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Planning for future solar power-now

Arizona's 30-MW Red Horse 3 solar project offers some great lessons in phased development planning and factoring in possible future additional phases.

By Tony Kryzanowski

While the growth in renewable energy development over the past decade has been nothing short of spectacular, the availability of power purchase agreements (PPAs) has required many developers to roll out projects in phases—which presents its own unique challenges.

The question is: when should developers factor in the potential for future expansion into their planning? Brian Hoopes, project manager with Swinerton Renewable Energy, has a straightforward response—the sooner the better. Swinerton is a well-respected engineering, procurement, and construction (EPC) contractor to the renewable power sector.

"I think it's always good to be proactive," says Hoopes. "Before you even begin construction of the original project, I think the question should be asked of the owner or the developer if there is the potential for expansion. And if there is, what capital investment makes sense for this facility with the potential for expansion." The one caveat is that the developer should have a reasonable expectation that additional PPAs at a reasonable rate of return will become available to justify expansion.

That was the case with the recently completed Red Horse renewable energy projects in Arizona. Luckily, the project owner had additional land available and had taken enough steps during the first phase of construction to take advantage of an expansion opportunity once another PPA became available. Swinerton was the EPC on both the Red Horse 2 and 3 renewable energy projects.

The recently commissioned 30-megawatt (MW) Red Horse 3 solar project near Willcox, about 80 miles east of Tucson, is an add-on to the 71-MW Red Horse 2 project, which features a rare combination of both solar and wind generation. The Red Horse 3 solar expansion project, started in December 2015, took roughly six months to complete and was brought on line in the second quarter of 2016. As with Red Horse 2, the power generated is being sold to Tucson Electric Power.

In the case of Red Horse 3, it worked out well for the owner; they were able to negotiate a second PPA with Tucson Electric Power and contract the same EPC as Red Horse 2, which worked well for many of the Red Horse 2 suppliers. Many area workers were also able to continue to bring home regular paychecks with the Red Horse 3 project expansion, as about two-thirds of the workforce on the project was local.


Red Horse 3 consists of 119,358 solar modules provided by JinkoSolar. The project also features single-axis trackers supplied by Array Technologies Inc. Blymyer Engineers and Kimley-Horn and Associates provided engineering services on the project. The central inverters were provided by a different supplier on Red Horse 3—Sungrow. It was Swinerton's first experience working with this global inverter supplier.

Sungrow provided its SG1000MX PV inverter for the project, which it says is designed to provide higher yield and high efficiency. The inverter is capable of working well in extreme weather and challenging landscape conditions, designed with a wide operating temperature range from -30 degrees Celsius to +55 degrees Celsius and the capability to maintain continuous and stable operation at high altitude.

Being located immediately adjacent to the Red Horse 2 project, Red Horse 3 offered some of the same construction challenges, such as being a relatively remote location at high altitude. There was no cell service, so it was difficult to coordinate the delivery of components and provide directions when delivery trucks took a wrong turn.

But here's a tip for developers thinking about renewable energy project expansion. Hoopes says there were definite advantages to contracting nearly all of the same suppliers and deploying very similar technology on the Red Horse 3 expansion project because it meant only having to deal with a small group of suppliers to complete technological integration across both projects. The operations and maintenance group maintaining the project generally had fewer contacts to maintain—with the same suppliers—and had similar technology to become familiar with. The technological outlier, with Sungrow as their inverter supplier, provided Swinerton with an opportunity to expand its vendor network with a company that has a good international reputation and was expanding its business presence in the U.S.

However, the uncertainty surrounding the availability of another PPA made for some tough calls. Hoopes says there was some discussion at the time of the Red Horse 2 project of another potential phase, to add a greater solar component to the overall site. However, nothing was certain until later, and the decision was made to design the overhead transmission line from Red Horse 2 to the substation for a certain amount of power generation that did not take into consideration the full power generation potential of a 30-MW expansion. Therefore, it became necessary to install a separate, underground transmission line exclusively from the Red Horse 3 solar farm to the substation, rather than tying into the existing overhead transmission line. While it would have been preferable to simply install another overhead transmission line, the local jurisdiction requested an underground connection. The only alternative was a 5.5-mile underground trench to connect the Red Horse 3 solar installation to the substation, which Hoopes says in that high desert environment, opened up the possibility of encountering unknown obstructions, which did occur.

 Since the construction team was aware of a potential expansion during the building of Red Horse 2, they chose not to treat the Red Horse 2 site in isolation, giving thought to the placement of project components to accommodate a potential expansion.

"We'd get a couple thousand feet trenched in a day, and then at one point, it took us four days to go 80 feet just because of how dense and strong the rock was below the surface," he says. This also influenced the wear and tear on the heavy-duty trencher used on site, as sometimes they'd wear through a set of teeth in one day. Fortunately, Swinerton had considerable experience with underground trenching because of the amount of trenching typically done to connect components on solar farms themselves.

"We trench and direct-bury conductors all over our solar sites," says Hoopes. "So our ability to self-perform the transmission line trench definitely kept the cost reasonable."

Ultimately, it worked out for the better, as there were advantages to the Red Horse 3 project having its own dedicated transmission line, being that the earlier phase was a wind/solar hybrid. Adding a greater solar component to the existing transmission line would have added a complicating element to individual control, management, and monitoring of the multiple generation resources.

Since Swinerton Renewable Energy and its suppliers had the experience of Red Horse 2 under their belts, and the knowledge of what they would encounter by way of soil conditions, construction of the Red Horse 3 solar project was fairly straightforward.  

Again, Red Horse demonstrates how tying in production from a future expansion is not always a simple task and something that should be considered very early on in the planning stages.

Hoopes says one of the biggest challenges on Red Horse 3 was to install the necessary hardware in the substation to be able to monitor, ramp up, and curtail power output from both Red Horse projects, to ensure that the owner was still generating power below each PPA cap, while still maximizing output from the site. One complicating factor was maintaining Red Horse 2 at or below the PPA cap of 71 MWs, with multiple generation resources and the different technologies of wind and solar generation. While that in itself requires careful monitoring, adding the Red Horse 3 project, connected to a separate 30-MW PPA, did require detailed planning and control systems in the substation to ensure that operations and maintenance technicians have the data and tools to manage power output from each generation stream.

"We built the master plant controller, we built the solar controllers, we integrated everything, so we understand and are familiar with the systems," says Hoopes. "So even with the addition of Red Horse 3, while it adds more complexity to the scenario of automatic and manual plant management, it's still components and facilities that we are familiar with."

Placement of site components to accommodate potential future expansion is something else that developers should consider early on. In terms of the Red Horse site management, because the team was aware of a potential expansion down the road during the construction of Red Horse 2, they chose not to treat the Red Horse 2 site in isolation, giving some thought to the placement of project components to accommodate a potential expansion.

"One good aspect to Red Horse 2 is that we didn't just sprawl wherever, but contained Red Horse 2 into the smallest footprint possible," says Hoopes. "We generally contained the layout, which left some buildable areas outside the Red Horse 2 project footprint. That was definitely one anticipatory act under Red Horse 2."

Overall, he says that the construction of the Red Horse 3 solar project was fairly straightforward because Swinerton and its suppliers had the experience of Red Horse 2 under their belts and the knowledge of what they would encounter by way of soil conditions.

While every renewable energy project has its unique features, the Red Horse project demonstrates that there are definite advantages and financial benefits to asking early on in the planning if there is the potential for project expansion—especially as it relates to sizing tie-in equipment like transmission lines, placement of site components, EPC selection, and selection of suppliers.