The solar thermal market has been somewhat under the radar for more than thirty years. After an initial boom in the 1970s, when solar thermal technologies became a potential solution to the energy crisis, the industry nearly collapsed in 1986. Since then, the solar thermal market has been slowly inching its way back into the spotlight. It seems that within the next five years, it may finally see the explosive growth it deserves.
WHAT IS SOLAR THERMAL ENERGY?
Solar thermal technology, unlike the more widely-known solar photovoltaic technology, uses the sun to create thermal energy, which can then be transferred to a system and stored. For example, a solar heating (SH) system can be used to heat a boiler or residential pool. The other form of solar thermal technology is concentrated solar power (CSP).
Whereas SH technology is only able to convert sunlight into thermal energy at moderate levels, CSP systems can produce steam at higher temperatures and can power electrical generators. In other words, CSP technology can be used on a utility-level scale, such as in power plants. It's no wonder then that the CSP market is forecasted to grow roughly 60%; ballooning to $25.8 billion in 2019 from just $2.4 billion in 2014. In fact, CSP technology may become a significant source of global energy over the next few decades.
THE DIFFERENCE BETWEEN SH AND CSP
Both forms of solar thermal technology absorb sunlight and convert it into energy to be stored in heated media, like water, antifreeze, or air. That thermal energy is then used to power a process or system through the heated media. However, SH systems cannot concentrate sunlight and achieve high temperatures, and therefore are not an efficient solution to large-scale energy needs.
On the other hand, CSP technology can provide massive amounts of thermal energy at very high temperatures. This is because the systems absorb sunlight and then concentrate it in a heat transfer fluid (HTF). The concentrated thermal energy is then stored or used to power turbines or generators powered by heat engines. What sets CSP apart from other forms of energy is that CSP can be stored efficiently and inexpensively. In fact, it costs 20 to 100 times less to store heat than it does electricity. What's more, the energy can be used at times where photovoltaic solar energy is unusable, like at night, or as supplemental energy during peak usage times.
THE HUMBLE BEGINNINGS OF UTILITY-LEVEL CSP ENERGY
Using CSP technology on an industrial scale isn't a new concept. In fact, the first solar thermal power plant was built in 1984 and is still in use today. SEGS1, located in the Mojave Desert in California, is the first CSP parabolic trough and is a part of the largest thermal power plant in the world. The parabolic trough, named for the shape of its curved sunlight collector, can concentrate the sun 30 to 100 times more than its normal intensity.
The sunlight is then sent through a series of pipes via an HTF, where it generates steam and powers a turbine, generating electricity. Normally, this process would use fossil fuels to heat the HTF and power the turbine. CSP technology nearly negates the need for fossil fuels. Most thermal power plants only use fossil fuel energy as a backup, if at all.
IS THE POWER TOWER THE CSP SOLUTION OF THE FUTURE?
Parabolic power plants aren't the only type of CSP technology, however. Solar power towers have been around almost as long and are actually more powerful than parabolic systems. These power plants use a central tower, surrounded by thousands of flat mirrors called heliostats to collect sunlight. The heliostats follow the sun as it moves across the sky, and the receiver can concentrate sunlight up to 1,500 times.
Because the thermal energy isn't moving through a series of pipes, such as with a parabolic trough, there is significantly less energy loss. Power towers offer an excellent alternative to other thermal energy plants. In fact, the 110 megawatt Crescent Dunes Solar Energy Plant in Nevada, which switched on in 2015, produces more than 500,000 megawatt-hours of electricity per year, powering approximately 75,000 homes.
Crescent Dunes is the first utility-level power plant to use molten salt as an HTF and storage media in the world. Molten salt is 100% "green" and offers better heat storage capabilities than other types of HTF. It is highly efficient and can be heated to more than 1000 degrees Fahrenheit, which is more than enough to produce the high energy steam needed for the turbines. Furthermore, the plant's hybrid cooling system negates the need for "wet" cooling towers, which greatly reduces water use. This is crucial in dry climates, which are traditionally where solar power plants are built.
THE ONE-TWO PUNCH: PHOTOVOLTAIC AND CSP
Solar photovoltaic (PV) energy has been used for years to generate electricity on both residential and utility-level scales. While PV is a more direct method of creating electricity, it cannot be stored efficiently and is rendered useless at night and on cloudy days. Solar thermal energy, on the other hand, can be stored cheaply for on-demand use during these times. Combined, these two forms of solar power may completely change the way we get our electricity, nearly eradicating the use of fossil fuels. A 2014 study predicted that by 2050, as much as 16% of the world's electricity will be generated by SPV power, while CSP will account for 11%. If that prediction is realized, the two technologies will reduce carbon dioxide emissions by more than 6 billion tons.
Over the next several years, we can expect to see innovations in CSP technology as the market evolves. The recent renaissance of CSP is more than welcome in a world where we are rapidly depleting our resources. Will CSP and SPV finally give us the power to stop relying on fossil fuels? The future of solar looks bright.