A new solar tower system is claimed to more than double the output of previous designs by using twin technologies to generate power day and night.
Researchers in Qatar and Jordan devised the “twin-technology solar system” by creating two towers – a smaller one enclosed by a larger one – that run air through two sets of turbines to generate power.
Solar updraft towers, which have been on the development blocks for decades but so far failed to break into the energy mainstream, have nothing to do with photovoltaic panels, working instead on the principle that hot air rises.
A huge circular glass collector – in this case 250 metres in diameter – suspended several meters above the ground uses the sun’s rays to heat the air beneath its canopy.
The collector slopes gently upwards towards a tall central tower, where the hot air rushes up to escape, passing through turbines to generate energy.
The researchers from Qatar University and Jordan's Hussein Technical University, who published their findings in the journal Energy Reports, say that an issue with the traditional design is that it has a low thermal efficiency (much lower than solar panels).
This means that the structures built must be very large to make them worthwhile, which has seen the concept hobbled by the high up-front costs involved.
Attempts at boosting efficiency over the years have included improving ventilation performance and increasing the chimney height, they said. But despite best efforts improvements were “modest”.
The idea that they devised is to build a secondary tower around the inner tower. At the top of the external tower, sprinklers spray a “mist of water” that is instantly absorbed by the “dry, hot air”.
The air then gets “heavier and cooler” and gravity drags it down the external tower in various columns. This creates a “downdraft” that is used to spin turbines located at the bottom of the external tower.
While the external tower performs best around noon when temperatures are highest and humidity is lowest, the researchers found it can operate throughout the day because solar irradiance “does not have a direct effect on its operation.”
This means the system can produce “24-hour power”.
The upside of this is that the researchers found their system produced 2.14 times the power of a traditional solar updraft tower.
The external tower may be more affected by seasonal variations in temperature and humidity, said the researchers, who noted large swings between the power it produced at different times of year.
Because the external tower’s performance is “greatly decreased in high humidity,” the researchers said the system is best deployed in “remote areas of hot and dry weather.” Its need for constant water access is another limitation.
Future work on the concept will investigate integrating other types of renewables technology, said the researchers, while also taking a “closer look at system scalability.”
