Changing Importance Of The Sources Of Energy

Humans have been using energy since the discovery of fire. The use of energy intensified since the Industrial Revolution and it is currently used in domestic and commercial buildings, industries and for transportation. However, pecking order of sources of energy continues to change.

Drivers Of Energy Use
As per the "Key World Energy Statistics" report by International Energy Agency's(IEA), in 2014 the global total primary energy supply was 13.7 Btoe (Billion Tonnes of Oil Equivalent). About four fifth of that is accounted by fossil fuels e.g. Coal, Oil and Natural gas. About 5% of that is contributed by nuclear fuels leaving the shares of others including renewables to less than 15%. The figures are different when it comes to source used for generation of electricity. The share of fossil fuels is two third and nuclear sources account for roughly 10%. The share of renewables including hydro is about a quarter.

The factors that will influence the energy use by the middle of the century, i.e. till 2050 would be as follows. As per IEA's, World Outlook Energy 2015, energy use worldwide is set to grow by one-third and this will be driven by emerging countries like China, India, Africa etc. This is less than the economic growth as energy efficiency will gain importance. Secondly, the share of renewable energy resources which are less polluting will increase at the expense of fossil fuels. Thirdly, share of electricity in overall energy use will increase. Advances in technologies will reduce the cost of producing each unit of energy but the reductions would be different for each source of energy. Finally, the COP21 Paris agreement aims to restrict global temperature rise this century well below 20C above pre-industrial levels and to pursue efforts to limit the temperature increase even further to 1.50C. The choice of fuels by the middle of the century will be decided by the above factors.

SOURCE OF ENERGY
Renewable energy sources
Renewable energy is generally defined as energy that is collected from resources which are naturally replenished e.g. sunlight, wind, rain, tides, waves, geothermal heat, biomass etc. They are generally geographically diversified as compared to other sources of energy. They produce less pollution than fossil fuels and leave less waste than nuclear fuels. Their fuels are either free or except for biomass do not suffer price variations as in case of fossil fuels. They are expected to play a larger role in fulfilling energy needs of the future.

They can be divided into three categories. First hydro and biomass are already established sources of energy. As per Energy Information Administration (EIA) of US, for 2016 in USA, it is estimated that they will account for about two third of energy consumption of renewable group. Secondly there are wind and solar which are rapidly capturing market share as their costs are plummeting. Third there are other sources e.g. waves, tides, ocean currents, geothermal etc. which may gain prominence in future once technological and environmental challenges are overcome. Except for geo thermal, the contribution of this last set of sources is small.

Solar
Solar power is conversion of sunlight to electricity either by using photovoltaic cells (PV) or by concentrating the sunlight using mirrors or lenses (CSP). The former results in direct generation of current while the latter uses the familiar method of generating steam to run turbines to generate electricity. The levelized cost of CSP methods is more and it can only be installed economically on larger commercial scale. One advantage of CSP methods over PV methods is that solar energy can be stored in the former case allowing it to be released to electricity generation system when sunlight is not there. While cost differential between the 2 methods will reduce as the public interest in CSP arises, it is unlikely to become cheaper than PV. In general, for solar power, operating costs are less and there is no pollution except for materials used for construction whose manufacturing may cause pollution. There is an additional issue that generation of electricity fluctuates, hence it has to be used in conjunction with other sources of energy. This also implies a low capacity factor which remains below 50%. Advances in battery technologies will help mitigate this problem. Today Solar power's contribution to electricity generation is small. However as per EIA's International Economic Outlook (IEO) 2016, Solar power will be the fastest growing energy resource till 2040. This is due to falling costs, support from government, use of smaller installations on rooftops, less maintenance as no movable parts, no bird deaths, no noise etc. It may become the leading renewable source by 2050 and share of PV methods will remain more than that of CSP methods.

Wind
Wind power constitutes to about 4% of global electricity generation. The wind turbines could be on land(onshore) or in a large water body(offshore). The former is cheaper to install while winds are stronger and more steady in the latter case. The levelized cost of electricity have fallen significantly. The operating costs are less and there is no apparent pollution except for materials used for construction whose manufacturing may cause pollution. Wind turbines may cause deaths of birds and also produce some noise. There is an additional issue that generation of electricity fluctuates. As per IEO 2016, Wind power will experience fast growth till 2040. Wind power share in the global electricity generation will increase significantly and it may become the leading renewable source by 2050 and share of onshore methods will remain more than of offshore methods.

Hydroelectricity
Hydro electricity contributes to one sixth of global electricity production. A variety of hydro plants exist that generate electricity from a few KWs to thousands of MWs. The operating costs are less and there is no apparent pollution. Also dams allow control of water, making it a flexible source of electricity. However, the construction of dam requires materials whose manufacturing may cause pollution. Dams are also sources of Methane due to decaying plant materials. Also large dams cause human displacement, submergence of vast tracts of lands and may induce seismic activity. The hydroelectricity capacity will grow steadily and as per IEA's "Technology Roadmap Hydropower", under 20C temperature rise scenario, its share in electricity production is expected to remain constant till 2050.

Biomass
This refers to organic material derived from animals or plants but unlike fossil fuels, it is of recent origin. This includes wood, wastes including municipality wastes, forest residues, manures, agricultural by products etc. One application is creation of biofuels i.e. Bioethanol, Biodiesel and Biogas. Bioethanol is produced by fermentation of carbohydrates and used after mixing with gasoline. Biodiesel can be used by itself or mixed with diesel. It is produced from oils or fats by transesterification. Both of them are used in transport. Biogas can be used in transport after compression but the use is less as compared to that of Bioethanol and Biodiesel. It is mostly used for heating and to some extent for electricity generation. Other biofuels are Biomethanol, Biobutanol, Bioethers etc. New biofuels are being discovered e.g. Algae biofuels, biofuels from Jatropha, Hydrotreated vegetable oil etc. Also new ways to process Biomass through Bio refineries are being researched. Bioethanol, Biodiesel and Biomass in general also emits pollutants but they can be considered atmospheric Carbon-neutral because the plants used to make fuel biofuels absorb Carbon Dioxide as they grow and may offset the Carbon Dioxide produced when a biofuel is made and burned. After incorporating proper cleansing technologies to reduce emissions, they emit less pollutants than fossil fuels. There are issues like food security, changes in land use, impact on natural environment, fluctuation in the supply and prices of feedstock, transportation costs, competing demands from other industries for feedstock etc.. Biofuels contribute to about 3% of transport energy as of now and their contribution to transport energy is expected to increase significantly by 2050.

Biomass also contributes to production of electricity. Biomass co-firing in modern coal power plants is an effective method to generate electricity. As per IEA, share of Biomass in electricity generation may touch 5% by 2050.

Geothermal and Others
Geothermal energy reflects the thermal energy stored within earth which was stored either during the formative years of earth or is released due to radioactive decay of various materials. Geothermal technology development has focused so far on extracting naturally heated steam or hot water from natural hydrothermal reservoirs and this has limited energy extraction at tectonic plate boundaries. However new technologies that can extract heat from hot rocks are being developed. One example being Enhanced Geothermal Systems (EGS). The environmental pollution is less but there could be land subsistence. Drilling is expensive and may induce seismic activity. Also the efficiency of electricity conversion is less as temperatures are low.
Geothermal energy is also an important source of heat and is used for heating homes as well as for industrial. Iceland uses Geothermal energy for most of its domestic heating.

Electricity can also be extracted from tides, waves and ocean currents. Currently these hydrokinetic methods are more expensive than other sources of energy though some tidal and wave plants do exist. There are environmental issues associated with them e.g. risk to marine life and noise etc. Share of of Geothermal and hydrokinetic methods in electricity production is less than 2%. Their share will increase but they will remain relatively smaller contributors in 2050.

NON-RENEWABLE ENERGY SOURCES
Natural Gas
Natural gas is a fossil fuel and is found where coal and petroleum is found. Following advances in fracturing technologies, Shale gas is becoming an important source of Natural Gas. Natural Gas is used for heating, cooking, generating electricity, in transport and in some chemical industries. As per the "Key World Energy Statistics" report by IEA, in 2014 Natural Gas' contribution to global total primary energy supply was 2.9 Btoe, so around one fifth. Its contribution to electricity generation was roughly the same. It is transported in compressed or liquefied form. Though mostly composed of methane, it is less polluting that other fossil fuels as burning of natural gas leaves water and carbon dioxide, the latter in smaller quantity. In addition, natural gas led generation technologies are more efficient than coal led generation in producing electricity. As per EIA's IEO 2016, Natural gas will witness fastest growth among fossil fuels as far as electricity generation is concerned and may become leading fossil source of electricity by 2050. Its share in transport will also increase significantly. It will also remain a key primary energy source.

Coal
Coal, the key catalyst of Industrial Revolution remains the largest source of electricity generation even today. Coal is also used in making steel, phosphorous, calcium carbide etc. Besides crude oil, it is the biggest primary energy source. Since it is the biggest source of Carbon Dioxide emissions, the use of coal will grow more slowly as compared to other fuels. The growth will be mostly outside the developed world. It should still remain a leading contributor to electricity generation in 2050.

Oil
Crude oil or Petroleum is the biggest primary energy source today. Its use is small when it comes to electricity generation but it is the main contributor for energy used for transportation. As per EIA's website in 2015, petroleum products provided about 92% of the total energy the U.S. transportation sector used. Distillation of Petroleum produces important industrial products which are used for producing lubricants, plastics, wax, tar, bitumen etc. Petrol and Diesel when used in transport produce not only Carbon Dioxide but also Carbon Monoxide, Nitrogen Oxides, particulate matter and Sulphur Dioxide. Petroleum faces competition from Natural Gas, Biofuels, Electricity for its use as fuel for transport. On one hand, Oil distillers are working to improve the quality of Petrol and Diesel while vehicle manufacturers are trying to reduce the emissions. Also in transport sector, a change in fuel will warrant changes in numerous vehicles. While its share will reduce, Petroleum should remain the dominant contributor of transport energy in 2050.

Nuclear
Nuclear energy contributes to slightly more than 10% of global electricity generation. The fuels are Uranium and Plutonium. Nuclear energy is also used for propulsion of ships and submarines. Some radioactive materials are also used in medicine and industry. Though there are no carbon emissions, handling radioactive wastes is a major concern. Also accidents can cause grave environmental damage besides risking life and health. Various new technologies to harness nuclear power are being researched. They aim to minimize the wastes, improve thermal efficiency, safety, change to more abundant fuel e.g. Thorium etc. However, electricity generation through Nuclear Fusion will take at least 2 more decades to become commercially viable. Electricity generation through nuclear fuels will continue to grow and as per IEA's "Technology Roadmap Nuclear Energy", under 20C temperature rise scenario, its share in electricity production is expected to remain constant till 2050.

Summary
The ongoing industrialization of Asia and Africa will drive the need of energy. However, concern on environmental impact will not only reduce energy intensity of processes but more importantly, the choice of sources. Technology will also play a key role in determining the choice of sources which need to be clean as well as commercially viable. As of now, renewable sources are on a faster tract than non-renewable resources.