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Saluting Solar Power

Arizona utility Tucson Electric Power and contractor E.ON took on some interesting challenges when building a 17.2-MW solar project at Fort Huachuca, a U.S. Army base in southern Arizona. But they were able to successfully complete the project, which is

By Paul MacDonald

When it comes to building a solar power project, developers and contractors are accustomed to looking at historical or environmental considerations-but having to consider unexploded ordnance when choosing a site is a whole other matter.

That was just one of a few different challenges Arizona utility Tucson Electric Power (TEP), contractor E.ON, and their military counterparts faced with building a 17.2-MW solar project at Fort Huachuca, a U.S. Army base in southern Arizona's Cochise County.

The two companies were able to work closely with the military base and the U.S. Army Corps of Engineers to successfully complete the project, which is now supplying one quarter of the electrical needs of the base.

TEP owns and operates the system, which now ranks among the largest solar power arrays on any U.S. Department of Defense installation in the world. Because TEP is combining its output with grid resources to serve the base under existing rates, the system is helping the U.S. Army work toward its overall goal of deploying one gigawatt of renewable energy by the year 2025, without increasing the base's energy costs.

While delivering the most advanced PV solar project available at the lowest possible cost, the project also exceeds the Buy American Act requirements to source 51 percent of project components from U.S. suppliers.

Added to this, TEP (as the utility provider) was able to streamline the interconnection process through its existing Fort Huachuca substation, reducing interconnection costs and improving the reliability of the system.

The utility has served Fort Huachuca since 1941, so it has a well established relationship with the base, stretching back more than seven decades. TEP also has an interest in renewable energy. The utility owns a 6.4-MW solar project in northeastern Arizona, which back in the day ranked among the world's largest grid-tied PV arrays.

Carmine Tilghman, senior director of energy supply and renewable energy for TEP, explains that the utility has two military installations in their service territory. In addition to Fort Huachuca, TEP also serves the Davis-Monthan Air Force Base.

The Davis-Monthan Air Force Base entered into an agreement with SunEdison, LLC to design, finance, build, operate, and maintain a 16-MW array on 170 acres of underutilized land at two locations on the base. Renewable energy credits from this project are sold to TEP.

TEP and Fort Huachuca were discussing a similar project. "Fort Huachuca had been asking TEP if we could facilitate some type of renewable energy development on the base," explained Tilghman. TEP had tried smaller scale solar and wind projects on the base, but the base was now looking for something larger—as in utility-scale size. "But under their policy, the base wanted TEP to pay for it and for their rates to stay the same. In the early years of renewable energy, that just wasn't going to be practical for TEP."


Later, when the U.S. Army came out with its goal of deploying one GW of renewable energy system-wide, there was increased interest in being involved with a renewable energy project at Fort Huachuca. The army had clearly made achieving the one GW of renewable energy a high priority—and the base asked TEP how they could help them contribute to that goal.

"By that time, TEP had a number of years investing in, owning, and operating renewable energy projects—we had gone from simply signing an agreement with a third party to having an active role in the development and construction of projects," explained Tilghman.

"We had considerably more in-house expertise and the personnel to facilitate these renewable energy projects. And if you can develop, build, and operate your own facility—rather than pay a third party to do it—it's a better investment for your ratepayers and your company."

In TEP's annual filing with regulatory agency the Arizona Corporation Commission, they asked to make a $40 million investment in a solar power facility at the base, and own and operate it.

"The commission agreed, and we were able to structure an agreement with the army that saw TEP own and operate the facility on the base, have it tie into the utility side of our substation on the base, and retain ownership of the renewable energy credits-but the army would be able to utilize the power as part of their one-GW goal," explained Tilghman.

The fort's history goes back more than a century-it was originally the product of Indian Wars in the 1870s and 1880s. Fort Huachuca is currently home to the U.S. Army Intelligence Center and the U.S. Army Network Enterprise Technology Command (NETCOM)/9th Army Signal Command. It is also the headquarters of the Army Military Affiliate Radio System, the Joint Interoperability Test Command, and the Electronic Proving Ground.

Considering all that is located on Fort Huachuca, it's not surprising that the base had some thoughts about where the solar array should be located.

"In Arizona, unlike a lot of places in the U.S., we have a fair amount of land available," notes Tilghman. The base also has a fair bit of land—some 73,272 acres, to be precise. "But it's still a military location, so they are very sensitive to the location and to outside traffic.

Tucson Electric Power owns and operates the solar project at Fort Huachuca, which now ranks among the largest solar power arrays on any U.S. Department of Defense installation in the world. The system is helping the U.S. Army work toward its overall goal of deploying one gigawatt of renewable energy by the year 2025.  

"So doing a construction project on base, with hundreds of vehicles coming and going, where the project was sited was coordinated closely with the fort. They have very sensitive missions at the fort, relative to communication and electronics, and we needed to be cognizant of that."

The 90-acre project site was quite far from TEP's substation on the base, which meant a longer interconnection, part of which had to go underground. The base helped out, arranging for additional site clearing and for on-site water usage, so water would not have to be trucked in.

"We had a very good and collaborative relationship with the fort and the army," said Tilghman. "They were very helpful in facilitating construction of the solar project."

The army also did the National Environmental Policy Act (NEPA) study that was required, since the project is on federal lands.

Tilghman said whether you call it planning, or coordination, more of it is required when you are working on a military base.

"The coordination was considerably higher than what you would typically find on an industrial property around the Tucson area. You're coordinating work crews on and off a military installation that need clearance to be there. There's the coordination of several hundred delivery trucks and arranging gate access so you don't impede the normal traffic flow on and off the base. How you store and fence product on site, inventory control—it is all a consideration."

But there were also benefits, he reports.

"There were some easier parts, such as permitting and development. You simply work with the Army Corps of Engineers and the engineers on the base, and provide them with your site prep and site construction documentation-everything is approved there. There are no other jurisdictions to go to for permit requests or zoning issues."

The base is zoned for, well, military use—including, in this case, a solar power project.

The site itself had already been cleared in terms of any historical markers—and, as mentioned, military ordnance was not an issue on this site.


A technical challenge was encountered with the soil conditions. Rock formations eight to ten feet below the surface were bending the piles, so they moved to pre-drilling the holes that formed part of the foundation for the solar racking system.

Some extra work was required for drainage, and this will be monitored into the future.

"We were working from past studies, to build in drainage in different parts of the site," explained Tilghman. "But the studies were based on past weather reports, and things do change." The area is now receiving higher than average rainfall. "We subsequently restructured some drainage to prevent erosion.

"You study things, and you work to get it right, but then nature can surprise you, and you get more rain or different soil conditions, and you make corrections or changes," added Tilghman.

E.ON, being a major construction contractor, was able to roll with the changes. That is definitely a quality TEP looks for in its construction partners, says Tilghman.

"E.ON has diverse experience, and they had a willingness to work on something they knew would be both unique, and that was going to involve some unknown situations that would arise—and they were prepared to deal with them."

For its part, Tucson Electric Power brings more than a century of experience as a major utility—it serves more than 415,000 customers in the Tucson area—and growing experience with renewable energy. It now has more than 400 MW of renewable generating capacity.

Over the last six years, TEP has done 20 utility-scale renewable energy projects varying in size and technologies. "That gets you a lot of experience," says Tilghman. "We could have opted to do just one big renewable project, and we would have been good for a long time.

"We went the opposite route, which is a lot harder and a lot more work-but we've gained experience, and now our team is fully capable of running an entire project from inception to completion and operation.

"We've built up our internal base so that when a customer comes to us and says they would like to do a solar power project, and they want help with it, there's very little that we're not capable of managing internally—and helping that customer reach their renewable energy goals."

TEP and E.ON worked together on procurement solicitations for the Fort Huachuca solar project. "We were able to leverage E.ON's contacts as an EPC, but it also allowed TEP to have input into the technology and make the decisions on the technology and components used, based on our own experience."

A technical challenge was encountered with the soil conditions on the Fort Huachuca solar project. Rock formations eight to ten feet below the surface were bending the piles, so they moved to predrilling the holes that formed part of the foundation for the solar racking system.  

The project has 57,420 BYD 300w and 305w polycrystalline solar modules, 16 SMA 850KVA inverters, and 144 Shoals combiner boxes. Ground-mount racking by Shoals Technologies Group and First Solar fixed-tilt racking systems were used on the project.

Security was especially important on the project. Usually, temporary labor for solar projects (because they are single construction projects and of relatively short duration) is hired by a contractor, such as E.ON.

"You go to temporary labor pools, and they provide you with a base of construction workers," says Tilghman. "And under normal conditions, the EPC or head contractor might require periodic drug testing or background checks—and that would be it.

"But with this project being on a military site, construction workers needed to be pre-cleared—name, social security number, drug tests, background checks," said Tilghman. "It's much more stringent access for construction workers, to the point that it was a little rocky in the first month or so because there were a lot of denials." Some infractions, such as a construction worker with a DUI, would not normally be an issue on a regular solar power project.

It eventually went more smoothly. "Once we got the list of infractions from the military, we could share that with the temp agencies, and they could do their own background checks and ensure the people they were sending to the fort met the conditions."

This being Arizona, there were some weather conditions that had to be worked through on the way to completion.

Though known for its warm, generally dry weather, Arizona has its share of summer and winter rainstorms, coming from either Baja or the Gulf of Mexico. "This can result in very fast forming storms and very heavy torrential downpours in a very short period of time," noted Tilghman.

Construction went through a summer storm season. Typically, the storms would come through in the mid-to- late-afternoons, so construction crews would start early, to get as much done as possible before shutting down for the day, due to the risk of lightning.

And they had to deal with the aftermath of the wet weather. "After the rain, it's a matter of whether you can continue with the site prep or the grading and clearing, or the panel installation," said Tilghman.

"We lost some days in there, but it was mostly all weather related. We knew we were going to have weather-related delays, we just did not know exactly what or when they were going to be."

Once the project was completed, the U.S. Army's Office of Energy Initiatives asked TEP to do a review and forward any suggestions on how future projects might be done differently.

"The number one recommendation we made, and this holds true for any long standing installation, whether it is military or industrial, is getting up-to-date documentation and having it all available before you start a project," says Tilghman.

"This base has been there for almost 150 years, and not all the as-builts, the sewer, water, and electrical were marked. We would run into things that people did not know were there."

That said, TEP was pleased with how the project came together. "It went extraordinarily smooth for the amount of coordination, time, and effort, and the different personnel that were involved with a project that is on a fairly sensitive military installation.

"We were able to work closely with the leaders at the base and the U.S. Army's Office of Energy Initiatives to develop a unique solar solution for a very valuable TEP customer," he added.