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Sandia and the Electric Power Research Institute (EPRI) Conference on O&M for PV Systems

Posted by: chris
June 28, 2013

Rebekah Hren - SEI PV Curriculum Team Member
Until about 2007 or 2008, nearly every PV system installed in the United States was a residential or commercial system, and the prevailing theory was that PV systems without batteries (grid-direct) were practically maintenance-free – just “install it and forget about it”. However, once smaller systems started to age, and larger solar farms and utility-scale systems came online, it became clear pretty quickly that “maintenance-free” was neither an accurate representation of the life-cycle costs, nor the operational requirements, of PV.  Every PV system, whether small or large, will be exposed to thermal cycling, harsh weather conditions, plus the additional effects of Mother Nature including nesting, gnawing birds and rodents. Eventually entropy takes hold and every PV system will need some amount of maintenance – hopefully it will be preventative maintenance, rather than reactive maintenance.  With somewhere around 8 gigawatts of PV installed in the U.S, the time has come to start paying attention to the maintenance required to keep our PV systems humming and churning out happy solar electrons.

Sandia and the Electric Power Research Institute (EPRI) hosted a conference on operations and maintenance (O&M) for PV systems in late April, in Palo Alto, CA. Many conference attendees pointed out that O&M may not be a precisely accurate description: activities occurring during the operations phase of PV systems are really just focused significantly on the “M”  – maintenance. But the “O” – operations of PV plants – is fast coming our way, in terms of reactive power control, low voltage ride through capabilities, and SCADA industrial control systems that are just starting to be integrated into PV systems in the United States.  These operational controls will enhance the ability of utilities to integrate larger – and more – PV systems into a robust grid network.

In terms of maintenance, rooftop PV systems tend to encounter some different problems than larger ground-mounted PV systems. Rodents and birds nesting under arrays are one major problem, as mice, squirrels, and rats love to chew through conductor insulation, causing arcing and ground fault potential. That doesn’t mean every ground-mount system is safe from rodents though; millions of dollars of direct-buried cables have been literally destroyed by burrowing rodents chewing through the insulation. Rooftop systems in general also encounter a greater range of thermal cycling than ground-mounted plants, which can cause conduit to pull apart or conductors to scrape against fittings, resulting in  damaged conductor insulation, which leads to arcing or ground faults.

Several companies with hundreds of megawatts of installed capacity shared the knowledge they have gained over the years at the conference. While an arcing or ground fault can be a very serious situation, by far the more common cause of lost production for PV systems is inverter failures, with ac subsystem problems coming in a close second (including transformer, ac switchgear, or utility connection problems).

There are two types of maintenance that occur at PV sites – scheduled and unscheduled. Scheduled generally includes, at minimum, an annual site visit with a long list of electrical and mechanical items to check, such as making sure there are no broken modules, a thermal scan of switchgear to look for loose (high resistance) connections, checking grounding continuity, etc. If a site has a data acquisition system, then maintenance also entails regularly checking data for signs of low performance. Unscheduled maintenance can happen anytime unforeseen problems occur, whether it is an inverter fault, a ground fault, a data acquisition system problem, or a non-electrical issue such as fence damage. The trick to a low-cost, effective O&M plan is keeping unscheduled maintenance to a minimum, through high quality installations, acceptance testing and professional commissioning, reliable equipment, and proactive preventative maintenance.

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