400 watt solar panels: a consumer guide

Solar panel efficiency keeps getting better. Back in 2013 - which really isn’t that long ago - I had 260 watt solar panels installed on my home.

Today, most homes will use solar panels in the 300+ watt range. But now, manufacturers are starting to put out panels that exceed 400 watts. These products are at the premium end of the market, which means that you can expect to pay more for them. However, they can actually help save you money too. This article will give you the lowdown on this latest development in solar panels.

Residential and commercial solar panels

Before we get into it, it’s worth explaining that solar panels come in two size ranges: residential and commercial. They differ by physical size, with residential panels being typically less than 80 inches long, while commercial solar panels are often 80 inches long or more.

Within a product line, a manufacturer will often offer panels in residential and commercial sizes. The technology is often the same. The only difference is the size.

Why bother with different sizes? Commercial panels might not fit as well on the small rooftops of houses. In addition, heavier commercial-sized panels often weigh more than 50 pounds, making them harder for small residential installation crews to handle.

Commercial solar panels have exceeded 400 watts for awhile now, but those are not what this article is about.

What are 400 watt solar panels?

A 400 watt solar panel has a nameplate rating of 400 watts of power output. In more technical terms, this means that the STC rating of the panel is 400 watts or more.

In practice, a solar panel doesn’t achieve its nameplate rating in the real world due to high temperatures and other factors. You can expect a panel to achieve perhaps 75-80% of its rated output, which means that a 400 watt solar panel might realistically only hit 320 watts on a cool and sunny day.

You can read my article on solar panel specifications to learn more about STC ratings.

Why 400 watts can be a bit of a marketing gimmick

The power output of a panel doesn’t actually tell you how efficient it is: remember that commercial sized panels use the same silicon but have higher output because they’re bigger.

While manufacturers are achieving 400 watts by using high efficiency silicon cells, often they also “cheat” a little by increasing the size of the panel.

For example, the older generation QCells Q.PEAK DUO G8 panel is available with a power output of up to 360 watts. In comparison, the latest G10+ panel is available in a 415 watt size.

While the G10+ has a rated efficiency of 21.1% and the G8 reaches only 20.1%, the G10+ is also 5.5 inches longer and 0.60 inches wider.

You’ll find that this is the case with other manufacturers too. This is why the 400 watt benchmark is a little misleading. The high output implies that a technological advancement has been made - which is partly true, because these panels use the highest efficiency silicon from a manufacturer. However, they’ve also made the panels bigger, which really isn’t an advancement.

What are the advantages of 400 watt solar panels?

These high output panels are a premium product, so expect to pay more. However, there are some advantages.

One is that you can use fewer microinverters or power optimizers. These inverter electronics are paired to each solar panel on your roof, so using high output panels means that you need fewer of them. This cost savings on inverter electronics might mean a lower total system price, even if it means spending more on the panels.

Another is that you can save on labor. Home solar installers really like to finish a job in one day if possible. If they can’t, sending the installation crew out for a second day will bump up the project costs - not just because of the labor involved, but also the scheduling challenge it adds. (Good solar installers tend to be very busy these days.)

If the crew needs to deal with fewer panels and microinverters, that’s fewer components they need to bolt down and wire together, saving them time and money.

How many 400 watt solar panels will your house need?

Assuming a real world performance of 80% of the STC rating, you would need about 4 or 5 of these panels to power a hair dryer. How about your whole house?

If you use The Solar Nerd calculator, you can get a quick estimate. After you put in the parameters for your home, the calculator will give you a range of the number of solar panels you will need for your home, depending on whether you choose relatively low power 300 watt panels or 440 watt panels, which are the highest output panels currently available.

(The calculator is just for a quick estimate, so get a home solar quote for a more accurate assessment.)

Which manufacturers have 400 watt panels?

400 watt panels are the latest trend, so many of the manufacturers have jumped on the bandwagon. Here’s a partial list of products that are currently on the market:

Bottom line: 400 watt panels might be right for your project, but read the specs closely

As you can see above, quite a few manufacturers have jumped on the 400 watt solar panel bandwagon, but not all of them are the same. For example, you can see that Mission Solar and SunPower both have 400+ watt products, but the Mission Solar panel is only 87% as efficient as the SunPower.

This illustrates the fact that if your goal is to minimize the footprint that solar panels have on your roof, you’ll want to pay closer to the efficiency numbers. That said, high output panels, regardless of their efficiency, have the advantage of giving your installation crew fewer parts to install, as well as needing a lower microinverter or power optimizer part count.