Solar & Home Battery Calculators
Engineering-grade battery calculators for solar energy storage, off-grid systems, and home backup power. Size your battery bank, estimate runtime, and convert energy units with transparent formulas.
Solar battery storage is the backbone of modern residential energy systems. Whether you are designing an off-grid cabin, adding battery backup to a grid-tied solar installation, or optimizing self-consumption to reduce electricity bills, proper battery sizing determines whether your system meets your energy needs or falls short.
The core challenge in solar battery design is balancing three competing factors: sufficient storage capacity to cover your consumption during periods without sunlight, depth of discharge limits that preserve battery cycle life, and system voltage compatibility with your inverter and charge controller. Getting any one of these wrong leads to either overspending on unnecessary capacity or experiencing unexpected power shortages.
Our solar battery calculators apply standard electrical engineering formulas to help you navigate these trade-offs. The Solar Battery Sizing Calculator takes your daily energy consumption, desired autonomy days, battery chemistry, and temperature conditions to determine the exact battery bank capacity you need. The Runtime Calculator estimates how long your battery bank will power a specific load, accounting for inverter efficiency, depth of discharge, and voltage sag.
For off-grid solar installations, battery sizing is especially critical. Without a grid connection to fall back on, your battery bank must store enough energy to power your loads through consecutive cloudy days. The standard approach is to size for 2–5 days of autonomy depending on your location's solar resource and weather variability. Our calculators help you determine the exact capacity needed for your specific conditions.
Grid-tied solar systems with battery backup follow a different design philosophy. Here, the battery primarily stores excess solar energy for use during evening peak hours or provides backup during grid outages. The battery bank can be smaller since the grid serves as a secondary power source. Our tools help you optimize the battery size for your self-consumption goals and backup requirements.
Available Calculators
Solar Battery Sizing Calculator
Size your solar battery bank based on daily energy consumption, autonomy days, battery chemistry, and depth of discharge.
Off-Grid Battery Runtime
Estimate how long your battery bank will power your off-grid load based on capacity, voltage, and discharge limits.
Energy Conversion (Ah ↔ Wh)
Convert between Amp-hours and Watt-hours for any nominal voltage. Essential for matching solar panel output to battery capacity.
Solar Battery Guides
How to Size a Solar Battery Bank
LEARNING CENTERHow Many Batteries for Solar?
LEARNING CENTERHow Much Battery Storage Do I Need?
LEARNING CENTERSolar Battery Backup Guide
LEARNING CENTEROff-Grid Battery Planning
LEARNING CENTERSolar Storage Sizing Guide
LEARNING CENTERHow Long Will My Solar Battery Last?
LEARNING CENTERHow to Size a Battery Bank
LEARNING CENTERHow to Calculate Battery Runtime
LEARNING CENTERBattery Sizing Reference
LEARNING CENTERBattery Depth of Discharge Chart
LEARNING CENTERBest Battery Chemistry for Solar
LEARNING CENTER24V vs 48V Solar Systems
Frequently Asked Questions
How do I size a solar battery bank?
Calculate your daily energy consumption in Watt-hours, determine how many autonomy days you need (typically 1–3 days for grid-tied, 2–5 days for off-grid), account for depth of discharge limits based on battery chemistry, and apply temperature derating. Our Solar Battery Sizing Calculator handles all these factors automatically.
How many batteries do I need for solar?
The number of batteries depends on your total daily energy consumption, desired autonomy, system voltage, and battery capacity. A typical home consuming 30 kWh per day with 2 days of autonomy would need approximately 60 kWh of usable battery storage. At 48V with 200Ah batteries (10.24 kWh each), you would need approximately 6 batteries.
What is the best battery chemistry for solar storage?
Lithium Iron Phosphate (LiFePO4) is the recommended chemistry for solar storage due to its 80–90% depth of discharge, 3000–5000 cycle lifespan, thermal stability, and low maintenance requirements. Lead-acid batteries are cheaper upfront but have lower usable capacity (50% DoD), shorter lifespan, and require regular maintenance.
How long will my solar battery last at night?
Runtime at night depends on your battery capacity, the load you are running, and system efficiency. A 100Ah 12.8V LFP battery (1,280 Wh) powering a 200W load with 90% inverter efficiency will last approximately 5.7 hours. Our Runtime Calculator provides precise estimates for your specific configuration.
Can I use solar batteries for home backup?
Yes. Solar batteries paired with a hybrid inverter can provide backup power during grid outages. The battery charges from solar panels during the day and can power critical loads when the grid fails. Size the battery to cover your essential loads for the desired backup duration using our Home Backup Battery Calculator.
What is the difference between off-grid and hybrid solar battery systems?
Off-grid systems are completely independent of the utility grid and require larger battery banks to handle multi-day periods without solar production. Hybrid systems remain connected to the grid but use batteries for self-consumption optimization, time-of-use arbitrage, and backup during outages. Hybrid systems can use smaller battery banks since the grid serves as a backup.