What Can a 400 Watt Solar Panel Run?

By Manual Thomas

Last Updated:

Not all solar panels are created equal.

Some are more powerful than others or can last longer.

And in this article, we’ll explore what a 400 watt solar panel can do, how much energy it produces, and how much it’ll cost you.

So without further ado, let’s dive into the world of 400-watt solar panels and find out what they can do!

Key Takeaways

  • The dimensions of a 400-watt solar panel are 80 x 40 inches and it weighs about 50 lbs.
  • The 400-watt solar panel generates about 1,761 kWh per day but still depends on the amount of peak sunlight available
  • A 400-watt solar panel can run many small appliances, such as a fan, laptop charger, TV, or LED lightbulbs.
  • You need a 12V battery with 183Ah and 80% DoD or a 24V battery with 148Ah and 50% DoD to store the power generated from a 400-watt solar panel.
  • A 400-watt needs a 41.7A charge controller to manage the flow of power between the solar panel and the battery.
  • You need a 270W inverter to convert the DC power generated by the 400-watt solar panel into AC power.
  • A 400-watt costs around $300-$900 excluding the cost of installation and other components necessary to complete your solar power system.

What Is a 400-Watt Solar Panel?

Before we get into what a 400-watt solar panel can run, let’s get one thing straight: what is a 400-watt solar panel?

Solar panels are rated in watts, which is a measure of the amount of energy they can produce under Standard Test Conditions (STC).

But how exactly do they test solar panels?

They expose them to light levels of 1,000W/m², cell temperature of 25°C, and a solar spectrum that matches the “air mass 1.5” solar spectrum.

Then they measure how much energy the panel can actually produce under these conditions over the course of an hour.

So 400-watt rating means that the panel will generate 400 watts of power for every hour of 1,000W/m² sunlight it receives.

How Much Power Does a 400-Watt Solar Panel Produce?

To calculate the total power output of a solar panel, you have to take into account the peak sunlight hours in your area.

You can use this calculator to find out the average number of peak sunlight hours for your location. Just enter your location and the calculator will do the rest.

I live in North Carolina, so I will use 5.12 hours of peak sunlight per day as an example.

Solar Panel Power Output (Wh) = Solar Panel’s Rated Wattage (W) x Number of Peak Sun Hours (h)

For our example:

Solar Panel Power Output (Wh) = 400 W x 5.12 h = 2,048 Wh per day

However, any solar system experiences some losses such as shading, electrical wiring losses, and thermal losses.

So, if we assume around 14% losses from these factors our total power output would be:

Solar Panel Power Output (Wh) = Solar Panel’s Rated Wattage (W) x Number of Peak Sun Hours (h) x (1-0.14)

For our example:

Solar Panel Power Output (Wh) = 400 W x 5.12 h x 0.86 = 1,761 Wh per day

What Will a 400-Watt Solar Panel Run?

Now that you know how much power a 400-watt solar panel can produce, let’s calculate how much power certain appliances can consume.

To do so, you can use this equation:

Appliance Required Power (Wh) = Appliance Power Rating (W) x Number of Hours Used (h)

Let’s suppose you have a laptop with an operating wattage of 45 watts and want to run it for 4 hours.

So the required power for your laptop would be:

Appliance Required Power (Wh) = 45 W x 4 h = 180 Wh

So, will the 400-watt solar panel be able to run your laptop? 

Of course, it will!

Since the solar panel generates 1,761 Wh per day and your laptop requires only 180Wh for 4 hours, it would be more than enough to run your laptop. 

But the question here is, how many hours exactly can you run your computer on a solar panel

We can calculate that by using this equation:

Number of Hours Laptop Can Run = Total Solar Panel Power Output (Wh) / Appliance Required Power (Wh) 

For our example:

The Number of Hours Laptop Can Run = 1,761 Wh / 45 Wh =39 hours.

Using the same method, you can see that a 400W photovoltaic panel can also run a room air conditioner for 3.5 hours.

I have a solar-powered shed that contains a TV, a small refrigerator, 3 LED lights, a laptop, 2 fans, a phone charger, and a Wi-Fi router, all of which are turned on for 4-8 hours a day. 

So, will my 400-watt solar panel be able to cover the power needs of all these appliances? 

To find out, you should construct a table as follows:

ApplianceNumberWattage/ApplianceHours of UsageTotal
Small Refrigerator 175W8 hours (30% duty cycle)600Wh
LED Lights35W8 hours120Wh
Laptop145W4 hours180Wh
Fan 250W4 hours400Wh
Phone Charger15W4 hours20Wh
Wifi Router110W7 hours70Wh
Total =1,710Wh

As you can see, all these appliances together consume 1,710 Wh per day, which is less than the total power output of the 400-watt solar panel. 

So yes! Your 400-watt solar panel will be able to run all these appliances at the same time.

What Battery Size Do I Need for a 400-Watt Solar Panel?

The solar panel will generate electricity during the day, but it can’t store it.

So, you will need to use batteries to store the energy so that you can use it at night or during cloudy days.

To calculate the battery size you need for a 400-watt solar panel, use this equation:

Battery Size (Ah) = Solar Panel Daily Output (Wh) / Battery’s Voltage (12/24V) / DoD (0.5/0.75/0.8)

We know that our 400W solar panel can generate 1,761Wh per day.

So, for a 12V battery with 80% DoD, we can calculate the required Ah as follows:

Battery Size (Ah) = 1,761 Wh / 12V / 0.8

Battery Size (Ah) = 183 Ah

So, you can use a 12V battery with 183Ah for a 400W solar panel or a 24V battery with 148Ah and 50% DoD to get the same result.

What Size Charge Controller for a 400-Watt Solar Panel?

Connecting your solar panels straight to your batteries is not a great idea as it can overcharge and damage your batteries.

Therefore, you need to use a charge controller between the solar panel and batteries.

Charge controllers regulate the flow of electricity from your solar panel to the battery, ensuring that it’s not overcharged.

To calculate the required charge controller size for a 400W solar panel, you can use this calculator.

For my example, I selected the following options:

  • Solar Panel Wattage: 400W
  • Solar Panel Voltage: 24V
  • Battery Bank Voltage: 12V

The result was that I need a 41.7A charge controller for my 400W solar panel.

I recommend you go for MPPT charge controllers because they are more efficient than PWM charge controllers and will give you better performance.

What Size Inverter for a 400-Watt Solar Panel?

Solar panels generate direct current (DC) electricity. Still, if you want to use it for your fan, TV, laptop, or any other appliance that runs on AC electricity, you need an inverter.

Inverters convert DC electricity to alternating current (AC) electricity and the size of the inverter you need depends on your total wattage load.

If we talk about a grid-tied solar system, we should multiply the solar DC rating (400W) by 1.15.

Therefore, you need an inverter of at least 460 watts for your 400-watt solar panel.

But we’re just talking about a small off-grid system running a few appliances here, so let’s calculate the exact size of the inverter.

The best way to calculate the size of the inverter for your 400W solar panel is to add up all the wattages of each appliance:

Solar Inverter Size (W) = Sum of All Appliance Wattages Running at the Same Time

Solar Inverter Size (W) = 80W + 75W + 5W + 45W + 50W + 5W + 10W

Solar Inverter Size (W) = 270W

In our case, you need an inverter of at least 270W to power all the appliances.

How Many 400-Watt Panels Does It Take to Power a House?

The short answer is it depends.

To calculate the exact number of solar panels required to power your home, you need to consider factors like your electricity usage, the peak sun hours in your area, the type of solar panel you are using, and any other equipment.

However, according to the EIA, the average monthly electricity consumption of a US home is 886 kWh per month or about 30 kWh per day.

So, if we assume a peak sun hour of 5.12 hours per day and system losses of 14%, the equation will look like this:

Number of 400W Panels = (Daily kWh Requirement * 1.14) / (Peak Sun Hours per Day*Solar Panel Output)

Number of 400W Panels = (30kWh * 1.14) / (5.12hrs * 0.4kW)

The Number of 400W Panels = 16.7 ~ 17

Therefore, it would take 17 panels with 400W capacity to power an average US home.

How Much Does a 400-Watt Solar Panel Cost?

A 400W solar panel costs between $200 and $300, depending on the type of panel and its efficiency.

But keep in mind that while the upfront cost of solar panels can be high in addition to other system components like batteries, inverters, etc. 

You can still save a lot of money in the long run by incorporating solar energy into your home.


How Many Batteries Will a 400-Watt Solar Panel Charge?

A 183Ah battery with a voltage of 12V and 80% depth of discharge (DOD) will be charged by a 400-watt solar panel without any issues.

How Fast Will a 400-Watt Solar Panel Charge a 12 Volt Battery?

A 400-watt solar panel will take about 4 peak sun hours to fully charge a 12V battery.

How Long Will a 400W Solar Panel Take to Charge a 100Ah Battery?

A 400W solar panel will take about 4 peak sun hours to charge a 100Ah battery.


As promised, I’ve covered the various aspects of using a 400-watt solar panel.

We went through what 400W means, how much energy will it produce, what appliances you can run with, and what size charge controller, battery, and inverter work best with 400-watt solar panels.

Do you still have any questions about 400-watt solar panels? Let us know in the comments and we’ll be happy to answer them.

Manual Thomas

Manual is an accomplished electrical engineer with seven years of experience in the solar industry. He has worked on a wide range of solar projects, from small residential installations to large commercial systems. When he’s not working on solar projects, Manual enjoys spending time outdoors and staying active. He is also an avid reader and enjoys learning about new technologies.er content writer

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