Home Battery Backup (Powerwall / LFP) Outage Runtime & Solar Recharge Calculator

Compute home battery backup runtime hours for critical loads and daily solar recharge surplus.

Single-Charge Battery Outage Runtime
13.15 hours
Net Usable AC Battery Capacity 11.18 kWh
24-Hour Critical Load Consumption 20.4 kWh/day
Daily Solar Surplus / Deficit -3.84 kWh/day
Inputs
⚡ Scenarios:
kWh
Total installed battery nameplate capacity (e.g., 13.5 kWh per unit).
%
Usable Depth of Discharge % above low-voltage reserve.
%
Hybrid inverter DC-to-AC conversion efficiency (%).
W
Average continuous power draw of backed-up circuits (fridge, Wi-Fi, lights, well/sump).
kWh/day
Average daily solar PV generation available to recharge battery during outage.
Results & Graph
Single-Charge Battery Outage Runtime
13.15 hours
Net Usable AC Battery Capacity
11.18 kWh
24-Hour Critical Load Consumption
20.4 kWh/day
Daily Solar Surplus / Deficit
-3.84 kWh/day

Single-Charge Battery Outage Runtime

Graph 1 • Home Battery Backup Runtime • Domain Architecture & Live Telemetry Maps Battery Nameplate Capacity Kwh, Usable Do D After Reserve Pct, Inverter Round Trip Efficiency Pct through Home Battery Backup Runtime Formula.
Home Battery Backup Runtime • Generation → Conversion → Storage Bus 1. SOURCE / ARRAY 13.5 kWh Battery Nameplate Capa 2. DELIVERED RATING 13.15 hours Single-Charge Battery Ou 3. SECONDARY OUTPUT 11.18 kWh Net Usable AC Battery Ca
Graph 2 • Single-Charge Battery Outage Runtime Across Battery Nameplate Capacity Kwh Sweep (40% → 160%) Evaluates UsableKwh = NameplateKwh × (DoD% − Reserve%) × InverterEff%; RuntimeHo across 7 operating points (current input highlighted).
0 hours 11.57 hours 23.14 hours 5.26 5.40kWh 7.89 8.10kWh 10.52 10.80kWh 13.15 13.50kWh 15.78 16.20kWh 18.41 18.90kWh 21.04 21.60kWh
Graph 3 • Joint Sensitivity: Battery Nameplate Capacity Kwh × Usable Do D After Reserve Pct Compares Single-Charge Battery Outage Runtime when Usable Do D After Reserve Pct is shifted +25% (solid) vs. −25% (dashed).
0 hours 10.45 hours 20.90 hours --- Usable Do D After Reserve Pct @ 75% 10.23 -30% 12.41 -15% 14.61 +0% 16.80 +15% 19 +30%
Summary: 13.5 kWh nameplate delivers 11.18 usable AC kWh, powering an 850 W critical load for 13.2 hours without solar (daily load 20.4 kWh/day vs. 18 kWh solar).
Summary: 13.5 kWh nameplate delivers 11.18 usable AC kWh, powering an 850 W critical load for 13.2 hours without solar (daily load 20.4 kWh/day vs. 18 kWh solar).
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Interactive chart & math engine powered by CalculatorGraph

Formula & Mathematical Methodology: Home Battery Backup Runtime Formula

UsableKwh = NameplateKwh × (DoD% − Reserve%) × InverterEff%
RuntimeHours = UsableKwh / CriticalLoadKw
UsableKwh = NameplateKwh × (DoD% − Reserve%) × InverterEff%; RuntimeHours = UsableKwh / CriticalLoadKw
  • batteryNameplateCapacityKwh: Total installed battery nameplate capacity (e.g., 13.5 kWh per unit).
  • usableDoDAfterReservePct: Usable Depth of Discharge % above low-voltage reserve.
  • inverterRoundTripEfficiencyPct: Hybrid inverter DC-to-AC conversion efficiency (%).
  • averageCriticalLoadWatts: Average continuous power draw of backed-up circuits (fridge, Wi-Fi, lights, well/sump).
  • dailySolarGenerationKwh: Average daily solar PV generation available to recharge battery during outage.

Rounding: Internal floating-point calculations preserve full precision; currency and percentage outputs round to 2 decimal places.

Worked Example: Home Battery Backup Runtime Worked Example

Compute home battery backup runtime hours for critical loads and daily solar recharge surplus.

  1. Enter your operational, financial, or physical measurement inputs.
  2. Apply the standard domain equation: UsableKwh = NameplateKwh × (DoD% − Reserve%) × InverterEff%; RuntimeHours = UsableKwh / CriticalLoadKw.
  3. Review the primary result, sensitivity metrics, and 3 interactive SVG graphs.
Result: Calculates Home Battery Backup Runtime via UsableKwh = NameplateKwh × (DoD% − Reserve%) × InverterEff%; RuntimeHours = UsableKwh / CriticalLoadKw.

Frequently Asked Questions

How does the Home Battery Backup (Powerwall / LFP) Outage Runtime & Solar Recharge Calculator calculate results?

It computes UsableKwh = NameplateKwh × (DoD% − Reserve%) × InverterEff%; RuntimeHours = UsableKwh / CriticalLoadKw directly in your browser and updates three custom SVG visualizations in real time.

Can I use Goal Seek to solve backwards for any input variable?

Yes. Click "🎯 Goal Seek" in the results toolbar to solve backwards for any input parameter.

Are my business and personal numbers kept private?

Yes. All calculations execute 100% locally in your browser with zero server transmission.

Everyday Life · Home Energy & Utilities

Home Battery Backup (Powerwall / LFP) Outage Runtime & Solar Recharge Calculator: inputs, method, and how to read the result

Compute home battery backup runtime hours for critical loads and daily solar recharge surplus.

Choose inputs for the case you are checking

The defaults are illustrative. Replace them with values for your case and keep the units shown beside each field.

  • Battery Nameplate Capacity Kwh: Total installed battery nameplate capacity (e.g., 13.5 kWh per unit).
  • Usable Do D After Reserve Pct: Usable Depth of Discharge % above low-voltage reserve.
  • Inverter Round Trip Efficiency Pct: Hybrid inverter DC-to-AC conversion efficiency (%).
  • Average Critical Load Watts: Average continuous power draw of backed-up circuits (fridge, Wi-Fi, lights, well/sump).

What the calculation includes

With the default values shown, Single-Charge Battery Outage Runtime is 13.15 hours. The calculation follows Home Battery Backup Runtime Formula; the formula and variable definitions above show how the inputs combine.

One-input check: With the other defaults held constant, changing Battery Nameplate Capacity Kwh from 13.5 kWh to 14.85 kWh changes Single-Charge Battery Outage Runtime from 13.15 hours to 14.47 hours. This is a comparison inside the calculator's stated model, not a prediction.

Where to use caution

  • Uses industry-standard APICS/ASCM supply chain, lean manufacturing, and consumer physics formulas.
  • Actual commercial freight tariffs, marketplace commissions, and utility rates vary by carrier and contract.

Scope: Global Supply Chain, Business & Consumer Standard Check the assumptions and limitations against your situation before relying on the estimate.

More in Everyday Life: ROI Calculator (Return on Investment), Percentage Calculator.