IVANPAH VALLEY, Calif. — Tower One glows white, so bright against the blue sky that even at midafternoon in the Mojave Desert it would be easy to conclude it is designed to illuminate the valley floor below.
In fact, hundreds of thousands of mirrors, carefully arranged across a broad swath of desert, reflect sunlight upward onto the tower and two others like it, heating them to 1,000 degrees Fahrenheit and causing the glow. Water in big pipes atop the towers turns to steam. The steam spins turbines, which generate electricity.
If all goes well, the Ivanpah Solar Electric Generating System will send that power across the Golden State early this year, becoming the largest solar plant in the world to concentrate the sun’s rays to produce electricity.
Such utility-sized solar plants are beginning to appear across the United States, with 232 under construction, in testing, or granted permits, many in the Southwest and California, according to the Edison Electric Institute, which represents utilities.
The scale of the largest plants is difficult to imagine in the eastern part of the country, where a relative lack of available open land and unobstructed sunlight have limited solar facilities to perhaps a tenth the size of the West’s plants.
But in the West, ample sun, wide-open spaces, financial incentives, falling costs, and state mandates have made big solar plants possible.
‘‘Right now you’re seeing the gold rush of renewable [energy] projects coming on line,’’ said Fong Wan, senior vice president for energy procurement at Pacific Gas and Electric, the big Northern California utility that has purchased about two-thirds of the electricity the Ivanpah plant will produce.
But even as the largest plants are helping utilities meet state requirements for renewable energy, the appetite for them may be waning, according to experts. The next phase of solar development — especially in the East — may feature smaller projects located closer to cities. Environmental groups want regulators to look at sites such as landfills and industrial zones before allowing construction in largely undisturbed environments such as deserts.
‘‘Part of the beauty is that solar is scalable, literally from the back of a cellphone all the way to a million panels in the desert,’’ said Rhone Resch, president and chief executive officer of the Solar Energy Industries Association. ‘‘The market is still trying to determine what is the optimal size.’’
The very largest plants, like BrightSource Energy’s $2.5 billion Ivanpah system and the Topaz Solar Farm, which will produce current with 9 million photovoltaic panels, can generate as much electricity as a coal or natural-gas-fired power plant.
But there is still a long way to go. In 2012, coal and natural gas plants produced 37 percent and 30 percent of US electricity, respectively, according to the US Energy Information Administration, while wind generated 3.5 percent and solar just 0.1 percent.
And the road to big solar energy’s development has been difficult. Lawsuits against the large plants accuse developers and the federal government of spoiling the fragile desert environment and wildlife habitats.