Feasibility of a Commercial Pressure Retarded Osmosis Power plant in Sri Lanka

By P.G.S.R.Wijetunga

Introduction

At present, most of the worlds energy supply is based on oil, natural gas and coal. The global reserves on these fossil fuels are finite and the relation between global energy consumption and environmental problems such as climate changes are widely recognized. Because of the environmental problems and the fact that the mining of fossil fuels becomes very expensive, it is essential to put the maximum drive to find new energy sources and develop existing technologies to achieve higher efficiency. Alternative energy sources, including solar, wind, tidal waves and biomass have been used to provide secure, sustainable and adequate energy sources. Pressure Retarded Osmosis (PRO) power generation is an upcoming green technology to generate electricity at zero greenhouse gas emission [1]. The salinity gradient between fresh river water and sea water separated by a membrane is the key parameter in osmotic pressure development [1]. This hydrostatic pressure can be used to generate electricity by sending pressurized water through a turbine. Sri Lanka is an island having many distinct rivers and most of them eventually flow into the sea. Thus it is a great advantage to have such water rich river basins in order to implement PRO technology in Sri Lanka and several other countries which have this kind of river basins can be used this technology to uplift the country electricity facility in a sustainable way [2]. Background and Motivation The world is moving towards a carbon neutral economy. The Ministry of power and energy of Sri Lanka in its policy has mentioned that it is targeting a carbon neutral economy by 2020. Under this scheme different forms of renewable energy sources available in the country such as solar, dendro, bio mass and wind are being used to generate electricity. In 2012 the contribution of those power plants to the national grid is 169 GWh, which still is approximately 1.5% of the total electricity generation in that year.

The technology of osmotic power is known for over a century, but the exploitation was not economically feasible for a long time. Nevertheless, positive developments in recent years initiated new studies to the exploitation of osmotic power at a laboratory scale. These studies concluded that osmotic power is a promising source of renewable energy in the future. The positive conclusions resulted in first prototype PRO plant which is being operated in the southeast of Norway since 2009. The main objectives of the prototype were to confirm that the design system could produce power on a reliable 24-hour/day production and for the testing of technology for further improvement of efficiency [1].

There are lots of such locations which have ability to harvest osmotic power all over the world. However, due to lack of testing units and appropriate experimental approaches, only little known about the Osmotic power generation. Therefore, analysis of Osmotic power generation oblige a comprehensive understanding of the ongoing processes.

Problem Statement

Similarly to any other country in the present world, the demand for electricity in Sri Lanka increases annually due to the population growth and rise in standard of living. Currently the electricity demand of the entire country is about 2100 MW and it is already being supplied by both hydro and thermal power plant. The country spends an immense amount of money for the thermal power generation in every year. This has cause an adverse effect on the countries energy security and economic. It is necessary to investigate new renewable energy sources in order to fulfill current electricity demand in Sir Lanka. Objective Pressure retarded osmotic power plants can operate as base load power plants. Which means it can generate a decided amount of power through-out the required time period. In contrast to a laboratory scale, a commercial osmotic power plant requires a suitable location and large civil infrastructure. Under this project feasibility of a commercial pressure restarted osmotic power plant will be analyzed.

References [1] Skramesto, O.S., Skilhagen, S.E. and Nielsen, W.K. 2009. Power production based on osmotic pressure. Article; Waterpower XVI.

[2] Manchanayake, P. and Bandara, C.M.M., 1999. Water resources of sri lanka, National Science Foundation.