IEEE Power & Energy Magazine - May/June 2014 - 95

In all the control actions, the controller's command
to each inverter is unique, given the specific conditions
each inverter is experiencing.

short-term solar generation forecasts is facilitating continued
efficient and reliable system operations. By providing pv
plants that can support the forecasting needs of grid operators, this variable resource can address the load-balancing
needs of grid operators. An advantage of solar in many markets is that its peak generation coincides with higher load
demand, making it more a valuable generation resource.

Grid Flexibility and Power
Systems Resource Planning
As the proportion of variable generation increases in the
overall generation portfolio, another integration concern is
that greater grid flexibility is required to provide the necessary power backup when the variable generation resource is
not adequate to meet the demand. this dictates an increased
use of conventional resources that are able to respond and
ramp up more quickly and a reduced use of inflexible generation resources. A recent analysis points out "that planning
the lowest-cost, lowest-risk investment route aligns with a
low-carbon future. From a risk management standpoint,
diversifying utility portfolios today by expanding investment in clean energy and energy efficiency makes sense
regardless of how and when carbon controls come into play.
placing too many bets on the conventional basket of generation technologies is the highest risk route."

Summary
We have described a utility-scale, grid-friendly pv power
plant that incorporates advanced capabilities essential to
supporting grid stability and reliability. it includes features
such as voltage regulation, active power controls, ramp-rate
controls, fault ride through, and frequency control. these
capabilities provide the intrinsic benefits of reliable plant
operation in the grid, which in turn results in additional
plant yield and potential additional revenue. Such capabilities are essential for successful the deployment of largescale pv plants.
A key component of such a grid-friendly plant is a plantlevel controller specifically engineered to regulate real and
reactive power output of the solar facility such that it behaves
as a single large conventional generator, although within
the limits dictated by the intermittent nature of the solar
resource. in cases where the plant output is constrained but
the plant has additional generation capability, this controller

may/june 2014

can reduce the impact of cloud passage and increase overall yield. plant-model validation against measured field data
demonstrates that the Wecc-proposed model for a solar pv
plant is adequately capturing actual plant behavior.

For Further Reading
R. Binz. (2012. Apr.). practicing risk aware electricity regulation: What every state regulators need to know. A ceres
Report. [online]. Available: http://www.ceres.org/resources/
reports/practicing-risk-aware-electricity-regulation
M. G. lauby, M. Ahlstorm, d. l. Brooks, S. Beuning, J.
caspray, W. Grant, B. Kirby, M. Milligan, M. o'Malley, M.
patel, R. piwko, p. pourbeik, d. Shirmohammadi, and J. c.
Smith., "Balancing act," IEEE Power Energy Mag., vol. 9,
no. 6, pp. 75-85, nov./dec. 2011.
Modeling and validation Work Group/technical Studies Subcommittee. (2011, Jan.). [online]. Available: https://
www.wecc.biz/committees/Standingcommittees/pcc/tSS/
MvWG/Shared%20documents/MvWG%20Approved%20
do cu ment s/ W e cc%20pv%20pla nt%20power %20
Flow%20Modeling%20Guide.pdf
R. piwko, A. ellis, R Walling, B. Zavadil, d. Jacobson,
M. patel, d. Brooks, B. nelson, J. Macdowell, c. Barker,
e. v. engeln, e Seymour, l. casey, e. John, W. peter, W. lasher, c.
loutan, l. dangelmaier, e. Seymour, and M. Behnke. (2012,
Mar.). Special reliability assessment: interconnection requirements for variable generation. neRc. [online]. Available:
http://www.nerc.com/comm/pc/integration%20of%20variable%20Generation%20task%20Force%20ivGt/Sub%20
teams/interconnection/neRc_ivGtF_1-3_dRAFt.pdf
Wecc Renewable energy Modeling task Force. (2012,
Sept.). [online]. Available: https://www.wecc.biz. https://
www.wecc.biz/committees/Standingcommittees/pcc/tSS/
MvWG/Shared%20documents/MvWG%20Approved%20
documents/Wecc%20Solar%20pv%20dynamic%20
Model%20Specification%20-%20September%202012.pdf

Biographies
Mahesh Morjaria is with First Solar, tempe, Arizona.
Dmitriy Anichkov is with First Solar, tempe, Arizona.
Vladimir Chadliev is with First Solar, tempe, Arizona.
Sachin Soni is with Arizona State University, tempe,
Arizona.
p&e

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Table of Contents for the Digital Edition of IEEE Power & Energy Magazine - May/June 2014