POWER April 2016 - 44

OPERATIONS & MAINTENANCE
(Requirements for testing, documentation and
maintenance-Part 1: Grid-connected systems-Documentation,
commissioning tests
and inspection), which requires documentation
of the system, array testing, and a wholesystem
performance test.
If the decision is made to outsource O&M,
vetting the financial solvency of the O&M
service provider will be necessary, because
financial distress could have a " negative
impact " on the level of system quality, says
the Solar Access to Public Capital (SAPC)
working group, whose membership includes
more than 450 solar developers, financiers
and capital managers, law firms, rating
agencies, accounting and engineering firms,
and other stakeholders engaged in solar asset
deployment.
Also, it is prudent to verify that a contractor
uses a company health and safety manual
to keep injuries at bay, making sure that all
site personnel will be equipped with complete
personal protective equipment for the
task, including fall protection from roofs and
arc flash protection for working on live circuits.
Finally, contracts should clearly articulate
insurance requirements, it recommends.
O&M Best Practices Are Evolving
Over the years, as more utilities have become
solar power generators, some common
goals have evolved that have given shape
to PV O&M best practices. Essentially, the
goals are to maximize system economics by
increasing plant uptimes and decreasing service
costs. Critically, operators also want to
protect asset value and longevity and comply
with applicable regulations.
Although practices and approaches are not
standard and have been implemented in various
proprietary ways, over the years a few
basic strategies to achieve these goals have
emerged. A handful of best practices guides
are also in the works, including one from
the PV O&M Collaborative, which is part of
SAPC. A free version of the group's working
paper (nrel.gov/docs/fy15osti/63235.pdf) has
been made available by the National Renewable
Energy Laboratory (NREL).
One setback to having different O&M
practices is that performance metrics are defined
differently, that paper notes. " A system
characterized by a guarantee to deliver 1,000
MWh/year would be difficult to compare and
bundle with another that has a guarantee to
be operational 90% of the time. Investors
need clear performance metrics and evaluation
methods. " Also, differences in types of
systems, geographic location, and climate
conditions can " confound securitization " by
investors, it says, noting that investors want
to know exactly how much it will cost to perform
required O&M. " Cost estimates must
44
Drones for Solar Plant Inspection
A notable trend involves the increasing
use of unmanned aircraft systems (UAS)-
drones-for a variety of operation and
maintenance tasks at solar facilities in
general and photovoltaic (PV) systems in
particular (Figure 3).
According to the Electric Power Research
Institute (EPRI), these devices can currently
perform a variety of tasks-including visual
imaging (of modules, wiring, and other
plant components), infrared thermography,
and vegetation monitoring-that have the
potential to update largely manual conventional
processes and more efficiently identify
and diagnose PV system performance
issues. And there are more applications under
development, including for data analytics
through pattern recognition and change
detection.
For utilities, given the falling system
costs and technical advancements, drones
offer wide benefits. As well as their time
savings and labor efficiency, they can
be dispatched flexibly to gain access to
locations (such as rooftops) not otherwise
easily reached. Measurements taken
via UAS imaging of rooftop and groundmounted
systems offer improved accuracy
over manual methods. And, the flexibility
of the UAS platform lets a single drone
perform a variety of tasks, creating benefit-stacking
opportunities.
be uniform and predictable so that they can
be bundled, yet they should reflect the factors
that cause O&M costs to vary from site
to site. "
A PV O&M Plan
SAPC recommends establishing an O&M
plan that considers the context of the performance
period required to generate a sufficient
return on investment. The O&M manager
should retain this plan and archive all initial
planning, warranty, design, and other system
specification documents; that manager
should also revise the plan as the system is
built, maintained, and modified over time.
Typically, the asset life-about 25 years-
is considered the performance period, even
though ownership may change. An aligning
monitoring program is also chosen, and a
system owner may seek a performance contract
wherein a specified performance indicator-such
as MWh/year energy delivery-is
guaranteed.
According to SAPC, though many perforwww.powermag.com
3.
Sun bird. Drones can perform a
variety of photovoltaic-related O&M tasks,
particularly those related to visual imaging.
Courtesy: Skycatch Inc.
EPRI noted in an August 2015 study,
however, that a number of challenges
must be overcome before the technology's
commercial appeal for PV O&M can
be unlocked. Foremost among them is the
" novelty of the technology. " Then, there
are public safety, privacy, and liability
concerns. (See " Leveraging Drones and
Robots for O&M Savings " in this issue or
online at powermag.com for more on the
legal and regulatory issues concerning
the use of drones.) " Though the technical
capabilities of UAS have improved drastically
over the past few years, features
such as 'sense-and-avoid' safety protocols
are needed to enable additional operating
functions (e.g., autonomous flights) that
can improve upon the tool's economic
proposition, " EPRI said.
mance indicators have been proposed, it is
prudent to select a type of key performance
indicator (KPI) that minimizes cost but ensures
optimal system performance under
varying conditions. KPIs include availability
(or " uptime " ), which refers to the percentage
of time that a condition is met- " usually that
the entire system is at full operating capability
and not impaired for any reason. " Other
KPIs include energy delivery, specific performance
(or energy delivery normalized by
plant rated capacity), percent of system rating,
and performance ratio (defined by IEC
61724 or ASTM E2848).
Finally, compared to residential systems,
utility-scale systems should have a larger
focus, including financial goals and detailed
monitoring. " The investment and revenue of
large systems justifies more detailed monitoring
for anomalies in performance and
increased communications and sensors to
trigger performance or corrective maintenance
activities and alerts, " SAPC suggests.
Considerations include monitoring with diPOWER
| April 2016
http://www.powermag.com http://www.nrel.gov/docs/fy15osti/63235.pdf http://www.powermag.com
POWER April 2016

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