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Battery Bank Guide
Battery Type Comparison
Type
DOD
Eff.
Cycles
$/kWh
Lead-Acid FLA
50%
85%
800
$150
AGM
50%
87%
1,000
$250
Gel
50%
85%
1,200
$300
LiFePO4
80%
95%
5,000
$500
Depth of Discharge (DOD)
DOD is the percentage of battery capacity that is used before recharging. Deeper discharge cycles reduce battery life significantly. Lead-acid batteries should never be discharged below 50% for acceptable lifespan, while LiFePO4 can safely go to 80% or even 90% in emergencies. Running batteries to 100% DOD will dramatically shorten their life.
Temperature Effects on Battery Capacity
Temperature
Capacity Factor
25°C (77°F)
100% (baseline)
20°C (68°F)
96% (1.04x oversize)
15°C (59°F)
90% (1.11x oversize)
10°C (50°F)
84% (1.19x oversize)
5°C (41°F)
77% (1.30x oversize)
0°C (32°F)
71% (1.40x oversize)
Charge Controller Types
PWM (Pulse Width Modulation)
• Lower cost, simpler design
• Panel voltage must match battery voltage
• Best for small systems under 200W
• 75-80% effective charging efficiency
MPPT (Maximum Power Point Tracking)
• 20-30% more efficient than PWM
• Handles higher panel voltages (steps down to battery voltage)
• Best for systems over 200W
• Essential for 48V battery systems with higher-voltage panel strings
Caribbean Solar Storage Considerations
• High ambient temperatures (25-35°C) — batteries need ventilation and shade
• Tropical humidity can corrode lead-acid terminals — use dielectric grease
• Hurricane season (June-November) — battery enclosures should be waterproof and secured
• High solar irradiance (5-6 PSH) means faster charging and more daily cycles
• Salt air in coastal areas accelerates corrosion — sealed batteries (AGM/Gel/LiFePO4) preferred
• Power grid instability in some Caribbean islands makes battery backup essential
Series vs Parallel Wiring
• Series: Increases voltage, same capacity. E.g. 4 x 12V 200Ah = 48V 200Ah
• Parallel: Increases capacity, same voltage. E.g. 3 x 12V 200Ah = 12V 600Ah
• Series-Parallel: First wire series strings for voltage, then parallel strings for capacity
• Keep parallel strings to 4 or fewer for lead-acid; LiFePO4 can handle more with BMS
Disclaimer: This calculator provides estimates for preliminary battery bank sizing. Actual performance depends on specific battery models, charge/discharge rates, ambient conditions, and system configuration. Always consult a qualified electrical engineer or solar installer for detailed system design and installation.
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