An innovative design can increase energy output from solar updraft towers by more than twofold and works in hot and dry conditions.
A twin-technology solar tower developed by researchers at the universities in Jordan and Qatar has been shown to deliver energy around the clock.
This innovation works effectively in hot and dry areas but does not need photovoltaic panels, according to new research.
Solar updraft tower is a technology that has been in development for many years but has not seen much progress going commercial. Much like solar panels, this technology can work only during the daytime but has failed to deliver significant returns to be considered an economical energy source.
A collaboration between researchers in Jordan and Qatar looked into this problem and found an issue with the design of the solar updraft tower. In a typical setup, a large circular glass collector is used to heat the air above it using sun rays. Since hot air rises upwards, it is directed to flow through a long updraft tower which is fitted with a turbine to generate energy.
A new solar tower design
In their investigation, the researchers found that such a design of a solar tower has a lower thermal efficiency – less energy is generated for the large heat that is produced by the system. To improve the output of the system, larger glass collectors need to be used, which further increases the input cost of the setup and pushes the concept away from commercialization.
Previous attempts at improving this efficiency have focused on increasing chimney height or improving ventilation but did not deliver high returns. The researchers’ innovative approach involved placing a secondary tower outside the updraft tower and sprinkling a mist of water on the dry, hot air that had been through the turbine once.
The addition of water makes the air heavier and cooler, which then begins to fall toward the Earth as a result of gravity. This downdraft is then allowed to flow through these smaller channels arranged externally to the chimney tower and also have turbines that generate more electricity.
Energy output and limitations
The researchers estimate their innovative solar tower design, dubbed Twin-Technology Solar System (TTSS) can produce 2.14 times the power of a traditional solar tower. This is not surprising since the TTSS design generates energy during both the upward and downward flows of air.
The external tower performs best during the afternoon when the temperatures are highest, and humidity is lowest. On the other hand, the inner towers work independently of solar irradiance and can continue to produce energy even at night, making this device a 24-hour power generator.
The researchers acknowledge that the performance of the device is greatly impacted in high humidity, and therefore, it is ideal for hot and dry weather Recharge News reported.
A simulation testing performed using local weather data from Riyadh City showed that a single TTSS could generate 753 MWh of energy annually with 350 MWh of energy being generated by the upward draft tower while the downdraft generated 400 MWh of energy.
The need for constant water in the system is also a limitation when using it in hot desert conditions. The researchers are now working on how the solution can be scaled up and integrated with other types of renewable energy.
The research findings were published in the journal Energy Reports.
Traditional solar updraft power plants work during the daytime as it is dependent on solar radiation to generate electricity. Hence, energy productivity, efficiency, and performance are limited. This work presents a novel attempt to increase the productivity of a traditional solar updraft system by combining it with a downdraft technology in one system, the Twin-Technology Solar System (TTSS). The TTSS comprises two co-centric inner and external solar towers, turbines, water sprinklers, and a collector. The inner tower works as a traditional solar updraft system, where the air is heated under the collector due to irradiance and then moved up the chimney due to the pressure column. While the external tower creates a downdraft wind by spraying water at the hot ambient air at the top of the tower. The hot air instantly absorbs the water and descends the tower to interact with the turbines at the bottom to produce electricity. This mode is independent of solar irradiance and can operate day and night. Hence, the TTSS generates electricity, daytime and night. A mathematical simulation model was developed based on the proposed system’s energy and mass balance equations to assess performance. The TTSS generated 752,763 kWh of electricity annually, 2.14 folds higher than a traditional solar updraft system. Consequently, a reduction of 677 tons of CO2 was achieved with production. The design is suitable for deployment in hot and dry weather areas, such as remote villages and deserts. Future work will investigate introducing other technologies to boost the TTSS performance.