What Solar Panel Size to Charge a 50ah Battery?

In many RVs and mobile homes, 50ah batteries are used for small loads. They are more affordable than larger batteries and easier to charge. But speaking of charge, how many solar panels will you need and what size?

A 250 watt solar panel can charge a 50ah battery in 3 to 4 hours under ideal weather conditions. With a 300 watt solar panel it will take about two hours to recharge the battery from zero 100%, provided there are five hours of sunlight.

How Many Solar Panels to Charge a 50ah Battery?

To figure out the size and number of solar panels required, you need to convert amp hours into watts and find out the battery voltage.

The conversion is battery amp hours x voltage = solar panel watts required

In this example you have a 12V battery like the Mighty Max 12V 50ah. It is completely discharge (0% power) and has to be recharged.

50 ah x 12V = 600W

You need a solar panel that can produce 600 watts in total power. With 5 hours of sunlight the solar PV system has to produce at least 120 watts an hour. A couple of 300W Renogy solar panel kits will be enough to get the job done.

A 150W solar panel can recharge the battery in 5 hours, so can a 200W, 250W, 300W etc. A 50W solar panel is too small, and a single 150W solar panel would need six hours. With 250W and 300W panels the most widely used, it will not take long to recharge a battery of this size.

Any of these panels will do, but a 200W, 250W or 300W is the most practical. The fewer solar panels to install the better. If the conditions are ideal the battery will go from 0% to 100% in an hour.

If you are not in a hurry you can use a smaller solar panel. It will take several hours to charge, but if time is not an issue it is a good option. However it is best to charge the battery as fast as possible because the weather can change.

What if My 50ah Battery is 24V? The conversion still works, but instead of 50 x 12 = W this time it is 50 x 24 = W. It is the same rule for 48V batteries as well.

Some people like to convert 12V solar panels into 24V to get more power. With batteries, the higher the voltage the more watt power available. But that also means a longer charging time.

While a 600W solar array can charge a 50ah 12V battery in an hour, it will take twice as long with 24V batteries.

50 x 12 = 600
50 x 24 = 1200

Both are 50ah but the watt capacity is double for a 24V battery. The solar panel voltage must also be higher than 12V, because a battery can only be charged with a higher power source.

How Long Does it Take to Charge a 50ah Battery with Solar Panels?

Whether it is 12V or 24V, another matter to consider is the weather. Because this more than anything determines how long the charge will be.

A completely discharged 12V 50ah battery can be recharged in an hour by a 600W solar array. Three 200W solar panels can also recharge the battery in 3 to 4 hours.

The two biggest factors that influence the charge time are the solar panel output and the battery depth of discharge. If you charge and discharge batteries frequently, knowing what these =do is crucial to getting the best results.

Solar Panel Output vs. Performance

The solar panel output rating does not equate to actual performance. If a solar panel is rated at 300 watts, that is the maximum power the panel can produce in ideal weather.

During the summer it is possible to get 300 to 600 watts an hour, enough for a 50ah battery. That number will drop during the afternoon as the sun goes down, but at least you got the battery charged.

But during cloudy days or really any time other than summer, it might take longer to top a 50ah battery. If you are used to seeing a full charge in an hour with your 600W solar array, it might take 90 minutes or even longer depending on the weather.

There is also the matter of geography. Some states get more sun than others regardless of the season. Summers in Nevada, Texas and Arizona are way warmer than in Washington, New York or Illinois. You have to adjust your calculations and expectations accordingly.

Battery Depth of Discharge

Depth of discharge (DO) refers to how much usable power is in the battery. A 70% DOD means 70% of the power is available. In other words, you have to recharge the battery when capacity drops to 30%. This has a big effect on the charge time, either increasing or reducing it as this example will show.

You have a 12V 50ah FLA battery and it is discharged at 50%. You connect it to the solar panel, making sure the battery and panel are the right distance and let the system do the rest.

50ah is 600 watts, but you are recharging it at the 50% mark so there is still 300 watts left. Your solar panel only needs to produce 300 watts to top the battery. It should take 30 minutes to fill the battery with a 600W solar array, or about four hours with a 200W PV module in ideal weather.

Even if the climate is less than perfect, recharging a 50ah battery at 50% is going to be much faster than recharging an empty battery. Since you are not supposed to let FLA batteries drop below 50%, this is the typical charge time you would get.

If you have a lithium battery it can be a different story. Lithium batteries are designed to be discharged up to 70% or a 100%. You get more power out of it, but this also means longer charge times if fully discharged. Lithium batteries also cost more than FLA, AGM or gel.

The 50% DOD is fairly standard for lead acid batteries, though a few AGM and gel are at 40% or 30%. With lithium it can vary by manufacturer so you have to read the product manual for details on usage.

How Long Does a 50ah Battery Last?

Two factors decide how long a fully charged 50ah battery lasts, the DOD and the amps drawn per hour. The following also applies to other battery voltages.

Since 50 amp hours = 600 watts, it is easy to get an idea of the battery lifespan. If you connect a 600 watt load to the battery, it will run out in an hour. Load with a 300 watt device and the battery lasts around two hours If the battery DOD is 50%, you have 300 usable watts.

But it is not that simple because of the way batteries work. The higher the amps drawn, the faster the battery gets discharged. Most batteries are rated at 5 amps per 20 hours. Meaning if the load draws 5 amps per hour, the battery is good for 20 hours.

If you connect a device to a 50ah battery and it draws 5 amps per hour, the battery gets discharged in 10 hours. If the device or appliance draws 10 amps an hour, the battery will empty in under 5 hours, because the higher the draw, the faster the drain.

All of these is a way of saying that no matter the battery size NK, the runtime cannot be predicted with any exactness. This has nothing to do with any solar panel flaw, but is simply how batteries function. However, you can make a decent estimate using the guideline above. And it is best to always have extra power available.

What 50ah Battery Works Best with Solar Panels?

A lead acid battery is the best option right now. It is more affordable than lithium and while lithium offers better performance and longer life cycle, the low cost lead acid will do fine.

50ah batteries are used to charge small appliances and devices. They are rarely used for extended periods so there is no need to spend more on lithium batteries. You might use a 50ah battery to run a 200W laptop and a few lights for an hour or two for instance. FLA batteries can do the job nicely.

Lithium batteries are ideal for large solar PV systems used for several appliances. If you have an off the grid setup where everything runs on solar power and a generator, a lithium battery bank is worth considering. But for small loads that a 50ah battery can handle, there is no need for it.

Why is My Solar Panel Not Charging My Battery?

The most likely reason is shading on the solar panel. Make sure there is nothing obstructing the cells’ pathway to the sun. If there isn’t any, check the charge controller if it is working. The battery may also take some time to charge if there is limited output from the panel.

Unless the solar panel is damaged, a charge will be produced. However it might take a while especially if there are clouds blocking the sun. The charge will accelerate or slow down depending on how much sunlight is accessible to the panels.

Conclusion

Charging a 50ah battery is simple enough especially if you know how many solar panels to use. With this guide you can charge any battery and know how long it might take.