Md Zillur Rahaman: As innovation brings down costs and starts to deliver on the promise of a clean future, renewable power is being popularized. It means renewable energy sources are increasingly displacing "dirty" fossil fuels in the power sector, offering the benefit of lower emissions of carbon and other types of pollutants. But not all sources of energy marketed as "renewable" are beneficial to the environment. Biomass and large hydroelectric dams create difficult tradeoffs when considering the impact on wildlife, climate change, and other issues.

Renewable energy is produced from the sources that do not deplete or can be replenished within a human`s life time. The most common examples include wind, solar, geothermal, biomass, and hydropower. This is in contrast to non-renewable sources such as fossil fuels. Most renewable energy is derived directly or indirectly from the sun. Sunlight can be captured directly using solar technologies. The sun`s heat drives winds, whose energy is captured with turbines. Plants also rely on the sun to grow and their stored energy can be utilized for bio-energy.

While renewable energy is often thought of as a new technology, harnessing nature`s power has long been used for heating, transportation, lighting, and more. Wind has powered boats to sail the seas and windmills to grind grain. The sun has provided warmth during the day and helped kindle fires to last into the evening. But over the past 500 years or so, humans increasingly turned to cheaper, dirtier energy sources such as coal and fracked gas.

Now it has become increasingly innovative and less-expensive to capture and retain wind and solar energy, renewable energies are becoming a more important global power source. The expansion in renewable energy is also happening at scales large and small, from rooftop solar panels on homes that can sell power back to the grid to giant offshore wind farms. Even some entire rural communities rely on renewable energy for heating and lighting.

Non-renewable, or "dirty," energy includes fossil fuels such as oil, gas, and coal. Non-renewable sources of energy are only available in limited amounts and take a long time to replenish. When we pump gas at the station, we`re using a finite resource refined from crude oil that`s been around since prehistoric times. Non-renewable energy sources are also typically found in specific parts of the world, making them more plentiful in some nations than others. By contrast, every country has access to sunshine and wind. Prioritizing non-renewable energy can also improve national security by reducing a country`s reliance on exports from fossil fuel-rich nations.

Many non-renewable energy sources can endanger the environment or human health. For example, oil drilling might require strip-mining Canada`s boreal forest, the technology associated with frocking can cause earthquakes and water pollution, and coal power plants foul the air. To top it off, all these activities contribute to global warming.

Humans have been harnessing solar energy for thousands of years--to grow crops, remain warm and dry foods. According to the National Renewable Energy Laboratory, "more energy from the sun falls on the earth in one hour than is used by everyone in the world in one year." Today, we use the sun rays in many ways--to heat homes and businesses, to warm water, or power devices.

Solar cells are made from silicon or other materials that transform sunlight directly into electricity. Distributed solar systems generate electricity locally for homes and businesses, either through rooftop panels or community projects that power entire neighborhoods. Solar farms can generate power for thousands of homes, using mirrors to concentrate sunlight across acres of solar cells. Floating solar farms--or "floatovoltaics"--can be an effective use of wastewater facilities and bodies of water that aren`t ecologically sensitive.

Hydropower is the largest renewable energy source for electricity in the United States, though wind energy is soon expected to take over the lead. Hydropower relies on water--typically fast-moving water in a large river or rapidly descending water from a high point--and converts the force of that water into electricity by spinning a generator`s turbine blades.

Nationally and internationally, large hydroelectric plants--or mega-dams--are often considered to be non-renewable energy. Mega-dams divert and reduce natural flows, restricting access for animal and human populations that rely on rivers. Small hydroelectric plants (below 40 MW), carefully managed, do not tend to cause as much environmental damage, as they divert only a fraction of flow.

Biomass is organic material that comes from plants and animals, and includes crops, waste wood, and trees. When biomass is burned, the chemical energy is released as heat and can generate electricity with a steam turbine. Biomass is often mistakenly described as a clean, renewable fuel and a greener alternative to coal and other fossil fuels for producing electricity. However, recent science shows that many forms of biomass--especially from forests--produce higher carbon emissions than fossil fuels. There are also negative consequences for biodiversity. Still, some forms of biomass energy could serve as a low-carbon option under the right circumstances.

Renewable energy accounts for 13.5 per cent of the world`s total energy supply, and 22 per cent of the world`s electricity. This system is a major topic when discussing the globe`s energy future for two main reasons: a) this system provides energy from sources that will never deplete and b) this system produces less greenhouse gas than fossil fuel energy systems produce.

While renewable energy system is better for the environment and produces less emissions than conventional energy sources, many of these sources still face difficulties in being deployed at a large scale including, but not limited to, technological barriers, high start-up capital costs, and intermittency challenges.

It is important to note that the terms `renewable energy`, `green energy` and `clean energy` are not interchangeable in all cases; for example, a `clean` coal plant is simply a coal plant with emissions reduction technology. The coal plant itself is still not a `renewable energy` source. `Green energy` is a subset of renewable energy, which boasts low or zero emissions and low environmental impacts to systems such as land and water.

Coal-based power plants are becoming obsolete globally and such projects should not be continued in Bangladesh as well. China, Japan, India and the UK have already banned the coal based power plants in their own country but they are investing heavily in Bangladesh`s coal power expansion whereas renewable energy can replace planned coal power projects as a lower cost alternative for electricity generation. Germany, one of the world`s largest consumers of coal, recently declared that they will close gradually all 84 of its coal power plants by replacing renewable energy.

The Australia-based Market Force that deals with environmentally sustainable economic issues recently released an alarming report that Bangladesh is likely to be hit by its own "carbon bomb" once its 30 coal-based power plants go operational altogether by 2031. Besides, the projects will put the country in a "trade deficit" of an estimated cost Tk. 170 billion annually to import coal. Solar energy systems don`t produce air pollutants or greenhouse gases, and as long as they are responsibly sited, most solar panels have few environmental impacts beyond the manufacturing process.

So, our government should once again look into the bad impact of coal based power plants and emphasis the low cost environment friendly sources of energy.

The writer is banker and freelance contributor