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United States

New transmission lines required to avoid curtailment

UNITED STATES: A new report from the Department of Energy (DOE) has found that if a small amount of transmission capacity can be added the US grid network, curtailment can be significantly reduced.

ABB upgraded the Celilo power station, part of the Pacific Intertie link in Oregon, in 2016
ABB upgraded the Celilo power station, part of the Pacific Intertie link in Oregon, in 2016

The report Reducing Wind Curtailment through Transmissions Expansion in a Wind Vision Future was complied by the DOE's National Renewable Energy Laboratory (NREL).

It used the DOE's March 2015 Wind Vision report as its basis to discover how the transmission system would manage 35% of electricity being sourced by wind power — which the DOE said was "plausible" by 2050.

The research discovered, however, that without a significant upgrade of the US western transmission network — on which the report focused — 15.5% of wind power would need to be curtailed due to grid limitations.

NREL suggested that if just four currently proposed transmission projects with 10.5GW of capacity could be realised — at an estimated cost of $10.1bn — curtailment rates could fall by half (7.8%) on the US western transmission network.

It cited the microcosmic example of Texas, which reduced curtailment rates from between 8% and 17% in 2009 and 2011 to 1% with new transmission lines and grid upgrades.

NREL simulated a number of scenarios to determine the best ways to avoid curtailment. To do this, it used Plexos, "an integrated modelling tool commonly used by utilities and transmission organisations".

The report found that the base load coal generation in western US was not to blame for curtailment, as the loss of that capacity was made up for by gas production.

NREL said this suggested it was therefore a location problem as to why wind was curtailed.

The report then looked at a scenario with "no transmission constraints" meaning energy would flow "as readily as it would on a copper sheet", the report stated.

It found that curtailment could fall to 0.5% in every season if the electricity system had no transmission constraints.

NREL said it was the transmission system that caused inflexibility in the system, rather than traditional generation sources.

The four planned transmission lines NREL used in its low-build scenario, which would halve the curtailment rate, would carry electricity from wind-heavy states such as Wyoming, Montana and New Mexico to states with less wind penetration — Idaho, Nevada and Arizona.

"We do not intend to suggest that these projects are likely to succeed based on this analysis, nor is this a comprehensive benefit-to-cost analysis for any of these projects... Our analysis considers only the avoided generation costs from a more efficient commitment and dispatch of the generator fleet enabled by additional transmission, which includes avoided curtailment," the report said.

The American Wind Energy Association (AWEA) welcomed the report, calling on states and the new federal administration to put transmission investment at the top of its agenda.

"Renovating and expanding our outdated electric grid aids national security while saving consumers billions of dollars and creating more ways Americans can earn a paycheck. And once built, expanded transmission opens new export markets for states like Wyoming, Montana, and New Mexico, which will be able to turn their wind resource into gold," said AWEA CEO Tom Kiernan.

AWEA said the addition of the four proposed transmission lines could save consumers $2.3bn a year.

Upgrades

Today, Swiss firm ABB announced it had been awarded the contract to upgrade the existing Pacific Intertie power link.

The 1,360km interconnector between Oregon and southern California has been transmitting electricity across western states since 1970.

ABB will upgrade the Sylmar converter station north of Los Angeles with its advanced digital control system — the same system ABB used at the other end of the link in Oregon during a 2016 upgrade.

"Other key components of the Sylmar station upgrade are AC and DC filters, shunt reactors, as well as measurement and auxiliary equipment," ABB said.

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