2.1. Fossil: renewable vs. sustainable
Although fossil fuels are created from the organic matters such as trees that can be planted or renewed, it is not considered renewable because the rate of fossil fuel consumption is much more higher than the rate of reproduction. But fossil fuel can be sustainable if we can control the limit of exploitation and consumption and balance it with other energy sources. Many experts belief that fossil fuel including coal cannot be sustained if people are still consuming it as usual . On the contrary, even renewable resources can become unsustainable if a resource is used up faster than it can regenerate and it will eventually be entirely depleted despite its renewability. Conversely, a non-renewable resource can be sustainable if it's used in moderation. In addition, if used without caution, these can be depleted in a short time . By 2012, these dense supplies of fossil energy provided 87 percent of global primary energy cosumption, and mostly used for the power generation, home heating, and transportation purposes .
Fossil fuels including oil, gas, and coal are natural energy sources which are made from dead organism through the geological processes over the period of hundred million years. Most researchers agree that a massive and widespread of coal deposits were formed in carbonneiferous period of the Paleozoic around 300 milion years ago. Lignin is a major component of the woody tissue that modern tree trunks are made of. It is tough for most organisms to eat , except for the white rot fungus that lives on dead trees. White rot fungi break down the lignin in wood , leaving the lighter colored cellulose behind, some of the break down both lignin and cellulose [4, 5].
Compare to other fossil fuels, coal has the largest available reserve in the form of a rock, which is mainly composed of carbon and other elements. Coal was formed from the plants decomposition that has a high energy potential, which is useful for both electricity generation and heating purpose . The ultimate energy source of coal is the sun because the energy stored within dead plant matter is what yields coal. The older is the coal maturity, the higher the energy content, begin with the highest Anthracite (31-36 MJ/Kg), Bituminous (25-34 MJ/Kg), Sub-bitumonous (19-30 MJ/Kg), and the lowest Lignite (12-19 MJ/Kg. Until recently, the electricity cost of coal power plant is the lowest compare to other power plant, ignoring the cost of externalities including environmental and social impact. The total reserve of coal as per 2012 is around 10 12 tonnes, where the United States is the largest, and coal exhibits a 109 year reserve to production ratio, means that from today, coal will be lasted in the next hundred years .
Despite the fact that coal is the less expensive, most available reserve, and most energy effective, coal is responsible for more emissions of carbon dioxide compare to any other fossil fuel. Coal is burned with the presence of oxygen in the atmosphere, which allows a chemical reaction between the carbon and the oxygen to form Carbon dioxide (CO 2 ). The production of CO 2 harms the environmental that leads to climate change. Evenworst, most coal contains large polluted elements including sulfur, mercury, and sometimes lithium and burning coal also causes the formation of both NO x and SO x [3, 5]. There are many other environmental impact in exploitating fossil fuel, beyond the burning of these fuels. Some of those are the habitat destruction during mining or excavation, loss of bio-diversity, and water pollution. Many countries show their concern about the impact of fossil fuel to the global climate and they have agreed to take effort in reducing environmental impact of fossil fuels by putting the mandatory polllution control in their legislation. More and more countries and environmental practitioners are concern about the utilization of biomass as coal substitution with almost zero CO 2 emission.