400 Watt Solar Panel (Everything you need to know)

With the 400 Watt solar panel, you can now produce more power in less space!

Solar Energy is fueled by innovation, constant research of efficiency and durability. The latest market standard, the 400 Watt solar panel, is now available to all, and it is a game-changer for residential solar systems.

Let’s take a deeper look into its specifications and we’ll see why 400w in one panel makes all the difference.

Interested in sizing your own solar system? Give our solar calculator a try.
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What Is A 400 Watt Solar Panel Made Out Of?

A solar system set up on a residential house

As magical as it sounds solar panels are devices that convert sunlight into electricity. They do so with few components and with no moving parts, making them the simplest and most robust energy production system ever made.

Their deep blue or black color is due to their main active material: silicon. Let’s see how we came out with this material over the years.

Modern science now clearly describes the working principle of solar panels. It took the work of many great scientists of the 20th century to fully explain the way solar cells operate – most notably the multi-Nobel Prize awardee, Albert Einstein

In 1905, in relation to quantum physics, Einstein theorized that light is both a wave and particle-carrying energy. The photon (a light particle and a wave) is born, and together with it, the photoelectric effect explains the generation of electrons (electricity) when a certain metal is exposed to light (the sun).

You might think that solar technology is old (more than one hundred years old) but from Einstein’s theory to the 2022 state-of-the-art 400-watt panel, generations of scientists worked together on one goal: improving efficiency.

The efficiency of a solar panel is basically the power output of the solar panel over the power it will receive from the sun.

Efficiency = Ppanel(W)/Psunlight(W)

Looking for the most efficient material to achieve the photoelectric effect, scientists found out that silicon was one of the best candidates. Later on, manufacturers also adopted silicon as it is easily accessible and widely available on the planet.

As an electricity generator, solar panels are by far the simplest systems. They are made of few components and with no moving parts.

  • Solar Cells
  • Encapsulant
  • Aluminum frame
  • Front window, self-cleaning glass
  • Silver/Copper current harvester
  • Regular DC wiring

The basic building block of your solar panel is the solar cell. Multiple solar cells are electrically connected to produce the powerful 400W solar panels.

Each solar cell is made of a crystalline silicon wafer, stripped with conductive layers for electricity harvesting (generally a mix of silver and copper).

The assembly of solar cells is then encapsulated and framed with aluminum – a front self-cleaning window completes the system.

And here you have a solar panel with 25 to 30 years of durability!

Most of the scientific research effort is focused on the active material. Thanks to years of research, silicon-based solar cells are now reaching their maximum theoretical efficiencies, scientists are looking beyond silicon for more efficient materials.  

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

solar panels facing the sun
Solar panels facing the sun

If you think that your 400-watt solar panel will produce 400w of power, you’d be both right and wrong. Let’s take a closer look to understand why.

Multiply the maximum system voltage (Volt) and the amperage (Amp) of the panel to obtain the instant output power (Watt) of your solar panel.

Ppanel(W) = Ipanel(A)*Vpanel(Volt)

In the specifications of your solar panel, you will find the circuit current and circuit voltage at their maximum values.

For a 400 watt panel, it’ll generally be 40 Volts and 10 Amps, which is equal to 400W!

So we can see that a 400w panel can produce 400w of power. But can it achieve that under real-life conditions?

Those figures greatly depend on the sun’s irradiance: the power of sunlight.

As a natural source of energy, the power of the sun is intermittent, it varies during the day and depends on your position on the planet.

To determine the power of their products, the industry has chosen a standardized test condition (STC) in a lab with direct sunlight irradiance power of 1000W/m2 at a temperature of 25°C. In real outdoor conditions, you will reach this sun intensity on a beautiful and clear day at the zenith (around noon).

A clear sky on a beautiful summer day, best conditions for solar production

As you can see, these ideal conditions are scarce in real life. Furthermore, other factors will influence the power output:

  • Outdoor temperature
  • Exposure of the panel and local shadowing
  • Cleanliness of the front window

Let’s see our tips to maximize your power output:

Natural cooling with a 15 cm space between your panels and the roof will do the job.

  • Cool down your panels!
  • Expose your 400 watt panels to full sunlight

Silicon solar panels love direct sunlight, avoid local shadow (from trees or other buildings), find the optimal angle to install them.

LocationOptimal Exposition Angle
Northern hemisphere37° to 45°
Southern hemisphere30° to 35°
  • Check your optimal tilting angle to maximize your production

Clean them from time to time. The 400w solar panels are self-cleaning. However, gentle water cleaning every month will slightly improve the power output.

We have created a DIY solar system guide where we talk about optimal exposition angle in-depth.

How Much Energy Does A 400-Watt Solar Panel Produce?

More than the power output of a solar panel, the real energy production in kWh is what matters the most to residential users. After all, is what we will pay our electricity provider at the end of every month, right?

To obtain your energy production, multiply the instant power output by the time.

Epanel(kWh) = Ppanel(kW)*Time(hour)

What can you expect from your 400 watt solar panel on an average day?

Let’s look at the photovoltaic production potential map.

Thanks to a constellation of satellites scanning the earth continuously, we now have a clear view of the solar energy received in every part of the planet.

Global solar energy production potential

As you can see, your production potential greatly depends on your location on the planet. With the same system, you might produce three times more energy in South Africa than in the United Kingdom!

Let’s take an example: in Los Angeles, California, the average energy production potential of a 1kW solar system is 1805 kWh/year, or 4.9 kWh/day.

With one 400w panel, your production potential is close to 2 kWh/day.

Evaluate your solar energy production potential here!

How Much Does A 400 Watt Solar Panel Cost?

The current buying price of a 400-watt solar panel is roughly 350 USD, but it is virtually free after a couple of years. What’s more, you will earn from it for more than 20 years.

Nowadays, the solar industry is unique.

It is blooming with constant technological development, enabling products with lower prices, better efficiency, and durability, lasting years.

In California, for example, the electricity costs 0.2559 USD per kWh, as one 400w panel is expected to produce 730 kWh per year, saving you 187 USD every year. In less than 2 years your panel is paid back, with 20 to 25 more years of production in sight!

So over its entire lifetime, your solar panel will easily save you more than 4500 USD!

How Many 400W Solar Panels Do You Need?

This depends on where you live and how much electricity you use. The more electricity you use and the less sun your home recieves the more 400 watt panels you will require, and vice versa.

You can use this formula to figure out how many panels your home requires:

So let’s assume your home consumes about 890 kWh a month (the U.S. average). You can find out how much your home consumes by checking your utility bill.

Next you need to use Global Solar Atlas to learn the peak sun hours of your location. Alternatively, you can use our peak sun hour data in the resources section of our menu.

Assuming you live in California, your home will experience about 5.2 peak sun hours a day or 156 a month.

Now that we have our data, we can implement the formula above.

(890 / 156) = 5,70 x 1000 = 5,700 watts.

Next we need to divide the total watts by the power rating of your solar panel, in this case we already know it will be 400 watts.

5,700 / 400 = 14

This means a home in California consuming 890 kWh a month will require x14 400 watt solar panels to offset their electricity consumption.

On average a 400W panel measures 6.5 x 3.2. This equals roughly 20.8 square feet.

Assuming our home required 14 solar panels rated at 400 watts, our roof would require 291 square feet of space for our solar array to be mounted.

What Can I Power With A 400-Watt Solar Panel?

You can power a refrigerator for 24 hours with a 400w solar panel!

Let’s see how:

A 400 watt solar panel can power most of your common household appliances. Ranging from a light bulb to a TV or computer.

Their lifespan will largely depend on the battery associated with your 400-watt solar panel.

The sun is a natural source of energy – its power greatly fluctuates depending on the weather conditions and the time of the day.

Solar panels are usually paired with batteries. They will store your energy and act as a buffer in case of a cloud passing by or any reduction of power output.

The batteries together with an inverter will provide the clean and stable power that is needed for our appliances. 

We’ve seen that a 400w panel can produce 2 kWh/day – storing your energy in batteries is a must for a stable power output over time. During battery storage and inverting, you will lose some of the produced energy. However, you can still hope to use at least 85% of what you initially produced.

A medium-size refrigerator with a freezer will consume around 1.4 kWh/day, still less than what your 400w panel can produce in one day.

But remember, we are working with natural elements here. So on a cloudy and/or windy day, the output of your solar panel won’t be enough for the refrigerator to run for the entire day.

Below, you can find examples of appliance running times. They are running on a 400w solar system paired with a 1 kWh battery pack

ApplianceHours of operation per dayTotal energy consumption (Wh)
5 Light bulbs (35 W)7245
1 65 inch LED TV  (120 W)4480
1 Laptop (70 W)4280
2 Smartphones (20W)240
1 Electric fan (40W)5200
 Total1245 Wh

Here is a list of power consumption of typical household appliances.

How Many Batteries Do I Need For A 400 Watt Solar System?

A 1 kWh lithium battery pack is the best partner for your 400 watt solar panel.

Two steps will help you size your battery system:

  1. Know your energy production capacity
  2. Estimate your energy consumption

A battery pack and inverter are a must to smooth out the rough energy production curve of your solar panel over the day and to store your production.

The inverter will convert the Direct Current (DC) of the batteries into Alternative Current (AC) used by all our appliances.

Store your energy and use it during nighttime or when the weather is not favorable.

In California, a 400w solar system will produce on average 2 kWh/day. A 1 kWh storage capacity is adequate with the 400w solar panels. At the end of the day, your battery will be full, giving you enough capacity to enjoy a whole relaxed night without a blackout.

How Long Will It Take A 400 Watt Solar Panel To Charge My Battery?

A full charge takes a couple of hours with a lithium battery but up to 12 hours for lead-acid batteries.

Forget about AGM, deep cycle, valve regulated, or other types of lead-acid batteries, they are all based on the same outdated technology and are definitely not the best for solar charging.

Lithium batteries are your best choice. Lead-acid batteries might require 12 hours or more to reach full charge due to technological limitations, whereas lithium batteries can be charged in just a few hours.

They also exhibit a high tolerance towards sharp power input variations, e.g. when a cloud suddenly shadows your panels.

A long lifespan, lighter weight, and higher power output make these the game-changer that we have been waiting for

They might require a bigger investment at first, but their durability and ease of use largely surpass the lead-acid technology – you won’t regret it.

Don’t forget that your charging abilities depend on the instant power output of your 400 watt panel.

Maximize the circuit current and voltage by optimizing the exposition of your solar panel to direct sunlight.

Charging will be faster around noon (between 10 am and 2 pm) when the solar irradiance is at its maximum.

How To Make Your Own DIY 400-Watt Solar Kit

Have you ever dreamed of living off-grid, with the sun as your only electricity source?

All you need are the four main elements below that compose your DIY 400w solar kit:

  • Solar panels for energy production (400 watt panel)
  • Solar charge controller for smooth battery charging (MPPT type)
  • Battery for energy storage (1 kWh, lithium type)
  • Inverter for stable usable AC current (Pure sine Wave, 2 kW max. power)

Get the latest 400w solar panels, they offer more power in a smaller space.

Then you will connect your solar panel to the solar charge controller.

The sun intensity greatly fluctuates during the day or in the case of instant shadowing by passing by clouds. Therefore, the circuit current and the circuit voltage of your system are never constant. As per its name, the charge controller will regulate the voltage and intensity from your 400-watt panel to your batteries.

Your best choice is the Maximum Power Point Tracking (MPPT) solar charger. It is designed to maximize the power output of your solar panel at any time and in any condition.

The best partner of your 400w solar panels are the batteries, they store your solar energy.

Choose lithium batteries!

They are perfectly fitted for solar charging, they have a high tolerance to intermittent charging, they are durable and lightweight compared to the outdated lead-acid batteries. For a 400W system, a 1 kWh battery is best suited.

You could already use your energy from the battery, this will be direct current (DC), usually 12V or 24V. In that case, you can only power Direct Current (DC) appliances.

All our home appliances are designed to use Alternative Current (AC, 220V, 50Hz). An inverter will convert the DC to AC. For a 400W system, choose a 2kW pure sine wave inverter. It means that you will be able to power up to 2kW of appliances at the same time.

Get some tools, 1 mm2 electrical cables, fuse box and you are on your way to an off-grid experience!

How To Maintain Your 400-Watt Solar Panel

All you need to do is clean the front window of your panel with clear water every month to remove the dust.

Cleaning the front window of your solar panel is a must! Don’t follow his example, he is stepping on the panel.

Every 3 years you should perform a visual inspection of the mounting rails of your 400-watt solar panel.

That’s it and you are good to go for 25 to 30 years!

Can I Use a 400 Watt Solar Panel On My Boat?

Yes you can. The average size of a 400W solar panel is around  79” X 39” X 1.4”, while they are fairly large they can still fit on most family sized boats that range between 20 to 30 feet.

However, most people tend to equip smaller sized solar panels on their boats. This is mainly because boats have very awkward angles, with varying amounts of open space. Smaller solar panels that make up a larger array can be spaced out in a way that best suits the shape of your boat.

We actually wrote an article which covers the 17 best solar panels for boats here. You will notice that we highlight the use of flexible solar panels quite often. Unlike roofs, boats are generally deisgned with curved angles, this makes mounting flexible panels much easier than fixed ones.

In summary, 400W panels are able to be used on a boat. However, we recommend using smaller sizes unless your boat is over 30 feet.

Specifications of a 400W panel explained – 6 Most important

All solar panels have standardized specifications but the abundance of technical terms and figures could be intimidating. Don’t worry, we have selected the most useful for you to choose your 400W solar panel wisely.

Now let’s explain what they mean with the example of a 400W solar panel from LG: LGNEON2 – 400W.

Technical specifications of a 400W solar panel

There are different specs categories:

  • General data
  • Certifications and Warranty
  • Electrical properties (STC)
  • Electrical Properties (NMOT)
  • Temperature Characteristics
  • Operating Conditions
  • IV curve
  • Dimension

In the general data, you will find information such as the type of solar cells used to make the panel, the dimension, weight, frame material, color…

Certifications and warranty are often specified as a quality guarantee, nowadays the regular warranty for a solar panel is 25 years (retain 80% of initial efficiency). You will also find 30 years warranty.

To measure the electrical properties there is a standardized procedure referred as STC (standard test condition) so that every solar panel could be compared. Recently, the NMOT (Nominal Module Operating Temperature) and NOCT (Nominal Operating Cell Temperature) procedures were introduced to better reflect the impact of temperature on the electrical performances.

Therefore, you will find electrical properties at STC and NOCT/NMOT.

Temperature Characteristics reflect the changes in electrical properties such as power output when the surface temperature of the panel increases.

The Operating Conditions are also indicated so you would know the operating limits of your system in terms of temperature, wind speed, number of panels connected.

The IV curve describes the electrical outputs of the solar panel (amps/volts) at different solar irradiance (from low light to full sun).

Finally, you will find a schematic representation of the solar panel with its dimensions.

6 of the Most important specifications for a 400W solar panel

These 6 specs are the most significant to evaluate the performances of solar panels:

  • Maximum Power (Pmax) at standard conditions (STC)
  • MaxPowerPoint Voltage (Vmpp)
  • MaxPowerPoint Current (Impp)
  • Temperature coefficient Pmax [%/°C]
  • Module Dimensions
  • Warranty

The maximum Power (Pmax) is the ideal power output of your solar panel, in that case: 400W.

The Vmpp or Voltage at Max Power Point and the Impp or Current at Max Power Point is the maximum voltage/intensity that your solar panel can reach under ideal conditions (STC). Those two values are important to calculate the electrical specifications of your solar panel array (when connecting multiple panels).

Pmax [%/°C] also called temperature coefficient shows the power loss for each increase in degree °C. For example, with a Pmax of -0.36, the power output is reduced by 0.36% for each °C increase above 20°C. This is significant as the temperature of a solar panel can reach 60°C (power loss of more than 14%).

The module dimension tells you if the solar panel can fit on your dedicated area (roof top, ground mounted, boat, RV…)

Finally have a quick look at the warranty, 25 years is now a standard.

Final Thoughts

Solar panels are one of the best energy production technologies mankind has ever created – they are virtually maintenance-free and have a long life span!

Combined with an ever-decreasing buying price, this is the most attractive energy production device for both residential and industrial use today.

Romain Metaye, PhD

Romain Metaye, PhD

Dr Metaye has a Ph.D. in chemistry from Ecole Polytechnique, France. He is a renewable energy expert with more than 11 years of experience within the research world. During his career, he supervised more than 150 projects on clean energy. Off-grid smart systems, solar energy, battery and the hydrogen economy are among his specialties.

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