What size battery is needed to run a house?
The battery size required to power a household depends on daily energy consumption and backup duration needs. For example, a typical U.S. home uses ~30 kWh/day. A 10–15 kWh lithium-ion battery system can support critical loads (e.g., refrigeration, lighting) for 8–12 hours, while full off-grid setups may require 20–40 kWh paired with solar. Always calculate peak load demands and depth of discharge (DoD) limits—lithium batteries often permit 80–90% DoD versus 50% for lead-acid.
How is household battery capacity calculated?
Battery capacity hinges on daily kWh usage and desired autonomy days. First, sum critical appliances’ watt-hours (e.g., fridge: 1.5kWh/day + lights: 2kWh). Multiply by backup days needed, then divide by battery DoD. For a 15kWh/day load with 2-day backup using lithium (90% DoD): (15×2)/0.9 = 33.3 kWh system. Pro Tip: Add 20% buffer for inverter losses and aging.
To break it down, start by auditing energy usage. A 3,000 sq.ft. home might require 30 kWh daily, but prioritizing essentials reduces this to 10–15 kWh. Lithium-ion batteries, with their higher efficiency (95% vs. lead-acid’s 80%), are preferred. For instance, a 10 kWh lithium battery at 90% DoD delivers 9 kWh usable—enough to run a 1.5-ton AC for 3 hours. Transitionally, if you’re using high-watt devices like electric heaters (1.5 kW), runtime plummets, emphasizing load management. Real-world example: A Texas homeowner with solar panels paired a 20 kWh battery to cover nighttime loads (8 kW peak), achieving 18 hours of backup. Always size inverters to match surge currents—oversizing by 25% prevents tripping during motor startups.
What factors reduce effective battery capacity?
Temperature, discharge rate, and aging slash usable capacity. Lithium batteries lose ~20% capacity at -10°C; lead-acid drops 50% below 0°C. High discharge rates (e.g., running power tools) can reduce effective capacity by 15–30% due to Peukert’s effect.
Battery performance isn’t just about specs. Cold weather drastically impacts chemical reactions—lithium’s capacity at freezing temps may dip to 80%, while lead-acid struggles below 50%. What if you’re running a welder? Rapid discharges generate heat, accelerating degradation. Pro Tip: Keep batteries in climate-controlled spaces (15–25°C ideal). A 10kWh battery cycled daily at 80% DoD lasts ~3,500 cycles (10 years), but at 100% DoD, lifespan halves. Transitionally, consider hybrid systems: Pairing a 48V lithium battery with a generator for peak loads extends runtime. For example, a cabin using a 5 kW inverter saw 30% longer backup by preheating batteries in winter. Tables below compare lithium and lead-acid under stress:
| Factor | Lithium-ion | Lead-acid |
|---|---|---|
| Capacity at -10°C | 80% | 40% |
| Cycle Life at 80% DoD | 3,500 | 600 |
RackBattery Expert Insight
FAQs
Briefly—yes, but runtime depends on AC size. A 3-ton unit (3.5 kW) drains 10kWh in ~2.5 hours. Pair with solar or limit usage to evenings.
How long do home batteries last?
Lithium batteries typically last 10–15 years (3,000–5,000 cycles at 80% DoD). Lead-acid lasts 3–7 years but requires more maintenance.