Types of Renewable Energy

5 Types of Renewable Energy and Characteristics Explained

Types of renewable energy are; artificially-regenerated, hydrokinetic, thermodynamic, renewable-clean, and renewable-unclean energies.

This article discusses the types of renewable energy and their individual characteristics, as follows;






1). Renewable, Clean Energy (as one of the Types of Renewable Energy)

Renewable, clean energy is a type of renewable energy that, in addition to being replenished naturally, can be harnessed with minimal environmental impact.

It is common for renewable energy to be also called clean energy, because majority of energy resources that are renewable, are also clean and sustainable for the ecosystem.

Not all renewable resources produce clean energy, because some of these resources, like biomass, contain significant amounts of carbon which are released into the atmosphere when it is burnt as a renewable fuel.

Examples of renewable, clean energy are; solar, hydro, wave, wind and tidal. These forms of renewable energy are not associated with any significant level of environmental degradation, either by greenhouse emission, desertification, deforestation, soil, water or air pollution.

Understanding the difference between renewable, clean; and renewable, unclean energies is very important when developing a scheme for energy decarbonization and transition.

In some cases, renewable, clean energy technologies can have some effects on the ecosystem. Examples of this include fouling and limitation of aquatic organic activities by hydro turbines and wave energy converters [4].

Such cases do not negate their status as clean energy systems because the effects do not come from the energy-utilization process itself, and can be mitigated with relative ease, by improving the systems and methods involved.






2). Renewable, Unclean Energy

Nearly all renewable energy resources are also clean, because they come from natural sources and are continuously recycled in the environment without toxic byproducts or waste [6]. This however does not imply that all forms of renewable energy are also clean.

Energy that is renewable but not clean, can be classified as a distinct type of renewable energy called renewable, unclean (or renewable, dirty) energy.

Generally, renewable energy is unclean when its conversion and/or utilization goes along with the emission of greenhouse gases or toxins. Often, this occurs when renewable energy is contained in an energy storage medium like water or renewable fuel.

In such cases, extracting the renewable energy requires the storage medium to be broken down though chemical reactions like combustion. As breakdown occurs, byproducts like carbon dioxide can be emitted.

A classic example of renewable, unclean energy is bioenergy; which can be extracted by the burning of raw biomass, or processed biofuel.

Studies have linked the burning of biofuel for energy, to severe cases of pollution and human health problems [2].

Carbon dioxide and other materials emitted from renewable, unclean energy resources can also contribute to climate change.

Geothermal energy can also be associated with the emission of large amounts of water vapor, which is a greenhouse gas.

It is often argued that these unclean renewable energy forms are carbon-neutral; meaning that all their carbon dioxide emissions are subsequently re-absorbed and recycled by the Earth's natural carbon cycle from which they were originally derived, so that the net emission is zero.

This is true, but can only hold provided the renewable resources are replenished at a rate equal to or greater than the rate at which they are used. For example, bioenergy is only carbon-neutral when biomass fuel is effectively regenerated through measures like reforestation and afforestation.

In real-life scenarios, such absolute and effective regeneration is hardly possible, for reasons like urbanization, negligence, and non-enforcement of regulations regarding bioenergy development. This means that all renewable resources linked to carbon emissions, are likely to have an adverse effect on the ecosystem.

Types of Renewable Energy: Bioenergy as an Example of Renewable-Unclean Energy (Credit: Bureau of Land Management Oregon and Washington 2016 .CC BY 2.0.)
Types of Renewable Energy: Bioenergy as an Example of Renewable-Unclean Energy (Credit: Bureau of Land Management Oregon and Washington 2016 .CC BY 2.0.)







3). Artificially-Regenerated Energy (as one of the Types of Renewable Energy)

Artificially-regenerated energy is a type of renewable energy that is not replenished rapidly in nature, but rather can be used in such a manner that mimics the sustainability of renewable energy.

It is called 'artificially-regenerated' because artificial systems and methods are required to maximize its potential.

A classic example of artificially-regenerated energy is nuclear energy in a breeder reactor.

Breeder reactors recycle nuclear waste continuously, so that radioactive fuel is consumed in a regenerative manner that is similar to the regeneration of renewable resources like biomass.

Uranium-238 in spent nuclear fuel, is non-fissile, and does not produce any energy in conventional nuclear reactors. In breeder reactors, however; bombardment of spent fuel rods with fast-moving neutrons induces an artificial process of rapid radioactive decay, which converts non-fissile Uranium isotopes to fissile Plutonium isotopes [1].

The mechanism described above establishes a seemingly renewable dynamic in the reactor, by allowing a small amount of nuclear fuel to be used, regenerated into a different radioisotope, and re-used.

While nuclear fuel is finite and non-renewable, breeder reactors multiply its potential as an energy source, so that it nearly matches the instantaneous potential of a naturally-renewable resource.






4). Hydrokinetic Renewable Energy

Hydrokinetic energy sources are renewable resources which occur as a result of the motion (kinetics) of water.

Basically, hydrokinetic energy works by the capture of flowing or falling water masses to extract large amounts of kinetic energy (alongside potential and thermal energies) that is converted to mechanical energy in a spinning or oscillating component like a turbine, which is then used to generate electricity.

There is no difference between hydrokinetic energy and hydro energy; as hydro energy is only a form of hydrokinetic energy, alongside wave and tidal energies.

The only form of renewable energy that cannot be described as a core example of hydrokinetic energy is ocean thermal energy. This is because it does not occur by reason of the motion or kinetics of water masses, but rather as a result of solar heating which establishes a thermal gradient in oceans; so that temperature tends to change significantly with depth.

Hydrokinetic energy can be used in any of its various forms, and may offer a flexible option for electricity supply in remote, off-grid locations [3].

Types of Renewable Energy: A Hydro-Power Plant for Harnessing Hydrokinetic Energy (Credit: Flood Risk Management NI 2009 .CC BY-SA 2.0.)
Types of Renewable Energy: A Hydro-Power Plant for Harnessing Hydrokinetic Energy (Credit: Flood Risk Management NI 2009 .CC BY-SA 2.0.)






5). Thermodynamic Renewable Energy (as one of the Types of Renewable Energy)

The concept of thermodynamics is related to renewable energy in that it explains the dynamics of renewable energy in any given system.

For example, we can link the first law of thermodynamics to renewable energy by observing an environmental system in which solar energy is not created or destroyed, but conserved in oceans and air currents, and reflected from the Earth's surface into the upper atmosphere.

However, when we mention thermodynamic renewable energy, we refer to a type of renewable energy that occurs primarily as heat, which may be conserved, converted, or transferred by any of the thermal energy transfer mechanisms including conduction, radiation and convection.

The most prominent example of thermodynamic energy is solar; which is also the ultimate energy form on Earth [5]. Other examples are geothermal and ocean thermal energies.







Types of renewable energy are;

1. Renewable, Clean Energy

2. Renewable, Unclean Energy

3. Artificially-Regenerated Energy

4. Hydrokinetic Renewable Energy

5. Thermodynamic Renewable Energy







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