Energy Storage Planner
Don't get left in the dark. Calculate the precise battery bank size for overnight usage or multi-day backup.
Storage Parameters
The Storage Formula
Battery capacity depends on how much energy you need, how long you need it, and how deeply you can discharge.
Required Wh (with DoD)
Total Wh = (Daily Wh × Days) ÷ DoD Dividing by DoD ensures you only use the safe portion of stored energy, protecting battery life and cycle count.
Amp-Hour Capacity
Ah = Total Wh ÷ System Voltage Battery capacity is rated in Ah at a specific voltage. A 200Ah 24V bank stores 4,800Wh of total energy.
How to Size a Solar Battery Bank
A battery bank stores solar energy collected during the day so you can use it at night or during cloudy periods. Getting the size right means you never run out of power during your designed autonomy window — and you don't destroy your batteries by over-discharging them. The key parameters are daily energy load (Wh), days of autonomy, system voltage, and Depth of Discharge (DoD).
Understanding Depth of Discharge (DoD)
DoD is the percentage of a battery's capacity you can safely use before recharging. Lead-acid batteries should not be discharged below 50% (DoD = 0.5) or their lifespan drops dramatically. Lithium (LiFePO4) batteries can safely reach 80–90% DoD, making them far more space-efficient per usable kWh.
Battery Chemistry Comparison
- Flooded Lead-Acid (FLA): Cheapest upfront cost. Requires regular water top-ups and venting. Maximum 50% DoD. Cycle life ~500 cycles at 50% DoD.
- AGM / GEL Sealed: Maintenance-free and spill-proof. 50–80% DoD depending on brand. Better suited to partial-state-of-charge operation than flooded.
- Lithium (LiFePO4): Premium cost but 2–4× the cycle life of lead-acid. 80–90% DoD, lighter, and no maintenance. Best long-term value for most solar installations.
Step-by-Step Battery Sizing
- Calculate Daily Wh Load: Multiply each appliance's wattage by the hours per day it runs. Sum all appliances.
- Decide Days of Autonomy: How many sunless days must the system sustain? 1–2 days is typical for grid-hybrid; 3–5 days for full off-grid resilience.
- Apply Your DoD Factor: Divide the total energy needed by your battery's DoD rating to get the required gross capacity.
- Convert Wh to Ah: Divide gross Wh by your system voltage (12V, 24V, or 48V). Higher voltage = fewer amps = thinner wire required.
- Select Battery Count: Divide the total Ah by the Ah rating of your chosen battery, then round up to the nearest whole number.