Is a 120 Watt Solar Panel Enough?

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Usually we add the appliance watts to figure out what solar panel size to get. But you can just as easily find out what a 120 watt solar panel can run with a bit of math. Best of all you can apply these principles to other solar panel sizes.

A 120 watt solar panel can generate 6 to 7 amps an hour on clear sunny days. If there are 6 hours of sunlight the panel can produce 36 amps or 720 watts, which can run a laptop, mobile devices, LED lights and a small fan.

What Can a 120 Watt Solar Panel Run?

A 120 watt solar panel can power various appliances and devices as long as they are under 120 watts an hour This solar panel can run even more appliances if paired with a battery, which we will look at later.

If there are 6 hours of sunlight and the solar panel produces 100 watts an hour, you can run any of the following. Note that you will need a high efficiency solar panel to do these. Our pick is the BALDR 120w PV module because it because it produces better results than other solar panels.

  • 32 inch LED TV – 5 hours
  • Air cooler – 6 hours
  • Aquarium pump – 5 hours
  • Ceiling fan – 5 hours
  • Cordless drill charger – 4 hours
  • Deep freezer – 5 hours
  • Laptop – 6 hours
  • Gaming console – 5 hours
  • Humidifier – 6 hours

These are just examples of what you can run with a 120 watt solar panel. Two things to keep in mind though.

First, the runtimes assume the solar panel produces at least 100 watts an hour. If the output is lower the runtime is going to be shorter. The load might not run at all if the output is too low.

Second, the power consumption varies depending on the model, manufacturer and design. This will affect the runtime.

In the example here for instance, we assume the laptop uses 100 watts. If there are 6 sunlight hours and the solar panel produces 100 watts per hour, the laptop can run for 6 hours.

But if the laptop uses more than 120 watts an hour, the solar panel will not be able to run it. If there are only 4 hours of sun the laptop can only run for that period, assuming the panel produces at least 100 watts per hour.

The runtimes assume you will not be using the appliances at the same time. If you do there will be less power available. For example if you run a 32 inch TV off a 120 watt solar panel, you won’t be able to load anything else since it consumes almost 100 watts.

If you have a USB phone charger you can use that to charge mobile devices and free up this panel for other applications.

Solar panels can run any load as long as it is within capacity. Now we will look at how much power this panel can produce.

How Many Watts Does a 120 Watt Solar Panel Produce?

There are a lot of factors that determine how much current a solar panel generates, but the most important is sun hours.

Number of sun hours per day x solar panel hourly output = total watts produced

If there are 6 hours of sunlight, a 120W solar panel can produce 720 watts a day.

There are some things to consider about this though. 720 watts is the highest possible output, but it can only happen under perfect conditions. In reality the output is probably going to be lower.

There are many reasons why solar panels do not produce their rated wattage. These include the following.

Sunlight Availability

Solar panel wattage ratings are based on the highest possible output. A 120 watt solar panel can generate 120 watts, but only under ideal weather conditions.

Ideal conditions mean no clouds, clear skies, no shading on the panel, the sun is high up the sky etc. Under these conditions the solar panel can produce 120 watts.

Solar panels produce current when sunlight makes contact with the PV cells. The higher the sun is on the horizon, the more sunlight reaches the solar panel.

But the sun’s position changes and by afternoon begins to set. So solar panels cannot maintain a consistent output. Under clear skies, a solar panel might average close to 100 watts or even near 120 watts. But there will be fluctuations and it will certainly drop by late afternoon.

Dirt, Clouds and Solar Power

Solar panels need a clear, unobstructed view of the sun to generate current. Leaves, dirt, clouds and dust particles can and will affect the output.

Under clear skies a solar panel can produce close to 120 watts an hour. Suddenly a cloud passes by and partially covers the sun.

Will this stop the solar panel from working? No, but the output is going to drop. By how much depends on the cloud size and how long it takes to pass the sun.

Dirt, dust, leaves etc. cause the same problems and much worse. Unless the wind carries them away, they will remain on the solar panel and prevent it from running at maximum capacity.

If you live in a typical climate, rain is going to wash away the dirt. But if you live in a dusty place, you have to clean the solar panels every few months. At least have a professional solar cleaning service go over it.

How Many Amps Does a 120 Watt Solar Panel Produce?

Most 120W solar panels have a nominal rating of 12 volts, but it can reach 18 volts during a charge. By dividing watts by volts we can figure out the amps.

120 watts / 18 volts = 6.6 amps

A 120 watt solar panel at 18 volts produces 6.6 amps an hour under normal conditions.

Most solar batteries need only 14.4 volts to charge, so you have to install a charge controller to prevent overcharging and overloading.

Do not be confused why a 12V solar panel charges up to 18V. The 12 volts is applicable only when the panel is not producing current. When sunlight hits the solar panel, the cells start producing electricity and the voltage rises.

For 12V 120W solar panels, 18V is usually the maximum though in some cases it might reach 20V. As the temperature rises, the voltage drops. From 18V it could drop to 17V or even lower.

If 120 watts / 18 volts = 6.6 amps, what happens if it drops to 17V?

120 watts / 17 volts = 7.05 amps

These specifications are for 12V solar panels. If you have a 24V solar system the figures are gong to be different. But you can use these same calculations to figure out the amps.

How Many Batteries Does a 120 Watt Solar Panel Need?

How many batteries you need depends on what you are trying to run with the solar panel. A 120 watt solar panel can charge a 50ah battery in 6 hours. This is if we assume there are 6 hours of sunlight and the panel output is at least 100 watts per hour.

By combining a battery with your solar panel, you get two benefits. You can now use solar power even without sunlight and you can extend the runtime of your appliance loads.

A 100 watt laptop can run for 5 to 6 hours on a 120 watt solar panel. But this assumes the panel produces 100 watts consistently over 6 hours. In cloudy weather this is unlikely. The other limitation is you can no longer use the laptop when the sun goes down.

If you charge a 50ah Ampere Time battery with a solar panel, the laptop can run for 10 to 12 hours. Assuming the panel produces 100 watts for 6 hours, you can switch to battery power and run the laptop for another 6 hours.

Because the current is stored in the battery, you can use it even without sunlight. You don’t have to worry about clouds or dirt because the output is going to be consistent.

We used a laptop as an example but you can do this with any appliance. As long as it is under 120 watts the solar panel and battery can run it.


120 watt solar panels are ideal for camping or if you are on a budget. And under the right conditions you can use it to run various appliances or devices. With the information given here you can determine if a 120W solar panel is ideal for you.