Wind powering up . . . again

Leeward Renewable Energy is bringing new life to older wind farms, most recently repowering two of its existing Texas wind farms, Sweetwater 1 and 2, an initiative that has delivered significant efficiency gains.

By Diane Mettler

In the past two decades, wind farms have sprung up all across North America and produced power for millions. Now, some of those wind turbines are starting to show their age. But with advances in industry technology, companies like Leeward Renewable Energy LLC are repowering those older wind farms and giving them a new life.

In 2017, the Dallas-based company chose to improve the output of two of its existing farms, Sweetwater 1 and 2 in Nolan County, Texas, which have been in operation since 2003 and 2005, respectively. The goal was to make them more valuable to Leeward, the landowner partners, and the wind farm's customers.

That was the first real year of the company repowering with today's more modern technology, using the partial repowering approach that it took with the Sweetwater projects, says Greg Wolf, Leeward's CEO. "We think that in a lot of ways Sweetwater was a first of its kind, and we anticipate much more repowering to follow."

The repowering required a solid partnership. For Leeward, it meant teaming with GE Renewable Energy to provide the wind turbines, and GE Energy Financial Services for tax equity financing. GE Renewable Energy also agreed to provide the operations and maintenance for the Sweetwater sites.

"Working with GE as our OEM partner has gone very well," says Wolf. "They were out in front of the repowering concept and how their technology would be upgraded." Carrying out the repowering work was Blattner Energy.

The Sweetwater 1 and 2 project was roughly a 136-megawatt (MW) undertaking. Leeward purchased the GE turbines to qualify for the PTC safe harbor, and the planning phase took a little over a year. The physical construction of the project was done largely in the fourth quarter of 2017.

"We spent considerable time preparing and evaluating the existing foundations, the towers, and collection system. We consulted with our own engineering team as well as third-party engineers for validation purposes," said Wolf.

Leeward was able to use the existing towers, infrastructure, and interconnection. With the set of GE turbines for Sweetwater 1, Leeward completely replaced the nacelle on the top of the towers. With Sweetwater 2, they also replaced the drivetrain and rotor.

During the construction phase, the farms were able to stay operating minus approximately two to six turbines that were being worked on, until all 86 were installed.

It sounds simple enough, but it wasn't without challenges. "Just like when you replace any older part with a new part, whether it is your automobile or air conditioning at home, it's certainly never seamless," says Wolf. "We worked through those issues as we were doing the actual replacement of the turbine parts. Once the project was completed and back on line, there was an adjustment period. But for the most part, it's been a success."

The repower has been paying off. Leeward has seen significant efficiency gains at Sweetwater 1 and 2—approximately 25 percent—and much lower operating costs.

"There's a certain fixed operating cost of maintaining and doing maintenance on any of the turbines," says Wolf. "But now that they have newer parts, they don't need as much maintenance. Also, because we're getting much more electricity production out of them, the unit cost on a dollar per megawatt hour basis just gets better."

Replacing parts is not always an option for older windfarms. Sometimes the existing tower has to be taken down and replaced to house the new technology. That was the case for the company's upcoming repower of its 15-year-old Mendota Hills Wind Farm in Lee County, Illinois.

Initially, Leeward had hoped to recycle the Mendota Hills' turbines, by sending them to a company who would want to redeploy the used turbines in either a low-cost area, an island setting, or where smaller turbines would work. Ultimately the cost to take them down and transport them didn't work out. Instead, Leeward will be taking down the turbines completely and recycling the steel.

"We've affectionately described this plan as the Paul Bunyan Approach," says Wolf. "We are working with an expert third-party decommissioning firm who will be draining all of the oil and other appropriate fluids out of the turbines. Then, the foundation is cut at its base like you would a tree. It's pulled over and brought down in the field. Fortunately, it's mostly farmland where our site is based. Once the turbine is felled, the steel from the tower can be recycled. Some of the other materials can be recycled as well. Others that can't be recycled will be properly disposed of.

"Mendota Hills is Leeward's oldest operating wind farm in our portfolio," explained Wolf. "The existing turbines are a much older technology with smaller rotor sets. We are going to be replacing 63 units of legacy Siemens Gamesa turbines with Siemens Gamesa SG 2.6-126 turbines and increasing the total capacity from roughly 50 MW to 76 MW. This repowering elevates a premier site that will benefit our customers and Lee County."

Wolf adds, "We're going to put up 29 turbines with 126-meter rotors, much bigger blades, bigger towers, bigger foundations—today's state-of-the-art wind turbines. Because of the vintage of the old turbines, there wasn't a cost-effective solution to repower those like we did with the GE turbines at Sweetwater. Reinvesting in Mendota Hills was really our best option."

The project commenced in March and is scheduled for completion in December 2018. Siemens Gamesa will continue to provide operations and maintenance for the Mendota site. And working together should go smoothly, as Mendota Hills is Siemens Gamesa's eighth project with Leeward, with joint projects spanning across four states and totaling over 400 MW. This is Siemens Gamesa's first full-scale repowering in the U.S. The EPC on the Mendota project is Mortenson Construction.

	The re powering of the two Sweetwater wind farms in Texas required a solid partnership. For the owner of the wind farms, Leeward Renewable Energy LLC, it meant teaming with GE Renewable Energy to provide the wind turbines and GE Energy Financial Services for tax equity financing.

The project is expected to generate 115 full-time construction jobs during the repowering process. It will also provide some permanent local jobs as well as a subcontractor base to maintain the project. The repowered project also means added revenue for Lee County, as it's expected to double its contribution in the first year in the form of property tax payments and triple its contribution throughout the lifespan of the repowered project.

The timing was perfect for repowering Mendota, says Wolf. Digital Reality, which is a data center and internet services firm, will be Leeward's customer for the power going forward.

"Prior to the repowering, we were just selling the power into the market. Our old contract had expired some years ago. It has been an un-contracted asset. So we had a little flexibility. There is lost revenue, but we didn't have a contractual obligation. When the project is complete, the contract to sell the power to Digital Realty will begin. We're very happy to have a leading clean technology company be our customer."

Leeward sees more repowering projects in the future. An independent power producer focused solely on renewable energy, Leeward's current existing portfolio is all wind. Some of these assets are more than 10 years old, utilizing technologies that were current at the time, but which are now less efficient and outdated. "These older farms are located on proven premier sites. As such, repowering, revitalizing, and upgrading them is the obvious next step," says Wolf.

Leeward is proud to be pioneering the new concept. "It's just a fact that wind technology has gotten so much better," said Wolf. He says it may be one of those situations where technology has actually gotten better faster than people thought it would over the last 10 years.

"It's now worthwhile to make that investment, swap out for materials that are lighter, moving to gear turbines that are more efficient, and enabling us to capture more electricity with the same amount of wind resource."

Wolf is proud how safely and efficiently his team has handled these new projects. Sweetwater 1 and 2 came in on time and on budget, and Mendota is on the same track.

"Our team did a great job," he says. "There was not a huge playbook for completing repowers. Certainly, there are some older wind farms utilizing the old lattice style, really small turbines that have been repowered over the years out in California and some other places. But Sweetwater and now Mendota are sort of early winners within the industry of repowering."

One thing that will be different going forward is a new owner for Leeward. The Canadian company OMERS Infrastructure Management will soon be acquiring Leeward Renewable Energy from ArcLight Capital Partners. But that's all that will be changing.

"Our team looks forward to continuing to operate our sizable portfolio safely, developing additional greenfield projects and executing on innovative repowering initiatives to build Leeward into an industry leader for years to come," says Wolf.