Harvesting solar energy is a growing industry, so new models of solar panels come out annually. The number of technologies, brands and models can be overwhelming for the customers. However, navigating through all of these is much easier with a rating system. So, one of the common questions we answered for you is how are solar panels rated?
How are Solar Panels Rated: Understanding the Process
When it comes to solar panel ratings, there are some things to consider. Specifically, there are certain parameters for module testing, equal for all manufacturers. These parameters are measured under certain lab conditions. The performance of each solar panel model under these conditions will determine the quality of that panel.
Types of Testing
Mainly, there are two big types of solar panel testing:
1. STC (Standard test conditions)
The STC test exposes the solar panel to artificial sunlight and measures its performance. The artificial light mimics the sunlight at noon, without any dust in the air. The temperature is 77℉ and the air pressure is 1.5. The panel’s final rating represents the output it gives under these specific conditions.
2. NOCT (Nominal operating cell temperature)
The NOCT tests differ from the STC tests because they include more factors and mimic a more realistic environment. Primarily, the temperature is 67℉, and the average wind velocity is 2.24 miles per hour. In addition, the wind blows into the back of the solar panel. Under these conditions, the average solar cell temperature gets to 118.4℉.
Factors in Rating
Both STC and NOCT testing conditions are quite reliable. However, as environmental conditions vary from location to location, they cannot be calculated precisely. For instance, the number of sunlight hours is not the same in California and Alaska. However, you can still rely on each individual factor of solar panel rating.
The most common solar panel rating factor is efficiency. It shows how much of the sun’s UV radiation can be transformed into electric energy. The efficiency of modules is a common rating factor for the whole solar industry, among both manufacturers and homeowners. Manufacturers compete every year to release the most efficient solar panel model.
A panel’s wattage shows its expected power output and is therefore another important rating factor. Typically, a rating scale for modules ranges from 250W to 400W. Of course, higher wattage brings higher efficiency. However, even though there are now modules of 400W or higher on the market, those between 300W and 400W are still the most popular. Additionally, low wattage modules also find their use in battery charging and other off-grid utilization.
When it comes to answering the question, How are solar panels rated, temperature plays a big part in it. The units of measurement are temperature coefficients, and every panel has three of them:
- current temperature coefficient
- power temperature coefficient
- voltage temperature coefficient
However, only the last two are important for rating. The current does not significantly change due to temperature, but the power and voltage do. For instance, when the temperature increases, the voltage decreases, and vice versa. Because of this, solar panels with low voltage and power temperature coefficients give changing environmental conditions less influence on the voltage.
As solar technology advances year by year, so do testing methods. Solar panel manufacturers are competing with each other to satisfy all of the required variables with every new module they release. It’s because of this that customers find it harder and harder to choose the right solar panels.
Fortunately, here at Atlantic Key Energy, our team of experienced personnel will always be there to help you decide. The question How are solar panels rated? is only a part of what you should know if you plan to go solar. If you wish to learn more, head to our blog, where we answered some other important questions about solar panels.