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400-watt solar panels: what to know

An in-depth, beginner’s guide to 400-watt solar panels

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There are plenty of options for wattage in the solar panel market (including 200-, 250-, 300- and 500-watt panels), but 400-watt panels are one of the most common choices you'll see in use on homes and commercial properties today. Although true power capacity depends largely on the manufacturer and model, 400-watt solar panels are pretty middle-of-the-road for new solar panel installations today.

A solar energy system made up of 400-watt solar panels could be right for you, depending on how much power you need and how many panels you want total.

Key insights

  • A solar panel’s wattage measures its ability to take in solar energy and turn it into electricity.
  • These solar panels have one of the highest capacities readily available on the market today.
  • One 400-watt panel can offset most appliances’ daily electricity use, and combining 400-watt panels together into a larger array can power your whole home without taking up too much room.
  • If you want access to solar power when the sun isn’t shining, you need to connect your panels to a battery or the energy grid.

What can 400-watt solar panels run?

In 2023, most commercially available, high-efficiency solar panels have wattages of around 400 watts, and 400-watt solar panels can run anything from homes to electric vehicles.

What can a 400-watt solar panel power?

If you're considering assembling your own solar energy system, a lone 400-watt solar panel with full sunlight exposure should be enough to power a single appliance or multiple low-power electronics every day.

Just be aware that if you want around-the-clock solar power, your solar panel must be connected to battery storage or the energy grid to safely process and transmit the excess electricity it produces.

We’ll go into more detail about estimating your potential power generation later, but you can expect a single 400-watt solar panel to produce enough daily electricity to run a television, set of lights, fan, laptop or any other device that's relatively energy-efficient, with enough output to occasionally run two or three at a time.

How many 400-watt solar panels do you need for a larger installation?

It may seem obvious, but the number of solar panels you need depends on how much electricity you hope to produce.

System capacity# of 400-watt solar panelsApproximate daily outputAverage annual productionExample use
0.4 kW 1 1,700 Wh 620 kWh Small RV or emergency backup
0.8 kW 2 3,400 Wh 1,241 kWh Full-time RV or off-grid cabin
7.2 kW 18 30,600 Wh 11,169 kWh Average home
12 kW 30 51,000 Wh 18,615 kWh Large home

To completely offset the energy use of the average American home, which consumes around 10,600 kWh of electricity per year, you would need to install roughly 18 400-watt solar panels.

That’s considerably fewer panels than you would need with a weaker wattage. Because a 400-watt solar panel takes up about 21 square feet of space, the typical U.S. home mentioned above would need only 380 square feet of usable space to accommodate enough 400-watt solar panels to offset its energy use. (In contrast, you’d need 40 200-watt solar panels for a similarly sized system, and they would take up over 720 square feet, which may be more space than your roof has available in full sunlight.)

Higher-wattage solar panels from manufacturers like SunPower are great for homeowners attempting to make the most out of their usable roof or property space.

When Chad, a ConsumerAffairs reviewer from Utah, called SunPower for an estimate, the company’s more efficient solar panels actually made the installation cheaper than a competitor's proposal. “It was quite a bit cheaper than the previous bid I had gotten partly because the efficiencies are so high and the quality that the other product quoted would require more panels, which increased the cost,” Chad said.

» MORE: Solar panel size and weight: a guide

How much energy can a 400-watt solar panel produce?

On average, a 400-watt solar panel can produce anywhere from 1.2 to 3 kilowatt-hours per day in North America, depending on its location, the time of year, the weather and the panel’s efficiency.

Although solar panels work in various capacities throughout the day based on light exposure, photovoltaic systems generate electricity at maximum efficiency during “peak sunlight hours.” On average, peak sunlight conditions usually last for between three and six hours each day in the U.S.

When you’re calculating how much energy your 400-watt solar panel can theoretically produce, resources like the Global Solar Atlas can help you discover your area’s expected number of peak sunlight hours and average solar power potential. For a bit of perspective, let’s look at how much power the Global Solar Atlas predicts a 400-watt panel could produce in two very different areas.

The Global Solar Atlas estimates a daily solar power potential of 4.982 kilowatt-hours per 1 kilowatt of system capacity in West Hollywood, California. Given that 400 watts is 40% of 1 kilowatt, a 400-watt panel could theoretically produce as much as 2 kilowatt-hours of electricity per day in this sunny Southern California city.

In Seattle, the Global Solar Atlas estimates just 3.429 kilowatt-hours of daily solar power per kilowatt of capacity installed. This equates to an average of roughly 1.4 kilowatt-hours produced by a 400-watt solar panel.

» LEARN: How do solar panels work?

Are 400-watt solar panels right for you?

If you’re looking to install a residential solar energy system, there is a good chance that 400-watt solar panels (or something similar) may be the best solar panels for your installation. (If you’re working with a professional solar company in 2023, it will likely recommend installing high-efficiency solar panels with capacities somewhere between 350 and 450 watts.)

With that in mind, even a 400-watt solar panel or two can also generate a tremendous amount of power in small-scale setups for off-grid use or backup home power. Just remember that whether you’re installing solar panels on your boat, van or house, consulting an expert is always a good idea for the safety of your property and investment.

» MORE: Best solar panels in 2023

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    How much do 400-watt solar panels cost?

    As of publishing, 400-watt solar panels typically cost between $300 and $600 per panel.

    Just be aware that the price of your solar panels is only part of what you can expect to pay when going solar, since you’ll also have to budget for wiring, an inverter and a battery system.

    How many batteries do I need for a 400-watt solar panel?

    Knowing that 400-watt solar panels can generate 2,000 watt-hours of electricity (or more) every day in peak conditions, you should consider a battery with a storage capacity of 2,500 watt-hours or greater.

    Although energy storage equipment can be expensive, there is no limit to the size of a battery a 400-watt solar panel could potentially fill over time, and it’s good to have more storage than you think you’ll need.

    How many amps does a 400-watt solar panel produce?

    While sending power to an inverter or battery through a charge controller, single 400-watt solar panels usually produce electricity with a current of around 10 amps. If you string multiple panels together in a parallel circuit, the amperage will increase with each panel you add, though.

    ConsumerAffairs writers primarily rely on government data, industry experts and original research from other reputable publications to inform their work. Specific sources for this article include:
    1. U.S. Energy Information Administration, “How much electricity does an American home use?” Accessed March 1, 2023.
    2. Global Solar Atlas, “Map.” Accessed Feb. 28, 2023.
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