J. Paul Riley

Optimum thickness of the nonconvective zone in salt gradient solar ponds

Abstract The nonconvective gradient zone of a salt gradient solar pond tends to more effectively transmit incident solar energy to the storage brine below as its thickness is reduced. However, that same gradient zone tends to more effectively reduce heat loss from the warm brines as its thickness is increased. Therefore, there exists an optimum gradient zone thickness for which the net rate of energy collected and retained is a maximum. This report describes a technique for using a numerical simulation model to determine the optimum thickness of the gradient zone in ponds; provided other basic design, operating and climatic factors are specified. Significant improvements in pond efficiency may be obtained if the thickness of the gradient zone is adjusted monthly, seasonally or even if maintained at the annual average optimum thickness as compared with operating the pond with other than an optimum gradient zone thickness.

A water requirement model for salt gradient solar ponds

A model for predicting the salt gradient solar pond (SGSP) area that could be maintained with a given water supply is presented together with several specific applications. For example, based on 30-year average water flows, the model predicts that 1.93 × 109 m2 (477,000 acres) of solar ponds, 1.02 × 109 m2 (253,000 acres) of evaporation ponds to recycle salt, and 0.51 × 109 m2 (125,000 acres) of freshwater storage reservoirs could be maintained at the Great Salt Lake of Utah. Water use requirements per unit of electrical energy from solar ponds are calculated as 600,000 m3/MW·yr. This is roughly 30 times the water evaporated per unit of electrical energy from coal-fired generating plants using wet cooling towers, but substantially less than water evaporation losses per unit of electrical energy produced from typical hydropower dams and reservoirs. It is concluded that water use requirements for solar ponds, although not necessarily prohibitive, are substantial; and in many locations may be the physical factor that limits solar pond development.

Suppression of wind-induced hydrodynamics in ponds

Abstract Significant economies of scale are an incentive for the design of large salt gradient solar ponds; however, wind induced mixing is more difficult to suppress on larger ponds because of the greater distance (or fetch) between dikes. Quantitative data are needed on the hydrodynamic effects of wind action on ponds protected with wave suppression systems. Experiments conducted at the Utah Water Research Laboratory measured wave height, wave length, and depth of disturbance of water in a test flume exposed to various air flows and wave suppression devices. Water depth was 30 cm in the 12.2-m-long test flume having a cross section 61 cm square. Air velocities ranged from 4.50 to 11.8 m/s. Experiments also were conducted with a sharply stratified system consisting of 15 cm of fresh water floating on 15 cm of salt brine in which the air velocities were observed at the point where gravity return currents and wave motion occur at the density interface. Results indicate that circulation currents may persist even if waves are effectively suppressed.

An investigation of a surface drift current return pipe system for application on salt gradient solar ponds

Abstract Based on the premise that wind-induced mixing could be the factor that limits the size of salt gradient solar ponds, this paper explores the notion of returning surface drift currents in pipes from the downwind end to the upwind end of the pond. An unstratified constant density pond subjected to a steady wind is assumed. A mathematical model is developed to predict the effect of such a pipe return system on drift and circulation currents. In an experimental study conducted in Utah State Universitys wind tunnel, set-up was measured on a shallow unstratified body of water to exposed wind at various speeds. The tests confirm that set-up may persist even when waves are suppressed. Circulation currents could be virtually eliminated with the return pipe system, but surface drift currents are increased. Larger scale tests on stratified ponds are needed.

Modelling the Effects of Climate Change on the Hydrologic Response of a Mountain Watershed

Climate changes are likely to have serious impacts on water supply and demand in arid and semi-arid basins. We consider CO2 - induced changes in vegetation and the changes in temperature and precipitation scenarios in this analysis. In this paper, we present application of a distributed parameter model to simulate the effects of climate and vegetation changes on the hydrologic response of Chalk Creek watershed in the Weber River basin in Utah. Leaf area index (LAI) is used as a measure of forest structure to quantify energy and mass exchange. Hydrologic response unit (HRU) is used to partition the watershed into spatially distributed units. Sensitivity analysis assumed changes in climate and plant variables over credible ranges of change based on the GCMs output and current literature. For the range of scenarios studied, the results suggest greater effect of warming on runoff than for cooling. A greater sensitivity of annual runoff to precipitation than to temperature was in agreement with the results of other studies done else where. The results, in general, indicate a marked shift in the timing and seasonality of runoff.