Methodology
Calculation version 2: a simplified planning model. It is not a claim of laboratory accuracy. Updated October 1, 2026.
Sizing
Operating mode: quantity × operating W × active hours × duty fraction. Average mode: quantity × average W × hours, with no second duty factor. Daily-energy mode: quantity × kWh/day × 1,000 × (plan hours ÷ 24).
Route energy is divided by the selected AC, USB, or DC efficiency. AC idle W × enabled hours is added only when AC loads exist. Required nominal capacity is battery-side energy ÷ [health × (start charge − reserve)]. Charge reserve and health are applied exactly once.
Runtime
Available energy is capacity × health × (start charge − reserve). Battery-side power is AC average W ÷ AC efficiency + USB average W ÷ USB efficiency + DC average W ÷ DC efficiency + AC idle power when enabled. Runtime is available energy ÷ battery-side power. A zero load has no runtime result.
Output and startup
Instantaneous AC demand sums quantity × operating W without duty-cycle reduction. Planning output applies the editable headroom once. Startup checks require documented magnitude and duration for both the load and station. Missing startup duration or operating demand leaves the check unknown. Supply voltage and frequency, USB power profiles, DC connectors, polarity, and shared port limits require separate manual confirmation; the calculator does not establish these connections. Marketing boost modes are not substituted for continuous or surge ratings.
Solar, charging cost, and conversion
Solar steady input is the lower of derated panel watts and the station limit, multiplied by charging efficiency, less concurrent battery-side load. When more energy is needed, nonpositive net power produces no charging time. A target already reached needs zero additional hours. Wall energy for a charge is stored-energy change ÷ charging efficiency. Wh equals Ah × nominal voltage.
Time windows and unknown inputs
Hours in an operating or average-watts row are total active hours within the plan window. Daily kWh is scaled to the full plan window. Average watts and daily energy already include the measured cycling; neither gets another duty factor. AC-enabled hours must cover the longest active AC row, and a daily AC energy row requires AC to remain available throughout the plan.
Instantaneous demand assumes enabled AC devices may run together. Startup scenarios consider one device starting while the others run; this does not prove multiple starts cannot overlap. A declared absence of additional startup demand must be justified by the equipment, not inferred from a low average.
Missing or invalid inputs produce a validation message or an unknown check. They are not interpreted as zero. A catalog match can satisfy the calculated energy requirement while output or connection checks still need confirmation.
Worked illustration
An illustrative eight-hour AC work session
This example uses a 60 W laptop, 30 W monitor, and 12 W router for eight hours inside a 24-hour plan. It keeps AC enabled for those eight hours. Replace every load with your own measurements.
- Energy delivered to the devices
- 816 Wh
- Estimated nominal battery capacity required
- 1,111 Wh
Assumptions: full starting charge, 10% stopping reserve, 100% capacity factor, 85% AC efficiency, and 90% USB/DC efficiency. AC idle draw is 5 W for 8 hours when an AC load is present. Values are rounded for display.
Operating and startup power are intentionally unestablished in this energy illustration. Check those requirements and the actual connections before choosing equipment.
Daily solar balance and charging boundaries
The optional solar daily balance uses stored input power × peak-sun-hours − concurrent battery-side watts × 24. It assumes that load continues all day and does not simulate hourly sunlight, overnight battery state, or weather. A positive balance is not a guarantee of continuous service.
Charging cost includes only the modeled charge interval and the entered per-kWh tariff. It excludes simultaneous appliance use, equipment cost, fixed charges, and unentered fees. Wh/Ah conversion uses the nominal voltage associated with the battery rating and does not estimate output losses.
Assumption sensitivity
Where shown, lower-loss uses AC 90%, USB/DC 95%, and 2 W AC idle; baseline uses visitor inputs; higher-loss uses AC 75%, USB/DC 80%, and 10 W idle. It holds consumption, reserve, and health constant and sorts outcomes numerically. This is not a confidence interval, probability, verified range, or worst case.
Evidence labels
Verified means the displayed core facts are traceable to cited manufacturer evidence for the identified market. Incomplete means important fields remain unresolved. Conflicted records a material disagreement rather than averaging it. Each consequential product group retains source IDs and a real access date.
What is not tested
The site does not conduct hands-on runtime, thermal, acoustic, safety, charge-curve, or efficiency testing. Calculated examples are labeled as estimates. It does not provide medical assurance, whole-home design, transfer-switch guidance, DIY mains work, solar wiring design, weather forecasts, or guaranteed outage coverage.
Corrections and versions
Use the contact and corrections page to report evidence errors. Corrections update the relevant record, verification date, and modified date. Formula changes increment the calculation version; shared links restore inputs and recalculate under the current method.