CEC Rating: Why Solar Ratings Matter?

FACTS CHECKED BY  Bob Smith

You might wonder why your solar panels produce less than 100% of their rated power. Therefore, it is necessary to understand what solar ratings are and how the standard solar ratings work. This guide will help you understand CEC rating and their importance. Also, we will provide you with some solar energy production terms to help you understand each tiny detail about your panels.

What is Solar Rating?

Solar rating is the evaluation of a solar panel‘s efficiency and performance. It indicates the power a solar panel can produce under specific conditions, like temperature increases, air mass, and wind speed.

There are some standard ratings in the solar industry. Here are the most important ones:

  • Peak/STC
  • PTC
  • CEC-AC
  • AC
Solar panel on a red roof

Solar panel on a red roof

PEAK/STC Rating

The Peak/STC rating is the maximum power output of a solar panel under standard test conditions. It is because it is the peak panel performance, meaning it only produces this amount of solar power under ideal conditions.

The standard test conditions are as follows

  • 1000 W/m² solar insolation is the sunlight a solar panel receives during its testing period.
  • 25 °C solar cell temperature: The solar panel temperature during testing.
  • An absolute air mass of 1.5 is a measurement of air density that impacts how much solar radiation a panel can absorb.

Things to know about Peak/STC rating

  • We measure the Peak/STC rating in DC(direct current.)
  • Peak/STC ratings require high solar radiation levels at a roughly 0 °C ambient temperature.
  • Peak/STC ratings are always the highest value as we measure them under ideal conditions. It is important to note that these conditions are not always representative of real-world operating conditions, and that’s why other ratings are also important.

PTC Rating

The Peak/STC is too ideal to be applicable in the real world. Therefore, the Photovoltaics for Utility Scale Application (PVUSA) team measures panel output under more realistic conditions.

PTC ratings use the same standards as Peak/STC ratings but also consider factors like wind speed and a slightly lower ambient temperature.

The standard test conditions are as follows

  • 1000 W/m² solar insolation
  • 20 °C at 10 meters above the ground
  • 1 m/s wind speed
  • An absolute air mass of 1.5

Things to know about Peak/STC rating

  • We measure the PTC rating in DC(direct current.)
  • PTC rating considers the effects of wind speed because solar panels are often installed outdoors, where the wind is a factor.
  • The PTC rating is more applicable to real-world scenarios and is a more realistic operating condition.
Solar Panels and Wind Turbines

Solar Panels and Wind Turbines

CEC or CEC-AC Rating

The California Energy Commission (CEC) has a rating system for solar panels known as the CEC-AC rating. Even if you are not in California, this rating is still critical, based on worldwide standardized testing procedures.

To calculate this rating, use the PTC/DC rating and multiply it by the number of efficient panels and DC to AC inverter efficiency. Here is the equation:

CEC-AC rating = PTC/DC rating x number of panels x DC to AC inverter efficiency

Things to know about CEC-AC rating

  • Solar panels produce DC (direct current) electricity, incompatible with the AC (alternating current) electricity that powers our homes and businesses. Therefore, we need inverters to convert DC to AC. That’s why it is essential to consider the DC to AC smart inverter efficiency when calculating the CEC-AC rating.
  • We are getting closer to the real production value with the CEC-AC rating.

AC System Rating

The AC system rating is another way of measuring the panel’s performance. This rating considers all the factors that impact a solar panel’s performance.

Besides the inverter efficiency, it also considers factors like shade, wiring energy losses, soiling, wiring energy losses, and transformer energy loss.

The AC system rating is usually 80% of the peak rating. This rating is the most accurate measure of a solar panel’s performance in the real world.

Solar Energy Production Terms

Renewable energy smart power grid system

Renewable energy smart power grid system

Annual Production: The amount of energy produced by a solar panel throughout the year.

System Production: The energy produced by a solar system during the system’s lifetime.

DC to AC Size Ratio: A measure of how efficiently an inverter converts direct current (DC) to alternating current (AC) energy.

Mismatch: The amount of energy lost when you connect two PVs that don’t have identical properties in a solar array. 

Production Simulation: A tool that estimates solar energy production based on the latitude and longitude of a location, as well as other factors like shading and roof pitch.

Capacity Factor: The amount of solar energy produced compared to what would be theoretically possible at the exact location.

PV Watts: A performance calculator tool that estimates energy production based on various factors, including solar irradiance and temperature coefficient.

Reverse Bias:

A drop in solar power output from one PV module compared to the others in its string is typically caused by a damaged or shaded cell.

Design Factor: The ratio of the proposed system summer output to the optimal system summer output.

Light-Induced Degradation: Solar energy degradation rate or a solar panel degradation rate is a phenomenon where panels produce less energy after prolonged exposure to solar energy.

Shading: The energy lost due to a shadow from trees, nearby buildings, or other obstructions.

Solar cells under the trees with shading from trees

Solar cells under the trees with shading from trees

Short-Circuit Current: The amount of current passing through the solar cell when there is no voltage applied to it.

Soiling: The amount of energy lost due to dust or debris on the surface of the panels.

The contrast between clean and dirty solar panels

The contrast between clean and dirty solar panels

System Loss: The conditions in the real world that reduce the performance of a PV system from what it’s rated for under STC (Standard Testing Conditions).

Azimuth or Orientation: The direction a solar panel is facing, usually measured in degrees from true north.

Pitch: The angle at which the roof of a building slopes away from the ground.

Tilt: The tilt of the panel is its degree about the horizon (180°).

Illustration of solar panels in different angles

Illustration of solar panels from different angles

Conclusion

By researching solar companies or panel manufacturers, you can minimize the risk associated with solar investments and ensure that your goals are met.

By following these tips, you can be sure you are getting the best performance from your panels.

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