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Solar power and energy security

IN the current energy crisis, the country cannot depend upon one source of energy supply and has to look for renewable sources. One of the best ways to generate utility scale electricity is through concentrated solar thermal power. Most of the areas of Pakistan have solar irradiation of 5kWh/m2/day which by all standards is very attractive for utility scale thermal power generation. With today’s technologies, it is possible to construct concentrated solar thermal power units of say about 25 MW capacities in modular form, up to any aggregate capacity. The country has been ranked among the most promising locations for solar thermal power generation and it has been estimated that in the (near) future, generation cost through CST may drop to 7-8 US cents /unit and that an area of about one sq. km may generate solar thermal electricity equivalent to about 50 MW of conventional thermal plant. In other words, a total area of about 100 sq. km (say 10 km x 10 km) is sufficient to compensate for the present shortfall of about 5,000 MW electricity. According to an estimate, power generation through furnace fuel oil (the main fuel option in Pakistan) costs around 19 cents per unit International funding for setting up “Green” energy projects is relatively easy to get on very attractive terms. Utility scale CST plants have been made economically feasible through bulk production of some of their components. Major components of the CST plants include; heliostat mounted solar reflectors, tower mounted boiler, heat energy storage unit and rest of the steam power plant. Heliostats keep the reflectors facing towards the sun; whereas all the reflectors concentrate the solar radiation to the tower mounted boiler. Boiler generated steam feeds steam turbine which ,in turn, drives the electric generator (see the figure). Waste heat from the turbine may be used in some industrial process or for air-conditioning. Some very successful technologies have been developed for storing heat energy during the non-sunny hours in the form of steam or molten salts. Bulk storage of heat energy is much cheaper than its storage as electrical energy through batteries. Existing steam power stations may also be converted to solar thermal completely or CST modules for additional steam generation may be added. These are not complicated technologies; most of the major components have been readily available for years. Computer controlled heliostats are manufactured by various companies or can be developed locally through available resources. During the recent years, the idea of solar thermal power generation has been catching up. More than one Giga Watt (1000 MW) of solar thermal plants are under construction in the world and more that about 14 Giga Watts plants are planned to be installed in near future.. The largest power plant based, on steam turbine technology through solar heat, is at Mojave Desert California and has the capacity of 354 MW. Today there are a good number of international companies who have developed complete plants for large scale power production and may be willing to install their CST technology plants in Pakistan. The country has proved through its nuclear and missile development programmes that our engineers and scientists are fully capable of performing any engineering feat. If these ultra hi-tech technologies can be developed, CST development is lesser daunting task. Self-reliance in this area may ensure our energy security. An independent team of engineers and scientists can be assembled from the government and private organisations which can be given the task of doing CST engineering, designing and development. Some major components can be sourced internationally like steam turbines and heat exchanger; while heliostats and other things can be designed to mass produce locally. A whole new industrial sector comprising of manufacturing, assembling, installation, as well as, operation and maintenance of the solar thermal plants may produce thousands of new jobs. The article has focused on the CST, however much of the “low quality heat energy (lower temperature)” requirements of the industry and households may be met through some other very promising solar heat technologies; thus reducing the burden on our depleting gas reserves.

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