Renewable Energy Library

Bio-Energy :
Bio-energy, is obtained from organic matter, either directly from plants or indirectly from industrial, commercial, domestic or agricultural products and waste.

The use of biomass is generally classed as a carbon-neutral process because the carbon dioxide released during the generation of energy is balanced by that absorbed by plants during their growth. However, it is important to account for any other energy inputs that may affect this carbon-neutral balance on a case-by-case basis, for example any use of fertiliser, or energy consumed in vehicles when harvesting or transporting the biomass to its point of use.

Since the bio-energy can provide an income, it is a way of paying for CO2 mitigation and land restoration. To derive maximum benefits, bio-energy production and use must be modernised. Developing countries have been particularly instrumental in pushing modernisation of biomass for energy as they are so heavily dependant on it, and likely to remain so. Both developing and industrialised countries are now realising they can benefit environmentally and economically.

Biomass are the residues obtained from pulp and paper operation, agricultural and forestry wastes, urban wood wastes, municipal solid wastes and landfill gas, animal wastes and terrestrial and aquatic crops grown solely for energy purposes, known as energy crops. In large quantities, the biomass source is called a feedstock.
Biomass can be burnt directly or it can be converted into solid, gaseous and liquid fuels using conversion technologies such as fermentation to produce alcohols, bacterial digestion to produce biogas, and gasification to produce a natural gas substitute. Burning plant biomass as a fuel source does not result in net carbon emissions since the bio-fuels will only release the amount of carbon they have absorbed during growth (providing production and harvesting is sustainable). If these bio-fuels are used instead of fossil fuels, carbon emissions from the displaced fossil fuels are avoided as well as other associated pollutants such as sulphur. The development of large-scale energy production from biomass will rely on specifically-grown energy crops. Nevertheless residues (from forestry, crops and dung) are invaluable as an immediate and relatively cheap energy resource. Wood can also be removed in a sustainable manner from existing secondary forests and plantations.

Biomass is already the fourth largest source of energy in the world supplying about 13% (55 EJ/yr; 25 million barrels of oil equivalent) of 1990 primary energy. It is also considered one of the main renewable energy resources of the future due to its large potential, economic viability and various social and environmental benefits. It is estimated that by 2050 biomass could provide nearly 38% of the world's direct fuel use and 17% of the world's electricity.

Biogas is a mixture comprising mainly methane and carbon dioxide. It is produced when organic matter decomposes in the absence of oxygen. This can take place in a landfill site to give landfill gas or in an anaerobic digester to give biogas. Sewage gas is biogas produced by the digestion of sewage sludge.

Landfill gas:
Landfill gas is a mixture comprising mainly methane and carbon dioxide, formed when biodegradable wastes break down within a landfill as a result of anaerobic microbiological action. The biogas can be collected by drilling wells into the waste and extracting it as it is formed. It can then be used in an engine or turbine for power generation, or used to provide heat for industrial processes situated near the landfill site, such as in brickworks. Landfill sites can generate commercial quantities of landfill gas for up to 30 years after wastes have been deposited. Recovering this gas and using it as a fuel not only ensures the continued safety of the site after land filling has finished, but also provides a significant long term income from power and/or heat sales.

Anaerobic digestion:
The biological processes that take place in a landfill site can be harnessed in a specially designed vessel known as an anaerobic digester to accelerate the decomposition of wastes. Anaerobic digestion is typically used on wet wastes, such as sewage sludge or animal slurries but the biodegradable fraction of municipal wastes can be added to wetter wastes to increase the biogas output.

There is no evidence to suggest that biomass production will conflict with food production, and with agro-forestry and integrated farming systems there is evidence that it could in fact enhance agricultural output.

Solid biomass can also be converted into liquid fuels that power cars, engines including those in diesel generators, and even industrial operations. Methanol, ethanol, biofuel and biodiesel can all be created from biomass.

Methanol is a wood alcohol which is not as efficient as gasoline as a fuel.

Ethanol, or ethyl alcohol, is a clear, colorless, flammable oxygenated fuel currently added as a gasoline additive to increase octane and lower tailpipe greenhouse gas emissions. It is biodegradable and water soluble. Ethanol (which comes from cellulosic biomass such as corn) is produced through fermentation at either a dry mill or at a wet mill. The dry mill process is simpler than the wet mill process. The wet mill breaks the corn into its components and processes each separately. In addition to ethanol, both processes also create distiller's grain, which is fed to farm animals.

Up to 24% ethanol can be added to gasoline before engine modifications are necessary. A blend known as E85, which is 85% ethanol and 15% gasoline, can be used to power flexible fuel vehicles (FFVs). Many cars on the market today are already built to run on E85. Brazil has had much success converting nearly all of its vehicles to run on E85 made from sugar. It even announced that it would stop importing oil by the end of 2006.

Ethanol has a better environmental profile than gasoline as measured at both the production facility and the tailpipe. Ethanol production plants produce less carbon dioxide, methane and particulates than gasoline refineries, which help meet clean air standards. A blend of 10% ethanol, or E10, yields a 26% reduction in greenhouse gases when compared to gasoline alone. For more information on ethanol is available on the Renewable Fuels Association website.

Biodiesel is the result of combining alcohol (including ethanol) with oil extracted from soybeans, rapeseed, animal fats, or other biomass. Biodiesel can be produced from any fat or vegetable oil, such as soybean oil often sold as 2% (B2) or 10% (B10) blends with diesel. �Concerns that biodiesel can't perform or flow well in adverse weather are based on myths,� Biodiesel performs very well in cold climates and is being used in airport snowplows and school buses. It also burns much cleaner than traditional diesel, making it more environmentally friendly.

Future biological methods for atmospheric CO2 reduction include laboratory based research on photobiology and photobiochemistry. Photobiology (efficient microalgal growth in photobioreactors and tanks/ponds to remove CO2 from flue gases) can provide a source of energy, chemicals and food, while wastes can be converted or recycled into useful byproducts (eg. fertilizer). Photobiochemical systems use the CO2 fixing enzyme Rubisco to store energy via organic compounds. These photobiological systems have a considerably higher photosynthetic efficiency than conventional biomass systems, and do not require high quality land or water so would not compete with agriculture and forestry.

Solar -Energy:

Sun is the main source of energy for our planet earth. Sun's radiations, falling on the earth, can be captured directly for the use in the modern technologies which at present make use of the fossil fuels responsible for the increased emissions of carbon dioxide. Methods of capturing solar energy are as follows: 

  • Active heating and cooling: e.g. a) water heater converts solar radiation into heat, which can be used directly or stored, b) night sky radiation cooling involves cooling of water in shallow trays exposed to night sky.
    • Solar photovoltaic (PV) panels comprising of solar cells directly convert solar radiations into electricity.
      • Passive solar energy design involving orientation, shape and fabric of a building's allows the solar radiations to enter directly in the indoor areas of the building, reducing the need for artificial lighting and heating.

      Active heating and cooling (Solar thermal energy)

      Active solar water heating uses flat plate solar energy collectors, usually on the roof of a building, to collect the sun's heat via water tubes attached to the flat plate and a water storage tank. The heat is primarily used for heating water in domestic applications, industrial facilities and commercial buildings and also has the growing market for solar swimming pool water heating. In solar thermal energy systems, when the solar energy is not available (in the night) or availability is low (under cloudy or dusty conditions), hot water can be stored for a limited period of time in well-insulated water tanks.

      Air may also be heated directly by sun's heat by circulating it through the metal channels or ducts attached to the flat plate collector.

      Night sky radiation cooling effect may also be used in various cooling requirements. Under clear night sky conditions when practically there is no solar radiation, the earth surface continues to emit infrared radiation to the sky and is cooled to temperature much lower than surrounding air temperature. Water in a shallow trough having large surface areas when exposed to clear night sky may be cooled to about 15­oC below air temperature.

      An overview of the status of the solar thermal technology developments in the European Union countries is given on the European commissions website and that for India is available on the website.

      Solar photovoltaic energy

      Solar photovoltaic (PV) process involves direct conversion of energy of sun's light into electricity using a semiconductor material, also called photoelectric effect. Energy of light radiations falling on the semiconductor material such as silicon is absorbed, and the electrons in the semiconductor are excited and broken free from their atoms. The free electrons flow through the semiconductor material producing electricity.

      Numerous solar PV cell technologies, including polycrystalline, mono-crystalline and thin-film have been developed. Small solar PV cells (1 or 2 watts) are arranged in modular panels which are mounted on a building roof or walls, and directly feed electricity into the heating or cooling equipment inside the building. In the latest PV technology, cells integrated into the roof tiles themselves are also available. PV technology has already found numerous uses including small electronic devices, military equipment and space research.

      Solar PV cells are also used in both stand-alone and grid-connected systems. As the solar energy is only available during the day and also varies in output due to dusty conditions or cloud cover, PV systems use batteries or other forms of electricity storage to store the electricity for periods when the solar energy availability is low but the demand is high.

      Passive solar design
      Passive solar techniques make use of solar energy by means of building designs that balance energy requirements, without the use of additional mechanical equipment. Such techniques include use of south facing windows in the northern hemisphere buildings to allow solar energy for heating the space, insulation of walls, roof and floors to minimise the heat loss, and natural ventilation. Building materials having large thermal mass are used to store solar energy for use when there is no sun shine.

      Day lighting
      Natural solar light can be allowed to reach inner space of a building using open plan floors or specially developed light pipes, to help reduce energy demand. Such natural light conditions also provide better quality light, better work efficiency and better health.

      Wind-Energy: Wind presents a vast source of renewable energy. For many centuries, wind mills have used wind flow, or motion energy (i.e. kinetic energy) of wind, for grain grinding, water pumping and still is extensively used for sailing and flying a kite.

      Wind energy is in fact an indirect form of solar energy. Winds are generated due to heating of air by solar radiations during the day, at variable rates in different parts of the hemisphere and rotation of the earth. Heated air rises up and cooler air replaces it resulting in wind. Wind movement on the earth surface is influenced by the terrain, water reserves, deserts, forests, vegetation and habitat developments.

      Wind or air in motion contains the "kinetic energy" which is converted into mechanical power by means of a wind turbine. The wind turbine is connected to a generator for producing electricity.

      Wind turbines are installed on high level of more than 30 metres above the ground or a tower to capture the most energy and to take advantage of faster and less turbulent wind.

      The modern wind turbines are of two basic types:

      Vertical axis wind turbines (VAWT) and

      Horizontal-axis wind turbines (HAWT)

      Vertical axis wind turbines have the vertical main rotor shaft. The main advantages of this arrangement are that the generator and/or gearbox can be placed at the bottom, on or near the ground, so the tower doesn't need to support it, and that the turbine doesn't need to be pointed into the wind. Drawbacks are usually the pulsating torque produced during each revolution, and the difficulty of mounting vertical axis turbines on towers. This means they must operate in the slower, more turbulent air flow near the ground, with lower energy extraction efficiency.

      Horizontal-axis wind turbines typically either have two or three blades. These three-bladed wind turbines are operated "upwind," with the blades facing into the wind. The other common wind turbine type is the two-bladed, downwind turbine. Horizontal axis turbines are the most common type used today.

      In a horizontal axis wind turbine, the wind turns two or three aerodynamic blades mounted around a rotor shaft. The aerodynamic forces (lift and drag) of wind produce mechanical power. This power rotates the blades and the shaft connected to a generator, normally via a gearbox, which produces electricity. The rotor blades and shaft are connected to the nacelle, which contains the gearbox and other power/mechanical components and is mounted at the top of the wind turbine tower. The nacelle rotates freely to allow aligning of the wind turbine blades with the direction of the wind and optimising extraction of wind energy.

      Capacity range of wind turbines varies from few hundred watts to several megawatts. Small capacity wind turbines, below 50 kW, are used mostly for stand alone applications such as homes, offices, telecommunications and commercial buildings.

      Larger capacity wind turbines, above 50 kW, are used in multiple numbers in wind farms, which provide bulk power to the electrical grid.

      Hydro energy :

      Hydro energy is derived from flowing water in rivers, water streams in mountains or from man-made installations where water flows from a high-level reservoir down through a tunnel and away from the dam. Energy from flowing water (or kinetic energy) has been used for centuries to turn water wheels attached to grinding wheels for grinding corn or flour or other machinery in mills and factories, specifically in Mesopotamia as early as 3000 BC. During the 18th century the application of waterwheels spread further into industry, driving a vast range of machines for every conceivable purpose, notably textile production. A century later there were over 20,000 waterwheels operating in Engalnd alone.

      Water wheel technology was largely replaced by steam power or fossil fuel energy in the Industrial Revolution.
      Hydro energy is now mostly used to generate electrical energy on large scale by collecting water in large reservoirs or dams called hydroelectric power.

      Turbines placed within the flow of water extract its kinetic energy and convert it to mechanical energy. This causes the turbines to rotate at high speed. The turbines drive a generator that converts the mechanical energy into electrical energy. The amount of hydroelectric power that can be generated is related to the water flow and the vertical distance (known as head) through which the water has fallen.

      In the smallest hydroelectric schemes, the head of water can be a few metres; in larger schemes, the power station that houses the turbines is often hundreds of metres below the reservoir.

      Hydroelectric systems can be connected to the main electricity grid, or can be part of a stand-alone power system. In a grid-connected system, any electricity generated in excess of consumption on site can be sold to electricity companies. In an off-grid hydroelectric system, electricity can be supplied directly to the user or via a battery bank.

      There are three main types of hydroelectric schemes:

      storage schemes

      run-of-river schemes

      pumped storage

      In storage schemes, a dam impounds water in a reservoir that feeds the turbine and generator, usually located within the dam itself.

      Run-of-river schemes utilise the natural flow of a river, where the continuity of flow can be enhanced by a weir. Both storage and run-of-river schemes can be diversion schemes where water is channelled from a river, lake or dammed reservoir to a remote powerhouse containing the turbine and generator. A canal or low-pressure tunnel transports the water to this end point and then back to the river or to another watercourse.

      Pumped storage incorporates two reservoirs. At times of low demand, generally at night, electricity is used to pump water from the lower to the upper basin. This water is then released to create power at a time when demand, and therefore price, is high. Pumped storage is not a renewable application as it is reliant upon an electricity supply and energy losses are always involved when pumping the water. However, by providing a rapid supply of electricity in response to sudden changes in demand, it does have value in aiding the overall efficiency of the generation infrastructure.

      In order to utilise the locally available energy sources, more attention is now being given to small hydro energy systems. Efforts are also being made to revive the old water wheel technologies which need minimal expertise. Smaller hydro energy systems fall in following three types:

      Micro-hydropower systems are relatively small power sources that are appropriate for individual users or groups of users who are independent of the electricity supply grid, having a generating capacity of less than 100 kW.

      Mini hydropower systems have an installation capacity of between 100 kW and 1000 kW (1.0 MW).

      Small hydropower systems have a capacity of more than 1.0 MW and up to 10 MW.

      Depending on the site, the following may be needed to develop a micro-hydropower system:

      an intake or weir to divert stream flow from the water course

      a canal/pipeline to carry the water flow to the fore-bay from the intake

      a fore-bay tank and trash rack to filter debris and prevent it from being drawn into the turbine at

      the penstock pipe intake

      a penstock pipe to convey the water to the powerhouse

      a powerhouse, in which the turbine and generator convert the power of the water into electricity

      a tailrace through which the water is released back to the river or stream

      Many micro-hydropower systems operate from "run of river," which means only a fraction of the available stream flow at a given time is used to generate power, and this has little environmental impact. The amount of energy that can be captured depends on the amount of water flowing per second (the flow rate) and the height from which the water falls (the head).


      The Earth's crust is a bountiful source of energy called geo energy and fossil fuels are only part of the story. Heat or thermal energy of the Earth is by far the more abundant resource. To put it in perspective, the thermal energy in the uppermost six miles of the Earth's crust amounts to 50,000 times the energy of all oil and gas resources in the world.

      Types of Geothermal Resources

      The temperature at centre of the Earth at 6400 kilometres depth is estimated to be 4000°C or higher. Partially molten rock, at temperatures between 650° to 1200°C, is believed to exist at depths of 50 to 60 miles (80 to 100 km). Heat is constantly flowing from the Earth's interior to the surface. Most types of geothermal resources, hydrothermal, geo-pressured, hot dry rock, and magma-result from concentration of Earth's thermal energy within certain discrete regions of the subsurface.

      Hydrothermal resources are reservoirs of steam or hot water, which are formed by water seeping into the earth and collecting in, and being heated by fractured or porous hot rock. These reservoirs are tapped by drilling wells to deliver hot water to the surface for generation of electricity or direct use. Hot water resources exist in abundance around the world. Technologies to tap hydrothermal resources are proven commercial processes.

      Geo-pressured resources are deeply buried waters at moderate temperature that contain dissolved methane. While technologies are available to tap geo-pressured resources, they are not currently economically competitive.

      Hot dry rock resources occur at depths of 5 to 10 miles (8 to 16 km) everywhere beneath the Earth's surface, and at shallower depths in certain areas. Access to these resources involves injecting cold water down one well, circulating it through hot fractured rock, and drawing off the now hot water from another well. This promising technology has been proven feasible, but no commercial applications are in use at this time.

      Magma (or molten rock) resources offer extremely high-temperature geothermal opportunities, but existing technology does not allow recovery of heat from these resources.

      Earth energy is the heat contained in soil and rocks at shallow depths. This resource is tapped by geothermal heat pumps.

      The geothermal resource is the world's largest energy resource and has been used by people for centuries. It is environmentally friendly and is a renewable resource of energy.

      Geothermal energy power plants
      Electric power plants driven by geothermal energy already provide over 44 billion kilowatt hours of electricity worldwide per year, and world capacity is growing at approximately 9% per year. To produce electric power from geothermal resources, underground reservoirs of steam or hot water are tapped by wells and the steam rotates turbines that generate electricity. Typically, water is then returned to the ground to recharge the reservoir and complete the renewable energy cycle. There are several types of geothermal power plant available, depending on the temperature and pressure of the geothermal source.

      Dry Steam Power Plants were the first type of geothermal power plant (in Italy in 1904). The Geysers in northern California, which is the world's largest single source of geothermal power, is also home to this type of plant. These plants use the steam as it comes from wells in the ground, and direct it into the turbine/generator unit to produce power.

      Flash Steam Power Plants, which are the most common, use water with temperatures greater than 182°C. This very hot water is pumped under high pressure to equipment on the surface, where the pressure is suddenly dropped, allowing some of the hot water to "flash" into steam. The steam is then used to power the turbine/generator. The remaining hot water and condensed steam are injected back into the reservoir.

      Binary Cycle Power Plants operate on the lower-temperature waters, 107° to 182°C. These plants use the heat of the hot water to boil a "working fluid," usually an organic compound with a low boiling point. This working fluid is then vaporized in a heat exchanger and used to turn a turbine. The geothermal water and the working fluid are confined to separate closed loops, so there are no emissions into the air. Because these lower-temperature waters are much more plentiful than high-temperature waters, binary cycle systems will be the dominant geothermal power plants of the future.

      Developing and commercializing geothermal power technologies contributes not only to a cleaner environment, but to a healthy industrial base, as well. Around the developing countries of the world, demand for electric power is burgeoning�and nearly half of these countries have geothermal resources. These markets have proven particularly receptive to clean energy produced with indigenous resources, creating attractive export options for geothermal technologies and expertise.

      Geothermal plants emit no nitrogen oxides and very low amounts of sulphur dioxide�allowing them to easily meet the most stringent clean air standards. The steam at some steam plants contains hydrogen sulphide, but treatment processes remove more than 99.9% of those emissions.

      Direct Use of Geothermal Energy
      Underground reservoirs are also tapped for "direct-use" applications in which hot water is pumped directly to heating system of greenhouses, spas, fish farms, and homes or buildings space heating and other hot water needs.

      In a typical application, a well brings heated water to the surface; a mechanical system piping, heat exchanger, controls delivers the heat to the space or process; and a disposal system either injects the cooled geothermal fluid underground or disposes of it on the surface.

      Direct-use systems typically require a larger initial investment, but have lower operating costs and no need for ongoing fuel purchases, therefore reducing life-cycle costs.

      Ground-source heat pumps
      Ground-source heat pumps (GSHP) extract heat from the earth which is a different form of geothermal energy. It is the low-temperature heat (10-20°C) that is found at relatively shallow depths within the earth's crust. This source of heat remains at a relatively constant temperature all year and can be taken from the ground itself or from groundwater. Heat pumps can increase the temperature to provide a more useful output temperature of around 40�50°C, ideal for low-temperature heating systems like under floor systems and radiant panels.

      Ground-source heat pumps are not strictly a renewable source of energy, because they require electricity to extract and make use of low-grade heat. However, there is no reason why this electricity could not be generated by another form of renewable energy. Heat pumps can be very energy efficient, producing four or five times the amount of heat energy for every unit of electrical energy needed. A heat pump takes the heat from a refrigerant fluid (or water) that is in contact with the ground, extracts the heat from this source and transfers it to a heat sink where it can then be circulated through a heating system. Although the refrigerant fluid is cooled by this process, it can be re-circulated back through the ground where it will absorb more heat before being passed through the heat pump again.

      In winter, heat pump systems draw thermal energy from the ambient temperature of the shallow ground, which ranges between 10° to 21°C depending on latitude. In summer, the process is reversed to a cooling mode, using the ground as a sink for the heat contained within the building. The system does not convert electricity to heat; rather, it uses electricity to move thermal energy between the building and the ground and condition it to a higher or lower temperature according to the heating or cooling requirements. Consumption of electricity is reduced 30% to 60% compared to traditional heating and cooling systems, allowing a payback of system installation in 2 to 10 years. And these low-maintenance systems have long lives of 30 years or more. Some systems are also capable of producing domestic hot water at no cost in summer and at small cost in winter. They can be used in most kinds of building and have both domestic and commercial applications.


      More than 70% of Earth's surface is covered by oceans which contain two types of energy:
      mechanical energy from waves and tides and  Thermal energy from solar radiations falling on the ocean surface making them the world's largest solar collectors.

      Even though the sun affects all ocean activity, tides are driven primarily by the gravitational pull of the moon, and waves are driven primarily by the winds.

      Wave Energy
      As ocean waves are created by the interaction of wind with the surface of the sea, waves have the potential to provide an unlimited source of renewable energy. Wave energy can be extracted and converted into electricity by wave power machines. They can be deployed either on the shoreline or in deeper waters offshore.

      The total power of waves breaking on the world's coastlines is estimated at 2 to 3 million megawatts. In favourable locations, wave energy density can average 65 megawatts per mile of coastline. Three approaches to capturing wave energy are:

      Float or Pitching Device or buoyant moored device
      The device floats on or just below the surface of the water and is moored to the sea floor. A wave power machine needs to resist the motion of the waves in order to generate power: part of the machine needs to move while another part remains still. In this type of device, the mooring is static and is arranged in such a way that the waves motion will move only one part of the machine. Electricity is generated from the bobbing or pitching action of a floating object which can be mounted to a floating raft or to a device fixed on the ocean floor.

      Oscillating Water Columns (OWC)
      An oscillating water column is a partially submerged, hollow structure that is installed in the ocean. It is open to the sea below the water line, enclosing a column of air on top of a column of water. Waves cause the water column to rise and fall, which in turn compresses and depresses the air column. This trapped air is allowed to flow to and from the atmosphere via a Wells turbine, which has the ability to rotate in the same direction regardless of the direction of the airflow. The rotation of the turbine is used to generate electricity.

      Hinged contour device
      Here, the resistance to the waves is created by the alternate motion of the waves, which raises and lowers different sections of the machine relative to each other, pushing hydraulic fluid through hydraulic pumps to generate electricity. A hinged contour device is able to operate at greater depths than the buoyant moored device. These shoreline devices, also called "tapered channel" systems, rely on a shore-mounted structure to channel and concentrate the waves, driving them into an elevated reservoir. Water flow out of this reservoir is used to generate electricity, using standard hydropower technologies.

      The main problem with wave power is that the sea is a very harsh, unforgiving environment. An economically-viable wave power machine will need to generate power over a wide range of wave sizes, as well as being able to withstand the largest and most severe storms and other potential problems such as algae, barnacles and corrosion.

      An overview of the status of the wave energy technology developments in the European Union is given on the European commission's website.

      Tidal Energy
      Tidal energy exploits the natural ebb and flow of coastal tidal waters caused principally by the interaction of the gravitational fields of the earth, moon and sun. The coastal water level fluctuates twice daily, alternatively filling and emptying natural basins along the shoreline. The currents flowing in and out of these basins can be exploited to turn mechanical devices to produce electricity.

      A variant of tidal energy is tidal stream (or marine current) technology. Tidal streams are fast sea currents created by the tides, often magnified by topographical features, such as headlands, inlets and straits, or by the shape of the seabed when water is forced through narrow channels.

      The technology required to convert tidal energy into electricity is very similar to that used in traditional hydroelectric power plants. Gates and turbines are installed along a dam or barrage that goes across a tidal bay or estuary. When there is an adequate difference in the height of water on either side of the dam, the gates are opened and the hydrostatic head that is created causes water to flow through the turbines, turning a generator to produce electricity.

      Electricity can be generated by water flowing both into and out of a bay. As there are two high and two low tides each day, electrical generation from tidal power plants is characterised by periods of maximum generation every six hours. Alternatively, the turbines can be used as pumps to pump extra water into the basin behind the barrage during periods of low electricity demand. This water can then be released when demand on the system is at its greatest. This allows the tidal plant to function with some of the characteristics of a pumped storage hydraulic facility. In order to produce practical amounts of electricity, a difference between high and low tides of at least 5 metres is required.

      The technology used for tidal streams is slightly different to that used in tidal barrages, and is still in its infancy. Tidal stream devices are similar to submerged wind turbines and are used to exploit the kinetic energy in tidal currents.

      An overview of the status of the tidal energy technology developments in the European Union is given on the European commission's website and that for India is available on the Indian Ministry of New and Renewable Energy (MNRE) website.

      Ocean Thermal Energy
      Oceans cover of Earth's surface makes them the world's largest solar collectors. The sun's heat warms the surface water a lot more than the deep ocean water, and this temperature difference provides exploitation of ocean thermal energy. Just a small portion of the heat trapped in the ocean could power the world.

      A process called Ocean Thermal Energy Conversion (OTEC) uses the heat energy stored in the Earth's oceans to generate electricity. OTEC works best when the temperature difference between the warmer, top layer of the ocean and the colder, deep ocean water is about 20°C (36°F). These conditions exist in tropical coastal areas, roughly between the Tropic of Capricorn and the Tropic of Cancer.

      Ocean thermal energy has been effectively used for many applications, including electricity generation. There are three types of electricity conversion systems: closed-cycle, open-cycle, and hybrid. Closed-cycle systems use the ocean's warm surface water to vaporize a working fluid, which has a low-boiling point, such as ammonia. The vapour expands and turns a turbine. The turbine then activates a generator to produce electricity. Open-cycle systems actually boil the seawater by operating at low pressures. This produces steam that passes through a turbine/generator. And hybrid systems combine both closed-cycle and open-cycle systems.

      Space cooling requirements for onshore buildings applications can be successfully met by direct use of cold sea water from deep sea levels.


      CHP or cogeneration is the simultaneous or sequential energy production of usable heat and power (usually electricity) in a single process from a common source of energy. Useful energy outputs can be more varied. Increasingly, heat is being used to drive absorption chilling, and in some cases power can be mechanical power e.g. to drive a compressor. The term CHP is synonymous with cogeneration and total energy, which are terms often used in other Member States of the European Community and in the United States. CHP uses a variety of fuels and technologies across a wide range of sites, and scheme sizes. The basic elements of a CHP plant comprise one or more prime movers (a reciprocating engine, gas turbine, or steam turbine) driving electrical generators, or other machinery, where the steam or hot water generated in the process is utilised via suitable heat recovery equipment for use either in industrial processes, or in community heating and space heating.

      Whereas an electricity-only plant is typically large, and connected at very high voltage to the grid transmission system, a CHP plant is typically much smaller, attached to a site which consumes the heat and power produced (or a large proportion of it), is sized to make use of the available heat, and connected to the lower voltage distribution system (i.e. embedded). Not only is CHP more efficient through utilisation of heat, it also avoids significant transmission and distribution losses, and can provide important network services such as black start, improvements to power quality, and the ability to continue to supply the site if the grid goes down.

      CHP usually displaces boiler plant and electricity only plant using a range of fuels and technologies. CHP typically achieves a 25 to 35 per cent reduction in primary energy usage compared with electricity-only generation and heat-only boilers. This can allow the host organisation to make substantial savings in costs and emissions where there is a suitable heat load.

      CHP power plants can be divided into five types: backpressure, extraction condensing, gas turbine heat recovery, combined cycle and reciprocating engine power plants.

      Backpressure power plant
      The simplest cogeneration power plant is the so-called backpressure power plant, where CHP electricity and heat is generated in a steam turbine. Another main component of the backpressure power plant is the steam boiler, which can be designed to fire solid, liquid or gaseous fuels.

      Extraction condensing power plant
      A condensing power plant is generating only electricity. However, in an extraction condensing power plant some part of the steam is extracted from the turbine to generate also heat.

      Gas turbine heat recovery boiler power plants
      In gas turbine heat recovery boiler power plants heat is generated with hot flue gases of the turbine. The fuel used in most cases is natural gas, oil, or a combination of these. Gas turbines can even be fired with gasified solid or liquid fuels.

      Combined cycle power plants
      Recently, natural gas fired combined cycle power plants consisting of one or more gas turbines, heat recovery boilers, and a steam turbine have become quite common.

      Reciprocating engine power plant
      Instead of a gas turbine, a reciprocating engine, such as a diesel engine, can be combined with a heat recovery boiler, which in some applications supplies steam to a steam turbine to generate both electricity and heat.

      Advantages of CHP include:

      Potential energy savings

      Security of supply


      Increases competition among producers

      Opportunity to create new enterprises

      Well-suited to isolated or ultraperipheral areas.

      Euroheat & Power Project of the EU indicates that huge heat losses appear in the EU energy balance. From the annual energy supply of 63 EJ, more than 20 EJ heat are lost in power plants, oil refineries, and industrial processes. Parts of these losses can be retrieved and distributed by district heating systems to heat urban buildings. District heating systems provide the necessary heat load for high-efficiency CHP plants and, at the same time, make it also possible to use renewable energy sources (RES). District cooling is emerging as a similar energy efficient tool for providing comfortable indoor climate during summers.

      Sustainable Building Technology
      The environmental problems arising from the industrial revolution and the population explosion of the last century resulted in a new era of environmental laws internationally. The international treaties addressed environmental concerns about ocean dumping, air pollution, endangered species, etc. Governmental and industrial leaders around the world have begun to consider a holistic way of protecting the environment, which is known as sustainable development. Recognizing that a holistic approach would require new levels of international collaboration on environmental issues, the United Nations hosted an Earth Summit in June 1992 in Rio de Janiero, Brazil. The Earth Summit attracted nearly all of the governments of the world, more than 100 of which were represented by their heads of state, and resulted in two landmark conventions on climate change and biodiversity. The 1992 summit also established sustainability as a goal leaders worldwide supported and agreed to work toward achieving.

      While renewable sources of power, like solar and wind, hold promise for producing energy with fewer environmental impacts, the ability of those power sources to contribute significantly to meeting our energy needs affordably is likely many years away. In the meantime, efficiently using energy in buildings through careful design and choice of building materials could go a long way to minimizing the environmental damage attributable to energy production.

      In addition to the land required to dispose of building-related construction and demolition debris generated, the amount of natural resources that are mined and harvested to supply building materials are considerable.

      Sustainable approaches to building and the industries can both improve productivity and open up new business opportunities by enabling better use of the earth's 'natural capital' natural resources and ecological systems that provide vital life-support services to society and all living things. There are many features of a building that contribute to its sustainability, and the products used in the building are key features. Other features influencing sustainability include the overall efficiency of the building, the impact the building has on both the habits of the occupants and the microclimate. Green building concept has created more widespread awareness of the challenges involved in using alternative materials and methods of construction, including earthen building technologies.

      The European Commission's document on sustainable development An European Union Strategy for Sustainable Development provides for support research activities related to sustainable development as a part of the European Research Area; guidance document for Member States to consider how to make better use of public procurement to favour environmentally-friendly products and services and encourage private sector initiatives to incorporate environmental factors in their purchasing specifications.

      ASTM International Standards on SUSTAINABILITY in BUILDING meets the worldwide growing demand for sustainable building standards and address environmental problems & challenges related to the design, construction, and operation of environmentally-sound and resource-efficient sustainable buildings.

      Standards cover:
      Site & Ecosystems land management, biodiversity impacts, and ecosystem functioning

      Water water efficiency and water quality impacts

      Energy energy efficiency, renewable energy, and atmospheric impacts

      Materials recycled contents, nontoxic and biobased products

      Indoor Environmental Quality indoor air quality, acoustics, and lighting

      Operations durability, waste management, maintenance, quality of life (QOL), and life cycle assessment (LCA).

      Energy efficiency
      Energy efficiency of a building envelop or a machinery equipment or a process for producing energy means the ratio of useful energy to actual input energy for heating, cooling, and lighting or process. Energy efficiency implies that:

      all the components of the building envelope including the doors, windows, walls, foundation, roof, and insulation need to work together to keep a building warm in the winter and cool in the summer.

      energy saving appliances and equipment should be used in buildings.

      renewable energy systems should employ energy efficient components.

      as the most of the renewable energy sources are of intermittent nature, efficient energy storage technologies need to be employed.

      Improving energy efficiency of a building envelop, machinery or equipment, both by reducing quantities of energy consumed and by changing processes, offers a promising method for sustainable development by reducing the investments in energy infrastructure, by cutting fuel costs. It will create environmental benefits through reduced emissions of greenhouse gases and local air pollutants.

      European Union's Green Paper on energy efficiency or doing more with less includes the energy policy measures and highlights that even without high and volatile oil prices, which have led to a downgrading of the prospects of economic growth in Europe, there would be very good reasons for the European Union to make a strong push towards a re-invigorated programme promoting energy efficiency at all levels of European society

      The United States and Japan have already taken initiatives to reach a maximum consumption figure of one watt for several types of appliance. In Europe, and still in the context of the eco-design directive, it is foreseen to:

      encourage and promote voluntary agreements;

      introduce, if necessary, implementing measures to reduce standby losses for certain groups of appliances;

      stimulate the development at international level of technologies and measures aiming to limit electricity loss in stand-by mode.

      In Cameroon, ARPEDAC  is actively involved in development, demonstration, and propagation of products based on renewable and clean energy technologies.


      Hydrogen is an energy carrier, not a primary fuel, but has a very promising future. It does not exist in pure molecular form naturally on Earth but it can be produced and converted into useful energy forms for use in any application in which fossil fuels (i.e. coal, petroleum and natural gas) are used today, without adverse effects on the environment. For example, Hydrogen can be used as a fuel in furnaces, internal combustion engines, turbines and jet engines as a clean energy source. Automobiles, buses, trains, ships, submarines, airplanes and rockets can run on hydrogen. Hydrogen can also be converted directly to electricity by the fuel cells, with a variety of applications in transportation and stationary power generation.

      Currently the annual world production of hydrogen is estimated to be around 500 billion Nm3 per annum which is used mostly as an industrial chemical, e.g. for ammonia production (for fertiliser manufacture), for desulphurisation and other processes in refineries, and methanol production.

      Hydrogen can be produced from water by using a variety of energy sources, such as solar, nuclear and fossils, and it can be converted into useful energy forms efficiently and without detrimental environmental effects. The only by-product is water or water vapor (if air is used for flame combustion of hydrogen, small amounts of NOx are produced). When solar energy - in its direct and/or indirect forms - is used to produce hydrogen from water, both the primary and secondary forms of energy become renewable and environmentally compatible, resulting with an ideal, clean and permanent energy system - the Solar Hydrogen Energy System.

      Main implication in the use of hydrogen for various energy applications is its safe storage. Tremendous amount of research and development global efforts are under way for safe hydrogen storage technologies suitable for various applications, e.g. Metal hydride technologies offer a variety of applications in refrigeration, air conditioning, hydrogen storage and purification.

      Hydrogen Production

      There are numerous ways of producing hydrogen from renewable energy sources. It can be produced from a variety of biomass feed-stocks, such as agricultural crops and wastes, sewage sludge or municipal solid waste, by thermo-chemical (pyrolysis or gasification) or biological processes that break down complex organic molecules into simpler molecules including hydrogen.

      Hydrogen can also be produced from renewably generated electricity, via electrolysis, to split water into hydrogen and oxygen. Wind and solar resources are much larger than biomass resources and it would be possible to produce electrolytic hydrogen in most parts of the UK. This provides a way of storing renewably generated electricity on a much larger scale than is currently possible with existing battery technology. As some renewable sources are intermittent (for example, electricity is only generated when the wind is blowing at certain speeds or if the sun is shining), the electrical energy can be converted to chemical energy in the form of stored hydrogen for use when renewable sources are not available. However, the efficiency of the best large-scale electrolysers is only about 70 per cent, and the subsequent conversion of hydrogen into electricity may not exceed 50 per cent.

      At present, the bulk of hydrogen (almost 50%) is produced most economically by steam methane reforming (SMR). Partial oxidation of hydrocarbon fuels can be competitive where a cheap source of oxygen is available. Both these processes result in the emission of carbon dioxide and need to capture and store carbon dioxide if a carbon emissions are to be controlled.

      Hydrogen can be produced by the following technologies:

      Steam methane reforming (SMR)

      Partial oxidation of hydrocarbons

      Clean coal gasification (with carbon capture and storage)

      Pyrolysis (decomposition of hydrogen in the absence of oxygen)

      Electrolysis of water (ideally using electricity generated from low carbon sources such as wind or nuclear)

      Photoelectrolysis (splitting of water with sunlight)

      Biological production of hydrogen (photosynthetic)

      Biological production of hydrogen (fermentation)

      Gasification of biomass

      Thermochemical cycles (powered by solar or nuclear heat)

      Hydrogen Storage

      Hydrogen needs to be stored on a wide range of scales to achieve a fully functioning hydrogen economy. Large, centralised storage would be required if hydrogen is produced in large plants for wider distribution; longer term or seasonal storage would be required in systems relying on large scale exploitation of renewable energy; comparatively small scale storage is required on board vehicles, for homes, and for portable devices.

      A wide range of potential hydrogen storage technologies are under research and development. Particular interests is being shown in solid-state hydrogen storage as follows:

      Compressed gas

      Liquefaction (LH2)

      Reversible metal hydride

      Alkali metal hydrides

      Carbon nanotubes


      Hydrogen use as energy carrier

      Hydrogen can be used in two main ways:

      in a fuel cell, where it produces zero emissions at the point of use

      in normal combustion, where it produces lower emissions of pollutants than fossil fuels.

      Fuel cells

      A fuel cell is an energy conversion device that uses an electrochemical process to convert hydrogen into electricity without combustion. It produces electricity with a conversion efficiency of up to 50 per cent. In a combined heat and power (CHP) installation, an overall efficiency of up to 80 per cent may be possible by utilising the heat that is also produced as a by-product of this process.

      Fuel cells principle was discovered over 160 years ago and until recently, their use was limited to the laboratory and in spacecraft applications such as the Gemini, Apollo, and space shuttles.

      Potentially, fuel cells can be made in any size to power anything, from mobile phones to large power plants. However, at present the costs are between 10 and 100 times higher (depending on application) than existing polluting technologies. Possible applications include replacements for internal combustion engines for transport, powering portable devices, and electricity and heat for homes and buildings.

      A fuel cell contains an anode and a cathode insulated by an electrolyte situated between them. Hydrogen is supplied to the anode while oxygen is supplied to the cathode. The two gases try to join, but because of the electrolyte, the hydrogen atom splits into a proton and an electron. The proton passes freely through the electrolyte. The electron takes a different route, creating an electric current before recombining with the hydrogen and oxygen, creating a molecule of water. This chemical process generates electrical and thermal energy but produces pure water as a by-product.

      There are many different types of fuel-cell technology, with different characteristics such as power output and operating temperature, and each fuel-cell technology will only be suitable for certain types of application, for example large or small-scale stationary power generation, transport or portable battery replacement.

      A fuel-cell system can utilise hydrogen from any source including hydrocarbon fuels, such as natural gas and methanol. However, emissions from this system can be lower than the cleanest method of normal fossil fuel combustion. Different types of fuel cell are distinguished by their different electrolytes and the different temperatures reached during operation.

      The major fuel cell technologies are:


      Proton exchange membrane (PEM)

      Direct methanol

      Phosphoric acid (operating temperature ~220oC)

      Molten carbonate (operating temperature ~650oC)

      Solid oxide (operating temperature ~500-1000oC)

      The low temperature fuel cells (alkaline and PEM), requiring hydrogen as a fuel, are the leading candidates for vehicle applications. Direct methanol fuel cells are being developed for consumer electronics applications. The high temperature fuel cells (molten carbonate and solid oxide) are able to use a wider range of fuels.