What Size Solar Panel to Charge a 100Ah 48V Battery? (Calculator + Chart)

Quick answer and calculator

A 100Ah 48V lithium (LiFePO4) battery stores 4.80 kWh. After accounting for 95% charging efficiency, you need to deliver approximately 5,053Wh from your panels. At 5 peak sun hours, that equals 1,010W.

AGM batteries at 85% efficiency need 1,128W. Flooded lead-acid at 80% efficiency needs 1,200W, though 48V flooded lead-acid banks are uncommon in modern installations -- lithium dominates at this voltage tier.

Sizing table by charge time and chemistry

These figures include chemistry-specific efficiency losses. At the 48V tier, lithium (LiFePO4) is the dominant chemistry due to its weight advantage, efficiency, and ability to handle deep discharge cycles.

Which solar panel to buy

For a 100Ah 48V battery, you need 1,000W to 1,200W of solar. Here are the practical configurations:

3 x 400W panels (recommended) -- Three 400W panels totaling 1,200W is the most popular configuration. Modern 400W residential panels (about 1.7m x 1.1m each) are widely available and competitively priced. This array charges a lithium battery in about 4.5 peak sun hours with comfortable margin.

4 x 300W panels -- Four 300W panels (1,200W total) offer more wiring flexibility. You can configure two series strings of two panels each, wired in parallel. This is a good option if your roof or mounting area suits smaller panels.

2 x 500W panels -- Two large 500W panels (1,000W total) minimize wiring complexity and mounting hardware. These panels are physically large (about 2.3m x 1.1m) and heavy (about 27 kg each), so they are best suited for ground mounts or strong roof structures.

5 x 200W panels -- Five 200W panels (1,000W total) work for installations with irregular mounting surfaces. The smaller panel size allows flexible placement, but the additional wiring and connections add complexity.

Charge controller sizing

The 48V battery voltage works in your favor for controller sizing -- the same wattage requires much lower current than a 12V or 24V system:

1,000W array: 1,000W / 48V x 1.25 = 26A. A 30A MPPT controller handles this.

1,200W array: 1,200W / 48V x 1.25 = 31.3A. A 40A MPPT controller is the standard choice.

1,600W array (oversized): 1,600W / 48V x 1.25 = 41.7A. A 50A MPPT controller provides maximum flexibility.

The controller's maximum input voltage (Voc) rating is equally important. Check your panel array's total open-circuit voltage at cold temperatures (Voc increases about 0.3% per degree C below STC 25 degrees C). For example, three 400W panels in series might have a combined Voc of 150V at -10 degrees C. Ensure your controller is rated above this value.

MPPT is mandatory for 48V systems

There is no practical case for PWM on a 48V battery system. Here is why:

PWM requires the panel array nominal voltage to closely match the battery voltage. A 48V battery charges at 54 to 58V (lithium) or 56 to 58V (lead-acid). To match this with PWM, you would need four 12V panels in series or purpose-built 48V panels, which are rare and expensive.

MPPT controllers accept a wide input voltage range (typically 100V to 250V depending on the model) and efficiently convert it to the battery's charging voltage. You can use standard, widely available residential panels (typically 30 to 50V Vmp) and wire them in series strings to achieve the optimal input voltage for your controller.

A quality MPPT controller for a 48V system (such as the Victron SmartSolar 150/35, EPEver Tracer 4210AN, or Renogy Rover 40A) costs $120 to $250 and converts solar energy at 96 to 99% efficiency.

Series vs parallel wiring for 48V systems

With 1,000W or more of panels, wiring configuration significantly impacts system performance:

All in series -- Three 400W panels in series produce about 120V Vmp at 10A. This minimizes cable current and allows small wire gauges (14 AWG for short runs). The MPPT controller efficiently converts this to 48V at about 22A. The downside: shading on any one panel reduces the entire string's output.

Series-parallel (recommended for larger arrays) -- For four panels, wire two pairs in series, then connect the pairs in parallel. Two strings of two 300W panels: each string at 72V and 8.3A, combined to 72V and 16.6A. This balances efficiency with shade tolerance.

All in parallel -- Produces the panel's individual Vmp (e.g., 36V for a single 300W panel) at combined current. This only works if the panel Vmp exceeds the battery charging voltage (54 to 58V for lithium), which most single panels do not. Generally not recommended for 48V systems.

For most 48V setups, series or series-parallel wiring with MPPT is the standard approach. Ensure the total series Voc stays within your controller's input voltage limit, especially at cold temperatures.

Real-world factors that reduce output

At 1,000W or more of solar, real-world derating has a significant absolute impact:

Temperature -- A 1,200W array at 65 degrees C cell temperature loses 12 to 20%, producing 960 to 1,056W. In hot climates, this can mean the difference between a full charge and falling 10 to 15% short.

Panel angle -- Fixed flat mounting costs 10 to 25% output. For a permanent off-grid installation, adjustable tilt mounts that track seasonal sun angle are highly recommended at this system size.

Shading -- With series-wired panels, a single shaded cell can reduce the entire string's output. Use bypass diodes (built into most modern panels) and plan installation to avoid shadows from 9 AM to 4 PM.

System losses -- Cable resistance, MPPT conversion, and connections account for 3 to 8% total. Higher-voltage series strings minimize cable losses -- a key advantage of 48V systems.

Plan for a real-world derating factor of 0.78 to 0.85. A 1,200W array effectively delivers 936 to 1,020W in typical conditions.

Keep Reading

• Solar Panel Charge Time Calculator
• What Size Solar Panel to Charge a 100Ah 24V Battery
• What Size Solar Panel to Charge a 200Ah 48V Battery
• Lithium vs AGM vs Lead-Acid Solar Batteries
• Peak Sun Hours by State
• Solar Charge Controller Size Calculator