How Long Will a 200W Solar Panel Take to Charge a Battery?

When people ask how long does a 200W solar panel take to charge a battery, they usually refer to 12V , 100 ah batteries, so that is what is covered in this guide. However you can use the formulas here for other battery and solar panel sizes as well.

A 200W solar panel can charge a battery in 5 hours. This assumes the battery has a capacity of 75ah and is rated at 12 volts.

How to Calculate 200W Solar Panel Charge Time For Batteries

Because solar panel output is in watts and battery capacity is in amps, we need to do some conversions.

Multiply battery amp hours by its voltage to get the watts t (AH x V = WH)

The formula is:

Battery capacity (in watt hours) / solar panel power (in watts) = battery charge time

In less than ideal conditions, double the charge time.

In ideal situations, a 200W solar panel generates 200 watts an hour. 12V 100ah is 1200 watts, so it would take 6 hours for the panel to charge 1200 watts into the battery (200 x 6 = 1200).

An efficient solar panel is going to speed up charging. Our pick is the Newpowa 210W PV Module as it charges rapidly and is compatible with different types of batteries.

But if is a cloudy day it might take 12 hours to charge the battery. Depending on where you are, that may be realistic or pessimistic. If you want to run appliances on solar power however you need to consider all scenarios. Most of the time the weather will not be perfect, so giving your panel extra time is often necessary.

In some cases it might take more than 6 hours but not 12. Solar panel performance depends on several variables as we shall show, and this also applies to the battery you are charging. Some batteries are more efficient than others, and the discharge rate is crucial too.

The computation given here assumes the battery is completely discharged. If you recharge at 50% (as should be the case with gel, FLA and AGM), the charge time will be 3 hours or so.

A 24V 100ah battery is going to produce different results because the 24V stores more watts.

100ah x 24V = 2400W

2400W / 200W = 12

It takes 12 hours to fully charge a 24V 100ah battery, double the time of a 12V. Keep that in mind if you want to use a 24V battery. While those are more efficient at discharging, it does take long to top off. You can use this formula for a 200ah battery as well.

What is the Charge Time For a Lithium Battery?

Lithium battery charge time is determined by dividing battery size in watt hours by volts. Charging a 100ah lithium battery with a 200W solar panel is often faster compared to a 100ah lead acid battery.

The Battle Born 100ah lithium batter for example, is equal to 1200 watts. However the charge time slows down at 90%, so a full lithium battery is really about 90%. With other battery types it could even be lower. This is not a battery defect, that is just how batteries charge and discharge.

The benefit of lithium batteries – one of many – is the high level of usable power. Depending on the manufacturer you could have a usable level of up to 90%, meaning you can use the battery until 10% is left. With other lithium batteries it is 30-35%, but still better than the 50% for FLA batteries.

Even so there are factors that could slow the charge time. Among them are:

• Solar panel voltage drop is greater than its rated peak voltage
• Energy lost as heat
• Energy consumed by circuits
• High temperatures are bad for batteries in general

Those factors above are applicable for lithium ion and lead acid batteries.

What is the Charge Time For a Lead Acid Battery?

There are many types of lead acid batteries, but what most share in common is you must never let them fall below 50%. A 100ah lead acid battery only has 50ah usable per charge.

You can only avail of half the capacity, but it does cut charge time by 50%. In effect your solar panel only needs to supply 50ah to top a 100ah lead acid battery, provided you recharge at 50% or higher.

Some lead acid batteries like AGM and gel have a better than 50% discharge rate. They are not as energy efficient as lithium, but at least the charge time will be faster.

Bear in mind that the stated battery capacity is not what your appliances will receive. There are energy losses in solar cables, inverters and solar panels. The energy loss varies but do not expect to get the full 100ah / 1200W to be available for your appliances or devices.

Why is My Solar Panel Taking So Long to Charge Batteries?

Solar panel ratings are based on maximum peak output. A 200W solar panel can produce up to 200W an hour, but it reality it is probably 280W to 290W an hour on a clear day. On cloudy days the output will be even lower. This doesn’t mean your solar panel is defective. There are simply a lot of elements that determine solar panel output.

Sun and Solar Panel Angle

You can expect 4 to 7 hours of sunlight every day depending on where you are. Obviously the more sun hours the better your solar panel will perform. But it’s also about the angle of the sun and your panel.

Directing your solar panel to true south helps, but as the sun angle changes so does the amount of energy your solar cells receive. Solar panels get the highest amount of energy when the sun is overhead. As the sun goes down, the energy and intensity decreases.

You can adjust the solar panel’s angle, but that is only possible if it is on a tilted RV mount . Even then it requires too much work. Even as the sun angles change your solar panel will still produce electricity, but it won’t be at 200W. There will be times when peak output is attained, but don’t expect it for the entire day.

Location and Season

A 200W solar panel in Nevada is going to charge batteries faster than a 200W solar panel in Seattle. Even if it is summer the sun intensity will be greater in some states due to their geographical location.

You always have to consider location when charging batteries or using solar power to run anything, be it appliances, tools or a shed. You can still charge batteries in cold climate locations, but it will take more time.

The season is tied in to this as well. It is true solar panels don’t perform any better at high temperatures, but intensity is higher during the summer. During the other seasons, the sun is lower on the horizon so solar panels cannot produce as much power.

So when we say it takes 6 hours for a 200W solar panel to charge a 100ah battery, we assume it is the summer or a clear day. The charge time will take longer during the cold season. It might even take a couple of days if sunlight is limited.

Efficiency

Have you seen solar panels advertised as 21% efficient, 23% etc.? The efficiency rating tells you what percentage of the sun’s rays hitting the solar cells gets converted into electricity. Most solar panel efficiency ratings are around 18%-25%, so the higher the better.

That efficiency rating may sound low, but a 20%+ efficiency is sufficient for residential and commercial use. This should not be confused with the rated output though. Rated output is measured in watts (200W for example), and output is usually 85%-90% effective. In ideal weather it can reach 100%.

Loose Wiring

Loose or faulty wiring will slow down charging or worse damage the solar system. Make sure your solar panels are grounded to avoid any potential accidents. If charging has slowed compared to the same time period before, check the system cables.

Slow charging is not the only potential problem with loose wiring. Solar arcing is often due to loose or damaged wires, and in a worst case scenario even start a fire. Again this can be avoided if the panel is grounded and there is sufficient space between your solar array .

Charge Controller Issues

The charge controller keeps track of the current flowing into the battery. It keeps the battery from overcharging, overloading or overheating. At least that’s how it is supposed to work.. A poorly made or incompatible controller can damage your panels.

Make certain the charge controller is compatible with your PV modules and battery before starting a charge. If you buy a solar panel kit, a charge controller may be included already. Refer to your solar panel manual for info on what charge controller size to get. A 12V solar system with 14 amps should have a 20 amp charge controller.

Conclusion

We all want our solar batteries charged as quickly as possible, but as discussed here, we need to be flexible with our time expectations depending on location and other factors. During hot sunny days you will get a full charge in 6 hours. But expect longer wait times during overcast days, so take the time to plan.