Any large-scale project carries with it some inherent disadvantages. Solar thermal power plants fall victim to several challenging, though not insurmountable, obstacles not common to other endeavors. Environmental benefits are offset by valid concerns, while the technology needed to truly advance solar as a viable energy source lags under the weight of difficult-to-find financing.
A product’s carbon footprint is determined not just by what the product itself produces but by the amount of energy required to manufacture it. Solar collectors are made in factories largely powered by fossil fuels using materials mined using fossil fuels, so that although electricity generated at a solar thermal plant is emissions-free, the manufacturing process still has a significant impact on the environment both on land and in the air.
Additionally, power generation from any energy source is water intensive. Solar thermal plants require water for steam to power the generator as well as for cooling and washing of the equipment. According to a U.S. Department of Energy report to Congress, older “once through” cooling systems used up to 27,000 gallons of water per megawatt, or MW, of energy produced. Newer evaporative cooling techniques reduce the number to approximately 500 to 600 gallons per MW, which is roughly equal to the water usage at a typical coal-fired plant.
No true breakthrough in solar power generation, be it concentrated solar power, or CSP, or photovoltaic solar power, is possible without an adequate and cost-effective means of power storage. Solar thermal plants obviously produce electricity only when the sun is shining, making cloudy days and nighttime hours a hindrance to the steady flow of electricity that the nation’s power grid needs.
Researchers at the Massachusetts Institute of Technology are experimenting with inexpensive catalysts that can split water into hydrogen and oxygen, with electricity produced during the day so that solar thermal power plants can use the energy stored in the chemical bonds of the hydrogen to generate power at night by means of fuel cells, but the work is far from complete. Alternatively, experimental heat transfer materials like molten salt can trap the heat energy generated by a solar thermal power plant for use later during nighttime hours. However, the most successful plant to do so, as of 2010, the Andasol station in Spain, gains only an extra six hours of power generation from the process. It’s a healthy start, but 24-hour per day power via some sort of storage technology must become a reality in order to make solar viable worldwide.
One of the advantages solar thermal power generation enjoys over its close cousin, photovoltaic solar power, or PV, is that it can be done at much larger scales less expensively than PV. The advantage becomes a disadvantage, however, when it comes to financing these large-scale projects. The costs are still far higher than coal plants based on units of energy produced, which makes initial cash outlays scary for potential investors. More money has flowed into smaller PV projects because of lower risk and less cash up front, according to Jonathan Fahey writing for "Forbes Magazine" in July 2010.
- National Renewable Energy Laboratory: Parabolic Trough Thermal Energy Storage Technology
- Popular Mechanics: Is MITs Latest Solar Breakthrough Just Hype?
- Union of Concerned Scientists: Environmental Impacts of Renewable Energy
- Forbes: Solar Thermal Hopefuls Make Their Case, Battle for Financing
- Solar Thermal World: Reduced Water Consumption in Concentrating Solar Power Systems