How much energy does a solar panel produce per square foot

Solar Insolation Maps From the National Renewable Energy Labs (NREL)

• There are Four Maps Here:
  • Average Yearly Sun- The first one shows the yearly average
  • Best Case - The 2nd one is the "best case" or June
  • Worst Case - The 3rd one is the "worst case" or December.
  • With Tracking Mount - The 4th map shows the worst case (January) again, but with a tracking panel mount, which follows the sun.

For designing a system, you nearly always use the worst case, or December-January map. "Flat-plate collector" is simply a solar panel.

The full set of maps (all 300 or so) are available at the NREL website:

• 
  Maps, solar radiation - These are the maps at NREL.

This first map shows the yearly average, in kilowatt-hours per square meter for an average yearly day.

Translation: At high noon on a clear day, each square meter receives 1000 watts of solar power. If you look at the large yellow areas, you will see that it gets around 6,000 watts on an average day. So, even though the average day is exactly 12 hours, the power you actually get on your panels is equal to about 5 to 6 hours of full sun per day. Since the typical modern solar panel is about 12% efficient, you will get about 700 watts per square meter of panel. So, if the map says that you live in a "six" area, you can expect sun power equal to 6 hours per day over the entire year.

This map shows the yearly average for an average June (best case) day.

A large portion of the country is now yellow, showing that good solar power is available for most of the country during the summer.

This map shows the yearly average for an average December (worst case) day.

As you can see, in the winter it's an entirely different story. Much of the country now gets an average of 4 hours or less of full sun hours per day.

This map shows the yearly average for an average January (worst case) day, but with a solar tracking mount.

Compare this to the previous map, and you can see what a difference a tracking mount system can make. The example shown is for 2-axis tracker, like the WattSun. A single axis tracker, like the Zomeworks, will be a little less, but still considerably more than a fixed array. The biggest problem with tracking mounts is that they give the biggest increase in the summer, while the biggest need for power is in the winter. If you have plenty of power in the summer, but fall short in winter, your best option may be to use a maximum power point tracker (MPPT Charge Controller). Tracking mounts used to make a lot more sense when solar panels were selling in the $10+ a watt range, but with current prices around the $4.50 to $5.50 per watt range, the economic advantages of tracking are less.

One of the most important features of a solar panel is how much energy it can produce. After all, that’s what they’re designed to do!

Prospective solar panel owners usually have a goal for how much energy they want to produce. Maybe it is 100% of their household needs, or even just 50%. In any case, there are a number of factors that will influence the energy production capabilities of a solar panel and how many panels they’ll need.

With the cost of solar dropping over 60% in the last 10 years, it is much more realistic for home and business owners to install solar panels on their property. In this post, we explore how solar panels function and produce energy.

First, let’s go over the basics.

Solar panels work by allowing particles of light, called photons, to knock electrons from their atomic orbitals. The electrons are captured on conductors in the form of an electric current and this electricity is harnessed and preserved. The area where this reaction occurs is called a photovoltaic cell or solar cell.

Solar panels (or modules) are made up of hundreds or thousands of these cells, and multiple solar panels make up a solar array. These arrays are connected into the existing electrical grid and/or battery storage so that the generated energy can be directed properly.

Key Solar Panel Terms: kW, kWh, DC, and AC

To fully understand the numbers, we need to go over some basic units.

• Kilowatt (kW): This is a measure of electrical power, which is equal to 1,000 watts. The electrical energy that is generated by a solar panel or a solar system can be expressed as watts or kilowatts.
• Kilowatt hour (kWh) – A measure of electrical energy that is equal to the consumption of 1,000 watts for 1 hour. The kWh is used as a billing unit for the energy consumed by individuals. One kilowatt-hour equates to 3.6 megajoules.

• Direct Current (DC) power: This is the form of the power that gets initially generated from the panel.
• Alternating Current (AC) power: Most household appliances use AC power. The DC electricity generated by solar panels gets converted into AC so that it can be used efficiently by consumers throughout their house.

How Much Energy Does A Solar Panel Produce?

To measure how much electricity a solar panel produces you’ll need two figures:

1. The solar output of the panel (measured in Watts)
2. The number of peak sun hours per day (in hours) for your area

Solar panel output varies by model and ranges from around 250 to 450 Watts. The Wattage output rating represents how much energy the panel can produce per hour under standard testing conditions.

In 2022, 400W panels are considered standard, so we’ll use this output for our example.

Peak sun hours is a measurement of how much usable sunlight your solar panels receive. This varies from over 5.75 hours per day in the Southwest to less than 4 hours per day in the northernmost parts of the US. Check the peak sun hours for your location here.

Since a majority of the US gets 4.5 peak sun hours per day or more, we’ll use 4.5 hours for our example.

To calculate how much a solar panel produces per day, simply multiply the solar panel output by the peak sun hours:

400W (output) x 4.5 hours = 1,800 Watt-hours per day

To convert to the standard measurement of kWh, simply divide by 1,000 to find that one 400W panel can produce 1.8 kWh per day.

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How much energy does a solar panel produce per month?

A 400W solar panel receiving 4.5 peak sun hours per day can produce 1.8 kWh of electricity per day, as we found in the example above. Now we can multiply 1.8 kWh by 30 days to find that the average solar panel can produce 54 kWh of electricity per month.

In sunny states like California, Arizona, and Florida that get around 5.25 peak sun hours per day (or more), the average 400W solar panel can produce 63 kWh or more of electricity per month.

To put that into perspective, average US household electricity uses 893 kWh per month, and ranges from 537 kWh per month in Hawaii to 1,200 kWh per month in Louisiana.

So to offset 100% of the electricity usage for the average household getting 4.5 peak sun hours per day, you’d need a 6.7 kW solar system. (6.7 kW x 4.5 sun hours per day x 30 days per month = 893 kWh per month). That would require 17 solar panels with 400W output.

In sunnier locations getting 5.25 peak sun hours per day, you’d only need a 5.67 kW system made up of 14 400W solar panels to get 100% offset.

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Things That Affect Solar Panel Production

To get an accurate picture of how much energy a solar panel can produce, you have to take into account a few factors like the type of panel and its environment.

As we mentioned above, the biggest factors are how many peak sun hours you get per day and the power output of the panel.  However, the design of the panel matters too.

Energy output varies by panel

There are thousands of solar panel models on the market, all with unique wattages, efficiency ratings, and degradation rates. In fact, we sorted through 750 panels available through the solar.com network of installers to identify some of the best solar panels for each category.

While there is a lot to consider, a good place to start is deciding between a monocrystalline and polycrystalline panel. Here are some features of each technology.

Monocrystalline solar panels

• Higher efficiency
• More expensive
• Better performance in high temperatures and shady conditions

Polycrystalline

• Lower efficiency
• Less expensive
• Less efficient at higher temperatures

Check this video to find out the difference between monocrystalline and polycrystalline panels. 

As you can see, each type of panel has its pros and cons. Polycrystalline, however, is a newer technology and will become more efficient over time, but if you were looking to generate the most power in the smallest amount of space, monocrystalline would be the way to go.

Cover Your Electricity Needs with Solar

To sum it up, an average 400W solar panel getting 4.5 peak sun hours per day can produce around 1.8 kWh of electricity per day and 54 kWh of electricity per month.

Solar panel production varies based on the output of the panel and the available sunlight. And the amount of electricity you need from your panels depends on your energy usage and your goals. Some homeowners wish to offset 100% of their electricity usage while others are okay with less.

Regardless, electricity from solar panels is cheaper per kWh than grid electricity in a vast majority of the US. The sooner you switch to solar, the sooner you can benefit from the long terms savings and price stability.

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