Solar Panel Rated vs. actual (Interesting!)

If you are curious why your solar panel-rated power output is different from what your solar panel produces, you are not alone.

Many people think that their solar panels are defective, but there are some excellent reasons why they are not producing the rated amount of power on their label.

In this blog, we discuss:

  • What solar efficiency is
  • Factors that drop solar energy production
  • Tips to overcome the factors that drop solar energy efficiency

Keep reading as we go over those “excellent reasons” why your solar panel rated vs. actual is not the same. We also give some tips that can help improve solar panel performance. 

Solar panels on a aroof mountains in the background

Solar panel rated vs. actual output.

Right off, there are some issues. Those issues include how the information is presented on the solar panel box. It’s a subtle thing, but it is essential.

When the box says 200 watts, it means “can,” not “will.” When you read 200 watts, it means that the panel CAN make 200 watts of energy at the optimum.

However, in the real world, there are some obstacles that solar panels face. Each of these obstacles can cause the efficiency of the solar panel to drop.

Here is a list of solar obstacles:

Natural Decay

The energy that travels throughout the solar circuit will naturally decrease. If the solar panel produces 300 watts of energy, by the time that energy passes through the controller, batteries, inverter, and then into the house, it will have dropped energy.

If you have solar batteries, the controller that protects the batteries will block a lot of energy that the solar panel sends through the circuit when the batteries are fully charged. 

See also: How Efficient are Solar Panels? Unveiling the Truth About Their Performance and Cost-Saving Potential

Inverter Loss

If the solar panel has an inverter attached to it, then you can lose energy by inverter inefficiency. Most have an efficiency rating.

For example, a microinverter with a 96% efficiency rating means that if your solar panel produces 300 watts, only 96% of those watts will pass through the inverter.

That process is also part of the natural decay process for solar energy. 

Dirty Panels

Seasonal dirt on the panels will cause refraction or deflection of incoming solar radiation. How much and dirt on your panel cause the solar panel to drop efficiency? That answer depends on how much dirt is on the panel. 


The weather is another inconsistent factor that can cause the efficiency of a solar panel to decrease. Clouds, rain, snow, hail, sleet, and even wind can cause less incoming solar radiation to be available.

These factors also include shading, such as when the sun’s movement causes a shadow to cover the solar panel.

When shading happens, some or all solar cells in the panel have no direct sunlight and therefore do not produce energy. 


If the solar panel overheats, it will produce less energy. One key reason why solar panels overheat is that they are installed too close to the roof’s surface, or in the case of mobile panels, they are lying on the blacktop. 

Panel orientation

If the panel is not facing the sun directly, it will receive less incoming solar radiation.

That is also a problem with the angle of the sun changing seasonally. Less incoming solar radiation means that less sunlight strikes the panel’s surface.

Seasonal changes in the sun’s pattern also mean shorter or longer days. Shorter days create a smaller window for your solar array to capture sunlight. 

As you can see, many factors can limit the amount of energy your solar panel produces. 

What is the rated power of a solar panel?

The rated power of a solar panel is the maximum power that the solar panel can produce if everything is working at peak efficiency.

For example, if the panel is rated at 200 watts, then the rated power is 200 watts, and that is the most power that the panel can create. Will it create that much power?

Of course, it can, but also expect other factors to decrease the maxim power of a solar panel. 

Is it worth paying for premium solar panels?

Yes, premium solar panels are worth the price; First, they produce more watts of energy than standard panels. Second, they degrade slower.

All solar panels degrade at around 1/2 percent per year. Premium solar panels are more expensive, but they produce a lot more energy over their lifespan. 

Is there a difference in the quality of solar panels?

Absolutely there is a difference in the quality of solar panels. Standard panels, which are less expensive, can be manufactured using inferior materials.

They also are less efficient, which means they produce less energy than high-efficiency or premium panels do.

  • If a standard solar panel has an efficiency rating of 17%, it will only take in 17% of the total amount of solar radiation that strikes its surface.
  • If a high-efficiency panel has an efficiency rating of 22%, it will take in more incoming solar radiation (22%) and produce more energy. 

Suppose you consider that solar panels often have a lifetime warranty of 25 years. In that case, a premium solar panel will produce a lot more energy over that period than a standard solar panel will.

It also means that you may need fewer panels in your array to achieve the same amount of energy if you go with premium panels. 

How much power does a 400-watt solar panel produce?

How you answer this question depends on how many hours of direct sunlight the panel receives and its efficiency rating.

We know that at its best, the panel can produce 400 watts of energy per hour. Under the best circumstances, if the panel receives four hours of direct sunlight, it will produce—1600 watts of energy in those four hours.

If the panel receives five hours of direct sunlight, it will produce 2,000 watts of energy in those five hours. Other factors can limit how much energy the solar panel produces. 

Tips to Help Increase the actual efficiency of your solar panel

  1. Plan on cleaning the solar panels at least seasonally and more often in fall, when leaves can accumulate quickly on the solar array. 
  2. Add additional panels if you live in an area where it becomes cloudy often or other airborne hazards, such as dust, occur frequently. The extra panels will help compensate for the shading from clouds, dust, rain, snow, etc. 
  3. Adjust the spacing between the roof and panels. If needed, adjust the space between the roof and the panels so the panels have more airflow. The added airflow will help keep the panels cooler, which will help all of them to produce more energy. 
  4. Double-Check the panel orientation and make sure they are facing true south. If needed, you can install a tracker that moves the panels in conjunction with the sun’s angle. 
  5. Increase the number of panels. If the array experiences a high percentage of natural degradation, increase the number of panels, or switch out components burning energy. If you have a solar battery storage system, you might consider adding additional batteries. If the array fills the battery quickly, more batteries mean more stored power. 


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Elliot has 20+ years of experience in renewable technology, from conservation to efficient living. His passion is to help others achieve independent off-grid living.

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