Renewable Sources of Clean Power

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WIND


Wind Farm

Wind farms are becoming a familiar sight in many locations globally. These farms consist of dozens, hundreds, and even thousands of individual wind turbines connected to the electrical grid. Wind flowing past turbine blades causes these blades to rotate, and this rotational motion drives electric generators.

Since wind is intermittent and variable, the electricity produced by wind must be supplemented by other sources of steady electrical generation or incorporate battery storage.

Windfarms are located both onshore and offshore. Onshore facilities benefit from lower construction and maintenance costs than offshore installations. They require large tracts of land situated commonly in wild and rural areas and can impact local flora and fauna by reducing natural habitats. Offshore locations generally benefit from steadier and more powerful winds.

As of 2018, wind power produced 4.8% of the global demand for electrical energy, up from 3.5% in 2015. Experts estimate that wind power's share of worldwide electricity production could cost-effectively rise to about 20%.

Wind energy production is generally complementary to solar energy production. Solar generates most of its electricity in the summertime, whereas wind generation tends to peak in the wintertime – together, they somewhat offset each other's seasonal variability.

HYDROELECTRIC


Hydroelectric dam
Hydroelectric dam with the reservoir in the background

Hydroelectricity is a common source of clean energy. The power of moving water drives turbines connected to electric generators to produce electricity. Moving water has been harnessed for centuries to rotate waterwheels to grind wheat to flour, power sawmills and textile factories and numerous other applications.

Three different means are employed to generate hydroelectricity at scale:

  1. The impoundment of water resulting from the use of dams creates water reservoirs. Dams also direct and control the flow of the reservoir water through turbine generators.
  2. Diversion facilities employ a series of channels or canals to direct flowing water to turbine generators.
  3. Pumped-storage facilities use the energy produced by solar, wind, or nuclear to operate large pumps that transport water up to a higher elevation storage reservoir or tank. When the demand for energy spikes, water is released from the reservoir, flowing back down and driving turbine generators to produce electricity.

Hydroelectric dam with the reservoir in the background

Hydroelectricity is a reliable source of energy and produces no harmful waste products. It is also a flexible energy source – throttling the flow of water through the turbines acts to control the amount of electricity generated. And once the hydropower facility is built, the cost to generate electricity is minimal.

However, creating the reservoirs in the first place represents a massive intervention of the local and regional environment, affecting plant and animal life both upstream and downstream of the dams, including the human cost of displacing entire communities. Constructing hydropower dams and facilities are often multi-billion-dollar endeavors that take years to complete. Further, dams slow the flow of water, creating sedimentation problems that can seriously affect operations over time, requiring costly routine remediation efforts. Although the risk is minimal, should earthquakes or substandard design and construction compromise a dam's structural integrity, the consequences can be catastrophic.

TIDAL AND WAVE


Tidal Power Station
Oldest tidal power station,
la rance in bretagne, france -
240 mw electrical generation capacity

Tidal energy and wave energy are intricately linked – both modalities employ the natural movement of ocean water to generate clean, renewable electricity.

During the Middle Ages, Europeans harnessed the power of tidal movements, using the water that pooled at high tides to drive waterwheels for grain mill operation when the tide receded and the pools emptied. Current designs use the power of tidal water to spin turbine generators and produce electricity.

Tidal barrages use dam-like structures to capture water at high tide, employing sluice gates to control water levels and direct flow back through turbine generators during ebb flow. Two-way tidal power systems generate electricity both on incoming and outgoing tides.

tidal tribune

Concerns with such structures include the disruption of the environment in tidal basins and estuaries from rising turbidity in the water (the amount of sediment stirred up and suspended) and fluctuations in water levels. Further, such structures can affect navigation channels and recreational areas.

Tidal turbines are another means to capture the energy of tidal and current motion. They are designed much like wind turbines, using rotating blades to generate electricity. These turbines, anchored to the seabed, are necessarily built much sturdier than wind turbines due to the density of water they operate within.

Wave energy is a well-recognized source of abundant, consistent and predictable renewable energy, especially for the many cities located on or near coastlines.

The scientific community calculates that the theoretical wave energy potential off the coasts of the United States alone amounts to over 2 billion megawatt-hours, representing around 64% of the total US electrical generation in 2018.

Designers have created various methods to harness wave energy. Several designs employ devices anchored to the seafloor and rising to just below the surface of the water. Vertical and elliptical wave motion from bobbing float mechanisms is converted to electricity using linear generators. Other designs incorporate narrowing channels to amplify the height and power of waves to drive turbine generators.

Wave energy
Wave energy converted to electricity using anchored bobbing devices

GEOTHERMAL

The thermal energy stored underground offers a compelling opportunity to enhance power generation in a sustainable and emissions-free manner. A United States Geological Society assessment from 2008 estimates that roughly 40,000 megawatts of power could be generated from known and undiscovered geothermal sources in the U.S. alone.

Aside from using geothermal heat pumps to directly heat and cool buildings, water or steam found at high temperatures of 300 to 700 degrees F (150 to 370 degrees C) arising in either dry steam wells or from hot water wells can generate geothermal electricity. These wells are drilled deep into the earth, up to 2 miles (3.2 kilometers) deep, to pipe the hot steam and water to the surface, powering a turbine to generate electricity.

Three basic types of geothermal power plants generate electricity from the earth's heat.

  1. Dry steam plants employ the steam generated from a geothermal reservoir to drive a turbine generator.
  2. Flash steam plants convert hot water existing at high pressure in underground reservoirs to steam at the surface to drive turbine generators. After the steam condenses to water in the process, it is pumped back underground to replenish the reservoir. These plants are the most common type of geothermal electrical generation facilities.
  3. Binary cycle plants transfer the heat energy from underground water and steam sources to vaporize another fluid to drive turbine generators.

The three types of geothermal power plants are illustrated below.

geothermal power plants

HYDROGEN

Hydrogen is the simplest, lightest, and most abundant element in the universe, consisting of one proton and one electron. Yet, due to its reactivity with other elements, pure hydrogen does not exist on our planet – it must be manufactured from hydrogen-containing compounds such as water and hydrocarbons. Most hydrogen produced today involves reforming natural gas using steam. However, the process releases greenhouse gases.

Renewable, sustainable 'green' hydrogen is produced by electrolyzing (splitting) water into its hydrogen and oxygen components using electricity generated from solar, wind, nuclear or other clean energy sources.

A hydrogen fuel cell combines hydrogen gas with oxygen in the air to produce electricity, heat and water. Fuel cells come in various versions, including polymer electrolyte membrane (PEM), direct methanol, alkaline, phosphoric acid, molten carbonate, solid oxide and reversible fuel cells. Most of these can be used in backup power and distributed generation applications to support existing electrical grids.

hydrogen fuel

BIOMASS

Sourcing organic materials and converting them to energy is what biomass energy is all about. Humans have been availing themselves of such energy for millennia, using wood as the fuel for fire.

biomass source
Courtesy ecoble.com

The combustion of biomass as a fuel source does not add to the net carbon content in our atmosphere. The process only releases carbon recently sequestered by the biomass plant sources (or the animals that eat plants) when they were alive and drawing in atmospheric carbon dioxide. Fossil fuels such as coal and oil, on the other hand, release carbon that was sequestered by plants and organisms living hundreds of millions of years ago, adding to the net atmospheric greenhouse gas content.

Clean burning fuels arising from biomass sources include:

  • Bioethanol created by fermenting carbohydrates from sugar or starch crops such as corn, sugar cane, and sweet sorghum to form alcohol
  • Biodiesel produced from oils and fats, using catalysts to exchange acid molecules for alcohol
  • Biomethane, generated from the natural decomposition of organic materials in landfills and sewage.

Vehicles with the appropriate conversion kits can burn such fuels in place of fossil-derived gasoline and diesel.

NUCLEAR FUSION

A great deal of work is ongoing to develop nuclear fusion as a practical and practically limitless clean energy source operating 24/7 year-round while producing little or no radioactive byproducts. This source of energy should not be confused with nuclear fission, the legacy atomic power option in use globally today that generates hazardous radioactive waste products.

Nuclear fusion is the energy that powers our sun and the stars. Nuclear fusion involves combining two hydrogen atoms at extremely high temperatures to form helium, releasing energy in the process. At scale, the amount of clean, carbon-free energy available from nuclear fusion is immense. Estimates suggest that one glass of water can provide enough fusion fuel to supply the energy requirements for one person's lifetime.

Creating the environment necessary to promote nuclear fusion and generate practical net energy production is an extraordinarily complex technical challenge.

Early designs, like the ITER in France, are massive construction projects costing tens of billions of dollars. However, companies like Commonwealth Fusion Systems and TAE Technologies are developing commercial fusion technologies that are much less costly and significantly smaller in size to serve residential, institutional, and industrial customers and support the build-out of decentralized electric grids.

Commonwealth claims its reactors will produce a net energy return of 10-to-1, meaning that for every kilowatt-hour (kWh) of energy required to initiate and operate the fusion reactor, the reactor will generate 10 kWh of energy in return. Results like these are exciting and promising indeed.

nuclear fusion
Nuclear fusion reactor concept,
courtesy commonwealth fusion systems