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Operations, Maintenance, and Solar Sheep

As gigawatts of commercial- and utility-scale PV power plants spring up around the world on a monthly basis, one critical industry sector that's growing in tandem is operations and maintenance, usually referred to simply as O&M. Whether the service is provided by the engineering, procurement, and construction firm or (sub)contracted to an outside vendor, the upkeep, performance, and ultimate profitability of a large solar installation depends in no small way on the competence and experience of the O&M team.

The recent Solar Power-Gen 2013 conference in San Diego featured several presentations about O&M best practices, innovations, and considerations as well as other related papers on performance monitoring and plant management. In an overview of “critical development aspects for operations and maintenance of PV systems,”SAIC’s Sean McPherson listed the basic scope of services, including visual and mechanical inspections; grounds maintenance; testing of strings, combiner boxes, disconnect switches, breakers, and cables; substation maintenance/relay calibration; infrared scans of modules, combiner boxes, switchgear, and substation; maintenance and cleaning of onsite meteorological stations; maintenance of spares inventory and inverters; revenue meter verification; monitoring of the project and dispatch response to alarms and alerts; and management or coordination of  warranty claims and repairs.

Providing many examples of real-world issues with what one might call caffeinated enthusiasm, John Previtali of Black & Veatch talked about the diagnosis of performance issues in PV plants, showing chart after chart of problematic situations and revealing their possible causes.  For example, one figure depicted what appeared to be an “immediate full inverter loss,” which was probably caused by an inverter issue, but could also have been attributed to an intermittent ground fault, but certainly warranted a check of the inverter fault codes. In another example, an immediate partial loss was also likely an inverter problem, but might also have something to do with a combiner box. Since the chart revealed no clear plateau effect (AKA clipping), a check of the inverter fault codes was again necessary as well as having a technician do a round of voltage testing. In yet another case, the figure revealed the partial loss of two inverters, which was probably not due to the inverters themselves, but more likely caused by something going on in the recombiner box or possibly in the inverter software. A check of the inverter input data to identify the problem in the array field as well as the work logs was recommended.

In the latter part of his presentation, Previtali challenged the audience to identify problems portrayed in a series of graphs. For the most part, the experts on hand did just that, deciphering the data to find performance issues traced to tracker misalignment, shading, and an irradiance measurement device in need of calibration. (He also took the opportunity to announce that his company has begun to offer both full-service and “a la carte” O&M services for large “commercial portfolios” and utility solar power plants—an interesting development since Black & Veatch has worked in an independent engineering capacity with most of the O&M companies and will now essentially also be competing with them.)

Drawing on the experience of supervising the O&M activities at the 51MW SunPower- and SMA-equipped Montalto di Castro PV plant in Italy, Francesco Belfiore of Golder Associates provided perhaps the cuddliest visual moment of the conference session. As he talked about such O&M “housekeeping” issues as managing water runoff and drainage, cleaning the panels, controlling rodents and other pests, and maintaining roads and other civil structures, he raised the topic of vegetation control. He then cued up a slide illustrating the key “method” for keeping the undergrowth from enveloping the arrays: a resident flock of grazing sheep, who wander among the panels. Their presence also has what he called “a positive effect on social and cultural continuity” (the sheepherders could stick around their historical lands) and provides a nonmechanical (and less damaging alternative) to power mowers and the like.

Belfiore did not indicate that there had been any calculation of the direct correlation of megawatt-hours of energy production to sheep headcount and amount of vegetation consumed by the wooly ungulates.

This article was originally published on and was republished with permission.

Lead image courtesy of Golder Associates

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