FOSSIL fuels — coal, gas, fuel oils — had for long been burnt during the past decades to generate electricity. The rich and developed countries have so far developed their economy by meeting their demand of electrical power from fossil fuels. In doing so, the power plants from those countries released thousands of tons of carbon dioxide in the atmosphere. Now, the excess of carbon dioxide in the air is the root cause for global warming and climate change. The world community is now alarmed to witness the harmful effects of climate change and has come forward to discourage fossil fuels and pay attention to renewable energy sources of the nature. They are investing in research in and development of technologies. Development agencies of the world also prefer and encourage investments in renewable energy field.
Bangladesh in unison with the international community endeavours to include renewable energy in the fuel mix of the power sector. With this end in view, it has established a separate authority named SREDA — Solar and Renewable Energy Development Authority — for the facilitation and development of solar power growth in the country. The government is implementing a vision of electricity for all by 2021 by employing miniature solar systems in the areas outside the coverage of national grid. By now 4.5 million solar home systems have been installed on remote houses under a project, implemented by IDCOL, is considered to be the largest in the world. A couple of universities are offering degrees and conducting research in the field of renewable/solar energy. A few professional associations are also playing active role in this field.
The Bangladesh government is keen to develop grid-connected solar parks to promote emission-free power generation. Engreen Sharishabari Solar Plant Ltd, of 3MW capacity, in Jamalpur is the first grid connected plant that went into commercial operation in August 2017. The plant installed 11,600 mono-crystalline silicon solar panels in eight acres of land adjacent to a Bangladesh Power Development Board substation. It is an efficient plant with optimum land usage, about 2.5 acres per megawatt which is ideal for Bangladesh. Six more solar parks with foreign collaboration are coming soon with combined capacity of 320MW. The government goal is 2,000MW by 2021. The Bangladesh Economic Zone Authority is going to develop a solar power hub of 1,000MW over 4,000 acres of land in the economic zone at Chandpur and another one 600MW over 2,000 acres of land in the economic zone at Mirsarai, Chittagong.
Renewable energy sources such as solar, wind and water, geo-thermal etc had always been in nature but was not used because of inefficiencies and high cost. They are all low-level energies mostly wasted in nature and availability depends much on geographical condition. The term renewable means to collect and upgrade the wasted energies into useful power. Bangladesh does not have much water and wind energy but it is blessed with abundant solar energy which has a potential for conversion into useful electricity.
The solar power is created in photovoltaic cells made of silicon. Photons, the light particles, are absorbed in silicon with release of electrons which flow under potential difference and produce electricity. It is a direct current and is converted by inverters into alternating current to suit the grid specification. A small portion of incident light is only absorbed and the remaining is lost by reflection and refraction. That is why the efficiency of solar panels is basically low-mono crystalline silicon type18 per cent and the thin film type 12 per cent.
A solar park can install thousands of panels containing millions of cells and groups them together in series and parallel circuits to deliver power at desired voltage. The panels are so mounted as to capture optimum sunlight throughout the year. Orientation of panel depends on the latitude of the place. In Bangladesh (latitude 23°N), the panels face south tilted towards equator. The angle of inclination is 38° in the winter and 7° in the summer.
The strong points of grid-connected solar power systems are: there is no fuel cost involved, there is no noise and vibration as plants operate in solid state without any moving components, there are no carbon foot prints and no emission of greenhouse gas, and environmentally-friendly. All these advantages made the solar power a favourite choice all over the world.
There are weaknesses too, namely, large area of land is required and the cost of plant is very high. Generation varies with weather condition. The clouds, rain, fog and even atmospheric dust reduce the panel performance. Also 100 epr cent solar grid is not possible as solar parks are inoperative at night.
A solar power plant, capital intensive it is, cannot compete with its counterpart of fossil fuel technology. Because it costs nearly double but produces one-fourth. So the government is to provide rebates and incentives to encourage this sector. If incentive is given in tariff, then the authority may keep an efficiency clause to motivate the entrepreneurs to go for the efficient plants. Because an inefficient plant takes more land and the land is scarce in the country.
Photovoltaic solar parks function in a unique way. They operates for a few hours by day time (effectively four hours) while the output fluctuates depending on the variation of intensity of sunlight called irradiance. A robust grid absorbs these fluctuations. After sunrise the solar parks will start pouring electricity in the grid which will have excess electricity in the morning. This excess electricity will help reduce power outages and even some conventional power plant will have a chance to stop and do necessary maintenance. But in case of grid failure, the solar plant is cut off from the grid automatically for safety reason and can resume supply only after the power is restored by conventional power plants. It cannot take part in the exercise of the restoration of power supply. Again the daily load curve of Bangladesh shows that the grid peak occurs in the evening whereas the solar peak will occur at noon. Therefore, broadly speaking, the solar power will be best used when the grid peak in the country will be shifted to noon. It will possibly happen in 2030s when the country will be heavily industrialised.
There is a good prospect of roof-top grid-connected solar power generation. The very positive side of roof top solar is the saving of arable land. This sector is waiting for the ‘feed in tariff’ policy from the government. In this scheme the utility authority, the Power Development Board is supposed to buy power at a premium price from qualified roof-top producers. As a result, the owners of buildings and industries will be motivated to install solar panels on roof to feed electricity to the national grid and earn a gainful side income. A good example is Germany where the roof-top solar units under ‘feed in tariff’ policy made a major contribution to the solar power generation. These units are basically small between 10kW to 100 kW and will face a challenge connecting to the existing grid. The area near the substations will be suitable to initiate this programme for easy grid connection. A collective approach may give a good result. It is possible that the qualified buildings in the vicinity of the substations can be grouped together in a network. Their combined outputs to the level of 1MW–5MW can be evacuated through a common step-up transformer to the high-voltage grid inside the substation.
The government policy is congenial and the cost of solar panels has considerably come down on the international market. The solar parks will now cost much less than before. The developers, at least those who already signed power purchase agreement with the government, can avail of this opportunity to complete the projects. The entrepreneurs in the pipeline may also expedite their initiatives to materialise their projects. Only then the government target of 2,400MW by 2021 could be achieved.
KM Mahbubur Rahman is a senior mechanical engineer and energy consultant.
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