off grid solar

Thank you for your post. To select batteries for your off-grid solar project, you’ll want to estimate the power needs of your cabin and select batteries that align with the specifications of your existing setup. Based on the details provided, here’s how to proceed:

Step 1: Energy Consumption Estimate

Estimate the daily energy requirements of the cabin by evaluating the appliances and their usage:

1. Lighting:

• Assume 5 LED lights at 10W each, used for 5 hours daily.

Power: 10W × 5 lights × 5 hours = 250 Wh/day

2. 120V Water Heater:

• A small water heater typically uses 1500W and runs for 1 hour/day.

Power: 1500W × 1 hour = 1500 Wh/day

3. Electric Oven/Range:

• A small oven uses around 2000W and might run for 1 hour/day.

Power: 2000W × 1 hour = 2000 Wh/day

Total Daily Load:

250 Wh (lighting) + 1500 Wh (water heater) + 2000 Wh (oven) = 3750 Wh/day

Step 2: Battery Bank Size

Factor in battery efficiency and depth of discharge (DoD) for sizing:

1. Battery Efficiency:

Assume ~90% efficiency.

2. Depth of Discharge (DoD):

Use 50% DoD for longevity in lead-acid batteries or up to 80-90% for lithium-ion batteries.

3. Days of Autonomy:

Account for 2 days of autonomy for cloudy weather.

Battery Capacity Calculation:

For a 24V system (common with Outback controllers):

You need a battery bank with at least 695 Ah at 24V to meet your needs.

Step 3: Battery Options

Here are some options based on your requirements:

Lithium-Ion Batteries (Preferred for Longevity and Performance):

1. Battle Born Batteries:

• 100Ah 12V LiFePO4.

• Two in series = 24V, combine multiple pairs to meet 695 Ah.

• Advantages: High cycle life, lightweight, no maintenance.

2. Simpliphi Power:

• 3.8kWh 48V battery (can reconfigure for 24V systems).

• Stackable, safe, high efficiency.

3. EG4-Lifepower4 Batteries:

• Affordable LiFePO4 batteries designed for off-grid systems.

• Scalable and easy to integrate.

Lead-Acid Batteries (Budget-Friendly but Require Maintenance):

1. Trojan T-105 RE:

• 225Ah 6V deep-cycle lead-acid batteries.

• Configure in series/parallel for 24V and required capacity.

• Heavy, needs regular maintenance.

2. Rolls Surrette Batteries:

• High-quality flooded or AGM deep-cycle batteries.

• Suitable for heavy cycling but bulky.

Step 4: Additional Considerations

1. Inverter Compatibility:

Ensure your DC-to-AC inverter supports the chosen battery voltage and capacity.

2. Battery Management System (BMS):

Use a BMS for lithium-ion setups to ensure safe operation.

3. Budget and Maintenance:

• Lithium-ion is more expensive upfront but lower maintenance and longer-lasting.

• Lead-acid is more affordable but requires maintenance and has a shorter lifespan.

4. Expandability:

Consider future energy needs when sizing the battery bank.