How big of a battery would you need to power a house?
Household battery systems typically require 10–20kWh capacity for daily use, depending on energy consumption patterns and backup duration needs. For homes with solar integration, sizing focuses on offsetting peak-rate grid usage (e.g., covering 2/3 of evening loads). Off-grid systems prioritize critical loads like refrigeration and lighting, often demanding 15–30kWh. Lithium-ion batteries (LiFePO4/NMC) dominate due to 90–95% efficiency and 3,000–6,000 cycle lifespans.
How is home battery capacity calculated?
Capacity hinges on load analysis and uptime goals. First, sum your essential appliances’ wattage (e.g., fridge 700W + lights 300W = 1kW). Multiply by desired runtime hours, then divide by battery voltage (48V common) and depth of discharge (DoD, 80% for LiFePO4). For 8-hour backup: (1,000W × 8h) ÷ (48V × 0.8) ≈ 208Ah.
Practically speaking, a 10kWh system (48V/208Ah) sustains 1kW loads for ~8 hours. But what if you need air conditioning? A 3-ton HVAC unit draws 3,500W, requiring 3.5kWh per hour. Here’s where tiered load prioritization helps—automatically shedding non-essentials during outages. Pro Tip: Use energy monitors like Sense or Emporia for 30-day consumption tracking to size accurately.
What’s the difference between solar backup and off-grid systems?
Solar backup batteries (5–15kWh) supplement grid power, storing excess daytime generation for evening use. Off-grid systems (20–50kWh) must handle 100% load coverage, requiring detailed seasonal usage analysis. Consider a Texas home with 25kWh daily use: A hybrid system with 15kWh battery + 10kW solar array cuts grid reliance by 70%, while full off-grid needs 25kWh storage plus 30% panel overcapacity for cloudy days.
| Parameter | Solar Backup | Off-Grid |
|---|---|---|
| Typical Capacity | 10–15kWh | 25–50kWh |
| Solar Integration | Grid-assisted | Mandatory 150% load coverage |
| Cost (USD) | $8,000–$15,000 | $25,000–$50,000+ |
How do battery chemistries affect capacity planning?
Lead-acid vs lithium-ion tradeoffs directly impact capacity needs. Though cheaper upfront, lead-acid’s 50% DoD limit effectively halves usable capacity—a 20kWh bank becomes 10kWh usable. Lithium’s 80–90% DoD and 5× cycle life justify higher costs for long-term use. Imagine powering a 2kW load: With lithium, a 10kWh system provides 4–5 hours; lead-acid requires 20kWh for equivalent runtime.
RackBattery Expert Insight
FAQs
Yes—modular rack systems allow capacity additions. Ensure inverters and BMS support parallel connections, keeping all battery banks within 0.5V voltage differential during integration.
How long do home batteries last?
Lithium-ion lasts 10–15 years (3,000–6,000 cycles at 80% DoD). Lead-acid requires replacement every 3–7 years (500–1,200 cycles). Cycle life directly impacts long-term kWh cost—lithium averages $0.15–$0.25/kWh over lifespan.