Solar power sprouts where potatoes once bloomed (photos)

The San Luis Solar Ranch in southern Colorado is expected to start producing power for the grid in the coming week and be officially commissioned in December. The 110,000 solar panels from SunPower will produce about 30 megawatts, or enough to power 7,500 homes during peak times. The valley has some of the best solar resourcs in the country. Editors' note: This slideshow was originally published November 9, 2011. It was expanded with additional images on November 28, 2011.

The traditional industry is agriculture in the San Luis Valley, which produces barley for Coors and others as well as potatoes, hay for livestock, and carrots. Officials in the six counties in the basin, which is surrounded on three sides by mountains, are eager to promote solar power development in the area because it will bring in much-needed revenue. But there are still concerns and questions from many in the community over how solar should be developed.

The operator of the San Luis Solar Ranch, Iberdrola Renewables, will have a station on site to monitor wind speed and weather. The panels are mounted on trackers, which have motors to position the panels to face the sun directly. When the wind reaches a certain speed, the trackers are designed to turn into a safe, horizontal position but the station operator needs to monitor weather as well. In particular, the main safety concern is lighting and heavy storms. The on-site operators will also be aided by Iberdrola's national control center, which monitors weather nationally and can also see how equipment is functionally remotely.

Operations Manager Nick Thiel shows off the custom PC application for monitoring the performance and safety of the San Luis Solar Ranch. The hardware in the field is equipped with thousands of sensors that report back on performance, which helps him find where potential problems are. For example, if one string of panels isn't producing as much power as the one next to it, that could indicate a problem. The system is designed to send him alerts and let him drill down to locate specific issues. Thiel is originally from Iowa and learned how to maintain wind farms and is now starting in solar with this plant.

The SunPower system has a sensor that detects the sun in the morning and motors position the panels to face the sun. Over the course of the day, the panels follow the sun to optimize power production. This solar farm will have single-axis tracking, but concentrating photovoltaic systems have more complicated two-axis tracking. That's needed to optimize the panel's direction so that it faces the sun as directly as possible.

Down the road from the San Luis Solar plant run by Iberdrola Renewables is another 30-megawatt solar plant under construction. This facility, though, will use different photovoltaic technology. Instead of using high-efficiency monocrystalline solar panels from SunPower, the Cogentrix plant here will use concentrating photovoltaic collectors. With this technology, mirrors, and lenses concentrate light onto triple-junction solar cells that produce much more power than traditional silicon cells. Those high-end cells are more expensive, so the concentrator shines more light onto them to maximize power. Utility Xcel Energy is also purchasing the power from this plant and Department of Energy provided a $90.6 million loan guarantee for the project. As you can see, the two-axis, sun-tracking system is more complicated and the panels themselves are much larger.

One of the primary constraints to more solar development in the San Luis Valley is the lack of transmission lines. For the Iberdrola plant, the operator had to have a substation installed to collect the power and send it off over a 115-kilovolt transmission line. The operator also had to upgrade that line to ensure the power can flow out to the purchaser, utility Xcel Energy.

The San Luis Solar Ranch is located where there once was a potato and carrot farm. Because of a shortage of water, an estimated 40,000 acres of agricultural land will have to be retired in the next decade. County officials hope that solar can help bring revenue into the valley by building on former agricultural land.

Even though the environment is very dry, dust does not appear to be a major problem for solar photovoltaic panels in the San Luis valley. Solar photovoltaics consume very little water compared with solar thermal technologies that make steam to generate electricity. Still, SolarReserve is proposing another large-scale solar project that uses concentrating solar power and steam to make electricity. Its molten salt uses less water than other solar thermal technologies, but the company will need to secure access to water rights to be permitted.

The San Luis Valley has already had two smaller solar projects installed, including this 8.5-megawatt plant owned by SunPower, a company that makes the high-efficiency panels and develops projects. It has trackers that follow the sun during the day, which is typical for a utility-scale project. But the panels themselves are also tilted to squeeze a bit more energy from the sun.

Third-generation cattle George Whitten and his wife, Julie Sullivan, were opposed to a solar project on a nearby property. The proposal from Tessera Solar would have placed 6,000 large solar dishes on a wetland, but it was blocked by local residents because of the noise it would create. Sullivan, who was flown to Arizona by Tessera to learn about the technology, is opposed to large-scale solar projects that would turn the valley into an industrial zone or adversely affect the environment. The company, meanwhile, went bankrupt in part because of dramatically lower costs from solar photovoltaic panels.

Any solar development in the San Luis Valley, like many areas in the West, competes for water resources. Irrigation systems like these draw on the aquifer to make high-value crops, such as barley for Coors beer. So far, the solar projects in the San Luis basin have used photovoltaic technology, rather than steam-producing concentrating solar power, in part because PV does not require a lot of water.