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Learn how to evaluate solar panels before purchasing. Discover the importance of efficiency, power and type of solar cell to ensure the best energy return in your home
The specifications detailed in a solar panel's data sheet provide information about its expected performance under specific conditions. When shopping for solar panels, it can be difficult to identify the most crucial metrics for choosing the best panel.
It’s a good idea to focus on key specifications like the panel’s power output, efficiency, and temperature coefficient. Depending on your location, other metrics may also be valuable. By considering these factors, you can make a more informed decision when selecting a solar panel and comparing solar quotes.
Power output
Listed as: Pmax, PMPP
Solar panel power output is a fundamental rating measured under Standard Test Conditions, a standardized set of laboratory conditions for testing all solar panels. Sometimes called wattage or panel size, wattage output describes the amount of energy a solar panel can produce.
Most residential solar panels these days generally have wattage ratings around 400 W. However, panels with at least 370 W can effectively meet most homeowners' needs.
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Understanding a panel's power output is crucial as it directly influences the number of panels needed to cover the electricity bill. Higher power output means fewer panels are needed.
It is important to note that although the panels are tested under STC for comparison purposes, their operation under real-world conditions will be different. To better understand performance In practical scenarios, some panels undergo additional testing under PVUSA (PTC) test conditions. Some manufacturers, such as Silfab, provide PTC ratings, which may also be labeled as NOTC (Nominal Operating Cell Temperature).
Module efficiency
A solar panel's efficiency represents the percentage of sunlight that the panel can convert into usable electricity. The average solar panel has efficiency ratings ranging from 19% to 21%, while the highest efficiency residential solar panels available today achieve maximum efficiency ratings of up to 22,8%. Increases in solar panel efficiency have occurred over time, and it's possible that new technologies will take us higher in the near future.
Some brands prominently highlight efficiency rating in their marketing to attract customers. However, it is crucial to note that wattage output is a more reliable indicator of a solar panel's energy production. The efficiency of the panel is already considered when qualifying its output.
Efficiency becomes particularly significant for homeowners with limited roof space. High-efficiency panels can generate more power in less space, making them an excellent option for smaller roofs. However, for those with ample space, panels within the average efficiency range are more than capable of meeting energy needs.
Temperature coefficient
Listed as: Temperature Coefficient (PMPP), Temperature Coefficient (Pmax)
Solar cells, built from semiconductor materials, see a decrease in voltage as their temperature increases. In simple terms, as solar panels heat up, their power output decreases slightly.
The effect that temperature has on solar performance is represented by the temperature coefficient, which measures how much power output drops for each degree above 25°C that reaches the surface of a solar panel.
Most solar panels nowadays have a temperature coefficient between -0,3% and -0,5% per degree Celsius. The closer the temperature coefficient is to zero, the better. For example, Panasonic's EverVolt panels stand out with some of the best temperature coefficients on the market at -0,26%.
Note that decreases in performance due to temperature are generally minimal. However, the temperature coefficient shows how the panel can handle real-world conditions.
Solar cell type
Each solar panel is made up of a series of individual solar cells that have been connected together. The type and construction of solar cells impact panel performance.
Monocrystalline solar cells are widely preferred for residential installations as they are the most efficient and look good. Some websites may mention polycrystalline and thin-film solar panels, but these are not typically used in residential installations.
As power cells Monocrystalline solar panels can be manufactured in several ways to improve performance. Modern solar panels use PERC (passivated emitter and back contact) or TOPCon cells, which feature additional layers to increase efficiency and output ratings.
Many manufacturers use halved solar cells, where the traditional cell is cut in half to reduce resistive losses, and the entire panel is wired to minimize shadow impact.
Dimensions
The physical size of a solar panel is a crucial factor, particularly for homes with complex or older roofs.
Typically, solar energy panels weigh around 18 kg, with dimensions exceeding 1,5 meters in length and 1 meter in width. Specific dimensions may vary between different solar panel models.
In most cases, residential roofs can easily support the additional weight of solar panels and accommodate a medium-sized solar system. However, for older homes, a professional inspection should be sought to ensure the roof can safely support the solar panels. Furthermore, if the roof has a complex shape, the dimensions of the panels become more important.
Your solar installer can usually find the right size panels for your home based on the characteristics of your roof.
Maximum surface loads
Listed as: Maximum static load, snow load, wind load
Solar panels are installed on the roof, exposing them to all the elements. Manufacturers design panels with this in mind, so they are built to withstand high winds and snow.
Most solar panels are rated to withstand 5000 or more pascals (Pa) of pressure, which is equivalent to 0,6 to 1,2 meters of snow, depending on the density of the snow. Some homeowners don't need to worry about this, but those who live in colder regions may want to know if solar panels covered in snow will affect them.
Additionally, the panels are built to withstand wind speeds of approximately 225 kilometers per hour, typically only experienced in hurricane conditions. If these winds are experienced, there will be more than just damaged solar panels to worry about.
Number of solar panels needed to service a house
The number of solar panels needed to meet a home's energy needs varies depending on several factors, such as the home's energy consumption, the efficiency of the chosen solar panels, and geographic location, which influences the amount of sun available throughout the day. year.
In general, a Brazilian home consumes, on average, around 250 to 500 kWh per month. Considering solar panels with an average capacity of 400 W and good sun exposure, it can be estimated that around 10 to 15 panels would be needed to fully cover the consumption of a typical home. However, this is a generalized estimate, and the exact number of panels may vary. It is always recommended to perform a detailed analysis with a professional solar installer to determine the ideal number of panels for your specific situation.
