All renewable energy source comes from the sun and we use it as directly and indirectly. Different types of renewable energy, such as solar heating is direct energy source whereas wind energy, bio-energy, bio-fuels are the example of indirect energy sources. The main features of renewable energy is that it can be used with any harmful pollutants.
Types of renewable energy
There are different types of renewable energy sources that are used in daily life. In this section we will provide you an overview and brief description of renewable energys.
At present 80% of the total rural energy consumption is met from the non-commercial energy in the form of traditional bio-mass such as fuel wood, animal dung and agro-waste. Renewable energy sources, viz. solar, wind and biomass have the potential to be utilized as supplementary types of renewable energy source.
More than 540 million tonnes biomass is available from various crop residues, agro-wastes and forestry produce. Besides, 27 million tonnes municipal waste is also available @ 0.4 kg/person/day with a calorific value of 850 kcal/kg, which has the potential to be utilized for energy production.
It is estimated that about 270MT of biomass is available from the forest that meets 40% of the energy needs. Growing stock of wood is estimated 4,741 million m3 in 1997 With an annual increment 88 million m3 (1.37m3/ha compared with world average of 2. 1m3/ha). Of the total biomass, 70% to 75% is used as fuel wood and animal feed and the remaining as energy source through direct combustion or processing of agro-produce.
The average biogas production is estimated 160 litres/kg dry matter. About 3 .93 million biogas plants have been installed by 2006-07, which are estimated to generate fuel gas equivalent to the saving of more than 3 million tonnes of fuel wood per year.
Besides, these plants are generating enriched organic manure, containing nitrogen equivalent to 0.85 million tonnes of urea per annum. More than 35 million improved chulhas have been installed till the end of 2006, which are expected to save over 11 million tonnes of fuel-wood per annum.
The direct combustion of biomass is used for cooking and for steam and power generation. The combustion involves evaporation of moisture, distillation and burning of volatile matter, and combustion of fixed carbon. High volume, low thermal efficiency, high tar or ash content, environment pollution and health hazards are the major concerns.
Thermal conversion efficiency of open fire is usually 5%, domestic chulha, 12%, smokeless chulha, 20% and improved cooking stove, 20 to 35%. The improved stove and furnaces, charcoal briquettes, fluidised bed combustion with optimum air or oxygen ratio can improve the thermal efficiency besides cleaner environment.
Gasification and producer gas
The gasification of agricultural residues implies extraction of a combustible gas by burning it under limited supply of air. During gasification the material is pyrolysed due to heat released from the combustion. In this process the material is converted into charcoal, tar and light gases.
This gas (CO) can be utilized in the engine or directly burn to generate heat. Three types of gasifiers are used, viz. up-draught, down-draught and cross-draught. The down-draught .gasifler is more suited to agricultural residues, because water vapour and the products of pyrolysis pass through oxidation and reduction zones in the producer gas plants (temperature 800°-1,100°C). As a result these are adequately reduced or cracked, resulting in lower tar and water vapour contents in the producer gas.
In this “types of renewable energy“, the microbial conversion of organic matter to methane is a process that is becoming increasingly attractive as a method of waste treatment and energy recovery. Anaerobic digestion of the materials rich in cellulose and hemlcellulose produce gas primarily consisting of methane and CO2, which is combustlble.
The digestible organic residue is converted into fat, cellulose and protein by hydrolytic bacteria, and acetogenic bacteria convert it into soluble simple compounds except acetate. These are then converted into carbon dioxide and hydrogen by homo-acetogens and fmally into ethane and carbon dioxide (biogas) by methanogenic bacteria.
Besides animal dung, selected crop residue, fruit and vegetable wastes, food-industry wastes, willow dust, seaweeds, water hyacinth, domestic garbage, sanitary land-fllls and night soil can also be used in biogas plants. Common weeds eg. water hyacinth and even human excreta can be used for biogas to light million of houses in the rural area. Floating metallic-type and fixed-dome (janta) type are the most popular designs being adopted in most of the states for cattle dung substrate.
Increasing cost of petroleum, oils and lubricants would require alternative fuels for mobile power sources. Biogas and producer gas can only partially substitute highspeed diesel in compression ignition engines. Biodiesel and alcohol are compatible with fuel injection system of compression engines.
Plant oils have been successfully used in compression ignition engines directly or after trans-esterification. Dual-fuel engines, which work on biogas and diesels, are being manufactured in India. The biomass also has the potential to be utilized as a supplementary fuel in internal combustion engines by converting into alcohol (biofuel).
Geothermal is one types of renewable energy which is available as heat emitted from within the earth, usually in the form of hot water or steam. Geothermal heat has two sources: the original heat produced from the formation of the earth by gravitational collapse and the heat produced by the radioactive decay of various isotopes. The geothermal system is made up of some main elements: a heat source, a reservoir, a fluid, which is the carrier that transfers the heat, a recharge area and an impermeable cap rock to seal the aquifer.
The heat source can be either a very high temperature (>600 °C) magmatic intrusion that has reached relatively shallow depths (5-10 km) or, as in certain low-temperature systems, the Earth’s normal temperature, which, as we explained earlier, increases with depth. It is very site dependent as the resource needs to be near surface and can be used for heating and power generation purposes.
It is most famous “types of renewable energy”. India receives 5,000 trillion kWh/year of solar radiation. Most parts of the country have 260-300 clear sunny days in a year. It is possible to generate 20 MW/km2 solar power. Presently, solar energy is being utilized through two different routes, namely solar thermal route and solar photovoltaic routes.
India is one of the 6 countries, those have developed the technology for manufacture of polysolicon material. About 191 MWp of module production has been achieved (2005-06). Over 1.95 million m2 of collector are has so far been installed, ranging from domestic water heater of 50-100 liters capacity to industrial and commercial systems.
Solar lighting and water pumping systems are now being used. Under the SPV programme, 565,828 solar lanterns, 317,066 home- lighting systems, 61,321 street-lighting system, 7,068 water pumping systems and non grid power plants or packs of 1.87 MWp aggregate capacity have been installed up to July 2007.
The wind energy is used for stand alone water pumping or power generation. The gross wind-power potential of India is estimated to be 45,000 MW though the present technical achievement is limited to 7,844.5 MW up to 2006 in the potential states, which places India in the fifth position in the world, after Germany, the USA, Denmark and Spain.
Winds are due to the fact that the Earth’s equatorial regions receive more solar radiation than the Polar Regions, setting up large-scale convection currents in the atmosphere. According to estimations from meteorologists, about 1% of the incoming solar radiation is converted into wind energy, while the 1% of the daily wind energy input is nearly equivalent to the present world daily energy consumption.
Wind has been the fastest growing renewable energy source in the U.S. over the last decade mainly due to very significant improvements in wind energy technology. The American Wind Energy Association predicts that 6,000 MW of wind power will be installed by the end of 2004.
This is enough to power 1.5 million homes. Wind power is one of the most efficient, deployable, scalable and affordable types of renewable energy technologies. Wind power is produced by the energy of the wind turning aerodynamic blades mounted to a hub. The hub is connected to a shaft that turns a generator.
It comes from water at work, water in motion. It can be seen as a form of solar energy, as the sun powers the hydrologic cycle which gives the earth its water. In the
hydrologic cycle, atmospheric water reaches the earth’s surface as precipitation.
Hydropower plants convert the energy of flowing water into electricity. This is primarily done by damming rivers to create large reservoirs and then releasing water through turbines to produce electricity.
Some of this water evaporates, but much of it either percolates into the soil or becomes surface runoff. Water from rain and melting snow eventually reaches ponds, lakes, reservoirs, or oceans where evaporation is constantly occurring.
Alternatively, hydropower can also be extracted from river currents when a suitable device is placed directly in a river. Hydropower results in no emissions into the atmosphere but the process of damming a river can create significant ecological problems for water quality and for fish and wildlife habitat. It is one of the most effective and potential “types of renewable energy“.
The devices employed in this case are generally known as river or water current turbines or a “zero head” turbine. This module will review only the former type of hydropower, as the latter has a limited potential and application.
Major constraints in use of renewable energy
Despite sincere efforts being made by the Central and State Governments for promotion of various rural energy technologies, their adoption has remained slow. A number of constraints related with the technological, socio-economical and the promotion aspects were identified for the slow adoption.
Improper selection of the beneficiaries and type or size of rural energy technologies is reported to be a prime cause in many non-functional systems. Other important constrains common to most of the rural energy technologies are as follows:
- 1. Much higher investment, requirements of a standby arrangement for reliable operation, lower unit cost of most of the commercial sources of energy primarily due to government subsidies, no financial benefit for non-polluting characteristics of renewable energy technologies.
- 2. Most rural energy technologies have a lower life span, and requires more attention in operation, servicing and repair. Repairs and servicing are not available easily at reasonable price. The typical examples are cleaning and tracking of solar panels; preparation of fuel for gasifiers and substrate for biogas plants, etc.