Part Two: DC Losses
Environmental Losses
Direct current (DC) losses occur before the solar panel’s energy is converted into alternating current (AC) by the inverter for use in the home and on the electric grid.
Environmental losses happen when energy is lost due to the irradiance or temperature of the modules. Two common environmental losses are cell temperature losses and irradiance mismatch losses.
Environmental Losses
Temperature Coefficients
The hotter a solar panel gets, the less energy it generates. This is referred to as solar cell temperature loss and is reflected in the temperature coefficient.
A solar panel’s temperature coefficient is expressed as the percentage energy output decreases for every 1-degree Celsius (°C) increase in temperature, starting at 25°C (77°F).
Note: Solar panel efficiency is tested at 25°C, which is why it is used as the temperature coefficient reference point.
If you’re looking to improve system performance in a warm climate, consider the:
- Roofing material – Some rooftops absorb more heat than others, impacting a panel’s performance
- Panel tilt – Flat mounted panels will get hotter
- Solar panel type – Thin film has a lower temperature coefficient than monocrystalline or polycrystalline.
Further reading: Temperature-Dependent PV Efficiency and Its Effect on PV Production in the World
Environmental Losses
Irradiance Mismatch Losses
Irradiance Mismatch losses occur when one module experiences either a shade or temperature variation that hinders the energy production of other modules on the same string.
The entire module’s energy production is determined by the solar cell with the lowest output. Similar principles apply to PV modules. When one module is experiencing cloud coverage, a hotter temperature, or leaf cover, the power being generated by the other modules on the string will be negatively affected.
Environmental Losses
How to Reduce Irradiance Mismatch Losses
Stringing Arrangements
A shaded module can bring down the power output of the string significantly, but it won’t have any effect on the parallel string. By grouping shaded modules into separate strings, the overall power output of the array can be maximized.
Module Level Power Electronics (MLPE)
Module-Level power electronics are devices that are attached to individual modules in order to increase performance under shaded conditions.
Two types of MLPE you can use to isolate the effects of irradiance mismatch are:
- DC optimizers: DC optimizers adjust the output voltage and current to maintain maximum power without compromising the performance of other modules.
- Microinverters: Microinverters can convert a panel’s output from DC to AC and will operate at its maximum power point without impacting the other panels.
Note: It’s important to use a PV production modeling program that assesses the hour-by-hour shading on solar panels to accurately account for irradiance mismatch.
Further Reading:
