POWER December 2012 - 48

RENEWABLES
FERC actions on variable energy resource integration. Source: FERC
FERC Order No.
Date
1980s
1996
July 2003
Mar. 2004
Action
NA
888
2003
Aug. 2003 NA
2003-A
Sept. 2004 NA
2005
2007
Jan. 2010
July 2011
California wind farms work to minimize power system disruptions should a
wind power plant problem arise.
Requires open access to transmission.
Large generator interconnection procedures for resources greater than 20 MW.
Northeast blackout. Aftermath prompts wind industry to pursue grid code,
recognizing wind plants have a role to play in grid stability.
Acknowledges different approach may be appropriate for generators relying
on newer technology, not traditional synchronous technology.
American Wind Energy Association submits grid code to FERC that includes
low-voltage ridethrough requirement.
661 and 661-A Adopts interconnection standards applicable to large wind generators.
890
Adopts transmission planning principles, ancillary service scheduling to address
generator imbalances, new conditional firm transmission product.
Notice of Inquiry Opens inquiry to explore extent to which barriers may exist that impede reliable
and efficient integration of variable energy resources.
1000
June 22, 2012 764
Addresses how public utility transmission providers plan for and allocate
costs of new projects on a regional and interregional basis.
" Integration of Variable Energy Resources " rule amends Open Access Transmission
Tariff to offer intra-hourly transmission scheduling and requires
meteorological and forced outage data to be provided to public utility transmission
providers for forecasting purposes.
pieces of equipment that convert DC output
from a wind farm or a solar array to AC for
distribution to a load or to the grid. Recent
technology advancements enable increasStructural
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ingly " smart " inverters to play starring roles
in efforts to integrate ever-larger amounts of
solar into the grid.
For now, however, a principal factor
limiting efforts to integrate an intermittent
distributed resource such as solar or wind
is voltage on a distribution feeder, said Jeff
Smith, a senior project manager with the
Electric Power Research Institute (EPRI)
in an interview with POWER.
" Some distribution feeders are short
and fat and others are long and skinny, " he
said. Identifying which can best accommodate
distributed solar can be difficult, since
no two distribution systems are alike. As a
rule of thumb, connecting an intermittent
resource near a substation has less impact
in terms of voltage fluctuations than connecting
it miles away. Work by EPRI, utility
partners, and the vendor community is
intended to enhance inverter capabilities to
bolster grid support and voltage control.
Solving for X and Y
For years, the equation that grid operators
had to solve in order to balance supply
and demand included a constantly varying
load met by a generally stable and known
amount of generation, most of it fossil,
hydro, or nuclear. The accelerating addition
of intermittent resources from renewable
energy over the past decade tacked a
big unknown-variability-onto the generation
side of the equation.
Now, instead of dealing with one unthe
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known variable involving demand, grid
operators regularly face a second unknown
variable, this time involving generation
resources. That's because intermittent resources
differ from conventional and fossilfired
resources in a fundamental way: Their
fuel source (wind and sunlight) cannot be
controlled or (for now, anyway) stored in
a practical and cost-effective manner (Figure
2). The challenge is particularly acute
in areas where DG resources make a significant
contribution to the generation mix,
including New Jersey, parts of California,
Colorado, and the Texas and Midwest grid
operating regions.
A further complication is that fuel availability
for variable resources often does
not match electricity demand in terms of
time of use or geographic location. For
example, peak availability of wind power
often occurs during periods of relatively
low electricity demand. And on hot, sultry
summer days when consumers in general
and grid operators in particular would kill
for a breeze, wind production often drops
to near zero.
Yet another complication is that the outSee
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POWER | December 2012
put of variable resources often is characterized
by steep " ramps " that can be caused
by clouds moving across a solar array or
the passing of a weather front that changes
how much wind is blowing. Managing
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POWER December 2012

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