(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 electricity storage.
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 Chart 1)
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. (Chart 2)
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 approach.
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 state.
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 28 countries.
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 objections.
All that may test policymakers' resolve to maintain the pace of renewable power additions. ($1 = 0.7518 euros) (Editing by Susan Fenton)