Can Double-Draft Design Make Solar Updraft Towers Viable?
Solar updraft technology has remained in the research and development phase due to high upfront construction costs and other drawbacks. A design that utilizes downdraft technology could dramatically increase energy output and turn solar updraft models into a commercial reality.
The shift toward renewable energy has spurred countless innovations. Engineers are harnessing solar, wind, and hydropower in new and exciting ways, but one possible method for capturing solar power has remained stagnant as researchers struggle to increase its viability: solar updraft technology.
Solar draft tower prototype in Spain. Image used courtesy of Wikidora via Wikimedia
A team of researchers in Jordan has designed a new twin-technology solar power system combining solar updraft technology with downdraft technology to maximize performance and make solar updraft towers economically advantageous. This model enhances productivity by creating a system that uses solar power during the day and still functions all night because downdraft technology can capitalize on cool air and the thermal power of rising warm air.
Barriers to Solar Updraft Implementation
The development of renewable energy sources is a complex dance of progress and setbacks, and for solar updraft technology, there have been more of the latter than the former.
The idea of leveraging solar energy and combining it with wind turbines to harness the power of heated air as it rises has existed for centuries. Even Leonardo Da Vinci made sketches of a kind of solar tower, which he referred to as a smoke jack.
Only a handful of prototypes operate, and the design fundamentals are consistent across each execution. A large solar collector, typically some type of glass covering, surrounds a tall vertical chimney so that hot air can be trapped and forced through the chimney. As the air passes through the chimney, it rotates turbines, thus producing energy.
While the design seems simple enough, the execution is not.
Some challenges that have proven difficult to overcome include the large spatial requirements needed for the solar collector at the base of the chimney, sometimes referred to as a collar collector. By sealing off the sides to prevent the air from exiting, the solar collector transforms ambient air into hot air, which then rises through the chimney. However, the collar must be large to generate enough heat, so each solar updraft system requires a significant amount of land and cannot be condensed as easily as other innovations, such as wind turbine farms, to maximize space limitations.
Design specs and estimated power output correlating with chimney height. Image used courtesy of the Journal of Advanced Review on Scientific Research
In addition to horizontal spatial challenges, the chimney must be very tall to produce enough electricity to justify building costs. A simple correlation between the height of the chimney and power output increases material costs and complicates maintenance.
Twin-Technology Solar System Design Innovation
Given these challenges concerning land use and construction costs associated with building a very tall chimney, one way to improve the design of solar updraft models is to strengthen the value proposition through increased power output.
One team of researchers has pioneered downdraft technology that can significantly increase power output by keeping the solar system in constant operation rather than only when the sun is available for heating ambient air.
Emad Abdelsalam, a researcher for the School of Engineering Technology at Al Hussein Technical University in Jordan, and his team have designed an external chimney that can surround the internal chimney and capitalize on the force generated by cold air as it descends in the same way the rising hot air powers the turbines.
Chimney with both updraft and downdraft channels. Image used courtesy of Science Direct
The Twin-Technology Solar System (TTSS) is designed to have a 45-foot diameter, and the chimney will rise to 652 feet. These dimensions are less important than the fact that this TTSS can operate around the clock, virtually eradicating one major drawback of typical solar updraft designs that limit operation to daylight hours. With the addition of downdraft channels, electricity production significantly increases, and this particular model can create 753 MWh every year.
One complication of this design is that it depends on a constant water supply to help cool the air as it passes through the downdraft channels. This drawback is compounded by the fact that this TTSS design is best suited to extremely arid environments.
Despite some steps that need to be taken before solar updraft technology is commercially viable, this TTSS innovative design shows how engineers can move solar updraft design out of the prototype stage and into fully operational commercial applications.
