Leah Kelley

Design of power systems for reverse osmosis desalination in remote communities

AbstractMany remote communities lack access to a reliable water supply. They often have access to brackish groundwater or seawater, making reverse osmosis desalination a possible solution. However, reverse osmosis desalination is an energy-intensive process and many remote communities are off the electrical grid. Determining the most economic reverse osmosis system configuration and electrical power source for a given remote community is a challenge due to their unique resource availabilities. This paper presents an optimization-based approach to compare the economics of different small-scale reverse osmosis systems and power sources for remote communities. In this approach, physical models describe the performance of electrical power systems composed of photovoltaics, wind turbines, diesel generators, batteries, and hybrid systems. These power system models are coupled to a reverse osmosis system model to determine the water production. An optimization is performed to determine the most economic power sy...

Enhancing the Performance of Photovoltaic Powered Reverse Osmosis Desalination Systems by Active Thermal Management

Reverse osmosis (RO) is a well-known process for desalinating seawater and brackish groundwater. Desalination is energy-intensive, so using photovoltaic (PV) panels to power the process is an attractive and cost-effective concept, especially for community-scale systems. Increasing the system efficiency will lower the total cost of water produced, making the systems more economically competitive for a greater number of geographic locations. It is noted in this paper that the amount of water produced by a PV-powered RO (PVRO) system can be increased if the temperatures of the solar panel and the reverse osmosis feed water are actively managed. For a given level of solar radiation, a photovoltaic panel produces more power at a lower temperature. Also, for a given power, an RO system produces more clean water at a higher input (feed) water temperature. An active thermal management system is needed to exploit these complementary characteristics by cooling the solar panel and warming the RO feed water, increasing the amount of fresh water produced. This can be accomplished by running the RO feed water through a heat exchanger attached to the back of the solar panel, cooling it. Furthermore, the ability to cool the solar panels permits the addition of low-cost, flat-plate concentrating mirrors to be used with the PV panels, which further increases the PV power output. The flow of the water through the respective units must be actively controlled as there are limits for the maximum temperatures of both the RO water and PV panels. In this paper, a concept for an active PVRO thermal control system is presented. Simulations and experimental results show the effectiveness of this approach. In experiment, a 57% increase in fresh water production was achieved. These experimental results agree well with simulation models.Copyright

Autonomous operation and maintenance of small-scale PVRO systems for remote communities

AbstractSolar-powered reverse osmosis desalination (Photovoltaic-powered reverse osmosis [PVRO]) is a technically feasible method of providing fresh water to many remote communities with saline water sources. To be practical, these systems must be well operated and maintained by non-experts. Their productivity is a complex function of their locations, water chemistry and demand, and the solar radiation history at their locations, which is quite variable with time. A key aspect of the maintenance program is the cleaning of the reverse osmosis (RO) membranes, including system flushing and chemical cleaning. Guidelines for cleaning from membrane manufacturers do not consider the complex, variable operating conditions for these small solar-powered systems. Local operators do not have the expertise to determine how and when cleaning should be done. While cleaning will generally improve clean water production, it is costly, requires the system to be shut down, and uses some of the clean water produced. Here, si...

Design Optimization of Sustainable Off-Grid Power Systems for the Developing World

Electrification of remote areas in the developing world can greatly improve the health and economic standing of the population. Unfortunately, providing power to these remote areas can be expensive and determining the most economical solution is not trivial. This paper presents a method to compare the economics of different small-scale power systems for developing world. In this method, models are developed to describe the performance of power systems composed of diesel generators, batteries with photovoltaics or wind turbines, and hybrid systems. These models are coupled to an optimizer to determine the lowest cost solution that meets the desired system reliability. The reliability is expressed as Loss of Load Probability, and is computed using hourly solar and wind data. In this paper, this method is used to design a power system for a small hospital in the developing world. The results are presented for three sample locations in Honduras, Pakistan, and Uganda. Results show that the economic attractiveness of different technologies varies greatly due to local climatic conditions. The variety and soundness of the solutions found using this method show that it can aid in the design of a small-scale power system for any location in the developing world.Copyright

Tip-over prevention: Adaptive control development and experimentation

Skid-steered, tracked, tele-operated robots are used to perform high-risk critical missions such as bomb disposal under conditions deemed too risky to send a human. Often the robots carry heavy payloads that raise their centers of mass, increasing the risk of tip-over. Since it is often not feasible to send a human to right a toppled robot, tip-over is equivalent to mission failure. Hence, an autonomous behavior to prevent robot tip-over is desired. In this research, a simplified model of mobile robot dynamics permits separation of pitch and roll stabilization. Adaptive control is used to stabilize the appropriate angle based on the normalized tip-over measure. Experimental validation of this control is successfully demonstrated on an iRobot Packbot and a Segway RMP 440.

Design and Experimental Validation of a Simple Controller for a Multi-Segment Magnetic Crawler Robot

A novel, multi-segmented magnetic crawler robot has been designed for ship hull inspection. In its simplest version, passive linkages that provide two degrees of relative motion connect front and rear driving modules, so the robot can twist and turn. This permits its navigation over surface discontinuities while maintaining its adhesion to the hull. During operation, the magnetic crawler receives forward and turning velocity commands from either a tele-operator or high-level, autonomous control computer. A low-level, embedded microcomputer handles the commands to the driving motors. This paper presents the development of a simple, low-level, leader-follower controller that permits the rear module to follow the front module. The kinematics and dynamics of the two-module magnetic crawler robot are described. The robot’s geometry, kinematic constraints and the user-commanded velocities are used to calculate the desired instantaneous center of rotation and the corresponding central-linkage angle necessary for the back module to follow the front module when turning. The commands to the rear driving motors are determined by applying PID control on the error between the desired and measured linkage angle position. The controller is designed and tested using Matlab Simulink. It is then implemented and tested on an early two-module magnetic crawler prototype robot. Results of the simulations and experimental validation of the controller design are presented.