What is waste heat recovery energy?

Waste heat recovery is the process of capturing and reusing the heat that is generated by industrial processes or combustion, which would otherwise be lost to the environment. This captured heat can then be used to generate electricity, heat buildings, or power industrial processes. Waste heat recovery can be applied to a wide range of industries, including power generation, petrochemical, and manufacturing, and can lead to significant energy savings and reduced greenhouse gas emissions.

Waste heat recovery can be done by using techniques such as thermoelectric generators, Organic Rankine cycle, and Kalina cycle systems, and heat exchangers. These systems can capture waste heat from sources such as flue gases, hot water, or steam and convert it into usable energy.

Overall, waste heat recovery can help to increase the overall energy efficiency of industrial processes, reduce costs, and reduce the environmental impact of these processes.

For Further Reading

Is nuclear energy renewable energy or not?

Although nuclear energy is considered clean energy its inclusion in the renewable energy list is a subject of major debate. To understand the debate we need to understand the definition of renewable energy and nuclear energy first.

Renewable energy is defined as an energy source/fuel type that can regenerate and can replenish itself indefinitely. The five renewable sources used most often are biomass, wind, solar, hydro, and geothermal.

Nuclear energy on the other hand is a result of heat generated through the fission process of atoms. All power plants convert heat into electricity using steam. At nuclear power plants, the heat to make the steam is created when atoms split apart – called fission. Fission releases energy in the form of heat and neutrons. The released neutrons then go on to hit other neutrons and repeat the process, hence generating more heat. In most cases the fuel used for nuclear fission is uranium.

Arguments for nuclear energy as a renewable energy

Most supporters of nuclear energy point out the low carbon emission aspect of nuclear energy as its major characteristic to be defined as renewable energy. According to nuclear power opponents, if the goal to build a renewable energy infrastructure is to lower carbon emission then there is no reason for not including nuclear energy in that list. [1]

But one of the most interesting arguments for including nuclear energy in the renewable energy portfolio came from Bernard L Cohen, former professor at the University of Pittsburg. Professor Cohen defined the term ‘indefinite'(time span required for an energy source to be sustainable enough to be called renewable energy) in numbers by using the expected relationship between the sun (source of solar energy) and the earth. According to Professor Cohen, if the Uranium deposit could be proved to last as long as the relationship between the Earth and Sun is supposed to last (5 billion years) then nuclear energy should be included in the renewable energy portfolio. [2]

In his article, Professor Cohen claims that using breeder reactors (nuclear reactor able to generate more fissile material than it consumes) it is possible to fuel the earth with nuclear energy indefinitely. Although the amount of uranium deposit available could only supply nuclear energy for about 1000 years, Professor Cohen believes the actual amount of uranium deposit available is way more than what is considered extractable right now. In his arguments, he includes uranium that could be extracted at a higher cost, uranium from the sea-water, and also uranium from eroding earth crust by river water. All of those possible uranium resources if used in a breeder reactor would be enough to fuel the earth for another 5 billion years and hence render nuclear energy as renewable energy. [2]

Arguments against nuclear as a renewable energy

One of the biggest arguments against including nuclear energy in the list of renewable is the fact that uranium deposit on earth is finite, unlike solar and wind. To be counted as renewable, the energy source (fuel) should be sustainable for an indefinite period of time, according to the definition of renewable energy.

Another major argument proposed by the opponents of including nuclear energy as renewable energy is the harmful nuclear waste from nuclear power reactors. Nuclear waste is considered a radioactive pollutant that goes against the notion of a renewable energy source. [1] Yucca Mountain is one of the examples used quite often to prove this point. Most of the opponents in the US also point at the fact that while most renewable energy sources could render the US energy independent, uranium would still keep the country energy-dependent as the US would still have to import uranium. [1]

Final words

It seems like at the heart of the debate lies the confusion over the exact definition of renewable energy and the requirements that need to be met in order to be one. The recent statement by Helene Pelosi, the interim director general of IRENA (International Renewable Energy Agency), saying IRENA will not support nuclear energy programs because its a long, complicated process, it produces waste, and is relatively risky, proves that their decision has nothing to do with having a sustainable supply of fuel. [3] And if that’s the case then nuclear proponents would have to figure out a way to deal with the nuclear waste management issue and other political implications of nuclear power before they can ask IRENA to reconsider including nuclear energy in the renewable energy list.


[1] K. Johnson, “Is Nuclear Power Renewable Energy,” Wall Street Journal, 21 May 09.
[2] B.L. Cohen, “Breeder Reactors: A Renewable Energy Source,” Am. J. Phys. 51, 75 (1983).
[3] J. Kanter, “Is Nuclear Power Renewable,” New York Times, 3 Aug 09.

More to Read

1. Renewable energy
2. Nuclear energy

Wind Energy

Wind power is the generation of electricity from wind. Wind power harvests the primary energy flow of the atmosphere generated from the uneven heating of the Earth’s surface by the Sun. Therefore, wind power is an indirect way to harness solar energy. Wind power is converted to electrical energy by wind turbines.

Wind Resource

Several different factors influence the potential wind resource in an area. The three main factors that influence power output are: – wind speed,
air density,
– and blade radius.
Wind turbines need to be in areas with a lot of wind on a regular basis, which is more important than having occasional high winds.

Wind Speed

Wind speed largely determines the amount of electricity generated by a turbine. Higher wind speeds generate more power because stronger winds allow the blades to rotate faster. Faster rotation translates to more mechanical power and more electrical power from the generator.

Turbines are designed to operate within a specific range of wind speeds. The limits of the range are known as the cut-in speed and cut-out speed. The cut-in speed is the point at which the wind turbine is able to generate power. Between the cut-in speed and the rated speed, where the maximum output is reached, the power output will increase cubically with wind speed. For example, if wind speed doubles, the power output will increase 8 times. This cubic relationship is what makes wind speed such an important factor for wind power. This cubic dependence does cut out at the rated wind speed. This leads to the relatively flat part of the curve, so the cubic dependence is during speeds below 15 m/s (54 kph).

The cut-out speed is the point at which the turbine must be shut down to avoid damage to the equipment. The cut-in and cut-out speeds are related to the turbine design and size and are decided on prior to construction.

Air Density

Power output is related to the local air density, which is a function of altitude, pressure, and temperature. Dense air exerts more pressure on the rotors, which results in higher power output.

Turbine Design

Wind turbines are designed to maximize the rotor blade radius to maximize power output. Larger blades allow the turbine to capture more of the kinetic energy of the wind by moving more air through the rotors. However, larger blades require more space and higher wind speeds to operate. As a general rule, turbines are spaced out at four times the rotor diameter. This distance is necessary to avoid interference between turbines, which decreases the power output.

More to Read

Hydro Energy

Hydropower extracts mechanical energy from water, transforming it into electrical energy to generate electricity. Water in the environment often has both gravitational potential energy and kinetic energy, which can generate electricity using a generator. Note that traditionally this does not refer to the energy obtained from flowing water in the form of tides. In the case of obtaining energy from the tides, the term tidal power is used. The amount of potential energy stored in a body of water at a hydroelectric dam is measured using the height difference between the head race and tail race, known as the elevation head (part of the hydraulic head). Roughly 1/6th of the electricity in the world comes from hydropower facilities, while values in the earlier twentieth century were much higher. In some countries around the world, hydroelectricity is the dominant form of electrical power generation.

Countries such as China, Canada, and Brazil are the leaders in total hydroelectricity generation with capacities of 200 GW, 89 GW, and 70 GW respectively. Other notable producers include Russia, India, Norway, Japan, and Venezuela (which is almost completely dependent on hydropower). See the data visualization below for more statistics on hydroelectricity around the world. Figure 2. Photograph of a water wheel in Syria in 1916 used here for irrigation purposes.


Humans have been harnessing energy from water for millennia, although not explicitly for electricity generation. The ancient Greeks used water wheels to grind wheat over 2000 years ago. Hydropower continued to be exclusively converted directly into mechanical power up until the end of the 19th century when electrical dynamos were attached to the shaft to generate electricity. Dynamos were the first type of electrical generator.

Hydroelectricity is generated at a hydroelectric facility which for large-scale generation includes a hydroelectric dam. At these facilities a dam holds back a large volume of water, creating a reservoir. This reservoir holds water at a higher elevation than the water on the downstream side of the dam. Compared to the water in the river, the water in the reservoir has a greater amount of potential energy. When a gate is opened at the top of the dam, the water from the reservoir flows through channels called penstocks down to the turbines. When the water reaches the turbines the potential energy it contains is converted into kinetic energy. This flowing water is then used to turn the blades of the turbine. As the turbines spin, they move a generator and generate electricity.

Although many hydroelectric facilities utilize dams, there are some types of systems that do not use dams and have very little water storage (meaning there is no large reservoir of stored water). These types of systems are known as run-of-the-river systems, and have been gaining popularity as an alternative to large-scale reservoir dams.[7]


Conventional hydroelectric generation relies on a hydraulic head difference created by man-made dams and obstructions. The majority of current hydroelectric generation is conventional and is comprised of hydroelectric dams and tidal dams. Unconventional generation techniques generally rely on flow rate or on a small head differential. These unconventional techniques produce less energy than conventional methods, but also have less impact on the surrounding environment.[7] Some examples of unconventional hydropower platforms are low head hydro, run-of-the-river systems, instream hydro, and kinetic tidal.

Each type of hydroelectric generation method has an associated output classification based on its capacity and are outlined in the table below.[8]

Large> 100 MW
Medium15 – 100 MW
Small1 – 15 MW
Mini100 kW – 1 MW
Micro5 – 100 kW
Pico~ 200 W – 5 kW

Benefits and Drawbacks

Hydroelectric power stations produce significantly fewer greenhouse gas emissions than other electricity generation options, such as the combustion of fossil fuels.[9] The cost of operation once the dams and reservoirs are built is relatively inexpensive and these facilities can operate at very high efficiencies.[3] However, the construction of these dams and reservoirs can result in habitat loss for aquatic species and an increase in greenhouse gas emissions due to the decomposition of organic matter in the newly flooded reservoirs.[9] For more information on the ecological impacts of hydropower facilities, see: water quality degradation and environmental impacts of hydropower.

The mechanical energy derived from hydropower is considered high-quality energy and can be converted to electrical energy with near 100% efficiency. This is because there are minimal amounts of thermal energy transformation involved, though there are still minor losses associated with friction and inefficiencies in the transportation of electricity (as a result of factors such as resistance in transmission lines). Overall, this means energy from water can be converted to electricity and delivered to the end-user with efficiencies higher than 90%.

For Further Reading

Geothermal Energy

Geothermal energy is a type of renewable energy that is generated by harnessing the heat from the Earth’s core. It is generated by tapping into the Earth’s internal heat, which is produced by the decay of radioactive materials and the gradual cooling of the Earth’s core. This heat can be used to generate electricity or to heat buildings. Geothermal power plants use the Earth’s natural heat to generate electricity, while geothermal heating systems use the heat to warm buildings.

More to read

Renewable energy
Wind energy
Hydro energy
Biomass energy
Solar energy

Biomass Energy

Biomass Energy

Biomass energy is a form of renewable energy that is generated from organic materials such as plants, crops, and waste products. These materials are burned to produce heat, which can then be used to generate electricity or to power vehicles and industrial processes. Biomass energy is considered to be a renewable energy source because the materials used to generate it can be replenished over time, unlike fossil fuels which are finite resources.

For Further Reading

Nuclear Energy

Nuclear energy is the one type of energy that can be released from the nucleus of an atom. There are two ways to produce this energy, either by fission or fusion. Fission occurs when the atomic nucleus is split apart. Fusion is the result of combining two or more light nuclei into one heavier nucleus.

Atoms are made up of several parts: protons, neutrons, electrons, and a nucleus. A nucleus is the positively charged center of an atom. Protons are positively charged particles, and neutrons are uncharged particles. Electrons orbit around the nucleus and are negatively charged. Fission can occur in two ways—first, in some very heavy elements, such as rutherfordium, the nucleus of an atom can split apart into smaller pieces spontaneously. With lighter (lower atomic weight) elements, it is possible to hit the nucleus with a free neutron, which will also cause the nucleus to break apart, and a significant amount of energy is released when the nucleus splits. The energy released takes two forms: light energy and heat energy. Radioactivity is also produced. Atomic bombs let this energy out all at once, creating an explosion. Nuclear reactors let this energy out slowly in a continuous chain reaction to make electricity. After the nucleus splits, new lighter atoms are formed. More free neutrons are thrown off that can
split other atoms, continuing to produce nuclear energy.

Figure: Nuclear Fission and fusion.

Nuclear energy can be used for various industrial applications, such as seawater desalination, hydrogen production, district heating or cooling, the extraction of tertiary oil resources, and process heat applications such as cogeneration, coal-to-liquids conversion, and assistance in the synthesis of chemical feedstock. A large demand for nuclear energy for industrial applications is expected to grow rapidly on account of steadily increasing energy consumption, the finite availability of fossil fuels, and the increased sensitivity to the environmental impacts of fossil fuel combustion. With increasing prices for conventional oil, unconventional oil resources are increasingly utilized to meet such growing demand, especially for transport.

Nuclear Power

Nuclear binding energy is the energy required to split a nucleus of an atom into component parts. The term nuclear binding energy may also refer to the energy balance in processes in which the nucleus splits into fragments composed of more than one nucleon. If new binding energy is available when light nuclei fuse, or when heavy nuclei split, either of these processes results in releases of the binding energy. This energy, available as nuclear energy, can be used to produce electricity (by nuclear power plant) or as a nuclear weapon.

Currently, at nuclear power plants, the heat to make the steam is created through nuclear fission which releases heat. In a nuclear power plant, uranium is the material used in the fission process and the heat from fission is used to create steam to turn a turbine which, in turn, produces electricity. However, nuclear energy can be as hazardous as any fossil fuel in terms of destruction of the environment and deserves some comment insofar as an appreciation of its use may assist in the general background and aid in putting fossil fuel resources into a more complete context.

Nevertheless, as long as suitable safety regulations are applied, energy from nuclear sources has shown potential to be a significant energy source in the future. The technology is known but has suffered some setbacks. Accidents and dubious claims of the ease with which energy may be derived from nuclear sources have reduced the credibility of the nuclear industry. Nevertheless, the potential still exists for the extraction of energy from nuclear sources. Hence, the continued use of the so-called conventional fuel resources is derived from the remains of ancient plants and animals. Those same resources have been instrumental in the phenomenal expansion of the industrialized world. And also, those same resources can have serious adverse effects on the flora and fauna (including man) of the world.

More to Read

Nuclear power plant
Renewable energy
Solar Energy
Wind energy
Hydro energy
Biomass energy
Geothermal energy

Renewable Energies

Renewable Energy

Renewable energy also called alternative energy or clean energy is the useable power that comes from renewable sources, such as the sun, wind, rivers, hot springs, tides, and biomass. Types of renewable energy include electric power generated by wind turbines, solar PV panels, biomass, waste-to-energy, and hydroelectricity [1, 2, 3]. While renewable energy is often thought of as a new technology, but the use of renewable energy has been started a long time before. Especially, harnessing the energy from nature has been used for heating, transport, lighting, and much more.

Renewable sources of power are traditionally included hydropower, land-based wind power, and solar PV. The emerging resources – such as marine, off-shore wind, and geothermal – will make a great impact on a sustainable energy future. Innovations and expanding renewable sources of power are critical for maintaining sustainable levels of power and protecting our planet from climate change. Supporting renewables, or using renewables at home, can speed the shift toward a cleaner energy future [1, 4, 5].

By tapping into natural heat beneath Earth’s surface, geothermal power can be used directly to heat homes, or for generating electricity. Geothermal heat can be captured and used to produce geothermal power using steam, which comes from pumped hot water beneath the surface, then rises to the top and can be used to drive turbines [4, 5, 6].

Hydroelectricity is generally more reliable than solar or wind energy (especially if it is tidal, not river-based), and also allows the energy to be stored to use when demand hits a spike. Another form of hydropower, which uses tidal streams twice daily to power turbine generators. In some situations, hydro may be most feasible as a commercial power source (depending on type, compared with other sources), but depending greatly on type of facility, can be used for off-grid, home-based generation. Commercial-grade wind energy generation systems can provide energy for a variety of different organizations, whereas individual wind turbines are used to help augment pre-existing power organizations. The term renewable expresses the nature of this kind of energy, which is available in spontaneously generated, infinite quantities, which are continuously renewed by nature, without any human interference. For example, a paper addressing development and characterization of a material to be used in a renewable energy system, without any measurements of the energy this new material would convert, would not qualify [5, 6, 7, 8].

By 2015, approximately 16% of total global electricity came from large hydroelectric plants, while other types of renewable energy such as solar, wind, and geothermal comprised 6% of total electrical production. In comparison, renewables at the start of the 21st century represented almost 20 percent of the global energy use, mostly derived from the traditional use of biomass, such as wood, for heating and cooking. Now that we have more innovative, lower-cost ways of harnessing and storing wind and solar power, renewables are becoming an even bigger power source, accounting for over an eighth of US generation. Hydropower is the nation’s largest source of renewable energy, although wind power is expected soon to supplant it [3, 4].

Businesses that have sustainability goals are also driving the growth of renewables, either through building their own facilities (e.g., solar rooftops and wind farms), procuring renewable energy via PPAs, and purchasing Renewable Energy Certificates (RECs). Some states are also including carve-outs–requirements that a specific proportion of the portfolio come from a particular source of power, such as solar–or other incentives to promote the development of particular resources. Renewable portfolio standards require electricity utilities to supply a specified percentage of their electricity from renewable or alternative energy sources by a specified date. Renewables are generated locally using systems or devices in place at where power is used (e.g., photovoltaic panels on public buildings, geothermal heat pumps, biomass-fueled combined heat and power) [9, 10].

Different types of renewable energy:

There are five major renewable energy sources, which are:


Solar Energy

Solar energy is the most common form of renewable energy. Solar energy is harnessed from the sun as a form of solar radiation, using the radiant light and heat from the Sun for practical purposes. The term solar power either is used synonymously with solar energy or is used more specifically to refer to the conversion of sunlight into electricity. Solar power is also called solar power.

The Sun is the most prominent source of energy in the solar system. The source of solar energy is the process of thermonuclear fusion in the core of the Sun. This energy is radiated from the sun in all directions, and a fraction of this energy reaches to the earth. The outer visible layer of the Sun (the photosphere) has a temperature on the order of 6,000 degree C (10,800 degree F). Above the photosphere, there is a transparent layer of gases known as chromospheres. The light emitted by the chromospheres is of a short wavelength. Finally, there is the corona. The corona is the outer part of the atmosphere of the Sun – in this region, the prominence appears. Prominence is immense clouds of glowing gas that erupt from upper chromospheres. The corona can only be seen during the total solar eclipse.

The Earth receives solar energy in the form of solar radiation. These radiations are comprised of ultraviolet, visible, and infrared radiation. The amount of solar radiation that reaches any given location is dependent on several factors like geographic location, time of day, season, land scope, and local weather. Because the Earth is round, the Sun rays strike the Earth’s surface at different angles ranging from 0 to 90 degrees. When the rays of the Sun are vertical, the Earth receives the maximum possible energy.

Generally, almost all renewable energies, notably excluding geothermal energy and tidal energy, derive their energy from the sun. For example, winds blow partly because of the absorption of solar radiation by the atmosphere of the Earth. Solar energy radiant light and heat from the Sun are harnessed using a range of ever-evolving technologies such as solar heating, solar photovoltaics, solar thermal electricity, solar architecture, and artificial photosynthesis.

Technologies for harnessing solar energy

There are many technologies for harnessing solar energy within these broad classifications:
(i) active solar energy,
(ii) passive solar energy,
(iii) direct solar energy,
and (iv) indirect solar energy.

Active solar energy systems use electrical and mechanical components such as tracking mechanisms, pumps, and fans to capture sunlight and process it into usable outputs such as heating, lighting, or electricity. On the other hand, passive solar systems use non-mechanical techniques to control the capture of sunlight and distribute this energy into usable outputs such as heating, lighting, cooling, or ventilation. These techniques include selecting materials with favorable thermal properties to absorb and retain energy, designing spaces that naturally circulate air to transfer energy, and referencing the position of a building to the Sun to enhance energy capture. In some cases, passive solar devices can have a mechanical movement with the important distinction that this movement is automatic and directly powered by the Sun.

Direct solar energy generally refers to technologies or effects that involve a single-step conversion of sunlight that results in a usable form of energy, while indirect solar energy generally refers to the generation of energy using technologies or effects that involve multiple-step transformations of sunlight that eventually result in a usable form of energy.

More to read:

Renewable energy
Wind energy
Hydro energy
Biomass energy
Geothermal energy