Renewable Energy refers to energy generated from natural resources which are replenished in the normal course. Solar energy, wind energy, tidal energy, etc as well as energy extracted from biomass and biofuels fall in this category.
We shall briefly look at the major renewable energy systems:
- Solar energy
- Wind energy
- Tidal (Wave) Power
Solar Power as Renewable Energy Source
The sun has a surface temperature of about 27 million deg. C. and emits radiations covering a wide range of frequencies in all directions. A part of the radiations fall on the earth as it goes round the sun. Allowing for the various losses of the radiation on way to the earth, on an average we receive about 800 W/m2 of solar power at the equator.
Solar radiations include infrared frequencies which provide heat and also visible radiations which provide light. The solar energy, therefore, can be used in a very versatile manner. Photovoltaic cell-assemblies as arrays and panels are used in isolated homes and communities for providing electricity; they are also used in large power stations for utility supplies. Heat for industrial processes as well as for supplementing the large thermal power stations is provided by using the solar concentrators in large installations.
This is a truly versatile renewable energy source which is inexhaustible and also totally non-polluting.
Wind Power as Renewable Energy Source
One of the cheapest sources of renewable energy is the wind energy. Windmills have traditionally been used for pumping water (as exemplified by Holland) or for grinding grains. These windmills have taken on the modern role of providing electricity superbly. The three bladed windmills use turbines connected to generators for producing electricity; they are installed in the form of large windmill farms over large areas.
Good wind sites are generally in remote locations often situated miles away from large load centers such as cities or industrial centers. In any case it would be difficult to install large banks of windmills within cities or near urban centers.
Rotation of Earth, unevenness in heating of the atmosphere by the sun, and irregular surface of the Earth are the basic causes of creation of winds. This is another manifestation renewable energy of the sun available in a different form.
Tidal Power as Renewable Energy Source
Tides take place due to relative motion of the earth, the sun and the moon, and the gravitational forces of these planetary bodies on the waters in the oceans. A huge amount of water moves twice a day in and out of estuaries as tides and harnessing this amount of water could yield a great deal of energy. In the olden times tide mills had been in use in Europe as well as in USA.
Tides are more predictable than wind energy and solar energy, and energy supply from tides would be reliable and plentiful. Tidal power generation has to be tied up with other large power systems because tidal power is available only when the tides move in or out, say for a maximum of ten hours a day. However there are large technological problems in converting the tidal flow into useful electrical power.
There are various countries actively involved in developing technologies for harnessing tidal power. It is generally widely acknowledged that tidal power has vast potential as renewable energy source for electricity generation in future.
Biomass as Renewable Energy Source
By photosynthesis chlorophyll in plants converts atmospheric carbon dioxide into carbohydrates. Biomass is like solar energy stored in the form of carbohydrates. You burn it and the solar heat is released.
Biomass has been used from ancient times for obtaining heat.
The modern technology can not only use biomass to produce electricity by burning it but can also convert it into biofuel which can be used in vehicles or convert it into combustible gases. Whichever route we take in using biomass, it is an unavoidable truth that we shall finally face the problem of releasing carbon dioxide into the atmosphere.
There are many plants which are suited to being used for generating electricity or for being converted into biofuels or for gasification. There is, however, a lot of work that needs to be done to avoid fertile land being switched from production of food to production of crops as biofuels or to avoid crops and their produce being used to produce biofuel instead of being used for human consumption (as in case of corn, for instance).