SUN RAY SOLUTIONS · SOLAR TOOLS

How long could a battery last?

Build a backup-load example and compare stored energy with what you want to run. Use your equipment’s actual values when available.

No signup required · Editable examples · Updated September 24, 2026

Energy-based runtime 24.5 hoursSee result details

Your battery scenario

All starting numbers are editable examples. They do not describe a specific product or a recommended system.

Usable battery capacity (kWh)Total usable storage across the proposed system, before the charge window below.Continuous AC output (kW)Use the system-level backup rating. Do not assume individual ratings simply add.Charge when outage starts (%)Check your starting state of charge.Charge retained / unavailable (%)Scenario floor. Verify how the actual system handles reserve during an outage.Energy delivered to loads (%)Example discharge allowance. Use 100% if usable capacity already accounts for these losses.Target backup time (hours)Estimate energy needed for this duration, without solar recharging.

What stays on?

Enter running watts and the share of time each load runs. Examples are assumptions, not appliance ratings.

Up to 10 loads. Use measured consumption when possible.

The math behind the plan

Available energy = usable capacity × (starting charge − retained charge) ÷ 100 × delivery percentage ÷ 100.

Average load = sum of each running wattage × its running-time share. Runtime = available kWh ÷ average kW. Capacity for your target = average kW × target hours ÷ the charge-window fraction ÷ delivery fraction.

The power comparison sums active loads as if they run together. It does not model motor-starting surges. A runtime can look adequate while the equipment’s power output is insufficient.

The California Air Resources Board backup-power guide explains the difference between stored energy, power demand, and runtime. Our example inputs are independent; no agency or manufacturer endorsement is implied.

REVIEW YOUR PROJECT

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Use the button above to add your inputs to this request. We confirm equipment, access, scope, and pricing before work is approved.

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Share what you know. We can work through the rest with you.

Proposed work dateEquipment brand/model, if knownWhat would you like to power in an outage?For example: refrigerator, lights, office, or air conditioning.Monthly electricity use or bill, if knownHow did you hear about us? (optional)Anything else we should know?

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