Residential solar systems come in different voltage, power, and energy efficiency ratings. Many solar panel parameters are technical and not convenient for users to refer to. However, some key ratings can help users select a photovoltaic system that is both affordable and highly efficient.
The most common way solar panel manufacturers attract customers is by using energy efficiency ratings, which indicate the ratio of sunlight reaching the solar panel to sunlight being converted into electricity. This seems like a simple formula, but the energy efficiency of solar panels is actually affected by many environmental factors, such as the panel's tilt and air temperature.
Solar energy system
To establish a standardized rating, solar panel manufacturers have adopted Standard Test Conditions (STCs) for evaluating panel efficiency, which include uniform sunlight, angle, air mass, and temperature conditions. Currently, the efficiency of solar panels is primarily between 13% and 18%.
STC ratings are determined by the solar panel manufacturers themselves. Many US states require manufacturers to conduct independent testing on their panels before they are released to the market. The US Photovoltaic Standard Testing (PTC) rating is more stringent, allowing for ratings of many different solar panels under the same conditions. The unit of measurement for PTC rating is watts. For example, a 190W solar panel might be rated 172. High-efficiency solar panels are typically more expensive.
Solar panels can last 25 to 30 years, or even longer, but their efficiency declines over time. Solar panel manufacturers typically only provide a guarantee for a certain percentage of the system's power output. A longer guarantee period and a higher guaranteed power output percentage indicate a more durable solar panel system. A 20-year guarantee of 80% power output is good, while a 25-year guarantee of 90% power output is even better.
Solar panels vary in voltage. For safety reasons, some people might compare open-circuit voltage ratings. However, the current-carrying capacity of a photovoltaic system is limited, and short circuits generally do not pose a safety hazard. Some solar panels have Underwriters Laboratories (UL) certification, which is a better indicator of product safety.
