Baltasar Peñate

Electrodialysis desalination designed for off-grid wind energy

An electrodialysis desalination plant has been set up and tested to treat brackish water while driven from an off grid wind energy system. The tests were carried out in the framework of a wider scope project, located on Gran Canaria Island (Spain). The main goal of this project was to test and identify the most suitable desalination systems for connection to the above-mentioned medium-scale off grid wind farm. After having previously analysed the behaviour of the system on-grid, the following stage was to develop an operational envelope for the electrodialysis reversal (EDR) unit while operating off grid, i.e., only coupled to the wind farm. The unit included power converters for the membrane stacks (DC-drivers) and variable frequency drivers (VFD) for the feed pumps. The tests were carried out to establish the power intervals for the EDR unit depending on the product flow rate specified as well as water quality. Product flow rate between 3 and 8.5 m3/h, power requirements between 4 and 19 kW, while product water conductivity ranged between 200 and 500 μS/cm were recorded. The desalination unit showed good flexibility, adapting smoothly to variations in wind power, even when sudden drops or rises occurred. The control system, slightly modified from a standard design, can cope with such sudden variations. Good agreement between performance predicted with software and the actual operating performance was observed. The presence of harmonics in the electric system due to DC drivers and VFD became harmful for the control and electric system, and care must be taken through appropriate mitigating measures.

Optimised desalination of seawater by a PV powered reverse osmosis plant for a decentralised coastal water supply

Abstract In the past decade desalination, especially by reverse osmosis, was established as a reliable and secure technology for the production of potable and agricultural water. The situation in Mediterranean countries as for example Spain can be described by a growing lack of water due to limited natural resources, an increasing water demand by agricultural and tourist activities especially in coastal areas. The tense situation is exacerbated by the infiltration of seawater to ground water aquifers in coastal areas thus naturally fresh water resources became salty. The installation of an efficient desalination technology requires an adequate energy supply. Whereas in most urban regions a secure, continuous energy supply is guaranteed in many rural coastal regions the lack of potable water is connected to a missing energy supply. This often provokes a situation like “without energy there is no water”. Due to the fact that almost 60% of the investment costs for energy supply systems are needed for the installation of the distribution system in rural regions decentralised conventional and renewable energy supply systems becomes an increasing importance. By the utilisation of renewable energy systems the producer is independent from any supply of fossil fuel resources as gas or diesel but has to take into account the changing energy offer by the sun or wind. But the combination of renewable energies and water production by reverse osmosis has become the key technology for decentralised water supply plants. In the past few years the Technological Institute of The Canary Islands (ITC) and the Aachen University of Applied Sciences are investigating the concept of seawater desalination by reverse osmosis supplied by renewable energies (PV). At the test field of the ITC in Pozo Izquierdo a pilot system called DESSOL was installed to demonstrate the technical feasibility of the technology. During the period of operation important results for the optimisation of the plant operation and the coordination and timing of the renewable energy system to the reverse osmosis plant operation were obtained. Thus for example a solar thermal system was integrated to the energy supply system to increase the daily water production. Thus the plant is now fed with pre-heated seawater. Actually the plant produces a medium daily amount of 3 m 3 /d of potable water. This experience has served for the manifestation of the technical concept of this plant type and could be transformed to much larger drinking water production systems without loosing the efficiency of the plant DESSOL. The reverse osmosis plant with a nominal production of 10 m 3 /d (specific energy consumption of 5.5 kWh/m 3 ) is supplied by a 4.8kWp PV generator and a 19 kWh battery back-up system. The energy system was optimised for the utilisation as energy supply for the reverse osmosis plant. The plant is operated automatically for an average of 8 h during summer and 7 h during winter time while the plant operation is adjusted to the changing energy production of the PV generator. The plant is equipped with a double flushing system with fresh water for the membranes and pumps during the daily periods when the plant is out of operation. In the full paper the principle construction details of the PV supplied reverse osmosis plant will be presented. Emphasis will be given to the description of the automatic control unit which adjusts the plant operation to the changing and discontinuous energy supply by the PV generator. The plant operation performance and the option of pre-heating the feed water will be discussed.

Electrodialysis desalination designed for wind energy (on-grid tests)

An electrodialysis desalination plant has been set up and tested while driven corn an off-grid wind-energy system. Prior to analysing the behaviour of the system off-grid, a thorough knowledge of the operational modes and constraints is required. That information is obtained through a number of tests done on-grid. This paper presents some results obtained while operating on-grid in a work carried out within the framework of a wider scope project, located in Gran Canaria Island (Spain). The main goal of this project is to test and identify the most suitable desalination systems for connection to the above-mentioned medium-scale off-grid wind farm. Afier preliminary modelling using proprietary software, a number of on-grid tests at different flow rates and futed feed conductivity were carried out. The results include curves for the relationship between voltage applied and product conductivity (between 100 and 280 pS/cm), as well as unit energy consumption (from 1.48 to 2.32 kWh/m3). The data gathered showed that EDR can easily adapt to a variable power supply such as wind energy, and they were used later in off-grid tests. Keywortis: Electrodialysis; Brackish water; Wind energy; Modelling; Control

Operating RE/Desalination Units

This chapter presents 10 small standalone RE (renewable energy)/desalination systems operating around the world, employing different technologies, such as PV/RO, solar/MED, etc. The examples show that several technological combinations are well enough developed to provide potable water under harsh conditions in isolated sites. However, even established technologies face problems and limitations. Continuous R&D in combination with wide scale implementation is needed to improve their reliability.

Design and testing of an isolated commercial EDR plant driven by solar photovoltaic energy

abstract The production of potable water from brackish water, tertiary treatments of treated wastewaters for irrigation and other allowed uses, and several industrial processes which use recycled water are the most important applications of electrodialysis (ED). During the last years, the number of pilot initiatives focused on renewable energy powered desalination has grown, being one of the most promising combinations of the ED powered by photovoltaic (PV) systems. ED combined with renewable energies becomes attractive for being a mature technology, which requires direct current (DC) power and is easily adapted for variable energy conditions. The present paper shows the design, installation, testing, and monitoring of a 100% isolated PV–ED system which is feasible for a commercial scale. The testing tasks have been performed in a 4 m3/h commercial-one stack electrodialysis reversal plant powered by two solar PV fields in parallel. For the DC energy required in the stack, a solar PV field has been designe...

Uninterrupted eight-year operation of the autonomous solar photovoltaic reverse osmosis system in Ksar Ghilène (Tunisia)

AbstractKsar Ghilene is a 300 inhabitant isolated village located in the Sahara desert at the South of Tunisia and belonging to the region of Kebili. Due to the particular location of this site, there was no local fresh water source before 2006 and this community had been depending on the external water supply, transported by trucks. The 10.5 kWp PV-powered RO desalination system (based on the international patent DESSOL®) with a nominal water capacity of 50 m3/d was commissioned in June 2006 and currently in operation. The whole project was developed by Instituto Tecnologico de Canarias within the framework of the Spanish–Tunisian cooperation, thanks to the economic support of the Spanish cooperation and the Canary Islands cooperation. This paper presents and assesses the operation data and lessons learnt with the whole system for the period 2006–2013.

Autonomous Desalination and Cooperation. The Experience in Morocco Within the ADIRA Project

Fresh water supply in the world, particularly in developing countries, is becoming a more and more challenging problem and affects many multidisciplinary aspects, such as security, health, development, economics and environment. The increment of population, the climate change and the environmental impacts on the water resources are generating a progressive reduction in the per capita drinking water availability, particularly in developing countries of Africa and Middle East. As a contribution to solve this situation, desalination technologies have been producing fresh water supply for more than five decades; the current capacity of desalinated water technology installed worldwide is over 45 million of daily cubic meters. Nevertheless, this solution has its own disadvantages; one of the main associated problems of these “water factories” is the requirement of energy (heat or electricity) for the desalination processes. This inconvenience can be solved currently for small water demands by the use of renewable energies, as solar or wind energy. The Instituto Tecnologico de Canarias (ITC) has been researching on desalination powered by renewable energies since 1996, installing, operating and testing ten different combinations of renewable energy technologies and desalination processes. Moreover, the ITC has installed five units (in real use, not demonstrative) operating in Africa: one in Tunisia (2006) and four in Morocco (2009). Concerning the environmental security of this kind of installations, there are three main topics to be discussed: (i) gaseous emissions – solar/wind powered desalination is a pollution free system during operation, since there is no need of fuel; (ii) brine disposal – rejected stream of water with high concentration of salts has to be properly treated to avoid a local environmental impact, especially in inland locations; (iii) solid wastes – the long term consumables of the system, as membrane modules, filters or batteries, have to be disposed in an appropriate area. As an example, this paper deals with the experience of desalting with solar PV energy in Morocco and points out not only the technical aspects of the implementation of this kind of cooperation projects, but also economic, environmental and social aspects.