Path-Q Solar
How should a battery quote identify the difference between usable and nominal capacity?
Answer
The quote should state nominal capacity and usable capacity separately, in the same units, and explain the operating limits or reserve that account for the difference.
Key points
- Nominal capacity is the battery's rated total storage; usable capacity is the amount available for the stated operating conditions.
- The quote should identify usable capacity at installation and any assumed depth-of-discharge or backup reserve.
- Compare proposals using usable capacity, usable power, duration, and warranty limits rather than nominal capacity alone.
What it depends on
- The battery model and operating mode
- Reserve settings and depth-of-discharge limits
- Whether capacity is stated at installation or at a later warranty point
Risks and trade-offs
- A larger nominal battery may provide less usable energy than a smaller battery with a higher usable fraction.
- Using the full capacity may affect battery life or warranty conditions.
- Usable energy and usable power are different; a battery may store enough energy but not support the required loads.
Information you may need
- Nominal and usable kWh
- Continuous and peak kW ratings
- Reserve, discharge, temperature, and warranty assumptions
- Whether the quoted capacity is guaranteed at a specified date or condition
Your next step
What to do next
Request a revised comparison table showing nominal kWh, usable kWh, usable kW, reserve percentage, and warranty capacity terms for every proposal.
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