • Temperature, installation conditions, and future expansion compatibility

Risks and trade-offs

  • Under-sizing may leave insufficient capacity later in the battery's life.
  • Over-sizing ties up capital and does not necessarily eliminate the need for eventual replacement.
  • Warranty capacity figures may not equal the energy available under every operating condition.

Information you may need

  • The loads the battery must support
  • Target backup duration and reserve level
  • The battery's usable capacity, degradation warranty, and expansion rules

Your next step

What to do next

Ask for a capacity-at-warranty-end calculation using your expected cycling pattern and required backup loads.

Path-Q

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SQ01273