This week the world’s largest solar plant began operating in the Mojave Desert near the California-Nevada border. An awe-inspiring sight, the Ivanpah Solar Plant covers a massive 3,500 acres of desert with a series of robot controlled-mirrors that reflect sunlight and concentrate it on three 69-storey high steam-generating towers. The solar plant cost $2.2 million and took over three years to build. The project has been developed by BrightSource Energy with investment from NRG Energy and Google.
The mirrored-based system the plant uses is known as solar thermal. The 350,000 mirrors are each 7 feet high and 10 feet wide, and controlled with computers to focus a large area of sunlight on one of the central towers. The towers produce steam at high pressures and temperatures of over 1000 degrees fahrenheit. The steam propels a turbine, which generates electricity in the same way as a conventional power plant.
The Ivanpah solar plant has a capacity of almost 400 megawatts (MW), which is enough to power 140,000 homes. An equivalent fossil fuel powered plant would produce this same amount of energy while emitting 400,000 metric tons of carbon dioxide per year. In effect Ivanpah will be the equivalent effect of removing 72,000 vehicles from the road.
The plant will account for nearly 30 percent of all solar thermal energy produced in the United States. Solar power currently is responsible for just under 1 per cent of the nation’s power output.
The 392 MW produced by Ivanpah compares respectably with the average output of a U.S. coal-fired plant of 667 MW. Both are much lower than the potential output of a hydroelectric plant — the Three Gorges Dam in China is the largest power plant in the world, and produces 22,500 MW, which is more than 50 times that of solar thermal. But the true test is perhaps is each plant's capacity when compared to the area used — Three Gorges Dam is situated on a giant 160,000 acre site. In this case nuclear plants are by far most “efficient.” The Kashiwazaki-Kariwa Nuclear Power Plant in Japan is producing 7.9 MW per acre of land used, compared with 0.1 MW per acre for the Ivanpah solar plant. Of course these calculations do not account for land lost due other important factors such as environmental waste.
Ivanpah improves upon other solar thermal systems by using a dry-cooling technology that reduces water consumption by 95%. This means the entire facility will use roughly the same amount of water as needed for two holes at a nearby golf course. Water conservation is hugely important given the location of solar plants in the desert.
The mirror-based system used at Ivanpah, differs from the more commonly known conventional panel solar technology, which is made of photovoltaic cells that convert sunlight directly into electricity. In theory, solar thermal plants can offer a significant advantage over roof-based systems — energy storage when the sun isn’t shining.
An Arizona solar power plant recently showed that it could generate power for six hours after sunset by heating molten salt. However this capacity hasn’t been built into the Ivanpah plant yet. BrightSource wants to develop storage down the road, but for its first massive project, chose not to. Advances in heat storage will be crucial in making solar thermal a reliable source of energy for widespread adoption.
Unlike photovoltaics which can be mounted on rooftops, solar thermal technology only works at large scale and in certain locations. In addition to size, large solar farms need added infrastructure in the form of transmission lines that shuttle the power to the cities that use it.
The Ivanpah plant was more expensive to build than a similar-size conventional solar-power plant would be today, because the price of rival solar technologies have plummeted in comparison. Advocates hope that the Ivanpah plant can help be a test case that will help drive the cost of thermal technology down.
Interestingly, the largest controversy surrounding the project has involved its environmental impact. Though barren to human eyes, the plant was built on an ecologically intact desert habitat. Project construction was temporarily halted in the spring of 2011 due to assess the plant’s impact on desert tortoises. Since being finished, dead birds from sparrows to hawks have been found on the site, with the suspected causes of death being collisions with mirrors and scorching.
These potential impacts on wildlife are of course dwarfed by the widespread environmental devastation caused by the use of fossil-fuels, but they’re still important to consider. A report by the California Energy Commission concluded that while the solar plant would impose "significant impacts on the environment ... the benefits the project would provide override those impacts."
Significantly larger solar thermal plants have been announced, with a plant in China slated to produce a whopping capacity of 2,000 MW. Meanwhile in the US, projects totalling an increase of 4,000 MW in capacity are being planned. However, as even a successful project like Ivanpah demonstrated, there are many challenges in making solar thermal plants operational. Brightsource have themselves cancelled projects totalling 1000 MW of capacity in the last year.
As other solar technologies have become far cheaper and natural gas-fired plants are five times less expensive to build, the federal guarantees required for launching projects like Ivanpah (which received $1.6 billion) have dried up. Brightsource last year announced that it would increasingly focus on markets outside the U.S.
Yet Ivanpah, as the world’s largest solar plant built so far, represents a significant touchstone. The key to expanding the use of solar and driving down costs is to show that it can safely and reliably be on the grid. California has helped to drive technology through passing laws that require state utilities to get one third of their electricity from renewable resources.
But we need more political leadership. With California on track to easily meet its renewable energy goals, the largest market for solar power in the US is drying up. To improve the technology we need to encourage more projects to get off the ground, and this is unlikely to happen unless other states pass similar laws. Increasing investments in natural gas, a form of energy that still contributes significantly to climate change, will drive energy prices down posing a further threat. Courage and visionary decision making will be needed to ensure that we keep making encouraging progress towards a bright future with renewables.