Solar electric power sites today are usually built using series-strings  of solar photovoltaic panels (modules) like the  ones shown. With 10 to 20 solar panels connected in series, each string typically generates 400-450 VDC at 5-9 amps contributing 2-4 kilowatts of power in full sunlight. Usually many strings are wired in parallel to a large inverter, masking virtually all individual faults, including connection failures. In a 250 kW commercial-scale installation with 100 strings of modules, a single connection failure would cause a loss of one string's output, only 1% of the total.

Site-level Monitoring:  Today's most common form of solar electric monitoring provides one measurement of output for the entire site and diagnostics from the inverter(s) in the system. Given the many variables affecting overall output, it is difficult to detect array underperformance of up to 10%, and arguably even harder to find it at initial installation. Should you suspect problems with the array (1,250 200-Watt modules in our 250 kW example), the only alternative is to deploy skilled technicians to the site to investigate by selectively dismantling the site. This process is both costly and hazardous

Courtesy of DOE/NREL, Credit - Warren Gretz

String-level Monitoring: In string-level monitoring, current and voltage for each string of solar modules is measured, making it easier to detect individual problems in the array. The nature and location of the problems is still unknown, however. This is particularly problematic if the string is underperforming or intermittent instead of fully failed. Even in the case of an outright connection failure, the problem location is only narrowed to 10-20 places, and final diagnosis still requires string disassembly and troubleshooting by skilled technicians, which is dangerous, time-consuming and costly. Beyond that, many other types of failures are not easily identified or diagnosed. While string underperformance can be detected using string-level monitoring, the reasons for it must be found manually.

Solar Array Diagnostics: Solar Sentry provides actionable diagnostics by collecting individual solar panel connectivity and performance information with patent-pending technology. Contemporaneous information is gathered every few minutes. It's then aggregated and transmitted via a secure VPN tunnel through the internet for analysis.  When problems are found, repair recommendations are generated that include a detailed problem description and location. When technicians arrive at the problem location, LED indicators on the equipment confirm that they are in the right location.

Meaningful Metrics: Since string performance depends on panel performance, and panel performance is not measured today, meaningful performance metrics are unavailable. This lack of information most certainly results in significant solar power generation underperformance over the projected 30-year lives of today's systems. Solar Sentry's approach not only collects a meaningful database of solar performance information, but also analyzes the information regularly, providing regular reports that characterize the health of the solar electric site and suggest specific corrective action.