Renewable Energy Resources
Solar Energy
• Solar energy is available in very large amount, thus considered perpetual energy resource and is considered major future source of energy.
• Ultimate source of energy in an ecosystem is Sun.
• Solar energy influences earth’s climate. Wind energy, biomass and hydropower are the resultant of solar energy.

Applications of Solar energy
A. Photovoltaic: Conversion of Solar Energy of Electricity
• Semiconductors when irradiated with sunlight, electrons present in their ground state get energized to jump to an excited state i.e. flow of electrons occur and generates electricity. The phenomenon is known as Photovoltaic’s (PVs).
• Thus, Photovoltaic’s are the arrays of cells consisting of semiconductors that effectively converts solar radiation into electricity (Direct Current), used to power bulb or equipment or to recharge a battery. An inverter converts DC to AC for, grid connected power generation.

B. Solar Thermal
• Solar Thermal Power systems, also known as Concentrating Solar Power systems, use concentrated solar radiation as a high temperature energy source to produce electricity using thermal route.

C. Other Applications of Solar Energy
• Solar cooker
• Solar water heater
• Solar furnace
• Solar power plant
• Solar toys
• Solar air-conditioning
• Solar vehicles
• Solar chimney
• Space cooling and heating
• Day lighting (solar street lights and traffic lights)
• Solar desalination

Advantages of Solar Energy
(i) It is renewable energy resource.
(ii) Solar power is pollution free.
(iii) Solar powered instruments are easy to install and use e.g. solar panels, solar water heaters, solar lighting, solar Pumps, solar fountains.
(iv) Long life and low maintenance.
(v) Solar system based electricity is a cheaper source of energy as compared to energy obtained from conventional electric systems.
(vi) Solar Photovoltaics are used for the electricity generation in remote and isolated areas e.g. forest, hills, deserts. PV is frequently used in watches, pocket calculators and toys.

Disadvantages of Solar Energy
(i) Solar energy production is hampered when the Sun is not available (i.e. during nights, less sunny days and cloudy days).
(ii) Technology is to be kept advancing in such a way to efficiently capture the solar radiations over a larger area.
(iii) Initial cost of installation is high. In case of photovoltaic cell, price of silicon wafers makes it very costly.
(iv) Solar cooking is a long time taking process. The food kept in the container can be over-heated if not removed from solar-cooker timely.
(v) Solar cooker cannot work as a substitute of LPG chullas because all type of foods cannot be prepared in solar cooker, e.g., chapatti.

Potential available in India
• India is endowed with vast solar energy potential. About 5,000 trillion kWh per year energy is incident over India’s land area with most parts receiving 3-5 kWh per sq. m per day. Based upon the availability of land and solar radiation, the potential of solar power in the country has been assessed to be 750 GW.

Hydro Energy
Generation of electricity by using the force of falling water is called hydro electricity or hydel power. It is cheaper than thermal or nuclear power. Dams are built to store water at a higher level; which is made to fall to rotate turbines that generate electricity.
The basic principle behind hydropower energy is the damming of rivers to create artificial in waterfalls, sometimes natural waterfalls are also used. The falling water is used to turn the turbines that drive electrical generators.

Advantages:
(i) Clean source of energy (eco-friendly or non-polluting).
(ii) Cheaper than thermal power plants.
(iii) Other benefits e.g. fishing, beauty of land- area.

Disadvantages:
(i) Reservoir Induced Seismicity (RIS). The continuous pressure of water column on the earth core increases the probability of occurrences of earthquakes.
(ii) Water-borne and water induced diseases are caused.
(iii) Flood is caused if leakage occurs in the dam.

Potential:
India is blessed with immense amount of hydro-electric potential and ranks 5th in terms of exploitable hydro-potential on global scenario. As per assessment made by CEA, India is endowed with economically exploitable hydro-power potential to the tune of 148700 MW of installed capacity.

Wind Energy
Wind energy is the kinetic energy associated with the movement of atmospheric air. Wind energy systems convert this kinetic energy to more useful forms of power.
The Indian wind energy sector has an installed capacity of 23,439.26 MW (as on March 31, 2015). In terms of wind power installed capacity, India is ranked 5th in the World. Today India is a major player in the global wind energy market.

Advantages
(i) Cost of production is not high, can be reduced by research.
(ii) Initial investment is moderate.
(iii) Operation and maintenance cost is not high.
(iv) Eco-friendly.
(v) Available in large amount.
(vi) Produce more energy due to high efficiency.
(vi) Land below turbines can be used for growing crops and stock (animal) grazing.

Disadvantages
(i) Availability depends on steady (continuous) winds or climate.
(ii) Unsteady winds affect power production.
(iii) Noise pollution (a) due to rotation of blades; (b) due to rotation of turbines.
(iv) Large open area is required for electricity production.

Geothermal Energy
Geothermal Energy is the energy obtained from heat stored in the earth crust and used for various purposes like electricity generation or direct heating applications. Geothermal energy is basically stored in earth crust up to depth of 3 to 4 km.
Hot water and steam from deep underground can be piped up through underground wells and used to generate electricity in a power plant.

Benefits of Geothermal Energy
• It is a clean fuel as compared to fossil fuel such as oil, gas or coal. A geothermal field emits only 1/6th CO2 as compared to any clean natural gas fired power plant. Binary plants are further less polluter among all geothermal power plants.
• Ground Source Heat Pumps can be a good source of saving money for consumers by reducing electricity bill as it includes only capital cost and maintenance cost is very less.
• The capital cost of geothermal power plant is very high but average units produced per year is very high as compared to other renewable energy resources such as solar, hydro, wind, etc.
• Salts and dissolved minerals contained in geothermal fluids are usually re-injected with excess water back into the reservoir at a depth well below groundwater aquifers. This system prolongs the life of the reservoir as it recycles the treated waste water.
• Geothermal Energy (Other than Power) can also be applied in Cold Storage, Tourist Resorts and pools, Melting snow, Poultry & Fish Farming, Mushroom Farming, Horticulture, Greenhouses, Aquaculture, Industrial processes, Space heating, etc.

Geothermal Energy in India
In India, exploration and study of geothermal fields started in 1970. The GSI (Geological Survey of India) has identified 350 geothermal energy locations in the country. The most promising of these is in Puga valley of Ladakh. The estimated potential for geothermal energy in India is about 10000 MW.
The major sites for geothermal energy are:
• Himalayas: J&K, HP and Sikkim; PUGA hot spring in J&K and Manikaran in HP.
• Sohana: Haryana, Rajasthan.
• Son-Narmada-Tapi (SONATA): MP, Chhattisgarh and Jharkhand; Tattapani spring in Chhattisgarh.
• Cambay: Mainly Gujarat and some parts of Rajasthan
• Godavari: AP
• Mahanadi: Orissa, Taptapani Spring in Orissa.

Hydrogen as a source of energy
• Hydrogen energy is at present only at the Research, Development and Demonstration (RD&D) stage.
• Hydrogen is burned electrochemically with oxygen to produce electricity. Electrodes are clipped in electrolyte preferably Sodium Hydroxide.
• Hydrogen and oxygen is passed in the fuel cell and following chemical reaction generates electricity:

Advantages of Hydrogen
(i) Hydrogen has highest calorific value (150 kj/g). Thus it is an excellent fuel.
(ii) It is an eco-freindly source of energy.
(iii) Source of hydrogen (water) is present in large amount.
(iv) Simplest and lightest fuel in gaseous form.

Disadvantages of Hydrogen
(i) Hydrogen gas is highly explosive (inflammable).
(ii) High (safety measures) are required in storage an transportation saferty measure.
(iii) Production of hydrogen is costly.

Biogas
Biogas is a combustible mixture of gases consists mainly of methane (CH4) and carbon dioxide (CO2) and is formed from the anaerobic bacterial decomposition of organic compounds, i.e. without oxygen. The gases formed are the waste products of the respiration of these decomposer microorganisms and the composition of the gases depends on the substance that is being decomposed.
The principal benefits of biogas include:
a) Conversion of natural organic waste into fertilizer: The conversion is carried out in a machine called the polythene bio gas digester. Cow dung slurry is put into the machine. The product is organic fertilizer of high quality. The fertilizer obtained is rich in nitrogen. It has been analyzed, that, fertilizer made by the polythene bio gas digester contains nitrogen content 3 times more than the product made by conventional processes. It is completely natural and free from harmful synthetic chemicals.

b) Eco friendly energy production: The calorific value of biogas is equal to that of half liter of diesel oil (6 kWh/m3). Methane is a key component of the gas. Biogas is fully capable of replacing other rural energy sources like wood, hard coal, kerosene, plant residues, and propane. Hard coal possesses a calorific value of 8.5kWh/kg per 0.7 kilograms. Larger biogas plants generate and feed electricity into mainstream power grids. Smaller biogas production units can support lighting and cooking requirements.

c) Considerable workload reduction in rural areas: This is particularly true for rural women engaged in day to day household work. Installing a biogas unit will relieve her of the tiring and tedious job of collecting and ferrying firewood. Since, biogas burns cleanly, the rural homes will not suffer from smoke and consequently rural denizens will suffer less from physical problems like bronchial complications. Cooking is also easier with a gas stove and takes less time.

d) Visible improvement in rural hygiene: Biogas contributes positively to rural health conditions. Biogas plants lower the incidence of respiratory diseases. Diseases like asthma, lung problems, and eye infections have considerably decreased in the same area when compared to the pre-biogas plant times. Biogas plants also kill pathogens like cholera, dysentery, typhoid, and paratyphoid.

e) Environmental benefits on a global scale: Biogas plants significantly lower the greenhouse effects on the earth’s atmosphere. The plants lower methane emissions by entrapping the harmful gas and using it as fuel.

f) Protects the earth’s natural resources: 1 biogas plant is computed to save 32 liters of kerosene and 4 tons of firewood every year. The organic chemical plant also contributes indirectly to the protection of soil.

Disadvantages of Biogas:
a) The process is not very attractive economically (as compared to other biofuels) on a large industrial scale.
b) It is very difficult to enhance the efficiency of biogas systems.
c) Biogas contains some gases as impurities, which are corrosive to the metal parts of internal combustion engines.
d) Not feasible to locate at all the locations.

Renewable energy can help in Sustainable development of India and therefore needs strengthening.