How do I calculate battery size for solar?

Multiply your daily energy use (Wh) by backup days, divide by usable depth‑of‑discharge (DoD) and system efficiency—as shown in calculators that convert Wh to Ah at chosen voltage.

What’s depth of discharge (DoD)?

DoD is the percentage of battery capacity safely usable during discharge. Lead‑acid typical is 50%, lithium‑ion is 80–90% depending on chemistry.

Does battery chemistry affect sizing?

Yes—lithium‑ion batteries offer higher usable capacity (~80‑90 % DoD) versus lead‑acid (~50 %), so smaller Ah capacity can meet the same energy need.

Is this calculator free to use?

Yes, our battery size calculator is completely free, covers lithium‑ion, AGM, and lead‑acid types, and requires no signup.

How many batteries do I need for off‑grid backup?

You’ll choose Ah capacity based on kWh need, then divide by each battery’s capacity (e.g. 10 kWh battery), rounding up. Efficiency losses and autonomy days affect total count.

Best Battery Size Calculator For Solar And Off-Grid Systems

Optimize your power backup

Calculate the perfect battery capacity for your solar system, inverter, or car with accurate battery size calculator

System Parameters

System Type

Daily Power Usage (kWh)

Required Backup Hours

System Voltage

Battery Type

Inverter Efficiency (%)

Battery Sizing Results

Required Capacity

Amp-hours (Ah)

Energy Storage

kWh

Recommended Size

Ah (commercial)

Depth of Discharge

80%

Daily Use

Enter your system details to calculate the required battery size.

Common Battery Sizes

Application	Typical Load	Backup Time	Recommended Battery
Small Solar System	500W	8 hours	400Ah 12V
Home Inverter	1000W	4 hours	200Ah 12V × 2
RV Power	300W	24 hours	300Ah 12V
Off-Grid Cabin	2kWh/day	3 days autonomy	600Ah 24V
Car Audio System	1000W	2 hours	100Ah AGM

The Complete Guide to Solar Battery Storage

Solar battery storage systems allow you to store excess solar energy for use when the sun isn’t shining. With the right battery solution, you can maximize your solar investment, improve overall system efficiency, and achieve greater energy independence.

Why Solar Batteries Matter

Installing a solar battery helps reduce grid reliance by storing extra solar energy for use at night or on cloudy days. Choosing the right solar battery size ensures steady power and greater system efficiency. According to Clean Energy Reviews, battery storage plays a vital role in maximizing the benefits of solar systems in residential setups.

Reliable Backup During Power Outages

Solar batteries provide backup when the grid goes down, keeping essential appliances running. A reliable battery size calculator helps determine the storage capacity needed for uninterrupted power. As explained in Renogy’s solar battery sizing guide, proper battery bank sizing is crucial for off-grid and backup power reliability.

Choosing the Right Battery

When picking a solar battery, consider capacity, efficiency, and lifespan. Lithium-ion batteries are the top choice for homes. Use a battery size calculator to find the best solar battery size for your energy usage and backup needs.

Calculate Your Battery Life

Battery Sizing Formula

Understanding how to calculate the ideal battery capacity is key when designing a reliable off-grid or hybrid solar system. Whether you’re using a manual method or a battery size calculator, this formula helps determine your solar battery size based on your specific energy needs.

Capacity (Ah) = (Daily Energy (Wh) × Autonomy Days) ÷ (Voltage × DoD × Efficiency)

Each variable in the formula plays a critical role:

Daily Energy – Total energy consumed per day, measured in Watt-hours (Wh)
Autonomy Days – Number of days you want the battery to operate without sunlight (typically 2–3 days for off-grid systems)
Voltage – Nominal battery bank voltage (12V, 24V, or 48V depending on your system design)
DoD (Depth of Discharge) – Percentage of the battery’s usable capacity (80% for lithium, 50% for lead-acid)
Efficiency – Inverter and battery charge/discharge efficiency (commonly 85% to 95%)

Battery Types Comparison

Lithium-ion

Depth of Discharge: 80-90%

Life Cycles: 2000-5000

Efficiency: 95-98%

Best For: Solar, EVs, High-performance

AGM

Depth of Discharge: 50-60%

Life Cycles: 500-800

Efficiency: 85-90%

Best For: UPS, Marine, RVs

Flooded

Depth of Discharge: 40-50%

Life Cycles: 300-500

Efficiency: 70-85%

Best For: Cost-effective backup

Battery Sizing Tips

Optimize your off-grid or hybrid solar battery system with these expert strategies. Using a reliable battery size calculator can help prevent under-sizing or overspending.

Always add 20% extra capacity for future expansion and seasonal variations
For solar systems, size your battery bank for 2–3 days of energy autonomy
Use lithium batteries for deep cycling and higher energy density
Match battery chemistry to your solar charge controller and inverter specs
Account for temperature impact on solar battery size and discharge rates
Use a battery size calculator to estimate daily load and runtime requirements
Install a battery monitor to track usage and optimize charging cycles
Review your energy habits regularly and resize the system if demand increases

Proper solar battery sizing improves reliability, extends battery lifespan, and ensures your system delivers consistent performance year-round.

Battery Sizing FAQs

How do I calculate battery size for a solar system?

To calculate battery size for solar:

Determine your daily energy consumption in kWh
Decide how many days of autonomy you need (typically 2-3)
Account for depth of discharge (80% for lithium, 50% for lead-acid)
Include inverter efficiency (85-95%)
Calculate: Battery Size (kWh) = (Daily Usage × Autonomy Days) ÷ (DoD × Efficiency)
Convert to Ah: Ah = (kWh × 1000) ÷ Voltage

Example: 5kWh/day, 2 days autonomy, 24V system, lithium battery (80% DoD, 95% efficiency):
(5 × 2) ÷ (0.8 × 0.95) = 13.16 kWh → (13160 Wh ÷ 24V) = 548 Ah

What size battery do I need for a 2000W inverter?

For a 2000W inverter:

Determine your runtime requirements
Calculate total energy needed: Watt-hours = Watts × Hours
Account for depth of discharge and efficiency
Battery Ah = (Watt-hours) ÷ (Voltage × DoD × Efficiency)

Example for 4 hours runtime at 2000W on 12V system with AGM battery (50% DoD, 85% efficiency):
Watt-hours = 2000W × 4h = 8000 Wh
Ah = 8000 ÷ (12V × 0.5 × 0.85) = 8000 ÷ 5.1 = 1569 Ah

This would require approximately 8 × 200Ah AGM batteries.

How to calculate lithium-ion battery capacity?

Lithium-ion battery capacity calculation:

Determine your energy needs in Watt-hours
Account for 80-90% depth of discharge
Include 95-98% efficiency for lithium batteries
Calculate: Capacity (Ah) = (Watt-hours) ÷ (Voltage × DoD × Efficiency)

Example for 5kWh system at 48V with 90% DoD and 97% efficiency:
Ah = (5000 Wh) ÷ (48V × 0.9 × 0.97) = 5000 ÷ 41.904 ≈ 119 Ah

Always check manufacturer specifications for exact capacity ratings.

What is the battery discharge rate specification?

The battery discharge rate (C-rate) indicates:

How fast a battery can be discharged relative to its capacity
1C = Full discharge in 1 hour
0.5C = Full discharge in 2 hours
0.2C = Full discharge in 5 hours

Key considerations:

Lead-acid batteries typically have 0.2C-0.5C discharge rates
Lithium batteries can handle 1C-3C discharge rates
Higher discharge rates reduce available capacity
Always check manufacturer’s maximum continuous discharge rate

How to calculate battery current?

To calculate battery current:

Current (Amps) = Power (Watts) ÷ Voltage (Volts)

For example, a 500W load on a 12V system draws:
500W ÷ 12V = 41.67A

Additional considerations:

Account for inverter efficiency (add 10-15%)
Consider surge currents for motor starting
Wire sizing must match current requirements
Fuses/breakers should be 125% of continuous current

What size battery for a 3000W solar system?

For a 3000W solar system:

Estimate daily production: 3kW × Peak Sun Hours
Calculate storage needed for nighttime/cloudy days
For 10kWh daily usage and 2 days autonomy with lithium:
Battery Size = (10kWh × 2) ÷ (0.9 × 0.95) ≈ 23.4kWh
At 48V: 23,400Wh ÷ 48V ≈ 488Ah

Recommended configuration: 8 × 200Ah 12V batteries in 48V configuration (400Ah total) or 4 × 300Ah 12V in 48V configuration (300Ah total)

How does temperature affect battery sizing?

Temperature significantly impacts battery performance:

Capacity decreases in cold temperatures
Add 20-30% capacity for temperatures below 10°C (50°F)
High temperatures increase discharge but reduce lifespan
Lithium batteries perform better in cold than lead-acid
Optimal temperature range: 20-25°C (68-77°F)

Always check manufacturer specifications for temperature derating factors.

How to size a battery bank for off-grid living?

Sizing for off-grid living requires:

Complete energy audit of all appliances
Calculate daily kWh consumption
Determine autonomy days (typically 3-5 days)
Choose battery type (lithium recommended)
Account for 80-90% DoD and 95% efficiency
Add 20% safety margin

Example for 10kWh/day with 4 days autonomy:
Battery Size = (10 × 4) ÷ (0.9 × 0.95) × 1.2 ≈ 56.1kWh

This would require approximately 24 × 200Ah 12V lithium batteries in a 48V configuration.