Introduction 

A present day estimate by National Geographic determined that we use 320 billion kilowatt-hours of energy every day. Today, most of this enormous requirement is addressed by burning fossil fuels. So far, fossil fuels have catered to our energy needs very efficiently, but they are also non-renewable and rapidly depleting. These fuel sources have also contributed greatly to greenhouse gas emissions and pollution. The time has come to find suitable and better replacements for fossil fuels.

Some of the future energy resources are discussed as below:

• Gas Hydrate
Gas hydrates are naturally occurring, crystalline, ice-like substances composed of gas molecules (methane, ethane, propane, etc.) held in a cage-like ice structure. (clathrate). Gas Hydrates containing mostly methane are considered a clean source of energy for the future.

They are found abundantly worldwide in the top few hundred meters of sediment beneath continental margins at water depths between a few hundred and a few thousand feet. They are present to a lesser extent in permafrost sediments in Arctic areas.

• Coal Bed Methane (CBM)
Coal bed methane (CBM) is simply methane found in coal seams. CBM is generated either from a biological process as a result of microbial action or from a thermal process as a result of increasing heat with depth of the coal.

It is called 'sweet gas' because of its lack of hydrogen sulfide. Unlike much natural gas from conventional reservoirs, coal bed methane contains very little heavier hydrocarbons such as propane or butane, and no natural gas condensate. It often contains up to a few percent carbon dioxide.

India has 400 billion cubic meters (M3) of CBM with a heat value of 8500-9000 KCal/M3 CBM, a clean fuel for power generation, is currently being wasted during coal mining.

• Shale gas
Shale gas refers to natural gas that is trapped within shale formations. Shales are fine-grained sedimentary rocks that can be rich resources of petroleum and natural gas. Sedimentary rocks are rocks formed by the accumulation of sediments at the Earth's surface and within bodies of water. Common sedimentary rocks include sandstone, limestone, and shale.

• Methane Hydrates
In sediments on the ocean floor, tiny bacteria continuously break down the remains of sea animals and plants, producing methane gas. Under the enormous pressures and cold temperatures at the bottom of the sea, this methane gas dissolves and becomes locked in water molecules to form crystals. These crystals cement together the ocean sediments into solid layers—called methane hydrates—that can extend down into the sea floor. Methane hydrates buried in the sediments of the ocean floor is a reserve of methane and can act as a future fuel.

• Hydrogen fuel
Hydrogen - a colourless, odourless gas is increasingly gaining attention as a future source of energy free from environmental pollution. Its new use has been found in the automobile and power generation sector. The biggest advantage with hydrogen is that it has the highest energy content per unit mass among known fuels and it burns to produce water as a by-product. It is, therefore, not only an efficient energy carrier but also an environmentally benign fuel as well.

It can be used as an electrochemical device converting chemical energy of hydrogen directly into electricity without combustion. It is a clean and efficient process of electricity generation. It can be used in UPS systems, replacing batteries and diesel generators. In view of the relevance of fuel cells in automobiles and power generation, several organizations globally are pursuing RD&D activities in this field.