Solar thermal power plants - which use high temperatures and pressure generated by sunlight to produce turbine movement - are an environmentally-friendly alternative to standard power plants. But this can be expensive, especially when it comes to equipment made from expensive metals and the solar high-accuracy concentrator technology used to harvest solar energy.
A new technology developed by Professor Avi Kribus of Tel Aviv University (TAU) combines the use of conventional fuel with the lower pressures and temperatures of steam produced by solar power, allowing plants to be hybrid - replacing 25 to 50 percent of their fuel use with green energy.
In a solar thermal power plant, sunlight is harvested to create hot high-pressure steam, approximately 400 to 500 degrees centigrade. This solar-produced steam is then used to rotate the turbines that generate electricity.
Though the environmental benefits over traditional power plants are undeniable, Kribus cautions that it is somewhat unrealistic economically for the current industry. The materials alone, which include pipes made from expensive metals designed to handle high pressures and temperatures, as well as fields of large mirrors needed to harvest and concentrate enough light, make the venture too costly to be widely implemented.
With his graduate student Maya Livshits, Kribus is developing an alternative technology called a steam-injection gas turbine. "We combine a gas turbine, which works on hot air and not steam, and inject the solar-produced steam into the process," he explains. "We still need to burn fuel to heat the air, but we add steam from low-temperature solar energy, approximately 200 degrees centigrade." This hybrid cycle is not only highly efficient in terms of energy production, but the lowered pressure and heat requirements allow the solar part of the technology to use more cost-effective materials, such as common metals and low-cost solar collectors.
The hybrid fuel and solar power system may not be entirely green, says Kribus, but it does offer a more realistic option for the short and medium term. Electricity from solar thermal power plants currently costs twice as much as electricity from traditional power plants. If this doesn't change, the technology may never be widely adopted. The researchers hope that a hybrid plant will have a comparable cost to a fuel-based power plant, making the option of replacing a large fraction of fuel with solar energy competitive and viable.