How Long to Charge 12V Battery with 100 watt Solar Panel?

Last Updated on July 16, 2022 by Kimberly Crawford

Solar panels are now being used everywhere, from charging car batteries to powering industrial plants. Solar power is a cheaper alternative to conventional electric power.

Therefore, people are now switching to solar panels to reduce their electricity bills. If you are unfamiliar with solar panels, they are composed of photoelectric cells which convert sunlight into electric power. These panels are connected to a battery that stores the electricity for later use.

Fortunately, charging a 12-volt battery with a 100-watt solar panel is not too draining and doesn’t take long, but factors still affect the charging time. These factors are: –

  • Charging capacity of the battery
  • Size or capacity of the solar panel
  • Weather conditions

The above-mentioned factors are interrelated and interdependent. Typically, all the above-mentioned factors affect the charge time directly. The higher the capacity of the battery the more output it will give. And the bigger the size of the solar panel the more power it will produce. Hence, it will charge the battery more quickly.

But that too depends on the weather, the more sunlight the panels will get, the more electricity they will produce.

However, there is a way of calculating charge time. Here’s how:

How to Calculate the Charging Time of a 100W Solar Panel Battery

solar panel

When calculating how much time would the solar panel take to charge a battery, you must know the battery size, solar panel output, and voltage. Since we are calculating the charging time of a 12V battery of (let’s assume) 50 amp by a 100-watt solar panel. Here’s what the calculations say.

Volts= 12V

Battery amps= 50amp

Solar panel output= 100W

[The first step would be to convert battery amps into watts.]



[Now we calculate the charging time.]


600/100=6 HOURS

According to the calculations, a 12V 50amp battery would take 6 hours to charge. If you have a battery of 12V and 100amp, you can calculate the charging time using the same formulas. But these calculations only provide you with an estimated time. In real life, some factors affect charging time. These are relevant to all sizes of solar panels.

Factors Affecting the Charging Time of a Battery

The above calculations and formulas are useful in assuming the sky is clear for solar panels to receive maximum sunlight, the battery to be completely depleted, and the solar panel to be at its peak capacity.

1. Charging Capacity of a Battery

In the above example, we have been calculating the charging time of an empty battery. However, in real life, the battery type and capacity affect the charging time. For example, an AGM (absorbent glass matt) battery or a gel battery must be recharged before its capacity falls below 50%.

So now we will have to charge the battery which is already at 50% therefore the charging time is also reduced to half. It takes lesser time to charge the battery which is at 50%. Due to technical reasons, a complete discharge of a battery is not good for its life cycle. The more you deplete the battery to zero, the sooner the battery will die out.

That is why these batteries are designed not to be completely depleted. You can try to deplete the battery, but it will most likely stop when it reaches 15% or 10%.

2. Size or Capacity of a Solar Panel

Solar panels are built and tested under supervised (ideal) settings to ensure maximum output. Therefore, the stated output of a solar panel, which in this case is 100W, refers to the maximum power it can give.

According to that, a solar panel of 100W cannot be expected to produce 100W. In ideal conditions, the panel may yield relatively close to that, but that too would only last for 5 to 6 hours each day.

Normally, a 100W solar panel would provide you with 90W, 85W, or even 80W depending on the weather. Let’s say the solar panel gives us 80W of power, according to the formula, that would mean: –

600/80= 7.5HOURS

A 50amp 12V battery would take 7.5 hours instead of 6 hours to charge from 0 to 100%.

3. Weather Conditions Affecting Charging Hours

Out of all the aspects that should be considered, the following have been the most significant. These will not prevent solar panels from producing electricity, but they will delay the charging or reduce output below 100 watts.

  • Clouds: Solar panels need direct sunlight for their photovoltaic cells to convert light into electricity. Cloudy weather is a hindrance in that process. The longer the cloud conceals the sun, the longer it takes to charge the battery. It is ideal to charge the batteries on a sunny day.
  • Dust/dirt or other Debris: The wind carries all sorts of debris which can disperse all over the solar panel. Even a tiny bit of dirt or debris might have an impact on performance since it will make it difficult for the solar panel to receive maximum sunlight.

Therefore, make sure the panel is clean when you place it down to charge.

Use water or light soap to clean the panel if necessary. Large solar arrays may need expert assistance but a 100-watt panel is easier to clean.

  • Orientation: For the solar panel to receive maximum sunlight, a solar panel must be oriented in the direction of the sun, preferably true south. That is because facing the true south will allow the solar panel maximum light compared to other orientations/directions.



How fast can 100W solar panel charge a battery?

This is a difficult question to answer because it depends on a number of factors, including the type and size of battery, the efficiency of the solar panel, and the amount of sunlight available. In general, however, a 100W solar panel will take several hours to charge a typical car battery. The exact time will vary depending on the factors mentioned above, but it is typically between 4 and 8 hours.

How many batteries can a 100 watt solar panel charge?

The answer to this question depends on a few factors, including the type of battery, the capacity of the solar panel, and the amount of sunlight available.

If we are talking about a lead-acid battery, then a 100 watt solar panel can fully charge a 50 Ah battery in around 8 hours of full sunlight. However, if the solar panel is only able to produce 50 watts of power, it would take twice as long to charge the battery.

The capacity of the solar panel also affects how many batteries can be charged. If a 200 watt solar panel is available, then two 100 Ah lead-acid batteries could be fully charged in the same amount of time as one.

As for lithium-ion batteries, a 100 watt solar panel can charge a 12 volt, 100 Ah battery in around 4 hours. Again, this time will double if the solar panel can only produce 50 watts of power.

How many amp hours does a 100 watt solar panel?

Assuming you are asking about a photovoltaic (solar electric) panel, the answer depends on the efficiency of the panel, and the sunlight conditions.

Under “ideal” conditions (i.e. perfect weather), a standard 100 watt solar panel will produce about 8.3 amps per hour. However, average real-world conditions are usually less than ideal, so you can expect to see production levels closer to 6 amps per hour.

Keep in mind that solar panels only produce electricity when they are exposed to sunlight, so their output will vary depending on the time of day and weather conditions. Additionally, solar panels tend to be less efficient in cooler temperatures, so you may see even lower production levels in winter.

How fast will a 200-watt solar panel charge a 12 volt battery?

The answer to this question depends on a few factors, such as the size of the battery, the efficiency of the solar panel, and the amount of sunlight available.

Assuming you have a standard 12 volt battery, and a 200 watt solar panel with an efficiency of 15%, then under ideal conditions (full sun) it would take approximately 133 minutes to charge the battery. However, in real world conditions, it is unlikely that you would achieve such high efficiency, so it would probably take longer.

If you have a larger battery, or a more efficient solar panel, then the time required to charge the battery will be less. Conversely, if you have a smaller battery or less efficient solar panel, then it will take longer to charge the battery.

It is also worth noting that the time of day and weather conditions can affect how quickly a solar panel can charge a battery. For example, if it is cloudy or foggy, then the solar panel will not be able to produce as much power and it will take longer to charge the battery.

Final Thoughts

Although bigger solar panels are also available, 100-watt modules remain popular owing to their mobility and adaptability.

However, some restrictions come when you are using solar panels regardless of the size. So before buying solar panels make sure you understand how they work and take the factors affecting charging time into consideration to ensure peak performance.

If, knowing all the tips/useful info we’ve provided, you’re still puzzled about what to look for when shopping, here’s a nice list of top solar generators.