Dan Weiner

Operation experience of a solar- and wind-powered desalination demonstration plant

Abstract The present work outlines the designing, erection and operation process of a stand-alone desalination plant powered by both solar photovoltaic and wind energy. Such a plant will serve small isolated communities in remote areas devoid of water resources. A specially customized code was built to simulate the operation of the installation in order to allow appropriate choice of components specifications. Site meteorological data were used to enhance prediction capabilities. The code continuously updates the instantaneous water lever of the reservoir as well as the current state of charge of the accumulators. Depending on these two variables, a logical decision tree is built to decide whether the cumulated wind and solar energy production can satisfy the load of the plant or additional energy must be provided from the accumulators or an auxiliary diesel engine generator. The process control system for such an installation must allow for operation in isolated areas where qualified maintenance personnel are scarce or remote. These are special considerations regarding the design philosophy in order to reach a state as close as possible to a maintenance-free system. In view of this consideration, several layers of back-up were built into the system such as a diesel generator (whose use is to be kept to a minimum). Also, the system has been designed to operate at about a 33% service factor. Two-day battery storage autonomy has also been provided. The desalination plant uses reverse osmosis technology. The plant has a maximum product capacity of 9 m3/d in view of future needs, even though it is designed to currently produce only 3 m3/d. The inlet water is to be provided from on-site brackish water wells. The local water quality is approximately 3500–5000 ppm corresponding to brackish water. The system has been designed based on the premise that the average on-site wind velocity is about 4–5 m/s and an isolation level of about 5–5.5 kWh/m2/d. The expected life-span of the plant is about 15 years. The system was successfully erected and has been continuously operated producing 3 m3/d. Experimental measurements are now in progress, and a comparison to theoretical predictions is presented. The time schedule for the whole project consisted of 6–8 months, including many changes required during construction.

Analysis and optimization of a compressed air energy storage system in aquifer

This paper discusses the thermo-economic analysis and optimization of a constant pressure Compressed Air Energy Storage system, in aquifer, subjected to an exogenous periodic electricity price function of the interconnection. The target function considered is the net benefit of the plant. It is related to the fundamental planning parameters of the system like the compressure pressure ratio, the maximum temperature ratio, the charging-discharging ratio and the plant capacity factor. The results of the analysis permit to obtain the optimal values of the fundamental parameters to be used in the planning process.

Novel Compressed Air Energy Storage (CAES)Systems Applying Air Expanders

In Compressed Air Energy Storage (CAES) systems, off-peak electric energy is consumed by air compressors that charge CAES reservoirs. During peak load hours, air released from the CAES reservoir expands, producing electric power. Two novel CAES systems, improving their reliability and efficiency, are introduced.The first system is the CAES Plant Integrated with a Gas Turbine (CAESIGT), in which 40 percent of the power output is produced by a standard gas turbine, and 60 percent by an air expander utilizing compressed air that is preheated by the exhaust gases of the gas turbine. For certain initial parameters of the compressed air, its temperature after expansion becomes lower than the ambient temperature. This cold air can be used as a source for refrigeration of the gas turbine inlet air and for other purposes.In the CAES system of the second type, multistage expansion of compressed air is applied. Reheating air between expander stages is provided either by refrigerated substances, by heat sources from surroundings, or by non fuel heat sources such as the waste heat from industry, solar ponds, etc.Thermodynamic and economic analyses of the novel CAES systems are carried out.Copyright

On the Optimal Location and Number of Intercoolers in a Real Compression Process

In this paper the optimal location and number of intercoolers in a real compression process, including pressure losses, is derived by minimizing the compression specific work. Consequently the series of intermediate pressure values where the system intercoolers should be located is evaluated. As a result a solution different from the classical-isothermal compression process is obtained. The ideal process is evaluated and verified as a particular case by assuming no pressure losses. In reality, minimizing the compression work is only a partial criterion of optimization and the final decision regarding the optimal number of intercoolers should be obtained by using techno-economic criteria.Copyright

Use of the Brayton Cycle in Solar Electric Power Generation

The utilization of gas turbines in a central receiver is an attractive alternative due to the ability of these prime movers to endure temperatures of about 2000°F while achieving high performance. In this paper the problems of modifying a 250 kW Allison Turboshaft Engine and its conversion into solar gas turbines are presented. The various solutions referring to the various system components, such as combustion chamber, hot pipeline, electric generator and control system are detailed.Copyright