Alternate Energy from Deserts

Abstract Due to rapid growth of the world's population and more demands for energy, and due to limited amount of fossil fuels (which provide 95 % of the world's energy needs), harnessing of alternate energy sources such as solar and wind power is going to be a necessity. Present estimates indicate that the amount of recoverable fossil fuel may equal 10 trillion barrels of oil, which at the present rate of consumption is enough to last 170 years. How can a growing demand for energy be met without radically altering the planet we live? Harnessing of solar and wind energies could be a solution. In addition to the mountain passes and high plateaus with potential high wind, vast and flat desert areas could be good candidates for harvesting both solar and wind power too. Desert areas are defined as those regions with less than 250 mm (10") of rainfall per year with a net loss of water due to evaporation. This includes about 10% of the Earth's total surface, or about 33% of the Earth's land surface. Little detailed information exits on the evaluation of radiation and wind over a desert playa. Playa refers to a desert basin with no outlet which periodically fills with water to form a temporary lake. Because of their low rainfall and high salt content, playas typically do not support agricultural activities and are generally inhospitable to human habitation. However, recent increase in solar and wind power generation efficiency, coupled with increasing demand for electrical power, suggest that the suitability of playas for harvesting wind and solar energies deserve investigation. This paper reports the annual radiation balance components and windiness over a playa located within the Great Basin occupying northwestern Utah, USA, and compares these measurements with comparable measurements from two other stations located in the non-playa environments of central and northern Utah. The purpose of this measurement program is to increase our knowledge of radiation and wind distribution at different ecosystems, and examine the possibility of harvesting solar and wind energies over the vast and flat playas of the Great Basin Desert in the USA with an area of about 190,000 square miles. We set up an automatic weather station in the middle of a desert, approximately 65 km east-west by 130 km north-south, located at Dugway(40 deg. 08' N, 113 Deg. 27' W, 1124 m above mean sea level) in northwestern Utah, U.S.A. This station measured the incoming (Rsi) and outgoing (Rso) solar or shortwave radiation using two ventilated CM21 Kipp & Zonen pyranometers (one inverted), the incoming (Rli or atmospheric) and outgoing (Rlo or terrestrial) longwave radiation, using two ventilated CG1 Kipp & Zonen pyrgeometers (one inverted), and the net (Rn) radiation using a Q*7 net radiometer. We also measured the 3-m wind speed (U3) and direction parameters such as temperature and moisture gradients, soil heat flux, surface soil temperature, and the air pressure for other purposes. The measurements were taken every two seconds, and averaged into 20-min, continuously, throughout the year. This article reports the two-year period comparisons of global or solar radiation and windiness over desert with two other stations in central (Hunter) and northern (Logan) Utah. The results indicate higher average monthly (higher during summer and lower during winter) solar radiation (Rsi,Dugway = 591 MJ/m2/month vs. Rsi, Hunter = 537 MJ/m2/month and Rsi,Logan = 516 MJ/m2/ month) and much higher mean 3-m wind (UDugway = 478 km/d vs.UHunter = 323 km/d and ULogan = 275 km/d) throughout the experimental period over the desert area. The windrose analysis indicates the calm condition was about 5 % over the desert during the experimental period. These data reveal the possibility of imultaneously (when these energies are available: daytime and the windy conditions) harvesting these two sources of clean energies at this vast and uniform desert area. Evaluation of the incoming solar radiation over the desert area in Dugway (Rsi,Dugway) showed, on the average, about 19.7 MJ/m2/d solar energy was received throughout the experiment. Assuming that only one third of this energy can be available using photovoltaic solar cells, we have about 6.6 MJ/m2/d = 1.53 * 10^2 J/m2/s (Watt) = 5.5*10^2 kWh from a 1 m x 1 m solar collector (average day length = 12 h). This available energy is higher during summer and lower during winter. Unlike solar power, wind power is not restricted to daytime generation of energy. The average wind speed at 10 m amounted to 5.5 m/s during the experimental period. The theoretical power (P) available from wind can be formulated as: P = (π/2) ρair E R^2 U20^3 where P is power in W, ρair = 1 kg/m3 is the air density, E = 30 % - 40% is the turbine efficiency, R is the turbine-blade radius in m, and U20 is the 20-m wind speed in m/s. U20 = U3 [Ln (20 / zo) / Ln (3 / zo)] where U20 and U3 are wind speeds at 20 m and 3 m in m/s, and zo = 0.0002 m is the aerodynamic roughness length over playa. Therefore, a single wind turbine with an efficiency of about 40 %, R = 10 m (installed at 20 m), and U20 = 5.85 m/s (average wind speed in playa at 20 m) would yield about 1.26 * 10^4 W = 4.54 * 10^4 kWh. The maximum (gust) wind speed was about 33.4 m/s. To prevent destruction of the turbine in winds greater than 10 m/s, the blade can be designed to gradually feather (reduce their angle of attack) as wind speed increases. Combination of solar and wind energies is a promising approach to alleviate current energy demands. Our study showed that the desert playas could be a suitable area to harvest renewable solar and wind energies. More detailed meteorological and engineering studies will be needed to explore this possibility. Keywords: Desert, radiation budget components, solar and wind energies, windiness.