Solar Panel Charge Time Calculator For 12V Batteries (100W-500W Panels)

How long will a 100W, 200W, 300W, 400W, or 500W take to charge? Most of the resources on solar panel charge time you find are quite complex. We’re going to simplify the whole thing.

In the end, you should be able to adequately calculate solar charge time for any 12V battery. We will help you with the calculations with a simple 3 step-by-step method.

On top of that, you can also use two very easy-to-use resources:

  • ‘Solar Panel Charge Time’ calculator. If you don’t want to check how to calculate the solar charging time, you can just skip to the calculator, and the calculator will do all the work for you automatically.
  • Calculated table of charging times for 12V batteries with 100W, 200W, 300W, 400W, and 500W solar panels.

Alright, let’s look at how to easily calculate battery charging time:

How Long It Takes To Charge A Battery With Solar Panels? (3 Steps)

To better illustrate charging times, we will use one of the most common examples:

How long will a 300-Watt solar panel take to charge a 12V 50Ah battery?

We have all the basic information that we need here. These include:

  • Battery size (50Ah or 50 ampere-hours).
  • Battery voltage (12V, standard voltage for batteries).
  • Solar panel size (300W).
  • Additional: We need to know peak sun hours (measure of solar irradiance, usually between 5 and 7 hours). On top of that, we also have to account for 25% of losses pretty much any solar panels have.

Step 1: Calculate the battery capacity in Wh (watt-hours)

We know that we have a 12V 500Ah battery. To be able to determine how long it takes for a solar panel to charge this battery, we have to calculate the total charge this battery can hold.

This is measured in Wh or watt-hours. Here is how we calculate the battery capacity in our example:

Battery Capacity = 50Ah × 12V = 600 Wh

Such a battery holds a 600Wh charge. All we have to do now is to determine how long it takes for a 300W solar panel to generate that amount of electricity.

Step 2: How much electricity does a solar panel generate?

Here the solar irradiance comes in. If you live in the southern US, you probably get 7 peak sun hours per day. If you live in the northern US, you probably get around 5 peak sun hours per day.

Let’s presume we live somewhere in the middle of the US and get 6 peak sun hours. We also have to account for 25% solar panel system losses (0.75 factor in the equation below).

Here is how we can calculate how much electricity does a 300W solar panel generate per day:

300W Solar Panel Electricity Generation = 300W × 6h × 0.75 = 1,350 Wh

That means that in 24 hours a 300W solar panel will generate 1,350 Wh of electricity.

Now we have all we need to calculate the solar panel charge time:

Step 3: Calculate how long will it take for a solar panel to fully charge a battery?

300W solar panel generates 1,350 Wh of electricity per day (24h). That’s 56.25 Wh per hour. To fully charge a 50Ah battery from 0% to 100%, we need 600Wh (from Step 1).

How many hours will it take to fully charge such a battery? Here’s how we calculate the charging time:

Charging Time = 600Wh / 56.25Wh per hour = 10.67 hours

Here you have it: A single 300W solar panel will fully charge a 12V 50Ah battery in 10 hours and 40 minutes.

You can use this 3-step method to calculate the charging time for any battery.

Let’s look at how we can further simplify this process with the use of a solar panel charge time calculator:

Solar Panel Charge Time Calculator (For 12V Batteries)

You just insert the size of the solar panel (wattage), size of the battery (in Ah), and peak sun hours in your location. The calculator will dynamically calculate in how many hours the solar panel will fully charge a battery from 0% to 100%:

0.00 Hours

Time It Takes To Fully Charge A Battery


You can check how the calculator works by using the example we used before. That’s the 300W solar panels for a 12V 50Ah battery. If you put these data into the calculator, with the 6 peak sun hours, you get the same result as we did with manual calculation:

Solar Panel Charge Time Calculator

Using this solar panel charge time calculator, we have calculated charging times for various sizes of batteries (with various solar panel sizes) at 6 peak hours. You will find them summarized in the table below:

Solar Charing Times (Calculated Table)

Solar Panel Size: 50Ah Battery (12V) 100Ah Battery (12V) 200Ah Battery (12V) 300Ah Battery (12V) 400Ah Battery (12V)
100W 32.00 Hours 64.00 Hours 128.00 Hours 192.00 Hours 256.00 Hours
200W 16.00 Hours 32.00 Hours 64.00 Hours 96.00 Hours 128.00 Hours
300W 10.67 Hours 21.33 Hours 42.67 Hours 64.00 Hours 85.33 Hours
400W 8.00 Hours 16.00 Hours 32.00 Hours 48.00 Hours 64.00 Hours
500W 6.40 Hours 12.80 Hours 25.60 Hours 38.40 Hours 51.20 Hours

These charging times are quite long. In order to reduce the charging times, you should use more than 1 solar panel. A 5kW solar system, for example, will charge a 100Ah 12V battery in a little over an hour.

2 thoughts on “Solar Panel Charge Time Calculator For 12V Batteries (100W-500W Panels)”

  1. Im trying to work this I have 8 255 watt solar panels with 4 230 AH lithium batreries if I did the math right. Being in anchorage alaska in June what. What hour peak? do i use

    • Hi there, you can use this Average Peak Sun Hours By US State chart. During the summer season, Alaska gets about 3.87 peak sun hours per day.

      Now, 8 x 255W = 2,040W systems. If you apply the expected 25% system losses, you can generate about 5.92 kWh per day. Those lithium batteries are 12V, right? All 4 of them will have 230 Ah x 12V x 4 = 11.040 kWh capacity (from 0% to 100%). It will take about 2 full days to charge them.


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