How long to charge a battery (using solar)

The charging time of a battery using solar depends on several factors, mainly:

  • the combined capacity (W) of the solar panel(s) used
  • how many hours of sunshine your location and panel receives
  • the battery’s capacity (Ah)

and the remaining charge in the battery. A deeply discharged battery will take longer to charge fully compared to one

that is only partially discharged.

Formula for calculating charging time of a battery using solar

To arrive at an estimate of how long it will take to charge a battery using a specific solar panel size, you can use the formula:

hours to fully charge the battery = Solar battery capacity (Ah)/(solar panel capacity  x solar panel efficiency)/solar panel voltage.

The calculator below is based on the formula described above.

Estimated charging time calculator using solar panels

Based on the formula above, you can use this easy and quick calculator to work out the time estimates (hours/ days) to fully charge a battery using a solar panel of a specific wattage.

Note: This calculator works for 12V battery banks only

When using the calculator above, should you have multiple solar panels charging the battery, use their combined wattage in the calculator.

For example, if  5 solar panels of 100W are charging a battery, then use the equivalent wattage is, 5 x 100W = 500W.

Using the calculator above, lets work through some examples.

# 1. Worked example: Estimated charging time for a 50Ah battery using a 100 W solar panel

Let us assume the 50 Ah battery bank has been discharged  to 50% and the solar panel is installed in a location with about 4 hours of sunshine.

The solar panel can be expected to charge the battery in about 4 hours.

# 2. Worked example: Estimated charging time for 200 Ah battery using a 100 W solar panel

Let us assume the 200 Ah battery bank has been discharged  to 50% and the solar panel is installed in a location with about 4 hours of sunshine.

The solar panel can be expected to charge the battery in about 17 hours.

# 3. Worked example: How long to charge a 200 Ah battery?

This depends on the available power from the charging source for a 200 Ah battery. For example,

Using solar,

  • a 100W solar panel in an area with about 4 hours of sunshine will take about 17 hours (assumes 50% discharge)
  • a 200W solar panel in an area with about 4 hours of sunshine will take half as much i.e. about 8.5 hours (assumes 50% discharge).

A 10A AC charger, assuming the battery was discharged to 50% of its capacity, will take about 10 hours.

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