The Abengoa Solana concentrating solar power project began operating this year at Gila Bend, Ariz., generating 280 MW, using a system of parabolic troughs.

This fall, three new solar power plants came to life on large tracts of undeveloped, remote lands in the western U.S. Although solar, these three installations are huge when compared with familiar, traditional rooftop photovoltaic (PV) systems.

Combined, these utility-scale power plants have the capacity to produce more than 800 MW of electricity, equal in output to a large coal- or gas-fired power plant. And one has the capability of storing and providing electricity to the grid for six hours—without sunshine.

The three are the California Valley Solar Ranch near San Luis Obispo in central California; the Abengoa Solana project in Gila Bend, Ariz.; and the Ivanpah Solar Electric Generating System in California’s Mojave Desert.

These are just the first wave of a potential tsunami of large solar plants that are newly operating, under construction, or being planned for the southwestern U.S. They are the fastest-growing sector of a rapidly increasing solar marketplace. However, whether more of these large plants follow will depend on how well these first few fare, and specifically if electric utilities want to buy more of the electricity these plants generate.

Success will also turn on whether developers can overcome growing opposition to the projects’ large size and the environmental damage and habitat destruction that can occur with their placement. Of particular concern is their effect on fragile desert ecosystems.

These plants are being built by a mix of engineering firms, energy companies, and solar equipment manufacturers that are benefiting from a host of state and federal incentives intended to reduce carbon dioxide and other greenhouse gas emissions from fossil-fuel power plants. The incentives require electric utilities to purchase growing amounts of renewable energy, such as solar-generated electricity, and these companies are quickly building new solar power plants to make money and meet that demand.

One of the most powerful drivers has been state renewable portfolio standards, particularly California’s requirement that electric utilities obtain 33% of their electricity from renewable energy sources by 2020. The requirement has put utilities on a hunt to purchase electricity generated by solar and wind to meet state quotas.

Also backing up these incentives and the push for renewable energy is a billion-dollar Department of Energy program to provide loan guarantees for large-scale renewable energy projects and a federal investment tax credit that provides a 30% tax credit for solar construction.

It’s a perfect storm for solar generation, notes Katherine Gensler, director of federal affairs for the Solar Energy Industries Association (SEIA), a trade group. By the end of the year, about half of the U.S.’s 9,500 MW of solar power will be generated by utility-scale power plants; most of this capacity came on-line in the past year.

SEIA figures show some 4,200 MW of utility-scale generation is now under construction and another 23,000 MW of utility-scale projects are being developed. More deals are being negotiated, analysts say.

California accounts for about half the installed utility-scale solar capacity as well as some 13,000 MW of the projects under development.

What will actually be built, Gensler and other analysts note, is a big question—one with too many variables that can be answered only over time as the solar marketplace shifts away from government support.

The federal tax incentive program ends in 2016, and it is unlikely DOE’s loan guarantee program will keep its pace. Consequently, the solar expansion numbers are murky, and although solar energy has been on a sharp growth curve over the past couple of years, it still produces only around 1% of U.S. electricity. But that could swiftly change in the topsy-turvy world of energy.

Each of the three newly operating units embraces slightly different technologies. The California Valley Solar Ranch uses 88,000 PV panels, a well-known technology used in rooftop solar installations that converts the sun’s energy directly into electricity. But unlike usual rooftop units that vary from a couple of kilowatts of electricity on a house to a couple of megawatts on a Walmart or IKEA warehouse, the solar ranch produces 250 MW and is one of the largest PV systems in the world. Currently, PV installations, overall, make up about 80% of the utility-scale projects, SEIA notes.

The Abengoa Solana project and Ivanpah Solar Electric Generating System are concentrated solar power (CSP) systems that together will produce more than 650 MW of electricity. Solana generates 280 MW by using a system of curved mirrors to focus solar energy. Ivanpah generates 130 MW of electricity now but will grow to 390 MW next year as its system of flat concentrating mirrors, coupled with three power towers, is finally complete.

Like PV, these CSP systems use sunlight as fuel, but they focus the sun’s thermal energy to heat a conducting medium, such as oil or molten salt. The medium carries heat that is used to drive water to steam, and like a conventional power plant, the steam spins a turbine to do work, in this case generate electricity.

Because CSP uses a medium that retains thermal energy, it can smooth out temporary generation fluctuations in sunlight from storms or a passing cloud, which interrupts PV-generated electricity production. On the other hand, CSP systems need intense light levels for its mirrors and lenses to properly focus light and energy. Therefore, CSP is usually limited to deserts and other high-sunlight areas.

A key advantage of CSP is that it can incorporate storage into its design. The Solana project does this by storing thermal energy in molten salts, from which it is released over time. Solana can stretch out electrical output for six hours without sunshine. Similar plants with storage are in the works. Storage could be a game changer for solar power.

But this solar expansion—whether PV or CSP—has a steep price tag. These three installations are billion-dollar projects: The two CSP facilities run at around $2 billion each; the PV ranch costs $1.6 billion. The estimates are fluid, and the CSP developers hope costs will drop with more construction.

DOE has thrown its weight behind utility-scale solar installations, offering $10.5 billion in loan guarantees to help developers obtain funding for 11 projects. About one-quarter of the total dollars back up five CSP plants, two with storage. The rest of the money supports six PV plants.

Of the 11, three are the large plants that just came on-line. Two are smaller PV projects that received loan guarantees and are in operation; they have a combined capacity of 200 MW. The remaining six projects that are in development will generate 1,700 MW.

One huge PV unit—the Desert Sunlight Solar Farm—will produce 550 MW when complete. It will be built by the thin-film solar manufacturer First Solar with support and financing from a consortium of solar developers. First Solar claims the facility will be the world’s largest solar farm.

Electric utilities like these big projects, explains Bob Gibson, vice president for education and communication at the Solar Electric Power Association, a nonprofit organization of utilities and solar-related manufacturers. Utilities, he notes, are familiar with the large size and can easily manage these installations.

“Right now, there are 300,000 small rooftop photovoltaic solar units operating in the U.S. and feeding electricity into the electric grid,” he notes. “That is a lot of individual transactions for an electric utility to manage.”

The big units, Gibson says, might help encourage a “solar evolution” for utilities and might lift solar beyond the niche technology it has been in the past and elevate it to coal-plant size.

“If the first utility-scale 100-MW-plus CSP projects are really successful, and we build more of them, and the cost really comes down nicely, CSP will perhaps be more attractive than PV at that point,” Libby says.

Utility-scale CSP with storage goes back decades. The technology got its first big start in the 1980s and ’90s when nine CSP power plants were built in the California desert. The Solar Energy Generating Systems (SEGS) produced 354 MW, making it the largest solar power installation in the world at that time. The company that built the plants morphed into what became BrightSource Energy, Ivanpah’s builder.

Initially, some of the nine facilities in the complex had the ability to provide three hours of thermal energy storage, but in 1999, SEGS caught fire and the storage system was damaged. It was not replaced when the facility was rebuilt and improved, according to DOE. Most of SEGS is still operational today.

“The SEGS plants have been operating reliably, providing steady power for over 20 years,” notes Frank (Tex) Wilkins, an energy consultant who is retired but worked for DOE on experimental solar projects when SEGS was under construction. “Their track record convinced the financial sector that there was little risk with the technology, making it easier for today’s CSP industry to get project financing.”

By Jeff Johnson,