Solar Panel Electricity Generation

“How much electricity does a solar panel generate?”

This is one of the most basic questions that people have about home solar power. This page will discuss the specifics about solar panel power output, efficiencies, and orientation.

Solar Panel Power Output

The power capability of a solar panel is measured in watts (volts times amps). A high majority of the solar panels that are produced for residential use have a wattage between 250 watts and 350 watts. A solar panel on a rooftop can produce as much as 5 hours worth of peak (close to maximum output) energy in a given day. If we take a 300 watt panel with exposure to 5 hours of light, that panel will produce 1,500 watt-hours or 1.5 kilowatt-hours of power.
solar panel
A good follow up question is then – “how many solar panels do I need?”

The average home in the United States uses approximately 900 kilowatt-hours of electricity per month. In the preceding example, it was determined that one solar panel can produce 1.5 kilowatt-hours of electricity in a given day, or 45 kilowatt-hours per month. Therefore, it would take 20 solar panels (900 kilowatt-hours divided by 45 kilowatt-hours/panel) to produce enough energy for the average home to completely offset its conventional energy usage. In this example, the solar panel system size is 6 kilowatts (20 panels times 300 watts/panel). Of course, home energy use can vary widely. Accommodating various system sizes is quiet easy for an experienced solar installer.

The following chart shows a rough approximation of when and how much electricity a typical 6kw solar panel system generates throughout an average day.

As you can see, the bulk of the solar power generated is between 9:00 am and 3:00 pm.

Solar Panel Efficiency

The efficiency of a solar panel refers to the percentage of sunlight that a panel can convert into electricity. The efficiency range based on the panels that are currently in the market place is 15 to 22 percent. A good majority of solar panels have a efficiency rating of about 17 percent.

Many might assume that higher efficiencies are better. Not necessarily. What matters is total wattage. Let’s consider an example. Panel 1 is 17 percent efficient with a power rating of 300 watts. Panel 2 is 20 percent efficient with the same power rating of 300 watts. How can they have the same power rating? Panel 2 is simply smaller in size, it can produce the same wattage with fewer cells. What really matters here is total power output. Some manufacturers charge a premium for higher efficiency panels. If a competing manufacturer’s panels can produce the same total wattage for less, then paying that premium would not make sense.

One consideration for a homeowner to end up choosing higher efficiency panels is a lack of roof space. Higher efficiency panels obviously means fewer are needed, so this may be more suitable for homeowners with smaller roofs. On the other hand, many people have enough space on their roofs to accommodate one or two extra lower efficiency panels with a total system size that can deliver all the power that is needed.

Solar Panel Orientation

Another important factor in solar panel electricity generation is the orientation of a solar panel system. This is referring to both the direction that the panels face and how much they are tilted.

In the United States, the optimal direction for panels to face is south because the sun is always in the southern half of the sky. Panels can be facing as much as 45 degrees to either the west or east from true south and still achieve approximately the same total power generation.
tilted solar panel
The other consideration for optimal power generation is angle. In the most ideal situation, solar panels are always perpendicular to sunlight. This is only possible with panels that are setup with solar trackers that track the movement of the sun. For most residential installs, this is not an option. Panels are placed directly onto rooftops and have the same angle as the roof. The good news is that the loss in efficiency from a sub-optimal angle is just a few percent. For those in the U.S. whom are having a ground mount system installed, the angle equation is simple. Take your latitude, multiply it by 0.76 and add 3.1 degrees. For example, for Denver its 40 x 0.76 + 3.1 = 33.5 degrees.

Conclusion

As you can see, there are a few factors that determine how much electricity a solar panel can generate. Total power output is affected by panel wattage, orientation, and angle.

While this information can seem daunting to someone who is just beginning to look into going solar, this is not a cause for concern. This is just one of the many things that is taken care of by a solar panel installer. Even homeowners who are quite handy and experienced with electrical issues should still utilize the services of professional solar installers to save time, ensure safety, and get it right.

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