Battery sizing should balance stored energy, available power, motor-start requirements, selected backup circuits, solar production and outage goals. HUS reviews those inputs for the actual home instead of choosing battery count from square footage or a generic package.
Reviewed by Los Angeles & Orange County homeowners
Battery sizing involves two separate measurements that both matter.
Kilowatt-hours measure how much total energy the battery stores. More kWh = longer backup duration for a given load. Tesla Powerwall 3: 13.5 kWh per unit. Enphase IQ Battery 5P: 5.0 kWh per module.
This determines how many hours your backed-up circuits can run before the battery depletes — assuming no solar recharging.
Kilowatts measure how much energy the battery can deliver simultaneously. A battery must have adequate continuous power output to handle peak startup draws — HVAC compressors, refrigerators, and other motor loads draw more on startup than at steady state.
Low power output means the battery may trip under heavy load even if it has stored energy remaining.
Battery count should come from measured or documented loads, not a generic home category. These are the inputs that change the design most.
For project decisions, compare essential-load backup, whole-home backup, backup load panel planning, and outage planning.
We review actual usage, priority loads, motor-start requirements, electrical architecture and expected solar production before recommending battery quantity or configuration. Tesla Powerwall and Enphase IQ Battery planning. Tesla Certified Premium Installer.
Battery capacity is measured in kilowatt-hours (kWh) — the amount of energy a battery can store and deliver. A 13.5 kWh battery (like one Tesla Powerwall 3) can theoretically power a 1,000-watt load for 13.5 hours, or a 2,000-watt load for about 6.75 hours. Actual runtime varies based on load mix, inverter efficiency, temperature, and battery state of health.
There is no reliable battery count based on home size alone. Whole-home backup sizing depends on the actual circuits and appliances to be supported, motor-start requirements, simultaneous demand, desired outage duration, available solar production, electrical architecture and system settings. One Powerwall may fit some designs while other homes require multiple units or load-management changes. We size from the actual load plan rather than a generic number.
Capacity (kWh) is how much energy the battery can store — it determines how long backup lasts. Power (kW) is how much energy the battery can deliver at once — it determines which loads can run simultaneously. A battery with high capacity but low power output may not be able to start an HVAC compressor even if it has plenty of stored energy. Tesla Powerwall 3 offers both high capacity (13.5 kWh) and high continuous power output.
Many homeowners want both. Sizing for backup means holding enough reserve capacity to cover critical loads during an outage. Sizing for solar self-consumption means matching battery capacity to your daily excess solar production. These goals often align — a properly sized battery can do both — but the priority affects how the battery is configured and what reserve percentage is set. We discuss both goals during your estimate and design to fit both where possible.
Solar may recharge the battery during an outage when the approved system configuration allows islanded solar operation and there is enough production after serving household loads. The amount of recharge varies with system size, shade, orientation, weather, inverter configuration and actual usage. We include the expected production profile in battery sizing rather than assuming solar continuously replenishes the battery.
Your utility bill shows monthly kWh consumption — divide by 30 for a rough daily average. The Tesla app and Enphase Enlighten app can give more granular data if a system is already installed. We review your recent utility bills and usage data during the estimate to inform our sizing analysis.
In many cases, yes. Tesla Powerwall 3 supports multiple units per installation, and Enphase IQ Battery 5P modules are inherently modular. However, adding units later may require panel space assessment and potentially additional electrical work. We design installations with future expansion in mind where possible and specify what a future expansion would require.
Tesla Certified Premium Installer. CSLB #1055444. We are not a tax advisor — consult a qualified professional for tax questions.
