Sustainable Land Development Today - January 2009 - (Page 39)

Estimates for the cost of electricity produced range from 6-31 cents per kWh, depending on the cost of land and financing. By comparison, a normal gas operated power plant can produce electricity for as little as six cents/kWh. Our investigation in combined land use may increase the financial viability of this renewable energy technology dramatically, allowing it to be applied beyond its current potential as an affordable, developing-world technology to a high tech source of first world power generation. can then function as thermal storage to reduce the effect of diurnal swing as well. The tanks can use the membrane to collect rain water, as well as tap into ground water. In desert situations briny groundwater can be desalinated using solar desalinators also underneath the membrane, depending on the water conditions and the type of algae grown. Using agriculture in combination with the updraft tower this system can be applied as both a sustainable economic strategy or for community restoration in developing nations. Agricultural Potential An important side effect of placing a large, transparent membrane over an area of land is the capture of evaporated ground water and its return back to the topsoil. This localized increase in land moisture can make the soil underneath the collector suitable for agricultural uses, through the effective creation of a partial greenhouse. In some cases, the land under the collector would not have been agriculturally viable without the presence of membrane. This means that certain barren lands could be reclaimed for productive use, making this energygeneration strategy more economically favorable while also building agricultural capital. The clearance height underneath the collector can easily accommodate farm equipment, and the supports for the collector can be far enough apart to allow the working of the land. Different kinds of crops can be planted depending on the local soil and moisture conditions, bearing in mind that the area near the center will have airflow too strong to allow plant growth. If the vegetation is very substantial, it may impact the output of the tower due to wind drag. However, increasing the distance of the membrane from the ground can mitigate this. Another potential agricultural use is the application of algae growth tanks underneath the membrane of the tower. Closed-culture tanks for biofuel production using, for instance, Botryococcus algae or open culture tanks with Spirulina as a nutritional source could expand the potential of the land to a large degree. Tanks underneath the membrane Co-Generation Potential Solar technologies, such as collectors that use solar radiation to convert water to steam or photovoltaic (PV) arrays, generate substantial excess heat. In the case of PV, high temperatures diminish their power generation capacity. Using the solar updraft tower in combination with solar collectors or PV arrays can improve the efficiency of both systems. The constant wind flow can air-cool the collectors while increase the energetic output per area of land used, making the solar updraft tower a more efficient proposition. Things to consider in terms of the efficiency of combining these systems include the loss of some direct solar radiation as a result of its deflection by the membrane, and the amount of cooling that can ideally be achieved. This strategy can also be combined with agricultural uses, where solar collectors or PV arrays would be placed at the center of the collector, where the winds are too strong for plant growth. cleaned, resulting in urban air quality improvement. Second, in cold climates, the heat dissipation of the urban environment can be buffered. The trapped heat will aid the power generation, but will also reduce the temperature gradient between interiors and exteriors, resulting in energy savings for building heating and higher insulation efficiencies. Third, in hot climates, a second layer with a semi-transparent PV membrane could be installed. This would partially block out the sun, causing the temperature gradient to drop. There will then be two layers generating convection, potentially increasing the efficiency of the tower. The top layer would ensure the heat is not trapped in the bottom layer, which will partially combat the urban, heat-island effect. More Benefits This unique, energy-generating concept is flexible. It does not need to be placed on any specific land type and the height of the collection membrane can vary. The efficiency of the tower might change depending on the resistance of the ground, but the advantage of using land for a productive purpose while at the same time generating electricity is a very attractive prospect. The solar updraft tower is one of the simplest and most straightforward of all renewable energy systems, and if designed properly, it can be applied in a great variety of circumstances. It lends itself well to the redevelopment of economically depleted areas, and for the generation of electricity in remote areas without the need for large maintenance crews. Except is currently investigating several other uses of the solar updraft tower, both for remote electricity generation and for urban use. SLDT About the author: Tom Bosschaert MSc MArch, is the founder of Except Architecture, Urban Design, Consultancy & Presentation, a new form of think-tank firm that re-integrates science with art for a sustainable society. He can be reached at +31 (0) 6 55530047, and www.except.nl. Urban Use A completely different alternative use is the urban application of solar updraft towers. A tower in a city could hardly be the size of one in an undeveloped setting, so its generative power would be diminished. However, it could provide three distinct advantages besides electricity generation. First, systems like these would be very suitable for highly polluted cities., The tower could be fitted with particulate, carbon and other filters. As the air flows through the chimney, it would be www.SLDTonline.com 39 http://www.except.nl http://www.SLDTonline.com

Table of Contents Feed for the Digital Edition of Sustainable Land Development Today - January 2009

Sustainable Land Development Today - January 2009 Contents Our Voice Your Voice The BottomLine SLDI in Focus Calendar Industry Rebound Will Require Balanced Approach What Happened to Fannie and Freddie? Added Value in Entitlements Industry Spotlights Technology Wastewater Innovation Classifieds Advertiser Index Editorial Board SLDT Resources Last Word

Sustainable Land Development Today - January 2009

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