Automatic identification of faulted strings in single inverter photovoltaic systems

One of the challenges in operation and maintenance of single inverter photovoltaic (PV) systems is identification of faulted strings. This is typically relevant to residential and small commercial PV systems, when a single mini-central string inverter is chosen for the system upon sizing and pricing considerations. While in multi-inverter systems, normalized inverter comparison can be utilized to automatically identify string malfunctions in mini-central inverters, this is not possible in single inverter systems and especially ones with just one max power point tracker (MPPT). The result is that numerous residential and small commercial PV systems operate for months and even years with faulted strings, which are not possible to detect via conventional monitoring methods and require costly periodic preventive manual inspections to address the issue.

Fig.1 Availability of a single inverter PV system, showing a drop upon acute string malfunction.

Several technologies can be utlized to provide a systemic solution to this problem. The obvious one is the utlization of micro inverters or string inverters equipped with power maximizers, where the strings malfunction detection issue doesn't exist (though there could be issues with automating such detection).

Fig.2 Daily power curve of a single-inverter commercial solar 50kW PV system, where a faulted string had been detected with Soltell's Sensorless technology and repaired that day in the afternoon.

However, the mainstream inverters in the commercial segment are string inverters without panel-level monitoring and the percentage of single-inverter PV systems there is quite high - many equipped with just one MPPT. Recently, some inverter manufacturers like Huawei and Billion Watts, have introduced a hardware solution - adding current sensors to each string thus allowing string-level monitoring. Despite the market success, the disadvantage of this approach is the lack of retrofit ability to existing PV systems. Moreover, additional sensors add-up costs and may require more sensor calibration and maintenance.

Fig.3 An electronic box of a single inverter commercial PV system with a burnt string connection, identified via Soltell's SysMap solution (2020).

Soltell Systems allows a different approach to automatically detect string malfunctions in single-inverter PV systems with a single MPPT - utilizing Soltell's proprietary Sensorless technology. This approach allows to identify inverter performance irregularities with an unprecedented accuracy level of <5%, which is sufficient to automatically identify faulted strings in most single inverter PV systems. This is both applicable to residential single inverter systems, where we typically find 2-4 strings and to small commercial PV systems, where 4-10 string inverters with one MPPT are utilized. Soltell's solutions for performance analytics are suitable for retrofit with various string inverter brands such as SMA, Fronius and more. The solutions don't require any hardware modifications and dramatically reduce the need for preventive maintenance inspections.

Interested to know more on Sensorless technology to measure PV performance and integrating it into your service application? Fill-in the demo request form or contact us to get more details.