How Many Batteries Can a 50W Solar Panel Charge?

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50W portable solar panels are very popular, as it offers plenty of power without being too heavy. You can use it for small appliances and you can combine it with another to create a 100W solar panel. But how many batteries can a 50W solar panel power? How effective is it for electronic devices and appliances?

A 50W solar panel can charge a 150ah deep cycle battery in six hours. This is possible if we assume ideal weather conditions and the solar panel can produce 50 watts an hour.

What is the Best Battery for a 50W Solar Panel?

A 50W solar panel can produce up to 300 watts with six sun hours, so the biggest battery it can charge in a day is 25ah. good choice would be the Kepworth 12V Universal 25ah LiFePO4 Battery as it works great with different types of solar panes.

If you are charging a higher capacity battery, a 50W solar panel won’t be enough. You can either buy a 100W solar panel like the Rockpals 100W Solar Panels or another 50W and connect the two. Remember that solar battery capacity is measured in amps while solar panel capacity is measured in watt hours.

To convert amp hour to watts, multiply the amp hour by its voltage. The result is the watt hour.

So for a 12V, 20Ah battery, that is 240 watt hours (12 x 20 = 240). Since a 50W solar panel can provide up to 250W, you can use it in this case. However we would recommend a 100W solar panel for regular 25ah and higher charging.

To calculate how many amp hours, divide the watt hours by the volt. Using our 50W solar panel and 12V battery example: 50/12 = 4.16. That’s 4 amps per hour so the panel can charge a 20Ah battery in 5-6 hours.

If it’s summer then the 50W panel will be fine. But if it’s cloudy, the solar panel production will dip. With dual 50W panels you can make up the difference and charge the battery to full capacity. The solar panel must also be properly oriented to receive the maximum amount of sunlight possible.

There are two things you need to consider, the solar panel watt size and the battery capacity. Make certain the battery you choose can draw the power you require. That is, if it’s fully charged it will provide the draw needed to last several days. Your solar panel must also have enough power to charge the battery.

How Long Will it Take a 50W Solar Panel to Charge a 12V Battery?

Divide the solar panel watt hours by the battery hours. This gives you a good estimate of the charging time.

Volts x amps = battery watt hour
Battery watt hour / solar panel watt hour = time it takes to charge

So if you have a 12V 20ah battery and a 50W solar panel:

12 x 20 = 240 watts
240 / 50 = 4.8

It will take 4.8 hours to charge a 20Ah battery with a 50W solar panel under ideal condition. This calculation assumes the battery is completely drained. If the battery isn’t 100% drained, you have to replace the battery watt with whatever amount needs to be charged in.

If you recharge a 20ah battery at 50%, the calculation would be:

12 x 10 = 120 watts
120 / 50 = 2.4

The charge time gets cut in half to 2.5 hours. This saves you a lot of time and prolongs the battery’s lifespan. Some would argue that this applies only to lead acid, but charging lithium ion before it drops below 40% helps extend its lifespan as well. While lithium ion is better at deep cycling, early recharging doesn’t hurt. Keep this in mind if you want to charge a 50ah battery with solar panels for instance.

If you need to use 240 watts a day, get a 40 or 50ah battery. This allows you to use all the watts you need without draining the battery down to zero. You may have heard this “charge at 50%” too often, but there is good reason for that. Lead batteries do not handle 0% charging well and it has a detrimental effect in the long term.

How Many Amps for a 50W Solar Panel?

This is another common question and it is answered in the calculations above. What this question means is asking is how many amps can a 50W solar panel power. A 50W solar panel can produce 4 amps per hour, so that is 20ah in 5 hours of sunlight.

A fully charged 20ah battery can power small appliances, a laptop, mobile devices etc. As long as the battery can store energy from a solar panel you can use it for years. A solar panel without a battery however, can only be used in the daylight as energy is not stored. Solar panel power is only in DC so you cannot use AC powered appliances. You’ll need an inverter for that.

Why is My Battery Taking So Long to Charge?

The most likely reason is there is not enough sunlight hitting the panel. All charge time calculations and solar panel ratings are based on ideal conditions. If the weather isn’t ideal -which is most likely the case – then the charge time will be slower.

The other reason is no solar panel is perfect. Some energy is lost during the transmission from the solar panel to the battery. This is normal and not a sign of damage. If you’re buying a solar panel, look for an efficiency rating of at least 20%. A rating between 20-25% is great and should produce outstanding results. No solar panel is 100% efficient, but 20+% plus clear skies are good enough.

Because solar panels are not 100% efficient, most users add 20% to the capacity they need, or add 20% to the total charge time.

12 volts x 20 amps = 240 watts
240 watts / 50 watts = 4.8

With an 80% efficiency rate (or 20% energy loss), divide the value by 0.8

4.8 / 0.8 = 6

So it is going to take 6 hours to fully charge a 20ah battery with an 80% efficient 50W solar panel

All these calculations are applicable to other solar panel and battery sizes. Simply replace the watts, volts, amp hours and available sunlight hours. Depending on the season and where you are, you could get up to 7 hours of sun or less than 5. That, more than anything affects charge time.

If you have sufficient power but the battery still isn’t charging, it could be there is a problem with the battery itself. Check first for signs of loose wiring. If they are tight, unplug the battery and look for signs of corrosion or damage. A corroded battery needs to be replaced immediately.

How to Make a 50W Solar Panel Charge Batteries Faster

The following tips applies to all solar panels and solar batteries.

Recharge at 50%: as previously mentioned, charging at this level is good for the long term. It also means reducing the charge time by 50%. This also means that 50W is definitely going to be enough. Even on cloudy days, charging will be faster.

Get a high rated solar panel: while sunlight is the most important, having a high efficient rating is essential. This is crucial in getting the most energy from the sun when it is available.

Know What Battery Capacity You Need: if you are constantly having to deplete the battery, you need a larger capacity. The money you spend on getting a higher capacity battery is going to pay for itself soon enough. Of course you should also pair it with a sufficiently sized solar panel. If that 50W panel isn’t enough, you can pair it with another 50W panel and build up an array.


It’s easy to get frustrated with solar panels if they don’t produce the energy you expect. but as we’ve shown, solar power can be very effective. Once you know how to compute the watts, amp hours and volts, it’s easy to see how you can maximize a 50W solar panel for powering batteries.