The Southwest Navajo Nation (SNN) in northeastern Arizona has to deal with poor water quality from regional wells. The people in the Black Falls area of the SNN, have to haul about 10 gallons per capita per day (gpcd) of potable water for household, driving an average of 30 miles per trip, costing at least $30 per 1,000 gallons of potable water and livestock water at a much greater cost. To put this cost in perspective, the people in nearby Flagstaff Arizona pay $3.85 per 1,000 gallons of potable water. The residents of the Black Falls area lack available, efficient, and affordable electricity or any kind of inter-residence electric infrastructure.
Through an agreement between the University of Arizona (UA) and the U.S. Bureau of Reclamation (Reclamation) a pilot-scale solar energy based desalination system was deployed in the Black Falls area in 2014 with a goal to produce 100 gallons of fresh water per day from brine water pumped from the Coconino Sandstone aquifer of the Little Colorado River basin. The water desalination facility operates as an isolated system, in semi-arid climate (Koppen climate classification BSk), located an elevation of 1,470 m above sea level, with an annual average wind speed of 4.77 m/s at 21.3 m hub height and a solar annual average global horizontal irradiance (GHI) of 5.23 kWh/m2/day. By 2015 the desalination research facility was functioning, powered by solar energy (electric and thermal) and backed-up by a propane gas generator. The technology initially selected for testing was sweeping gas membrane distillation (SGMD), in which water is evaporated across the membrane interface between brine and carrier gas in order to purify the water. Operating experience demonstrated that the solar energy supply was insufficient to produce the desired amount of desalinated water and that associated costs (equipment and operation) were high. Northern Arizona University began working with UA in 2015, and undertook a detailed thermodynamic and energy analysis of the desalination system. The energy analysis reveals that the SGM desalination system at 78.8 L/day (20.8 gal/day) requires 26.8 kWh/day (power of 3.35 kW) of electricity and 85.8 kWh/day of thermal energy (power of 10.7 kW). In addition, this study reveals that the CPV is not capable of providing the required thermal energy and electrical energy (50% and 15% deficits). The deficit of electricity led to exploring wind power. The conducted wind resource assessment for the desalination facility, reveals that a single wind turbine rated at 2.4 kW at a hub height of 21.3 m is able to produce 4.0 MWh of electricity (approximately the 40% of the required electric energy). Four different system design scenarios were explored, three consider using existing equipment and one using new equipment (design from scratch). The system design analysis reveals that adding a wind turbine increases the cost of the electricity. However, the system design analysis reveals that adding a backup generator decreases the cost of the electricity. Finally, this thesis describes that the energy system design from scratch and able to supply electric energy at the lowest cost (0.35 $/kWh) is through a combination of PV (3 kW), CPV (5.2 kW), batteries (6 kWh), converter (4 kW), and a backup generator (3 kW).
|Advisor:||Acker, Thomas L.|
|Commitee:||Vadasz, Peter, Wade, Jennifer L.|
|School:||Northern Arizona University|
|School Location:||United States -- Arizona|
|Source:||MAI 56/03M(E), Masters Abstracts International|
|Keywords:||Homer, Hybrid system, SGMD, Solar desalination, Wind energy, Wind resource assessment|
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