Capturing the Desert Sun

In sunny Las Vegas, the water utility has installed a far-flung solar generating system that powers its own facilities and feeds renewable power to the electrical grid

By Tom Gibson

At Springs Preserve, Sean Vallesteros shows the structure for supporting
bi-facial solar panels above the parking lot along with a mesh beneath them to reflect sunlight upward.

Staying at the Circus Circus Hotel and Casino in Las Vegas, I see the vast magnitude of the famed Strip and the frenzied construction adding even more megahotels to it. I wonder where all the resources come from to support such development and how sustainable it is. Having rented a car, I drive out a side road behind the hotel and head north. Soon I discover a Las Vegas away from the glitz, where real people actually live normal lives, in houses no less, not hotels.

Motoring through suburban residential areas, I arrive at Springs Preserve in the northwest part of the city. Sean Vallesteros, assistant electrical engineer in the Maintenance Engineering Division of the Las Vegas Valley Water District (LVVWD) is there to meet me. With highrise hotels along the Strip visible in the distance, he shows me some of the infrastructure that supports both the strip and the rest of Sin City.

This is notable because LVVWD initiated a 3.1-megawatt, $22.6 million solar power generation project in 2004 as part of Nevada’s 2001 Renewable Energy Law to add to Nevada Power’s renewable energy portfolio. The last phase of the project was completed in 2007. One of the largest solar projects in the country, it consists of six solar power systems, five located at reservoir sites within the water distribution system and one at Springs Preserve.

The solar energy generated supports on-site operations and also feeds excess power back into Nevada Power’s electrical grid. Over the projected 30-year life of the systems, they will save an estimated 5.8 million barrels of oil. Shawn Mollus, director of engineering at LVVWD, says, “Just what we save with the pollution and the environment makes it a real fulfilling project to see out there functioning on an existing site.”

Much of Vegas’ water comes from snowmelt in the mountains, which I see towering in the distance. Sitting at the northeast edge of the Mojave Desert, the area only gets an average of 4.5 inches of rainfall a year. Snowmelt flows to the Colorado River, and some 85 percent of LVVWD’s water comes from nearby Lake Mead, formed by Hoover Dam along the Arizona border.

Reservoirs in the system work in conjunction with each other, each at a different elevation. Water is pumped uphill from one reservoir to another then gravity fed to the distribution system to service nearby residents. Some 32 reservoirs and tanks, 35 pumping stations, and 4000 miles of pipe comprise the system, which has 800 million gallons of drinking water capacity. Reservoirs range from 10 million gallons to 30 million gallons in size. The system serves 1.25 million residents and 40 million visitors a year.

Parking lots cover underground reservoirs at Springs Preserve, and solar panels shade cars.

As director of engineering, Mollus heads four major engineering divisions within LVVWD. “We’re heaviest in civil engineering. We do a lot with pipelines and pumping stations, so we also have a couple of mechanicals, structurals, and electricals.” He’s a civil engineer himself with a degree in construction engineering from Missouri Western State University and has worked at LVVWD for 22 years.

Vallesteros served as a field engineer for the solar project, handling day-to-day coordination with crews doing the installation. He coordinated with the operations group, as the system was being built on operational facilities.

An Idea Comes from Within

According to Mollus, the idea for the LVVWD solar project actually originated around 2000. “Solar has always been an interest of quite a few of us, even though we are civil engineers. Being in the desert southwest, there’s not a better place to have it. The idea got kicked around by three or four people within the engineering department.”

“We have a great matchup because we have reinforced concrete reservoirs located underground, and they typically sit on 5- to 10-acre sites and have a pumping station at the site, which is a huge electrical load,” Mollus adds. In places like Las Vegas, they cap reservoirs so the water doesn’t evaporate. And adding to the convenience, they’re already fenced in.

Mollus continues, “So, we had the real estate, which is really expensive here in Vegas, and a place where we could put solar panels right on top of the reservoir. The engineering group thought we would start off with a five-million-dollar demonstration project just to see how well it fit. And from there, it just kind of took off.”

Then, opportunities came up with respect to legislative action that allowed for renewable energy credits. When the project idea went public, PowerLight Corporation in Berkeley, California heard about it and offered to do the project, since they had the expertise in both the technical and legislative aspects. They were in the state lobbying for legislation under review, and PowerLight convinced LVVWD that if legislation passed, the project could be done cheaper. Nevada Power, the local electric utility, was involved in the relationship as well.

As engineering director for LVVWD, Shawn Mollus headed engineering efforts for the solar generation project.

It had now become a much larger project that bypassed the demonstration phase. LVVWD engineers evaluated about 20 sites and found the first five or six that best fit the profile for installing solar panels. Then they entered into a contract for a turnkey system with PowerLight, who handled design, construction, and maintenance. Staff engineers handled design review and coordination with existing facilities at the sites.

In 2007, PowerLight became part of SunPower, headquartered in San Jose, California. SunPower originally focused on producing the highest efficiency solar cells in the world, which they began manufacturing in 2004. PowerLight was one of their largest customers. According to Julie Blunden, vice president, public policy and corporate communications, the cost of panels is only about half that of a total typical solar-generating system, so they brought in PowerLight to reduce costs in the other aspects of installing a system.

Multi-Faceted Site
According to Blunden, Springs Preserve created a high profile for the project, as aesthetics became important there. “This is an example of how a solar system can enhance the appearance of a facility, rather than looking like a spaceship that landed on the roof.”

In addition, most of the water for the Vegas strip comes from Springs Preserve, so it ranks as a key operational facility. Two older above-ground steel tanks, 10-million gallons each, some of the larger ones you’ll see, sprawl on the grounds. In the 1960s and 1970s, above-ground steel tanks saw common use, especially for smaller systems. In later years, utilities went more to the underground reinforced-concrete tanks; two such reservoirs lie under the parking lots. And many active wells here feed into the reservoir system. In summer, they supplement about 10 percent of the water from the Colorado River with well water.

The solar panel system at Springs Preserve consists of 2200 panels with 409 kilowatts (kW) peak capacity. Some panels are fixed and tilted 15 degrees to the south, while others rotate to track the sun. They are mounted on a structural steel framework over the parking lots, also providing shade for up to 200 parked cars. Unlike at other sites, LVVWD didn’t have open spaces here for placing panel arrays. These are bi-facial solar modules, which generate electricity from both sides of the panel. A tensioned fabric layer below the modules provides shade to parked cars while it reflects sunlight onto the back of the panels.

While touring Springs Preserve, I found myself standing at the birthplace of Las Vegas, which was founded in 1905 as a railroad town. Artesian springs here provided a water source originally for Native Americans and later desert travelers. The city developed around this spring-fed wetland, originally known as Las Vegas Springs. Now it’s a 180-acre cultural and historical center with displays on the area’s water history and sustainability, a network of walking trails, gardens, and a restored wetland. Solar power generated here feeds both the preserve and operational facilities.

Next, Vallesteros and I drove to nearby Ronzone Reservoir, where 4005 panels in 7 arrays spread over the flat grounds yield 821 kW peak capacity. “We had to drill about 1000 holes for the foundations,” he says, pointing to the structural supports for the panels. Here, they placed the structures on footers in the soil, which were poured-in-place concrete.

Over 4000 solar panels generate power at Ronzone Reservoir.

At the other sites, they placed structures on top of existing concrete reservoirs. Two feet of earth fill lies on top of the reservoirs, mostly to keep heat from the structure. They had to excavate that to get to the top of the reservoir.

SunPower does its own structural design for the panel support structures, using structural engineers on staff. They determine the maximum wind load the panels could see and conduct wind tunnel testing on their designs.

Vallesteros showed me the gearmotor drive used to rotate the panels at Ronzone to face the sun. The small motor is geared down to provide high torque to power many panels at a low speed. They use the SunPower Tracker T0 system, which increases energy capture by up to 25 percent over fixed systems. “It takes an hour and a half to cycle the panels through their full rotation.”

Matt Campbell, product line manager for ground-mounted systems at SunPower, says they used off-the-shelf tracker designs for the project. At Springs Preserve, “it had some customizations that enabled it to be elevated so it could accommodate the bifacial solar panel.” Each bank of trackers and panels has its own motor and controller, with one drive motor required per 200 kW of capacity.

The controller has a GPS (Global Positioning System) function, which gives latitude, longitude, and precise time and has an astronomical algorithm. “So you know exactly where the sun is, and then it has a tilt sensor built onto the tracker. It uses that as its source of feedback on where the tracker is positioned,” Campbell explains. “Then it goes off the astronomical lookup tables, takes the feedback from the position sensor, and puts the tracker in the right position so it’s pointed at the sun.”

Leaving the panel arrays, I stroll with Vallesteros to a bank of large electrical equipment under a roof. “We have three inverters here that convert DC power generated to 208 volts AC. Then a transformer steps it up to 480 volts,” he explains. A data acquisition system monitors daily system performance. Most facilities are unmanned, remotely controlled from headquarters through a SCADA (supervisory control and data acquisition) system.

A New But Exciting Experience
When I asked Sean to describe the experience of working on the solar project, he replied, “It was new to me. I found it very exciting. My specialty is power, so it was a good fit. It took a lot of time to do this.”

At Ronzone Reservoir, Sean Vallesteros shows how a gearmotor rotates a bank of panels to track the sun.

In reflecting back on the project, Mollus says, “It has worked even better than we thought on all fronts. On the production end, we’re probably producing about 15 percent more than even our highest projection. As far as publicity and meeting our mission with sustainability, you couldn’t ask for anything better.”

Referring to Springs Preserve, Mollus adds, “It’s viewable. You get a lot of people coming in, a lot of visitors interested in it. Most water facilities, you design, build, and hide them. In fact, you put heavy security around them so no one ever gets to see them. So this was a nice change.” Since the project was completed, “I’ve had hundreds of calls from private and public agencies wanting to get into that and see how well it worked for us.”

With the success of the solar project, Mollus sees more of it coming in the future, “Hopefully we’ll be ready to go with round two and build another facility the size of this one. It’s worked out so well, we’re definitely looking to expand it. Our goal is to use renewable energy on all of our facilities. All together, we probably have over 100 sites, including wells, pumping stations, and reservoirs. So we have a great opportunity to take advantage of solar.”

As I leave Ronzone Reservoir, I make my way through neighborhoods to Interstate-15 and head south to the airport. Paralleling the Strip, I see the huge hotels that line it – The Mirage, New York New York, the Venetian, to name a few. Cranes tower overhead as they erect even more buildings. I still wonder about the sustainability of the area, but at least I know LVVWD is doing its part as they supply water and generate additional electrical power using renewable energy.

Taking Charge

Linda Zhang spearheaded the engineering and marketing behind Ford Motor Company’s conversion of the popular F-150 pickup truck to an electric vehicle

Recycling Goes Intelligent

Armed with artificial intelligence, robots are working in recycling facilities to address contamination, safety, and manpower issues

All Things Chemical Process Engineering

Headquartered in Oak Ridge, Tennessee, engineering firm Process Engineering Associates specializes in one discipline, but they apply it to many types of projects all over the world

Transforming the Grid

Engineers at the FREEDM Systems Center at North Carolina State University are developing solid-state transformers that promise to make the electrical grid more reliable and facilitate renewable energy such as wind and solar

Down with the Dam

Old dams are being taken down around the country for environmental and safety reasons. In Massachusetts, the story of the Upper Roberts Meadow Reservoir Dam removal project shows the complexities involved and the opportunities for engineers.