What Are String Inverter Limitations in Low Light?

Limited Power Output in Low Light Conditions

String inverters are designed to operate at optimal levels when exposed to direct sunlight, typically around 800-1000 W/m². However, in low light conditions, such as during early morning or late evening hours, or in areas with heavy tree cover or shading, the power output from the string inverter can be significantly reduced. This is because the inverter’s ability to convert DC power from solar panels into AC power is compromised when the input voltage is lower than the inverter’s minimum operating voltage, usually around 200-250 VDC.

Increased Power Loss Due to String Impedance

In low light conditions, the string impedance (resistance) increases, which leads to higher power loss as the current flowing through the string encounters more opposition. This can result in a decrease in the overall system efficiency, typically by 10-20%, depending on the system design and the available light. To mitigate this issue, system designers often use techniques such as using a higher number of series-connected modules, employing a more efficient inverter, or implementing a derating factor to account for the reduced light conditions.

Techniques to Optimize String Inverter Performance

One technique to optimize string inverter performance in low light conditions is to adjust the inverter’s settings to accommodate for the reduced voltage and current levels. This can be achieved by increasing the inverter’s maximum power point tracking (MPPT) voltage range or reducing the inverter’s minimum operating voltage. Another technique is to use a smart inverter that can dynamically adjust its settings based on real-time monitoring of the solar array’s performance. By implementing these techniques, system designers can help to mitigate the limitations of string inverters in low light conditions and ensure optimal system performance.