There is a fine line between having a solar panel and knowing the size of solar panels to charge your 100ah battery. So what size solar panel to charge a 100ah battery? For a 12v battery and considering exposure to 6 hours of intense sunlight, the simple answer will be 240 watts.

If batteries constitute your solar installation kit, you’ll need an inverter, charge controller, and solar panels. These batteries extract the electrical energy obtained from your solar panels instead of transmitting that energy back into the grid. The amount of energy that can be stored depends on the capacity. Almost all batteries have a particular amp hour rating, but it’s not advisable to wait till they drop to 45% before recharging them.

In this article, you’ll learn the different types of 100ah batteries, how many solar panels are necessary to charge, the factors influencing the charging time of your solar panels and batteries, how to measure your solar panel size, the best time to charge, and how to calculate the time it takes to charge.

The Different Types of 100ah Batteries

There are different types of 100ah batteries:

  • Lead-acid batteries
  • Gel batteries
  • Lithium-ion phosphate batteries
  • Absorbed glass matt batteries

The lead-acid batteries need to be maintained from time to time. The gel batteries have a lesser charger rate and battery output than absorbed glass matt batteries. Although lithium-ion phosphate batteries are the costliest solar batteries, they have a very long lifespan and a DoD score of 100% to recoup for their heavy price.

How many Solar Panels does it take to charge a 100ah Battery?

A 12v battery can be charged by solar panels ranging from 240 watts and upwards of 500-watt solar panels. It takes about 5 to 6 hours of sunlight. It can be a single panel of the above-mentioned wattage or two panels of 120 watts each.

But, you need to know the process of measuring panel size.

How to Measure your Solar Panel Size?

To properly measure the size of the panel to power your battery, apply this formula below:

  • Battery voltage x Battery amp hours (Ah) = watts
  • Hours of watt / number of hours of available solar power= watts of solar panel
  • Watts of solar panels + 20% extra solar panel power = panel watt size that you need

Calculating with the above-mentioned figures:

  • 12V x 100 ah battery = 1200 watts
  • 1200 watts / sunlight for 6 hours = 200W panel
  • 200W + 20% additional watts = 200w + 40 extra watts = 240w

What are the factors that influence the charging time of your battery and panels? Knowing this information about your battery system is important for a successful setup. The factors include the availability of solar energy, the level of effectiveness of the panels, and the type of charge controller.

The Exposure or Availability of Solar Energy

How does this factor influence the charging time? The panels rely on sunlight to function and power your battery. When the weather is sunny, the solar panels store an ample amount of energy within record time. Even in this ideal weather, a temporary passing of a cloud can affect the charging of the panels and battery. However, when the weather is cloudy, the storage of solar energy and the charging time will be much slower. If it’s extremely cloudy, the solar panels may even stop charging.

Depending on the functionalities of that panel, it can either go back to recharging from the very beginning or resume from where it stopped once the weather improves.

The Level of Effectiveness of the Solar Panels

Solar panels don’t perform flawlessly even in the best working conditions. Why so? This is because a loss of energy is always experienced when the panels receive energy from the sun. Hence, you need a bigger panel than what your battery requires. For example, for a 100ah battery, a 240-watt panel is required, but you can go further to get a panel size up to 300w.

The given time of 5 to 6 hours for your battery to charge when powered by a 240w panel is accurate as long as there’s no obstruction. The slightest obstruction between panels or in their way can make the charge slower or even stop it altogether.

The Type of Charge Controller

The type of controller also affects how the battery charges. For example, for a 240w panel, a 300w charge controller is necessary.

solar charge controller

There are the PWM and the MPPT charge controllers. The PWM is the more commonly used from the pair. MPPT has more capacity, but it’s more expensive. If you’re opting for PWM, a 30A charge controller can do the job.

How to Determine the Charge Time?

How do you determine the charging duration of your battery?

Note that the availability of sunlight greatly affects the duration. For example, if there are less than 5 hours of sunlight, the duration of charging will be longer.

See below:

  • Total watts of the panel / battery voltage = amps
  • Battery capacity / amps = time needed to charge

Using our numbers:

  • 240 watt panel / 12V battery = 20A
  • 100 ah battery / 20A = five hours needed to charge

Can a 100w Solar Panel Charge a 100ah Battery?

Yes, it can charge it. Your panel has an output of 100W, so about 7A.

How long will a 100W solar panel take to charge a 100Ah battery?

It would take about 14 hours to charge the battery. This may not be possible in one day if the weather condition is less than ideal.

The Best Time to Charge

You should note that the type of battery determines the best time to charge. Watch the video below and learn, how to check your battery charge level:

  • Lead batteries should be recharged when they drop to 50%.
  • Gel batteries should be recharged when they drop to 50%.
  • Lithium batteries should be recharged when they drop to 35-40%.

Never wait for the battery to drain before you recharge entirely. This weakens its lifecycle over time.

Last Words

This information about your battery will prove to be very helpful for your battery life and the choice of your solar panel size. If you have any questions, please feel free to let us know in the comments.

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