Understanding Solar Panel Specifications

Michael Tobias
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    - The rated wattage of a solar panel is the electricity output under Standard Test Conditions (25°C and solar irradiation of 1,000 watts per square meter).

    - The energy conversion efficiency is closely related to wattage, telling you what percentage of solar radiation is converted into electricity.

    - Monocrystalline panels have higher wattages and efficiency values than equally-sized polycrystalline panels. However, polycrystalline panels have lower costs, and both options are financially viable.

    - Solar panels come with two types of warranties: The product warranty applies when the panel fails during its coverage period, and the power output warranty establishes a minimum productivity level your solar panels will keep over time.

    - The temperature coefficient describes the solar panel’s performance at higher temperatures. Solar panels with smaller coefficients are less affected by temperature, making them a better option for hot climates.

    Solar panels are currently getting a lot of hype, but this is justified by their performance and return on investment. Solar power is the fastest growing electricity source in the US as of 2021, closely followed by wind power and ahead of all fossil fuels. Actually, many states have been retiring their coal fleets in recent years.

    The solar federal tax credit will remain available at its current value of 26% until the end of 2022, unless Congress decides to extend it again. Home and business owners will still be able to claim a 22% benefit in 2023, and there will only be a 10% tax credit for businesses from 2024 onward. The installed solar capacity in the US has already surpassed the 100 GW mark, and it could reach 250 GW by 2026.

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    If you’re interested in solar power for your home or business, you might be asking yourself which solar panels to use. Fortunately, there are many excellent brands in the market, and you can’t go wrong if you hire an NABCEP Accredited PV Installation Company. However, it’s useful to know the main specifications of solar panels when comparing them.

    1) Understanding the Rated Wattage of Solar Panels

    solar panels

    The wattage of a solar panel is the electricity output produced under Standard Test Conditions: solar cell temperature of 25°C, solar irradiance of 1,000 watts per square meter, and 1.5  air mass.

    (As a side note, the air mass describes the distance traveled by sunlight, between the point where it enters the Earth’s atmosphere and the solar panel location. This depends on the sun’s position in the sky, which in turn depends on your geographic location and the time of the day.)

    Keep in mind that the rated wattage of solar panels is measured under controlled laboratory conditions. A rooftop installation only gets maximum sunshine for a few hours around noon, and the actual wattage will be different from the nameplate value. However, solar panels with higher wattage will produce more kilowatt-hours per year.

    The efficiency of solar panels describes how much sunlight is converted into electricity. For example, if a solar panel has an area of 1.6 m2 and the solar irradiation is 1,000 W/m2, it gets 1,600 W of sunlight. If the electricity output is 355 W under these conditions, the solar panel is 22% efficient. The best polycrystalline panels have typical efficiency values close to 17%, while the best monocrystalline panels are now above 22%.

    Solar panel efficiency ratings may seem low, but keep in mind you’re using a free energy input that produces no emissions. Fossil fuel power plants are technically “more efficient” than solar panels, but their energy inputs have a cost while producing emissions.

    2) Solar Panel Warranties

    solar panel warranty

    Solar panel manufacturers offer two types of warranties, a product warranty and a power output warranty, each with a different coverage period. Having a solid warranty is important, since it ensures a free replacement if any of your panels fail prematurely. However, getting a professional installation is equally important, or otherwise the warranty may be voided.

    The product warranty is like any other warranty you get with electronic devices. If any of your solar panels malfunction within the coverage period, the manufacturer will give you free replacements. A 10-12 year product warranty is standard in the solar industry, but you can get warranties of up to 25 years depending on the brand and model.

    The power output warranty is also known as the performance warranty, and it’s a bit more complex than the product warranty. However, it can be summarized in the following points:

    • Solar panels degrade over time like any product, and their electricity production decreases slowly. Leading manufacturers will normally specify 2-3% degradation on year one, and then 0.50% or less per year.
    • Let’s assume the specifications of your solar panels indicate a 3% loss on year one and then 0.50% per year. They will have at least 92.5% of their initial capacity after 10 years, and 85% of their initial capacity after 25 years.
    • If your solar panels degrade faster than the specified rate, the power output warranty applies and you can get replacements.

    Solar panel manufacturers normally offer a 25-30 year power output warranty. Using the example above, this warranty would apply if your solar panels have dropped to 85% capacity after 10 years, since they should still have 92.5% of their initial capacity according to specifications. However, the warranty claim would not apply if the solar panels still have 93% capacity after 10 years, since it’s above the specified value.

    3) Solar Panel Temperature Coefficient

    temperature coefficient

    As the temperature of solar cells increases, their electricity output decreases. However, this effect is not equal among all brands and models. To get an idea of how temperature will affect your solar panels, you can look for the temperature coefficient, which is measured in percentage loss per Celsius degree. Keep in mind that the temperature rise is calculated with respect to 25°C, which is part of the Standard Test Conditions.

    For example, a solar panel with a temperature coefficient of -0.50% per °C would lose 10% productivity with a temperature rise of 20°C. However, a solar panel with a coefficient of -0.26% per °C only loses 5.2% of its productivity with the same temperature rise.


    There are many high-quality solar brands in the market, as mentioned above, and you can get excellent results with any of them. However, there are still cases where you will want to focus on certain performance metrics.

    • Solar panels with a high wattage and efficiency are recommended when you have limited space, since they will generate more electricity using the available area.
    • If you live in a place with hot weather, look for solar panels with a low temperature coefficient to mitigate the effects of heat.

    With respect to warranties, you should look for at least a 10-year product warranty and a 25-year performance warranty, since this is considered the industry standard. However, many brands offer even better warranty terms.

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    Tags : renewable energy Solar Power solar energy solar panels

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