Workspace
The calculator's own fields, action and results arrive with the verified pack when you load it. Nothing is computed in this page.
Hybrid & backup · the outage bill
Backup energy required for an outage
Price an outage in kilowatt-hours: the energy a constant load draws across the hours the grid is down, and the signed margin left in usable capacity.
Verified engine
What the engine returns
Two figures return: the energy the outage bills, and the signed margin left in the 10 kWh once that bill is paid. Here the margin is the reading that matters — it is the slack available for the outage running long, the load creeping up, or the bank being colder than its rating assumed. The rest of this cluster takes over from the bill: the inverter pages ask whether the load can be CARRIED at all, and the recharge page asks how long the sun needs to pay the deficit back.
Inputs the result is built from
Constant backup load
Outage duration to ride through
Available usable capacity
How the result is derived
MethodThe constant backup load is multiplied by the outage duration to give the energy required, and that requirement is subtracted from the available usable capacity to give a signed margin; the declared reverse workflow solves for the outage duration a fixed energy budget rides through.
StandardConstant-load outage energy, needed kWh = load kW × outage hours, with signed margin vs. usable capacity
GuardA zero outage duration is refused — the pack ships that refusal as a declared test vector. An interruption of no length has no energy bill, and a zero here almost always means the field was skipped rather than the grid never failing.
How the margin moves with the outage length
Which side of enough the margin lands
Why an outage is an energy bill, and the signed margin is the verdict
The first figure is the bill: power times duration is the energy the outage will draw through the meter that no longer runs. It is deliberately indifferent to WHERE that energy comes from — battery, generator, or a neighbour’s extension lead — because the demand exists before any supply is chosen, and mixing the two questions is how backup plans flatter themselves.
The second figure is the verdict. Subtracting the bill from the usable capacity on hand returns a margin in kilowatt-hours that keeps its sign: positive means the stored energy outlasts the interruption with something to spare, negative means the lights go out before the grid comes back, and the pack ships a declared warning that fires on exactly that shortfall rather than leaving it to be noticed.
The capacity term must be USABLE energy — the nameplate already discounted by the depth of discharge, as this pack’s battery cluster computes it. Entering the label figure here overstates the margin by the held-back fraction, which for some chemistries is half the battery, and turns a failing plan into a passing one on paper alone.
Read the shape of the relation: the bill grows linearly in both load and hours, so a plan has two equally priced levers. Shedding half the circuit buys the same hours as doubling the storage, and it is usually cheaper. The declared reverse workflow works the other lever for you — fix the energy available and it returns the outage duration that budget can ride through.
The constant backup load is multiplied by the outage duration to give the energy required, and that requirement is subtracted from the available usable capacity to give a signed margin; the declared reverse workflow solves for the outage duration a fixed energy budget rides through.
When this calculation is used
- Auditing an outage plan before buying anything: does the bank as installed actually cover the interruption being planned for?
- Sizing the deficit a generator or hybrid arrangement must make up when the margin comes back negative.
- Solving backwards — the declared reverse workflow — for the hours a fixed usable capacity can carry the essential circuit.
- Comparing load-shedding options on equal terms: rerun with each candidate circuit and watch the margin change sign.
Worked example
Run the pack’s own anchor: a 1 kW essential circuit — refrigeration, a router, some lights — riding through an 8-hour overnight outage, with 10 kWh of usable capacity standing behind it.
Two figures return: the energy the outage bills, and the signed margin left in the 10 kWh once that bill is paid. Here the margin is the reading that matters — it is the slack available for the outage running long, the load creeping up, or the bank being colder than its rating assumed. The rest of this cluster takes over from the bill: the inverter pages ask whether the load can be CARRIED at all, and the recharge page asks how long the sun needs to pay the deficit back.
The pack also declares the failing case: push the same 10 kWh against a 2 kW load for 6 hours and the margin returns negative, firing the declared shortfall warning. A signed margin is the point — a plan that fails on paper is a plan that can still be fixed.
What each input represents
Constant backup load
The steady power the backed-up circuit draws during the outage, in kilowatts. Use the time-averaged draw of the ESSENTIAL circuit from a meter or an energy audit, not the sum of every rating plate in the house — the outage bill should price what will actually run, and nothing that would be shed anyway.
Outage duration to ride through
How many hours the interruption is planned to last. Utility outage history, not optimism, is the honest source; fractional hours are legitimate for riding through a rolling blackout, and a multi-day storm belongs here as its hour count rather than in a separate mental unit.
Available usable capacity
The energy actually available to be drawn, in kilowatt-hours — nameplate already discounted by the depth of discharge. This is the figure the margin is judged against, so any flattery in it propagates straight into the verdict.
Assumptions and limits
- The load is constant for the whole outage; a duty-cycling circuit is represented only as well as its time-averaged power represents it.
- Discharge-path conversion losses are not deducted here — the runtime sibling carries the efficiency term — so the margin is slightly kinder than the wire.
- The usable capacity is taken as fully deliverable: no temperature derating, ageing fade or rate effect shrinks it, and each has its own sibling in this pack.
- Nothing recharges during the window. Any daytime solar contribution shortens the real bill, so the arithmetic is deliberately pessimistic in that direction.
What the guards protect against
- A zero outage duration is refused — the pack ships that refusal as a declared test vector. An interruption of no length has no energy bill, and a zero here almost always means the field was skipped rather than the grid never failing.
- The load must be positive and below a utility-scale cap: a zero load has nothing to back up, and a figure beyond the cap is far more likely a watt entry standing where kilowatts belong.
- The outage duration is bounded to hundreds of hours, not seasons — a figure entered in minutes, or a wish to ride out a whole winter, falls outside the declared range and is refused as a unit or scoping error rather than billed in silence.
Provenance
Constant-load outage energy, needed kWh = load kW × outage hours, with signed margin vs. usable capacity
The constant backup load is multiplied by the outage duration to give the energy required, and that requirement is subtracted from the available usable capacity to give a signed margin; the declared reverse workflow solves for the outage duration a fixed energy budget rides through.
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.