The modern half-cut monocrystalline PERC panels offered by Building Services Plovdiv achieve an efficiency between 20 to 22% under standard testing conditions.
The standardised test conditions used by the manufacturers are 25°C air temperature, 1000 watts per square meter (1 kWh/m²) of solar irradiance, and an air mass of 1.5.
In practice, many factors can negatively influence the performance of a solar panel. Among those are dust that will inevitably accumulate, partially shaded panels due to shadows cast by clouds, trees or other objects, and high ambient temperatures. Actual power output will vary from zero to as high as the design specification when the conditions are ideal.
The trend is for panels to become both more efficient and cheaper. Solar panel technology is ever-evolving, and the panels available today far surpass those available just ten years ago.