Plan afoot to make cheaper concentrating solar power

Inspired by green hybrid electric cars driven by a mixture of gas and electricity, researchers have turned their attention to the greening of power plants too. Most power plants, explains Avi Kribus professor at Tel Aviv University (TAU) School of Mechanical Engineering, create power using fuel.

And concentrated solar thermal power plants, which use high temperatures and pressure generated by sunlight to produce turbine movement, are currently the industry’s green alternative, but a prohibitively expensive option. The technology developed by Kribus combines fuel with the lower pressures and temperatures of steam produced by solar power, allowing plants to become hybrid, replacing 25 to 50 per cent of their fuel use with green energy, the Solar Energy Journal, reports.

In a solar thermal power plant, sunlight is harvested to create hot high-pressure steam, about 400 to 500 degrees centigrade. This steam is then used to rotate the turbines to generate power. Though the environmental benefits over traditional power plants are undeniable, Kribus cautions that the “complex solar technology” is somewhat unrealistic economically for the current industry.

However Kribus, with his graduate student Maya Livshits, 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,” said Kribis.

With graduate student Maya Livshits, Kribus is developing a steam-injection gas turbine. The gas turbine uses a mixture of hot air and steam. "We still need to burn fuel to heat the air, but we add steam from low-temperature solar energy, approximately 200 °C," Kribus said. This hybrid cycle is highly efficient in producing energy and the lower 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.

They have performed a thermodynamic analysis of this hybrid cycle, finding that this approach has the potential to have an overall conversion efficiency (with fuel and solar contributions) from heat to electricity in the range of 40–55%. The system has the potential to use very little water because the injected water can be recovered and recycled with the use of a very low cost condenser.

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. They are starting to collaborate with a university in India to further develop the technology and are looking for corporate partnerships willing to put the hybrid technology into use. It’s a stepping-stone that will help introduce solar energy into the industry in an accessible and affordable way, Kribus says.