Solar power keeps getting cheaper, but there's a reason why utilities still turn to fossil fuels: it's expensive to store solar energy for use at night or on a cloudy day, times when solar doesn't work. But a massive new solar plant, sprawling over 1,670 acres near Las Vegas, was designed to solve that problem. It provides energy on demand, even when it's dark.
Sitting in the Nevada desert, the new Crescent Dunes Solar Energy Project is covered with more than 10,000 mirrors, each the size of a small house, that track the sun throughout the day and focus it on a receiver filled with molten salt. The salt, heated to almost 1,000 degrees Fahrenheit, stores the energy as heat, so it's always ready when it's needed. When the grid needs power, the heat in the salt is released to turn water into steam, which drives generators to make energy. That can happen whether the sun is shining or not.
"Whether it's in the daytime or the nighttime, it provides base-load stable power," says Kevin Smith, CEO of SolarReserve, the company that built the new plant. "If you get a bit of cloud cover that goes across at three o'clock in the afternoon, we're always drawing out of storage, so we continue to operate at 110 megawatts. We don't miss a beat, and the utility doesn't see any fluctuations in the power output over the day."
Though people tend to use more power during the day when the sun is shining, peak periods for utilities often run into the night as well. That's even more true in Las Vegas.
"In Nevada, with Las Vegas as their main load center, the utility's peak goes upwards to kind of midnight," says Smith. "So their peak is more of a noon to midnight kind of structure." That means a normal solar plant—using PV panels, the kind of technology people have on their roofs—wouldn't be able to meet demand without batteries or some other type of storage.
"The difficulty has been not only the cost but also the efficiency of batteries," says Smith. "To get the size we've got, you'd need football fields of batteries . . . If you took all the utility-scale batteries and added them up around the world, this is bigger than those put together." Right now, batteries are typically only used for very short backup—10 or 20 minutes at a time—rather than running all day.
As the first utility-scale solar plant of its kind in the world with built-in storage, Crescent Dunes cost around $1 billion to build. That's cheaper than a solar PV plant with battery storage. It's actually also cheaper than building a brand-new coal plant (with modern environmental protection) or a nuclear plant.
"People have a tendency to compare our technology to a coal plant that was built 30 years ago. It's fully depreciated, and they don’t have to pay for the capital anymore, and it's just the cost of burning fuel," says Smith, who previously worked on traditional energy plants.
The next projects the company are working on are 30% to 40% cheaper, and they expect cost to keep coming down. The biggest markets are outside of the U.S., in places such as Chile and China, where governments have committed to rely on renewables. "They're finding out that they have to put storage on the grid or they're going to have blackouts," he says.
One of the company's next projects, a one-gigawatt plant in China, will be 10 times as large as the one near Vegas. By 2020, China plans to build 10 more—the equivalent of 100 solar farms the size of Crescent Dunes.
Though that's still just a fraction of the size of the solar PV market, the company expects the new technology will grow. "Right now, we think we're the most competitive storage technology out there," says Smith.
All Photos: SolarReserve