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Giant wind farm nears approval for new, longer blades

State regulators appear set to approve a plan to install longer and lighter turbine blades at Oregon’s largest wind farm.

Caithness Energy LLC says the blades will do a better job harvesting power in low wind speeds. They could also earn the wind farm’s owner a valuable tax credit.

Caithness is asking for permission to “repower” the three units of the Shepherds Flat wind farm, which totals 238 turbines in Gilliam and Morrow counties. The Energy Facility Siting Council late last month posted a proposed order backing the move for one of the units, along with draft orders for the other two units.

Caithness’ plan is to keep the original turbine foundations and towers in place while replacing the turbines and associated machinery with “more technologically advanced equipment” that would boost generation without changing the wind farm’s footprint or nameplate capacity.

The overall rotor diameter and rotor swept area, now 100 meters, would increase to 127 meters, or nearly 417 feet.

Shepherds Flat went into operation in stages early last decade, and was completed in September 2012. At a total of 845 megawatts, it was called “one of the world’s largest wind farms,” and it retains that stature, representing about a quarter of Oregon’s total wind power capacity.

In its original site certificate, Caithness said “the wind facility is expected to have a useful life of at least 25 to 30 years,” but noted that lifespan could be lengthened with repowering.

Repowering has become common with wind farms built in the 2000s – Portland-based PacifiCorp is repowering around 1,000 megawatts of wind projects in the West as part of its $3 billion Energy Vision 2020 plan. But this is the most recent vintage wind farm to propose repowering.

In addition to delivering improved energy production, the repowering could qualify the turbines for another round of the federal production tax credit, which lapses after 10 years of operation.

It’s hard to say how much that would be worth to Caithness, which didn’t immediately return a request for comment. At its full value, the credit is worth $24 per megawatt-hour, and annual generation at Shepherds Flat has frequently topped 1.7 million megawatt-hours. The value of the credit to Caithness would depend on the project’s qualification under IRS standards for the size of the investment and start date.