Renewable Energy power from any source that replenishes itself. Most renewable systems rely on solar energy directly or through the weather cycle as wave power, hydroelectric power, or wind power. In addition, the gravitational force of the moon can be harnessed through tidal power, and the heat trapped in the centre of the earth is used via geothermal energy systems. Renewable energy has zero purchase price and has non-depleting sources whose conversion into energy is free from emission and radiation, contrary to the conventional fossil fuels (oil, gas and coal) and nuclear fission materials.
It should be noted that compared to the conventional energy systems the renewable energy system has certain limitations viz, (i) very low conversion efficiency, (ii) very high capital cost, (iii) non-feasibility of devising a single large-sized conversion unit and (iv) uncertainties in the availability of the source. Because of the intermittent nature, some conventional power source is to be provided as 'back-up' if uninterrupted supply is essential. Nevertheless, renewable energy systems are making inroads, though slowly, into the electrical energy sectors of an increasing number of developing as well as developed countries. In the developed countries, the penetration of renewable sources is mainly due to strict enforcement of environmental regulations regarding fossil fuel and nuclear power plants to prevent global warming.
The conventional resources in Bangladesh are inadequate for supplying the energy needs to bring in a significant improvement in its economy for a long period, say for about 50 years. Therefore, it is essential to think about the renewable energy sources available in the country and develop technologies to harness them. In developing countries like Bangladesh renewable energy plants are considered mainly as an option for remote locations where the infrastructure needed to obtain for supply from the grid is not affordable.
The energy content of the renewable sources can be converted directly or indirectly into various forms of energy - mechanical, thermal and electrical. As electricity is the most convenient form of energy, the discussion that follows focuses on generating electricity from renewable sources.
Hydropower A cheap and clean method of power generation. Generation of electricity using the potential and/or kinetic energy of water can be done mainly in three ways, viz conventional hydro, wave and tidal power generation schemes. The conventional hydroelectric plant involves the construction of a water reservoir through building a dam or barrage across a river to obtain the required water head for driving a turbine. Depending upon the reservoir capacity and water head, hydroelectric power plants are classified as large (water head in excess of 30m, output more than 5 MW), mini (water head 15m to 30m, output 500 kW to 5 MW) and micro (water head 3m to 15m, output 10 to 500 kW).
The scope of hydropower generation is very limited in Bangladesh as the country consists of low and flat lands except some hilly regions in the northeast and southeast, and some high lands in the north and northwestern part. The only hydropower station of the country, the karnafuli hydro power station with a generation capacity of 230 MW by 7 units (3 units of 50 MW and another 4 units of 20 MW capacity) is located in Kaptai (rangamati district) across the river karnafuli.
A number of feasibility studies made in the 1980s revealed that 15 rivers/chharas (rivulets) have the potential for siting mini-hydropower stations of 10 kW to 100 kW capacity. These are: the sangu river (Tarasa Chhara and Dohazari), matamuhuri river (Champatoli, chittagong hill tracts), tista river, foy’s lake (Pahartali, Chittagong), Chhota Kumira (Sitakunda upazila, Chittagong), Hinguli Chhara (Mirsharai upazila, Chittagong), Suwalak river (Bandarban), Nikhari Chhara (Barlekha upazila, Maulvi Bazar), Madhav Chhara (Barlekha, Maulvi Bazar), Ranga Pani Gung (Jaintiapur upazila, Sylhet), Bhugai-Kangsa (Nalitabari upazila, Sherpur), Marisi river (Jhenaigati, Sherpur), punarbhaba (Singraban, Thakurgaon), Talma (Panchagarh), and Pathraj (Fulbari upazila, Dinajpur). It is estimated that an annual total of 1,156,320 kWh of electricity in the Chittagong-Bandarban area, 6,306,041 kWh in the Sylhet-Maulvi Bazar area, 858,336 kWh in the Mymensingh-Sherpur area, and 1,870,752 kWh in the Dinajpur-Rangpur area could be generated.
Tidal and Wave Power During high tide, water can be trapped in the coastal basin, creating a head difference during low tide and this water head can be used to drive a turbine. France has a 240 MW Tidal Plant on the estuary of the river Rance. Canada, Russia, Australia, England have completed surveys and proposals are being evaluated by the respective governments. Bangladesh has good potential for tidal plants along its southern coast. The power of the sea wave depends on the wave height and wave period. The Oscillating Water Column method is technically feasible and becoming economically attractive. This type of wave energy harnessing device is being commissioned by several countries such as the United Kingdom (500 kW), Ireland (3.5 MW), Norway (100 kW), India (150 kW), etc. Bangladesh has potential for harnessing wave power from the bay of bengal.
Solar energy Derivation of energy from the Sun's radiation. Solar energy is harnessed using solar cells (photovoltaic or PV cells) made of panels of semiconductor material (usually silicon), which generate electricity when illuminated by sunlight. Bangladesh is geographically located (20'34 to 26'38 North latitude) in a favourable position to make use of abundant sunlight for most of the year, except about three months, June to August, when it rains excessively. The amount of solar energy available in Bangladesh is high, around 5 kWh/day per square meter or 2.61011 MWH/year on the total surface area of the country, enough to meet the total demand of the country. A very small amount of the available solar energy is now used traditionally in our country for open air-drying of agricultural products, production of salt from seawater, drying of cloth etc. For utilising this energy efficiently and cost-effectively reliable solar devices and systems have to be developed. In Bangladesh, research and development work to harness solar energy in the form of heat has been going on for many years at Dhaka University, bangladesh agricultural university (BAU), bangladesh university of engineering and technology (BUET), solar park (Solar Energy Research Centre) of dhaka college, and BCSIR laboratories.
Various types of solar water heaters have been fabricated and tested by different organisations. Two solar hot water systems of 400 litre capacity at an average temperature of 55o-60oC per day were designed and fabricated using mostly locally available materials under the CHOGRM (Commonwealth Head of Government Regional Meeting) programme. Performance studies of the above hot water systems show that they can be used for 330-350 days in a year in small-scale industries in different regions of Bangladesh. Water at such temperature is required in hotels, hospitals and in small industries. Parabolic reflector type solar cookers have been fabricated and tested in BCSIR. Cooking using this type of solar cookers is possible when the solar radiation is high but during the monsoon these do not work due to low intensity of irradiation.
In the renewable energy research centre of Dhaka University a box type solar cooker has been developed where solar as well as electrical energy can be used as the source of energy. During bright sunshine hours the cooker is operated by solar energy and during the periods of low intensity of illumination a few watts of electricity are utilised as an auxiliary source. This cooker can be used in homes, tea-stalls and community centres where electricity exists.
Most of the electricity generators in Bangladesh are run by natural gas and diesel. Only about 8% of the total population has connections to the national grid line. In the villages the situation is worse. Even if the rural electrification board (REB) takes the electric grid line to all villages of the country, which will be an extremely difficult and expensive task to accomplish, the majority of the village households will not be able to have electric connections due to poverty. The photovoltaic system can provide energy in the villages where electricity distribution lines do not exist.
The Bangladesh Power Development Board (BPDB) currently has two major solar photovoltaic installations at Kaptai for a rainfall measuring station and at Aricha for East-West Interconnector, and some transmission towers (for example at the Karnafuli river crossing in Chittagong) where solar photovoltaic system is used for lighting.
As of 1998 the total peak capacity of the country's various photovoltaic projects, all implemented in the stand-alone mode, is about 150-kWpk (kilowatt during peak insolation). These have been operating mainly in rural areas and tea gardens far from the grid and in cyclone shelters and hospitals in a number of isolated islands fulfilling the various purposes such as home lighting systems, water pumping, signalling and communications, and emergency medicine or vaccine preservation etc. The owners of these plants are the Rural Electrification Board, some NGOs (non-government organisations), the bangladesh atomic energy commission (BAEC), Local Government Engineering Department (LGED) and some private parties. Some of the projects worth mentioning are a 62-kWpk plant of REB at a remote village of Narsingdi and an approximately 2-kWpk plant at a tea estate in Sylhet.
In Bangladesh, a number of local companies are manufacturing photovoltaic solar panels and other accessories for small and medium-size solar energy systems. As of 2000, the local market price of a typical PV home lighting system comprising a 40-Wpk module, a 100 Ah (Amps-hour) battery and a pair of DC fluorescent lamps is about Tk 25,000.
Hydrogen energy Hydrogen is the simplest and most common element in the universe. It has the highest energy content per unit of weight of any known fuel (52,000 Btu per pound or 120.7 kilojoules per gram). When cooled to a liquid state, this low-weight fuel takes up 1/700 as much space as it does in its gaseous state. This is one reason hydrogen is used as a fuel for rocket and spacecraft propulsion, which requires fuel that is light, compact, and has a high energy content. The only hydrogen plant of the country is an auxiliary unit of eastern refinery limited, Chittagong. The unit produces hydrogen of 99.9% purity from steam reforming of natural gas. Hydrogen is a by-product of Eastern Refinery, but the production volume is low and the entire output is used up in different industries.
Wind energy It had been used earlier for several centuries to propell ships, drive windmills, pump water, irrigate fields and perform numerous other tasks. Generation of electricity by the kinetic energy of wind requires a minimum average wind speed of 21.6 km/hr, which equals 11.67 knots (1 knot = 1.85 km/hr). But the yearly average wind speed all over Bangladesh is only 2 to 3 knots, which is not suitable for generating electricity. However, in certain specific sites such as Patenga (Chittagong) and Cox's Bazar which are coastal areas and Jessore which is an interior site but not too far from the sea, the recorded wind profiles show that an average speed marginally equal to the required minimum wind speed is available only for 2 to 3 hours (not consecutively) of certain days in the months of June to August.
A project in wind resource measurement (known as WEST) has been undertaken by the Bangladesh Centre for Advanced Studies (BCAS) in collaboration with LGED and the Energy Technology Support Unit, UK. The project prepared its final report in January 1998 after taking continuous measurements through 1996 and 1997 at 25m height in selected sites along the coastline beginning in Teknaf in the east and ending at the edge of the sundarbans. The measured average annual wind speed in the seven stations range from 2.96m/sec for Teknaf and Noakhali to 4.54 m/sec for Kuakata. Obviously, this is not a very favourable wind speed for electricity generation, though in well-chosen sites such as Kuakata, Kutubdia or Charfasson, it is still possible to generate an annual total of 150 MWH electrical energy with a 150 kW capacity turbine, as the estimate in the WEST project shows.
A number of small wind generators have been installed by various agencies in the coastal areas. These include wind generators by installed Grameen Shakti at its Chakaria Shrimp Farm (1 kW, 300W) and another by brac and GTZ (a German NGO). BRAC alone has installed 11 wind turbines at various coastal sites. These are small low cutting, DC operation type systems, supplying power to the target group to improve their quality of life. Four bigger wind generators are in the process of installation by Grameen Shakti at various coastal sites and are due to go into operation by 2002. Three of these have a capacity of 1.5 kW and the fourth 10 kW.
In the context of Bangladesh, photovoltaic generation is more promising and viable than wind, mini/micro hydro, wave or tidal electricity generation because the uncertainty in the availability of sunlight and difficulty in its conversion are very much less though the capital cost of PV modules is more than that for wind or water power. When compared with electricity generation from conventional sources, the PV modules cannot compete on cost basis but its merits are unique so far as the question of serving the rural and offshore communities at a good number of places in Bangladesh far away from the grid is concerned. Moreover, with continued research on semiconductor materials and mass production, the capital cost of PV modules has been falling rapidly and is expected to compete with conventional modes generation by the year 2030. [S Shahnawaz Ahmed and Rafiqul Islam]