|Fig. 1: The three towers of the Ivanpah facility. (Source: Wikimedia Commons)|
The Ivanpah Solar Power Facility is a Solar Thermal Plant in California's Mojave Desert(Fig. 1). It has the highest energy output of the four Solar Thermal Plants currently in operation in the United States.  Over the life cycle of the station, 13.5 million tons of carbon dioxide emissions will be avoided as it provides power to 140,000 nearby homes each year.  As shown by global solar insolation charts, the deserts of the south and southwestern United States have great potential for solar energy production. In fact, we could satisfy all of our current energy needs with just 1% of the earth's landmass.  Despite this, last year solar thermal power accounted for less than 1% of power generation in the United States. Due to its efficiency, sustainability, and falling costs, solar thermal power will likely be a significant factor in the planet's transition to clean energy.
Net nameplate capacity: 377 MW 
Average generation/day: 377 × 24 × .314(capacity factor) = 2841 MWh/day
Capacity cost for deliverable power: $5800/KWh 
$1.6 billion loan guarantee for United States Department of Energy 
$3 billion estimated total economic benefit 
Ivanpah and plants like it use thousands of "heliostat mirrors" to concentrate sunlight into a central tower, where it is used to super heat a material. Ivanpah uses fresh water, though many other plants use salt. At Ivanpah, the liquid begins in a "cold" tank where it is kept at 290°C. It is then sent to the central receiver tower, where the concentrated sunlight heats it to around 565°C. It is then passed to a "hot" tank, then to a steam generator. Here, the boiling water is used to produce steam, which is used to spin turbines, generating electricity. The water is recycled continuously, so there is no waste or loss. The Ivanpah station uses 173,500 heliostat mirrors to concentrate sunlight into the central tower. The mirrors follow the sun's movement throughout the day to maximize the amount of light directed.
Photovoltaic generators convert sunlight directly into energy using semiconductors. They rely on other sources of electricity to generate power, and can only operate while the sun is shining. Solar thermal can potentially run throughout the night (if salt is used, it can be stored overnight). Photovoltaics have a much greater gird- connected capacity however, at 800MW. 
The most significant drawback of a station like Ivanpah is the large block of land it requires. With typical solar panels there is more flexibility, as you could have one panel installed on the roof of a home or thousands installed contiguously in a desert. The intention of clean energy is to protect and preserve the earth; Ivanpah has had to make several allowances in defense of the environment to preserve this intention. In 2010, project was scaled back from the original 440 MW design to avoid encroaching on the habitat of the desert tortoise.  The lives of desert birds are also in peril, as they are attracted to the super-heated zones created by the mirrors. They are ignited by the molten air and then plummet to the earth; as many as three hundred charred bird carcasses were collected around the outskirts of the Ivanpah station over a three-month observation period.  Perhaps the most unsettling consequence of construction is the "fugitive dust emission" phenomenon. In erecting the stations, an enormous amount of earth is dredged up by the heavy machinery. If this earth is not allowed to settle as the facilities continue operations, it can lead to widespread airborne dust and dust storms in the area. 
Under Governor Jerry Brown's PATHWAYS Project, the government and people of California have committed to reducing greenhouse gas emissions in the state "to 80% below 1990 levels by 2050".  Stations like Ivanpah are necessary if this commitment is to become a reality. Ivanpah would not have been built without a $1.6 billion loan, and its construction required an enormous block of land and had some notable environmental consequences. However, it now provides power to over 100,000 homes and prevents millions of tons of carbon dioxide emissions each year. Even more promising, costs for solar power projects including those like Ivanpah are falling every year. 
© Grady Williams. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
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