How to read and understand solar panel specifications
A solar panel is a technical component for generating electricity. For the user, it is important to understand which data are crucial for a purchase and how to evaluate a product. In addition to the raw data, there are other specifications that can be critical when buying solar panels. Apart from performance data, there are different types of panels. How a layperson can find the right panel for themselves in this context will be discussed below.
Basic Terms and Key Figures Explained
Without going into too much detail, there are two types of panels. A basic distinction is made between monocrystalline and polycrystalline solar panels. The efficiency is slightly higher in monocrystalline panels, which results in higher electricity yields, but they are also slightly more expensive. Those who are not limited by space can benefit from the better price-performance ratio of polycrystalline panels. An alternative to crystalline panels are the so-called thin-film panels, which are often used on RVs.
Among the types of panels, there are glass-foil panels, glass-glass panels, and half-cell panels. Glass-glass panels are more expensive and heavier than the somewhat simpler glass-foil panels but have a longer lifespan due to the double glass protection. Both types typically use full cells. The so-called half-cell panels are an advancement of the other two types. What is special about them is that the full cells have been split. The half-cells are wired separately and operate independently of each other. Their advantages include optimized shading tolerance, higher energy yield under partial shading, lower cell current, which improves efficiency, and an extended lifespan due to the lower currents.
The module efficiency is also very important for the user. It indicates how efficiently the panel converts solar energy into electricity. In this context, the temperature coefficient is also important. It indicates how the module's performance changes with temperature fluctuations. Generally, a negative temperature coefficient means that performance decreases at higher temperatures. This is typical for most panels, and many people are unaware that solar panels operate better in cooler conditions. A look at the data sheet should also indicate the temperature range in which the product works best.
The Importance of Performance Values and Efficiency
To assess a solar panel's performance, the most important values are the watt-peak (Wp) power, efficiency, and the rated power of the panels. An average panel has a power of about 400 Wp. Monocrystalline panels can reach up to 650 Wp, while polycrystalline panels range between 280 Wp and 320 Wp. In terms of efficiency, there are two ranges between mono- and polycrystalline panels. Monocrystalline panels typically have an efficiency between 18 and 22.8%, while polycrystalline panels range from 16 to 18%. For thin-film panels, the range is between 12 and 19%, so it is very important for the user to pay close attention to this value. The rated power of a panel refers to the maximum achievable power under standardized test conditions. These conditions are solar radiation of 1,000 watts per square meter at a panel temperature of 25 degrees Celsius.
Understanding Durability and Warranty Conditions
In Germany, the warranty period is 2 or 5 years, depending on the installation of the panels. During this period, the seller must address any material defects. In addition to the statutory warranty period, manufacturers often provide an additional manufacturer's warranty, which is subject to the exact wording of the respective manufacturer. A performance warranty guarantees the efficiency of solar panels for a certain period. Typically, 80% of the original power is guaranteed after 25 to 30 years. Manufacturers usually guarantee the lifespan of panels for 20 to 25 years.
Tips for Evaluating the Quality of Solar Panels
To evaluate the quality of solar panels, the previously described parameters are assessed. An efficiency between 21 and 22.9% is considered very good, and a rated power under test conditions (STC) of 445 watt-peak is also good. For performance and product warranties, the longer, the better. Additional seals of approval and certifications can increase trust in the product regarding reliability, environmental friendliness, and similar factors.
Clarifying Common Misunderstandings About Solar Panel Specifications
A common misunderstanding is that high efficiency automatically leads to better energy yields. While the value is important, it must be read in conjunction with the other specifications of a panel.
Regarding durability, there are differences depending on the manufacturer and the panel's construction. As mentioned earlier, for example, glass-glass panels are more durable than glass-foil panels.
The rated power is the power a panel achieved under standardized test conditions. It serves as an excellent comparison basis between different panels, but the actual performance of a panel in operation depends on many factors such as the location, orientation, and prevailing weather conditions.