Workspace
The calculator's own fields, action and results arrive with the verified pack when you load it. Nothing is computed in this page.
Bank sizing · nameplate to usable
Usable capacity from depth of discharge
Discount a battery bank’s nameplate by its depth of discharge to find the energy a load can actually draw — label capacity versus capacity in service.
Verified engine
What the engine returns
What returns is the usable capacity in kilowatt-hours — the slice of the label a load may actually consume. Hold it against the two days of demand the autonomy sizing promised to cover: the two figures should agree, because this multiplication is that sizing division run back the other way. It is also the number to carry into the runtime page, which turns energy into hours, and into the cycle-cost page, which prices it.
Inputs the result is built from
Nameplate bank size
Depth of discharge (fraction)
How the result is derived
MethodThe nameplate bank size is multiplied by the depth-of-discharge fraction, returning the usable energy in kilowatt-hours; the declared reverse workflow solves for the nameplate a required usable capacity demands.
StandardNameplate-to-usable relation, usable kWh = bank kWh × depth of discharge
GuardA depth of discharge above one is refused — the pack declares that refusal as a test vector. No design can draw more than the bank holds, and the ceiling catches percentages entered where decimal fractions belong before they inflate the usable figure a hundredfold.
How the usable capacity moves with depth of discharge
The usable share of the nameplate bank
What stands between the label on a battery and the energy a load can draw
The nameplate is a property of the hardware; the usable capacity is a property of the DESIGN. Between them sits a choice: how deeply each cycle is allowed to bite. In service that choice is enforced by the battery management system’s cutoff, so the held-back remainder is not a hidden reserve a determined user can raid — it is capacity the installation has decided, for good reasons, never to touch.
The reason is longevity. Cycle life and cycling depth trade against each other in every chemistry: cells cycled shallow outlast the same cells cycled deep, often by a large multiple, so the depth of discharge is where hardware life is purchased with capacity. This pack carries a dedicated depth-versus-life sibling for that curve; here the chosen fraction simply arrives as an input, preferably straight from the manufacturer’s rating at the cycle count the design targets.
Usable energy is the currency the rest of this cluster trades in. The sizing page divided by this same fraction to demand a nameplate; the runtime page consumes the usable figure this page produces; the cycle-cost page amortises the bank over it. Whenever two battery quotations disagree confusingly, converting both to usable kilowatt-hours is the fastest way to make them commensurable, because different chemistries wear very different fractions on the same size of label.
The relation is a single factor, and that plainness is the point: the discount never compounds and nothing else hides in it. The pack also declares the reverse workflow — fix the usable energy a plan requires, and the engine returns the nameplate to shop for, which is the direction a purchase actually runs.
The nameplate bank size is multiplied by the depth-of-discharge fraction, returning the usable energy in kilowatt-hours; the declared reverse workflow solves for the nameplate a required usable capacity demands.
When this calculation is used
- Comparing quoted banks on one scale, where different chemistries put very different usable fractions behind similar-looking nameplates.
- Translating a spec sheet into the energy an outage plan can actually count on before any runtime arithmetic begins.
- Solving backwards — the declared reverse workflow — from the usable energy a design requires to the nameplate that must be purchased.
- Auditing an installed system, where the energy metered out before the cutoff engages should track the label times the configured depth.
Worked example
Stay with the cluster’s reference system: the pack’s anchor carries the sizing scenario’s bank forward at 25 kWh of nameplate, operated at the same 0.8 depth of discharge the sizing assumed.
What returns is the usable capacity in kilowatt-hours — the slice of the label a load may actually consume. Hold it against the two days of demand the autonomy sizing promised to cover: the two figures should agree, because this multiplication is that sizing division run back the other way. It is also the number to carry into the runtime page, which turns energy into hours, and into the cycle-cost page, which prices it.
Run the same 25 kWh label at half the depth of discharge and the usable energy falls in exact proportion — same nameplate, materially smaller battery in service. That is why a bank is never fully described by the number in its product name.
What each input represents
Nameplate bank size
The rated energy capacity on the bank’s label, in kilowatt-hours — the figure quotations and datasheets lead with. Use the as-built total across every module actually installed. It is a rating at nominal conditions, not a measurement, and everything this page says flows from discounting it rather than trusting it.
Depth of discharge (fraction)
The fraction of the nameplate the design permits each cycle to draw, as a decimal strictly between zero and one. Take it from the manufacturer’s rating at the cycle life the design targets, not from optimism: the same cells carry different honest fractions depending on how long they are expected to last. The default supplied here is illustrative only.
Assumptions and limits
- The depth of discharge is treated as a hard boundary, enforced exactly; real cutoffs engage across a small band of voltage rather than at a razor edge.
- The nameplate is taken at face value and at nominal temperature — cold weather shrinks deliverable capacity below the label, and this pack’s temperature-derating sibling handles that.
- The figure describes a healthy bank. Calendar and cycle ageing fade the nameplate itself over the years, which the pack’s degradation calculators estimate separately.
- Usable energy is counted at the battery terminals: inverter and wiring losses on the way to a load are the runtime page’s efficiency term, not part of this discount.
What the guards protect against
- A depth of discharge above one is refused — the pack declares that refusal as a test vector. No design can draw more than the bank holds, and the ceiling catches percentages entered where decimal fractions belong before they inflate the usable figure a hundredfold.
- The depth must also exceed zero: a zero fraction describes a bank nothing may draw from, and the engine refuses to dress that up as a usable capacity of nothing.
- The nameplate must be positive and below a utility-scale cap, which turns a watt-hour figure entered where kilowatt-hours belong into a refusal instead of a thousandfold error travelling into every downstream page.
Provenance
Nameplate-to-usable relation, usable kWh = bank kWh × depth of discharge
The nameplate bank size is multiplied by the depth-of-discharge fraction, returning the usable energy in kilowatt-hours; the declared reverse workflow solves for the nameplate a required usable capacity demands.
Screening and reference material, to be checked against the governing standard and a qualified engineer; not a design determination. The signed pack carries its own citation, and the page reports the verification state of the release it mounted.