Can an 80W Solar Panel Charge a 12V Battery?

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Portable solar panels come in all shapes and sizes. The 80 watt solar panel is one of the more popular, offering a nice balance between power and size. You can use it for any number of applications, off grid or grid tied. But can an 80 watt solar panel charge a 12V battery? 12V batteries are the most frequently used in solar power systems, so is it possible?

It will take 3 days for an 80W solar panel to charge a 12V 100ah battery provided there are 5 hours of sunlight available,. The fewer sun hours available, the longer the charging time will be.

How Much Power Does an 80W Solar Panel Produce?

An 80W solar panel can produce 400 watts in 5 hours only under the best conditions and peak sunlight. The solar panel cannot produce 80 watts an hour the whole day. In fact most panels produce about 70%-90% of the maximum capacity. If you want to charge a 75Ah 12V battery like the Mighty Max 12V it will take a couple of days.

We all want our solar panels to produce 80 watts, but there are numerous factors that affect energy production like available sunlight, panel design, location etc.. If you want to get maximum value from your solar panel and batteries, knowing how these solar panels and batteries work is necessary.

Let’s say you have an 80W solar panel and want to charge a 30Ah 12V battery. There are 6 hours of sunlight available. To calculate:

30Ah x 12V = Watts
Watts / sunlight hours = solar panel watts needed

In this case, multiply 30 by 12 and you get 360. Divide 360 by 6 and you get 60 watts. So an 80 watt solar panel like the Sunpals Solar Panel Kit is sufficient to charge a 30Ah 12V battery in 6 hours. If you have a larger solar panel then the charge time will be faster.

Can an 80W solar panel charge a 40Ah battery? Let’s do the calculations.

40Ah x 12V = 480
480 / 6 hours = 80

You get 80W, which is right at the limit. Does this mean an 80W solar panel can charge a 40Ah 12V battery? No, because some energy is lost during the procedure. We can only get the theoretical maximum of 80W if the solar panel is perfectly oriented towards the sun and there will be no clouds during the 6 hours of charge time.

That’s not likely to happen so you should get a larger solar panel to compensate for it. If the solar panel is 80W, assume that it can produce up to 60W maximum. This applies to other solar panel sizes as well. Note that this calculation assumes there are 6 hours available. You have to adjust the hours as necessary, but the steps are the same. Click here to see how much sunlight is available in your state.

Output Panel Voltage & Charge Controller

The voltage panel on solar panels affects charge time as well. All open circuit panels have a voltage difference, and this lowers the voltage that can be drawn from it. For 80W solar panels the maximum point is usually 20V 4A.

What does this mean? If you use a PWM charge controller, any power or voltage above 14.4V (14.4V and higher) is discounted. PWM charge controllers only use the 14.4V needed for loading, the rest is not used. If you have an MPPT charge controller, you will be able to use more power. However MPPT charge controllers are more expensive and often not bundled with solar panel kits.

What is the Safe Battery Discharge Level?

The discharge level refers to how low the power has dropped. With lead acid batteries it should not be allowed to drop below 50%. If you have a 70Ah lead acid battery, recharge it when the level drops to 35Ah. This is necessary to prolong the lifespan of the battery. You’ll have to replace it eventually, but you put off that time by years.

Lithium ion batteries are a different matter. Some manufacturers say their battery can be discharged to 0%, while others say recharge at 35%. Check the instructions that came with your battery for the best results. So how does this affect the performance of an 80W solar panel?

Discharging a lead acid battery at 50% does two things. First, you won’t need as much power from the solar panel. In our calculations we used the whole battery capacity, under the assumption it was 100% drained. But what if you recharge it at 50%?

It would look like this:

20Ah x 12V = 240
240 / 6 = 40

Recharging a lead acid battery at 50% only requires 40 watts, something your 80W solar panel can handle. Even if there are only 5 hours of sunlight available, the amount required is still within reach.

20Ah x 2V = 240
240 / 5 = 48

Rounding off you need 50 watts to charge the battery, which your solar panel can produce. This calculation assumes the solar panel produces 4A or 10Ah to 20Ah per hour. With that figure the battery will be charged in 5 hours. Unfavorable weather (cloudy skies, overcast, etc) causes the amps to drop. You could end up with 2A or 3A and a lower Ah.

The RTE (round trip efficiency) may also affect solar panel battery charging. RTE means every time you recharge a battery, you have to put in more than what came out. For lead acid batteries this means an additional 1.1Ah for every Ah taken out. This is not much though, and should not be a factor unless the weather is really overcast.

What Can an 80W Solar Panel Power?

So an 80W solar panel can charge a 30Ah 12V battery, but what else can it do? On its own, not much except charge a few small devices. This is true for all solar panels regardless of wattage. A battery is required to store all the energy the solar panel has absorbed.

If you have a battery and 6 hours of sun, the solar panel can produce up to 400 watts of power. Some of that will be lost during the transmission so it will be less than 400W by the time it gets to the battery. Of course you won’t get perfect sunny days all the time, so on the average an 80W solar panel can produce up to 350 watts a day.

That is sufficient to power up a TV, charge a laptop and lights. You can run a few small appliances as well. Of course you cannot run them all at the same time. The 350 watts is also applicable only during sunny weather. Expect shorter peak sun hours during the fall and rainy / winter season.

What you can do with an 80W solar panel depends on how much power you’re getting and how many devices you are using. Refrigerators, microwaves and washing machines are too much for an 80W solar panel. But for notebook computers, smartphones and other small devices it will be sufficient.

What is the Right Battery for an 80W Solar Panel?

A 12V 35Ah battery is the right one for an 80W solar panel. The solar panel can charge it with 5 hours of sunlight. A 40Ah 12V battery needs 80W to fully recharge, but as explained here, solar panels do not produce the power they are rated for. So an 80W solar panel can generate up to 60W on average.

There are ways to overcome this limitation. You could connect two or more 80W solar panels to gain additional power. You could also charge the battery before it drops to 0%, This cuts down the number of watts required for the battery.

Another way to determine the right battery is to consider how much you will load. What will you use the battery for? How many devices will you run? Is 80W enough? These are the questions you need to answer to find out what battery to get.

While 80W is enough to fully charge a 30Ah battery, it will not be sufficient for large appliances like an air conditioner. You have to consider if the battery and the solar panel are capable of delivering the power you require.


An 80W solar panel is designed for multiple applications. In this article we focused mostly on charging 12V batteries, but as was also made clear here, you can use it for various applications in your home, RV and other situations. As long as you know what the numbers are, you’ll get a lot out of any solar panel.