(The author is a Reuters columnist. The opinions expressed are
his / her own)
By Gerard Wynn
LONDON, Sept 12 Texas wind farms are benefiting
from transmission upgrades in the western half of the state, in
a lesson for Europe where a rapid rollout of variable renewables
has raced ahead of supporting infrastructure.
It is well known that in China wind turbines stood idle for
months without a grid connection a few years ago, something
Beijing sought to tackle by slowing wind farm development.
Variable wind and solar power must not only be connected to
the grid, but must also be managed to help operators cope when
they are unavailable or in surplus.
Options for such management include increasing the capacity
of flexible gas-fired back-up; expanding transmission capacity;
and new electricity storage.
Such integration has lagged in Europe and the United States.
Without these, grid operators will resort to reducing demand
or supply as renewable power reaches higher grid penetration.
Reducing supply includes spilling wind power on windy days
(called curtailment); being wasteful, this increases the full
cost of renewable power.
The widespread use of curtailment illustrates how strategic
infrastructure is still lagging, including transmission and
WIND ON THE PLAIN
Texas is the clear U.S. wind power leader with more than
double the installed capacity of second place California, at
12.2 gigawatts as of the end of 2012, according to the American
Wind Energy Association.
There have been two problems regarding grid integration in
Texas, in addition to variability.
First, the vast majority of wind resources - more than 80
percent - are in the western portion of the state, which has
much lower electricity demand than centres in the south and east
in Dallas and Houston.
Second, the western wind power resources poorly match the
electricity demand profile, blowing most strongly at night.
That contrasts with coastal wind in the state, which almost
perfectly matches demand which peaks in the early evening. (See
The result was massive wind curtailment in the state, which
peaked at nearly a fifth of available wind power, or 3,972
gigawatt hours, in 2009, according to data from the U.S. Energy
Efficiency and Renewable Energy (EERE), an office of the
Department of Energy.
That has since fallen to 3.7 percent in 2012, or 1,038 GWh.
EERE data are corroborated by the Electric Reliability
Council of Texas (ERCOT).
"The volume of wind actually produced was approximately 96
percent of the total available wind in 2012, up from
approximately 92 percent in 2011," ERCOT said in its latest
"State of the Market Report", published in June.
Chart 1: (page 65) goo.gl/OaHIEn
Chart 2: (page 44) goo.gl/jp2W4K
The reason for the drop in Texas wind power curtailment is a
massive build-out of western transmission capacity.
That construction is a result of a systematic approach which
followed some obvious blunders.
In 2002, some 758 megawatts (MW) of wind were interconnected
to a substation with only 400 MW of transmission, according to a
report by the National Renewable Energy Laboratory, "Integrating
Variable Renewable Energy in Electric Power Markets".
That underscored the need for a centralised, coordinated
In 2005, the Texas legislature passed Senate Bill 20, which
established the Texas renewable energy program and directed the
Public Utilities Commission of Texas (PUCT) to develop
competitive renewable energy zones (CREZ).
The PUCT designated zones in 2008, and a number of
transmission projects were selected to transmit 18,500 MW of
wind power from the CREZs to the eastern, more populated area of
The transmission projects are expected to be completed by
the end of this year.
Evidence so far is that the European Union is failing in a
similar centralised approach made more complicated by involving
In its "10-year network development plan 2012", the European
Network of Transmission System Operators for Electricity
(ENTSOE) identified the need to invest 104 billion euros ($138
billion) in 52,300 km of extra high voltage transmission at 100
bottlenecks, the vast majority of which were related to the
integration of renewable power.
ENTSOE said that there would be a "material delay to the
delivery of one third of the investments".
Building out transmission capacity is capital-intensive and
can be delayed by planning objections along selected routes.
It is also complicated in geographically isolated regions,
including islands like Britain, or peninsulas like Spain,
countries which each have large wind resources and some of the
smallest interconnections with the rest of Europe.
One alternative to building out transmission is to install
energy storage technologies to increase the flexibility of
renewable power, but these also face difficulties.
Chemical batteries are energy-intensive, which may make them
unsuited at present to grid-scale applications, according to
Stanford University research.
A study published this week in the journal "Energy and
Environmental Science" showed that it was actually more
efficient, on an energy life-cycle basis, to curtail wind power
than to store it using chemical batteries.
Large-scale, geologically based storage technologies such as
pumped hydropower and compressed air storage are less
energy-intensive, but both require particular terrain.
Pumped hydropower acts as hydropower in reverse, pumping
water uphill when electricity is in surplus, releasing it to
drive turbines during peak demand.
Compressed air storage uses off-peak electricity to drive
compressors which force air into an underground storage
reservoir, such as a rock cavern or abandoned mine, releasing it
during peak demand, when it is used to increase the output of
existing gas engines.
The simple answer is that a combination of approaches is
required to integrate more variable renewable power, depending
on the local circumstances.
The difficult part comes when all options involve trade-offs
including high capital costs, bigger energy bills and community
All that may test policymakers' resolve to maintain the pace
of renewable power additions.
($1 = 0.7518 euros)
(Editing by Susan Fenton)