8 types of Renewable energy (part 1)

Bio-fuel & Biomass Biogas
Distributed/Embedded Generation Fuel Cell/ Hydrogen / Batteries
Energy from Waste Solar
Water (hydro, Tidal, wave) Wind

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Biomass is derived from plant material and animal wastes. It can be used to generate electricity and or heat and to produce transport fuel.

A very wide range of biomass can be used for energy purposes. Examples include agricultural wastes, eg straw and other crop residues; crops grown specifically for energy production, eg willow, miscanthus, oil seed rape and wastes from a range of sources including food production. The nature of the fuel will determine the way that energy can best be recovered from it.

Dry biomass fuels

The most straightforward way to recover energy from dry biomass fuels is by combustion to provide heating or hot water. These types of applications range in size from simple log fires and stoves, to sophisticated wood or straw fuelled boiler systems, usually with automatic fuel handling and control systems.

CHP is becoming an increasingly attractive option for biomass plant, offering a reliable low-cost heat source for industrial or commercial uses (such as a district heating system for a small community), together with electricity that can be sold to the local grid. Forest residues, industrial wood wastes and a range of agricultural wastes are often readily available as fuel for CHP plant. However, energy crops, such as wood coppice (willow or poplar in cooler climates, wattle and eucalyptus in warmer climates), or perennial grasses such as miscanthus, are becoming increasingly important. These may be grown specifically for use as a fuel, and can provide long-term secure resources. Biomass fuels are increasingly being used with advanced conversion technologies, such as gasification systems, which may offer superior efficiencies compared with conventional power generation. Gasification is a thermochemical process in which biomass is heated with little or no oxygen present to produce a low-energy gas The composition of the gas will depend on the nature of the gasification process used. The gas can then be used to fuel a gas turbine or a combustion engine to generate electricity.

Wet wastes

Cattle, pigs and poultry all produce slurries that can be used to produce biogas. The slurries can be fermented in an anaerobic digester to produce a gas that is mainly methane and carbon dioxide. The gas can be used in gas engines to generate electricity or in boilers to provide process heat or space heating. Some 40-60% of the organic matter present in the slurry is converted into biogas. After maturation, the remainder provides a stabilized residue that can be used as a soil conditioner.

Distributed / Embedded Generation

The electricity supply network in the U.S. is tailored to deliver power flows from large fossil and nuclear plant, down through progressively lower voltage levels to reach business and domestic customers.

The vast majority of renewable power plants are small in comparison with conventional plant and they are connected to the lower voltage distribution grid rather than the high voltage transmission grid. The term for this form of generation is "embedded" or "distributed generation".

There is a great deal of work going on to modify the U.S. Electricity Distribution and Transmission networks to accommodate the increased amount of embedded generation required to meet the country's demand

Energy from waste

Wastes represent an increasingly important fuel source. Using wastes as fuel can have important environmental benefits. It can provide a safe and cost-effective disposal options for wastes that could otherwise present significant disposal problems. It can help reduce CO2 emissions, through displacement of fossil fuels. Methane is 23 times more damaging than CO2 for global warming. If biodegradable waste is diverted from landfill methane emissions can be avoided.

Any energy that is recovered from biological wastes can be regarded as renewable energy. It comes from plant material (either directly, or in the case of animal wastes, paper or card, indirectly). As plants grow they absorb carbon dioxide from the atmosphere. When this biomass material is used as a fuel, the carbon dioxide is returned to the atmosphere in a "carbon neutral" cycle. If biomass is used to displace fossil fuels instead of being left to decompose naturally, it will actually help to limit the emission of carbon dioxide and methane into the air.

There are many ways of combining waste disposal with energy recovery. A number of well established technologies are available for generating heat or power from wastes. There are also new technological developments, especially in power generation, which have the potential to increase the efficiency of energy recovery.

Recovering energy from wastes from municipal or industrial sources can turn the problem of waste disposal into an opportunity for generating income from heat or power sales. The safe and cost-effective disposal of these wastes is becoming increasingly important worldwide, especially with the demand for higher environmental standards of waste disposal and the pressure on entities to minimize the quantities of waste generated and disposed to land.

The technology

A very wide range of municipal or industrial wastes may be used as fuel. The nature of the waste and the waste disposal method will determine the way that energy can be recovered. Dry household, commercial or industrial wastes can either be burned (combusted) as raw waste, or they may first undergo some sorting or processing to remove waste components that can be recycled separately.

Combustion with energy recovery

Waste combustion with energy recovery is an established way to dispose of wastes. It decreases the volume of the waste and allows for recovery of metals and other potentially recyclable fractions. After further basic treatment, most of the remaining residue can be combined with other materials and used as an aggregate material. Any residue that is landfilled is biologically inactive and does not generate potentially harmful emissions.

The heat recovered from these plants can be used to generate electricity, or can be used for industrial heat applications. The size of energy from waste plant is designed to meet the waste disposal needs of the community, taking into account the potential for waste minimization and recycling. Plants that generate electricity can typically process a large amount per year, and from this they can generate huge amounts of electricity. Power is produced from these wastes by using the steam raised in the combustion process to drive a steam turbine to generate electricity, in a similar manner to a conventional coal fired power station.

Combined heat and power (CHP) is an attractive option where there is a market for the heat . This could be a factory or district heating system for a small community.

Advanced thermal technologies

Where the waste stream is of a uniform nature, for example if it has been processed into a homogenous fuel, it is better suited to the more "advanced technologies", such as gasification or pyrolysis. Wastes that are not uniform in composition, for example municipal wastes, are less suited to treatment by advanced technology, although the technology is rapidly developing to handle more challenging wastes.


Gasification is one of the newer technologies that is increasingly being used for waste disposal. It is a thermo-chemical process in which biomass is heated, in an oxygen deficient atmosphere to produce a low-energy gas containing hydrogen, carbon monoxide and methane. The gas can then be used as a fuel in a turbine or combustion engine to generate electricity. Gasifiers fuelled by fossil sources such as coal have been operating successfully for many years, but they are now increasingly being developed to accept more mixed fuels, including wastes. New gas clean-up technology ensures that the resulting gas is suitable to be burnt in a variety of gas engines, with a very favorable emissions profile. Gasifiers operate at a smaller scale than incineration plant, and can also be provided in modular form to suit a range of different scales of operation.


Pyrolysis is another emerging technology, sharing many of the characteristics of gasification. With gasification partial oxidation of the waste occurs, whilst with pyrolysis the objective is to heat the waste in the complete absence of oxygen. Gas, olefin liquid and char are produced in various quantities. The gas and oil can be processed, stored and transported, if necessary and combusted in an engine, gas turbine or boiler. Char can be recovered from the residue and used as a fuel, or the residue passed to a gasifier and the char gasifed.

Strict environmental standards now apply in all U.S. states governing the emissions from energy from waste plant, particularly of heavy metals, furans and dioxins. All energy from waste plant must now meet these standards, which can be achieved through the installation of extensive state-of-the-art gas cleaning systems.

Water (Hydro, Tidal, Wave)

Hydro power is produced when the kinetic energy of flowing water, is converted into electricity by a turbine connected to an electricity generator.

Hydropower can be exploited at various different scales. Large-scale typically means massive amounts of grid-connected generating capacity and is usually associated with a dam and a storage reservoir. There are many large schemes in the U.S, which were built during the  late 1900s. The potential for identifying new large-scale schemes is now more limited, not only because there are fewer commercially attractive sites still available, but also because of environmental constraints.

Schemes of less amounts now offer a greater opportunity for providing a reliable, flexible, and cost-competitive power source with minimal environmental impacts. These small-scale schemes are making an increasing contribution towards new renewable energy installations in many regions of the world, especially in rural or remote regions where other conventional sources of power are less readily available. Small scale schemes can be associated with a dam and storage reservoir or can be located in a moving stream ("run of river").

Tidal Power

Tidal power can use either conventional or new technology to extract energy from a tidal stream. It is usually deployed in areas where there is a high tidal range. Typically a barrage with turbines is built across an estuary or a bay. As the tide rises, it creates a height differential between the inner and outer walls of the barrage. Water can then flow through the turbines and drive generators. Some tidal barrages operate on both the rising and falling tide, but others, particularly estuarine barrages, are designed to operate purely on the falling tide.

It is also possible to make use of the tidal flow that occurs between headlands and islands or in and out of estuaries. It is this application that is the focus of much research and development, and new products for this purpose are now being commercialized. These “in-flow” tidal turbines can be arranged singly or in arrays, allowing a range of power outputs to be produced.

Wave Power

The power of the waves is readily visible on nearly every ocean shore in the world. There has been much research to harness the power of these waves, and various machines have now been developed. These fall broadly into three categories:

Machines which channel waves into constricted chambers. As the waves flow in and out of the chamber, they force air in and out of the chamber. These airflows are in turn channeled through a specialized turbine, which is used to drive a generator. This type of machine is principally designed for use on or near the shore, or for incorporation into breakwaters. Commercially, this kind of machine is the most advanced and is particularly advantageous when incorporated into coastal protection.

Fixed or semi-fixed machines which utilize the pressure differential in the water that occurs at a submerged point as the wave passes over that point. The pressure differential is used by a variety of means to cause a fluid to flow in a circuit, which is then used to drive a turbine and generator.

Machines which utilize their buoyancy to cause movement in a part of the device as it moves up and down in the wave. The movement is used either directly or indirectly to drive a generator.



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