Automatic detection of faulted strings in single inverter photovoltaic systems

Detecting faulted strings presents a notable challenge in the operation and maintenance of rooftop photovoltaic (PV) systems, particularly in residential and commercial installations. These systems often employ a single mini-central string inverter due to cost and sizing considerations and have varying array angles, which pose a challenge to compare inverter power characteristics. Unlike larger-scale multi-inverter PV systems, which leverage normalized inverter comparisons to detect string malfunctions automatically, rooftop single-inverter systems lack such diagnostic capabilities. This limitation is especially pronounced in systems with only one maximum power point tracker (MPPT) combining multiple strings, where remotely identifying a string fault is even more complex.

As a result, many small-scale PV systems operate with undetected string faults for extended periods of time. Conventional manual monitoring methods are insufficient to pinpoint these issues, leaving faults unresolved unless addressed through preventive on-site technician inspections, which are both labor-intensive and expensive. The inability to promptly identify and fix string malfunctions not only reduces system efficiency, but also impacts the long-term reliability and economic viability of these installations.

Fig.1 Availability of a single inverter PV system, showing a drop upon an acute string malfunction (2020).

Several technologies can be utlized to provide a systemic solution to this problem, enabling remote identification of string faults. The obvious one is the utlization of micro inverters or string inverters equipped with power maximizers, where string malfunction detection can be performed remotely, though there are still issues with automating this process.

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 (2020).

However, mainstream photovoltaic inverters in the commercial and industrial segments are string inverters without panel-level monitoring and the percentage of single-inverter PV systems there is quite high - many equipped with just a single MPPT. Recently, some inverter manufacturers have introduced a hardware solution - adding current sensors to each string, thus practicallly allowing string-level monitoring. Despite the overall market success, the disadvantages of this approach is the lack of retrofit ability to existing PV systems and the need for a smart solution to interpret the data. Moreover, additional current sensors do 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 enables a different approach to automatically detect string malfunctions in single-inverter PV systems with a single MPPT - utilizing Soltell's proprietary Sensorless technology. This technology embedded in the SysMap solution enables 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 a single MPPT are utilized. Soltell's solutions for performance analytics are suitable for retrofit with various string inverter brands such as SMA, Fronius, Sungrow, Huawei, Growatt and more. Sensorless solutions don't require any hardware modifications and dramatically reduce the need for preventive maintenance inspections.

Interested in Sensorless technology to measure PV performance and automatically detect string malfunctions? Fill-in the demo request form or contact us to get more details.