Home Battery Sizing Guide for Los Angeles
Choosing the right battery size is the most important decision in a home storage project. Too small and the battery cannot cover your backup priorities. Too large and you pay for capacity you never use. We size every system through a load analysis specific to your home — not a rule-of-thumb guess. Tesla Certified Premium Installer.
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Capacity vs. power: understanding both before you size.
Battery sizing involves two separate measurements that both matter.
Capacity (kWh) — how long
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.
Power (kW) — what can run at once
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.
How we size a battery for your home.
- →Step 1: Identify backup priorities. Whole-home or essential-load? Which specific circuits need to stay live during an outage? Are you prioritizing backup resilience, daily solar self-consumption, or both?
- →Step 2: Review your usage data. We review your recent utility bills to estimate daily and monthly kWh usage, peak demand periods, and seasonal variation. This grounds the sizing in your real consumption — not an average-home assumption.
- →Step 3: Load calculation. We calculate the combined wattage of your critical backed-up loads (refrigerator, HVAC if applicable, lighting, outlets) and their startup peaks. This determines the minimum power output and capacity required.
- →Step 4: Solar pairing (if applicable). If your home has solar or is adding solar, we factor in expected daytime generation and battery recharging to model backup duration and daily self-consumption cycles.
- →Step 5: Specify units and configuration. Based on the load analysis, we specify the number of Tesla Powerwall 3 units or Enphase IQ Battery 5P modules, the backup reserve percentage, and the Gateway or System Controller configuration settings.
Approximate capacity by use case.
Note: these are illustrative ranges, not guarantees. Actual runtime depends on your specific loads, configuration, solar production, and temperature. We provide site-specific estimates, not these ranges, for project decisions.
Use the table as a starting point only. For project decisions, compare essential-load backup, whole-home backup, backup load panel planning, and PSPS outage planning.
What makes Los Angeles battery sizing different.
- →HVAC is the dominant load. In hot LA and OC summers, central HVAC accounts for the majority of household energy use during peak afternoon hours. Whether and how you back up the HVAC system is the single biggest decision in sizing a whole-home battery.
- →Solar production is high. LA’s high sun hours mean a properly paired solar + battery system can sustain backup for extended periods during daytime outages. We factor local irradiance and system orientation into our modeling.
- →PSPS outages can last days. In wildfire-risk zones served by SCE and in some LADWP areas, PSPS (Public Safety Power Shutoff) outages can last 24–96 hours or longer. Multi-day backup requires solar pairing or multiple battery units.
- →NEM 3.0 for SCE customers. For SCE customers, sizing for daily solar self-consumption under NEM 3.0 is also part of the sizing conversation — the battery handles both backup reserve and daily self-consumption optimization.
Start with a load-based sizing estimate.
We size every system through analysis of your actual usage, loads, and solar production — not a one-size formula. Tesla Powerwall and Enphase IQ Battery. Tesla Certified Premium Installer. CSLB #1055444.
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Home battery sizing questions.
How is home battery size measured and what does kWh mean?
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.
How many Powerwall units do I need for whole-home backup?
It depends on your home’s total electrical load and how many hours of backup you need. A small to medium home with modest loads may manage with one Tesla Powerwall 3 (13.5 kWh). Homes with larger loads, EV chargers, or pool equipment, or homes wanting extended multi-day backup with solar, may need two or more units. We size based on your actual load analysis — not a generic number.
What is the difference between battery power (kW) and capacity (kWh)?
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.
Should I size my battery for backup or for daily solar self-consumption?
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.
How does solar affect battery sizing?
Solar recharges the battery during daylight hours, which can extend backup duration significantly during daytime outages and enables daily self-consumption cycles. A home with solar may need less total battery capacity than the same home without solar, because the panels continuously replenish stored energy. We factor your solar system size and production profile into battery sizing during the estimate.
How do I know how many kWh my home uses per day?
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.
Can I add more batteries later if I start with one unit?
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.
Get a real battery sizing estimate for your home.
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