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What is Renewable Energy?

Renewable energy is energy that is generated from natural resources that are continuously replenished. This includes sunlight, geothermal heat, wind, tides, water, and various forms of biomass. This energy cannot be exhausted and is constantly renewed.

These days, using terms like renewable energy, green energy and clean energy are all becoming more and more common. Most of us are aware that wind energy and solar energy are renewable energy sources. But do you know the other things on the list? Apart from the popular names like wind and solar, there are in fact a ton of renewable energy sources. Mainly, anything that can be used to create energy that will quickly renew is nothing but a form or source of renewable energy.

Firstly, it’s crucial to understand that what conventional energy sources are. Conventional sources have been used from ancient times and include materials like coal, natural gas, oil, and firewood.

You will notice that water, wind, sun and biomass (vegetation) are all available naturally and were not formed. The others do not exist by themselves, they were formed. Renewable energy resources are always available to be tapped, and will not run out. This is why it is also called as “Green Energy”.

When can energy be called Renewable Energy?

If energy can be classified under one of the below categories, then it can be classified as ‘Renewable’.

  • When its source cannot run out (like the sun) or can easily be replaced (like wood, as we can plant trees to use for energy)
  • When their sources are carbon neutral. This means they do not produce Carbon compounds (such as other greenhouse gases).
  • When they do not pollute the environment (air, land or water)

Renewable energy can be converted to electricity, which is stored and transported to our homes for use.

What are the Types of Renewable Energy?

An Overview

Most renewable energy comes either directly or indirectly from the sun. Sunlight, or solar energy, can be used directly for heating and lighting homes and other buildings, for generating electricity, and for hot water heating, solar cooling, and a variety of commercial and industrial uses.

The sun’s heat also drives the winds, whose energy, is captured with wind turbines. Then, the winds and the sun’s heat cause water to evaporate. When this water vapor turns into rain or snow and flows downhill into rivers or streams, its energy can be captured using hydroelectric power.

Along with the rain and snow, sunlight causes plants to grow. The organic matter that makes up those plants is known as biomass. Biomass can be used to produce electricity, transportation fuels, or chemicals. The use of biomass for any of these purposes is called bioenergy.

Hydrogen also can be found in many organic compounds, as well as water. It’s the most abundant element on the Earth. But it doesn’t occur naturally as a gas. It’s always combined with other elements, such as with oxygen to make water. Once separated from another element, hydrogen can be burned as a fuel or converted into electricity.

Not all renewable energy resources come from the sun. Geothermal energy taps the Earth’s internal heat for a variety of uses, including electric power production, and the heating and cooling of buildings. And the energy of the ocean’s tides come from the gravitational pull of the moon and the sun upon the Earth.

In fact, ocean energy comes from a number of sources. In addition to tidal energy, there’s the energy of the ocean’s waves, which are driven by both the tides and the winds. The sun also warms the surface of the ocean more than the ocean depths, creating a temperature difference that can be used as an energy source. All these forms of ocean energy can be used to produce electricity.

Non-conventional (or unusual) sources of energy include:

  • Solar Energy
    • Photovoltaic Systems
    • Solar Hot Water
    • Solar Electricity
    • Passive Solar Heating & Daylighting
    • Space Heating & Cooling
  • Wind Energy
  • Geothermal Energy
    • Geothermal Electricity Production
    • Geothermal Direct Use
    • Geothermal Heat Pumps
  • Bioenergy
    • Biofuels
    • Biopower
    • Bioproducts
  • Hydropower
  • Ocean Energy
  • Hydrogen & Fuel Cells
  • Green Power

Mankind needs to understand that all the conventional sources will soon become rare, endangered and extinct. Also, since they produce lots of carbon dioxide that leads to the greenhouse effect in the atmosphere (uranium leaves different dangerous byproducts), they need to be avoided.

Similarly, we hope that all the non-conventional sources of energy become conventional, common, and every day. They are also free, green and emit no carbon dioxide (with the exception of biomass, but it prevents the production of methane, which is a greenhouse gas 21 times more dangerous than CO2).

Let’s now understand all the above-mentioned energies in detail.

What Type of Energy is Solar?

Solar panels convert the sun’s light into usable solar energy using N-type and P-type semiconductor material.  When sunlight is absorbed by these materials, the solar energy knocks electrons loose from their atoms, allowing the electrons to flow through the material to produce electricity. This process of converting light (photons) to electricity (voltage) is called the photovoltaic (PV) effect.  Currently, solar panels convert most of the visible light spectrum and about half of the ultraviolet and infrared light spectrum to usable solar energy.

Solar energy technologies use the sun’s energy and light to provide heat, light, hot water, electricity and even cooling, for homes, businesses, and industry.

There are a variety of technologies that have been developed to take advantage of solar energy.

Solar Energy Technologies:

  • Photovoltaic Systems
    • Producing electricity directly from sunlight.
  • Solar Hot Water
    • Heating water with solar energy.
  • Solar Electricity
    • Using the sun’s heat to produce electricity.
  • Passive Solar Heating and Daylighting
    • Using solar energy to heat and light buildings.
  • Solar Process Space Heating and Cooling
    • Industrial and commercial uses of the sun’s heat.

What is Wind Energy?

We have been harnessing the wind’s energy for hundreds of years. From old Holland to farms in the United States, windmills have been used for pumping water or grinding grain. Today, the windmill’s modern equivalent – a wind turbine – can use the wind’s energy to generate electricity.

Wind turbines, like windmills, are mounted on a tower to capture the most energy. At 100 feet (30 meters) or more above ground, they can take advantage of the faster and less turbulent wind. Turbines catch the wind’s energy with their propeller-like blades. Usually, two or three blades are mounted on a shaft to form a rotor.

A blade acts much like an airplane wing. When the wind blows, a pocket of low-pressure air forms on the downwind side of the blade. The low-pressure air pocket then pulls the blade toward it, causing the rotor to turn. This is called lift. The force of the lift is actually much stronger than the wind’s force against the front side of the blade, which is called drag. The combination of lift and drag causes the rotor to spin like a propeller, and the turning shaft spins a generator to make electricity.

Wind turbines can be used as stand-alone applications, or they can be connected to a utility power grid or even combined with a photovoltaic (solar cell) system. For utility-scale sources of wind energy, a large number of wind turbines are usually built close together to form a wind plant. Several electricity providers today use wind plants to supply power to their customers.

Stand-alone wind turbines are typically used for water pumping or communications. However, homeowners, farmers, and ranchers in windy areas can also use wind turbines as a way to cut their electric bills.

Small wind systems also have potential as distributed energy resources. Distributed energy resources refer to a variety of small, modular power-generating technologies that can be combined to improve the operation of the electricity delivery system.

How can Geothermal Energy be tapped?

If you remember your school lessons, it states that far beneath us, the earth is hot. The thermal energy that rises from the earth’s core in the form of heat to where we stand on the ground is known as geothermal energy. It’s interesting to know that the word “geothermal” originates from the Greek origin γη (ge), meaning earth, and θερμος (thermos), meaning hot. Geothermal Energy is a very abundant source of energy that has been many times neglected in the clean energy rush. Hopefully, its use will grow over a period of years as it is clean, widely available, and consistent/stable.

Geothermal energy is the heat from the Earth. It’s clean and sustainable. Resources of geothermal energy range from the shallow ground to hot water and hot rock found a few miles beneath the Earth’s surface, and down even deeper to the extremely high temperatures of molten rock called magma.

Almost everywhere, the shallow ground or upper 10 feet of the Earth’s surface maintains a nearly constant temperature between 50° and 60°F (10° and 16°C). Geothermal heat pumps can tap into this resource to heat and cool buildings. A geothermal heat pump system consists of a heat pump, an air delivery system (ductwork), and a heat exchanger-a system of pipes buried in the shallow ground near the building. In the winter, the heat pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat exchanger. The heat removed from the indoor air during the summer can also be used to provide a free source of hot water.

In the United States, most geothermal reservoirs of hot water are located in the western states, Alaska, and Hawaii. Wells can be drilled into underground reservoirs for the generation of electricity. Some geothermal power plants use the steam from a reservoir to power a turbine/generator, while others use the hot water to boil a working fluid that vaporizes and then turns a turbine. Hot water near the surface of Earth can be used directly for heat. Direct-use applications include heating buildings, growing plants in greenhouses, drying crops, heating water at fish farms, and several industrial processes such as pasteurizing milk.

Hot dry rock resources occur at depths of 3 to 5 miles everywhere beneath the Earth’s surface and at lesser 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 heated water from another well. Currently, there are no commercial applications of this technology. Existing technology also does not yet allow recovery of heat directly from magma, the very deep and most powerful resource of geothermal energy.

Many technologies have been developed to take advantage of geothermal energy – the heat from the earth. NREL performs research to develop and advance technologies for the following geothermal applications:

Geothermal Energy Technologies:

  • Geothermal Electricity Production
    • Generating electricity from the earth’s heat.
  • Geothermal Direct Use
    • Producing heat directly from hot water within the earth.
  • Geothermal Heat Pumps
    • Using the shallow ground to heat and cool buildings.

What is BioEnergy?

We have used biomass energy or bioenergy – the energy from organic matter – for thousands of years, ever since people started burning wood to cook food or to keep warm.

Biomass (also known as ‘plant material’) is quite different from all the renewable energy sources mentioned above. Biomass is a renewable source as it gets its energy from the sun (the world’s largest renewable energy source… of course) and can renew or reproduce quickly enough that it is essentially an infinite resource. As we all know, plants retain the energy of the sun. When they are burnt, the stored energy gets released again (so that way, we can make some use of it to create electricity or heat). So, biomass is nothing but a natural type of energy storage. But it needs to be used sustainably, not too fast. It also doesn’t require too much contribution from humans such as fertilizers and pesticides to remain truly renewable.)

And today, wood is still our largest biomass energy resource. But many other sources of biomass can now be used, including plants, residues from agriculture or forestry, and the organic component of municipal and industrial wastes. Even the fumes from landfills can be used as a biomass energy source.

The use of biomass energy has the potential to greatly reduce our greenhouse gas emissions. Biomass generates about the same amount of carbon dioxide as fossil fuels, but every time a new plant grows, carbon dioxide is actually removed from the atmosphere. The net emission of carbon dioxide will be zero as long as plants continue to be replenished for biomass energy purposes. These energy crops, such as fast-growing trees and grasses, are called biomass feedstocks. The use of biomass feedstocks can also help increase profits for the agricultural industry.

Biomass Energy technology applications:

  • Biofuels
    • Converting biomass into liquid fuels for transportation.
  • Biopower
    • Burning biomass directly, or converting it into a gaseous fuel or oil, to generate electricity.
  • Bioproducts
    • Converting biomass into chemicals for making products that typically are made from petroleum.

What is meant by Hydropower Technology?

Hydroelectric power generates about 10% of the nation’s energy. Credit: US Army Corps of Engineers

Flowing water creates energy that can be captured and turned into electricity. This is called hydroelectric power or hydropower.

The most common type of hydroelectric power plant uses a dam on a river to store water in a reservoir. Water released from the reservoir flows through a turbine, spinning it, which in turn activates a generator to produce electricity. But hydroelectric power doesn’t necessarily require a large dam. Some hydroelectric power plants just use a small canal to channel the river water through a turbine.

Another type of hydroelectric power plant – called a pumped storage plant – can even store power. The power is sent from a power grid into the electric generators. The generators then spin the turbines backward, which causes the turbines to pump water from a river or lower reservoir to an upper reservoir, where the power is stored. To use the power, the water is released from the upper reservoir back down into the river or lower reservoir. This spins the turbines forward, activating the generators to produce electricity. A small or micro-hydroelectric power system can produce enough electricity for a home, farm, or ranch.

Hydro energy can be easily tapped from the existing large-scale hydroelectric dams in the country. But then there are also many other methods like small-scale hydro technology, tidal power technology, wave power technology, pumped-storage hydro technology, run-of-river hydro technology, ocean thermal energy technology, marine current energy technology, cosmotic energy technology, and much more! Simply put, water is available in many places and many ways, so the energy from that can be captured using many different types of technology.

How can we use Ocean Energy?

The ocean can produce two types of energy: thermal energy from the sun’s heat, and mechanical energy from the tides and waves.

Oceans cover more than 70% of Earth’s surface, making 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 creates thermal energy. Just a small portion of the heat trapped in the ocean could power the world.

Ocean thermal energy is 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 vapor 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.

Ocean mechanical energy is quite different from ocean thermal energy. 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. As a result, tides and waves are intermittent sources of energy, while ocean thermal energy is fairly constant. Also, unlike thermal energy, the electricity conversion of both tidal and wave energy usually involves mechanical devices.

A barrage (dam) is typically used to convert tidal energy into electricity by forcing the water through turbines, activating a generator. For wave energy conversion, there are three basic systems: channel systems that funnel the waves into reservoirs; float systems that drive hydraulic pumps; and oscillating water column systems that use the waves to compress air within a container. The mechanical power created from these systems either directly activates a generator or transfers to a working fluid, water, or air, which then drives a turbine/generator.

How can we use Hydrogen Energy?

Hydrogen is the simplest element. An atom of hydrogen consists of only one proton and one electron. It’s also the most plentiful element in the universe. Despite its simplicity and abundance, hydrogen doesn’t occur naturally as a gas on the Earth – it’s always combined with other elements. Water, for example, is a combination of hydrogen and oxygen (H2O).

Hydrogen is also found in many organic compounds, notably the hydrocarbons that make up many of our fuels, such as gasoline, natural gas, methanol, and propane. Hydrogen can be separated from hydrocarbons through the application of heat – a process known as reforming. Currently, most hydrogen is made this way from natural gas. An electrical current can also be used to separate water into its components of oxygen and hydrogen. This process is known as electrolysis. Some algae and bacteria, using sunlight as their energy source, even give off hydrogen under certain conditions.

Hydrogen is high in energy, yet an engine that burns pure hydrogen produces almost no pollution. NASA has used liquid hydrogen since the 1970s to propel the space shuttle and other rockets into orbit. Hydrogen fuel cells power the shuttle’s electrical systems, producing a clean byproduct – pure water, which the crew drinks.

A fuel cell combines hydrogen and oxygen to produce electricity, heat, and water. Fuel cells are often compared to batteries. Both convert the energy produced by a chemical reaction into usable electric power. However, the fuel cell will produce electricity as long as fuel (hydrogen) is supplied, never losing its charge.

Fuel cells are a promising technology for use as a source of heat and electricity for buildings and as an electrical power source for electric motors propelling vehicles. Fuel cells operate best on pure hydrogen. But fuels like natural gas, methanol, or even gasoline can be reformed to produce the hydrogen required for fuel cells. Some fuel cells even can be fueled directly with methanol, without using a reformer.

In the future, hydrogen could also join electricity as an important energy carrier. An energy carrier moves and delivers energy in a usable form to consumers. Renewable energy sources, like the sun and wind, can’t produce energy all the time. But they could, for example, produce electric energy and hydrogen, which can be stored until it’s needed. Hydrogen can also be transported (like electricity) to locations where it is needed.

What is Green Power?

Green power is electricity that is generated from resources such as solar, wind, geothermal, biomass, and low-impact hydro facilities. Conventional electricity generation, based on the combustion of fossil fuels, is the nation’s single largest industrial source of air pollution. The increasing availability of green power enables electricity customers to accelerate installation of renewable energy technologies. As more green power sources are developed – displacing conventional generation – the overall environmental impacts associated with electricity generation will be significantly reduced.

Benefits of Green Power

Choosing green power offers a number of benefits to businesses and institutions, including:

  • Environmental stewardship – Many innovative organizations are establishing environmental commitments to make their operations and practices sustainable. Choosing green power is a simple step towards creating a more sustainable organization.
  • Public image – Green power can help improve an organization’s public image by demonstrating environmental stewardship.
  • Customer loyalty – Demonstrating environmental stewardship through green power may help increase an organization’s customer and investor loyalty.
  • Employee pride – Employees prefer to work for companies that give back to their communities and to the environment.
  • Power portfolio management – Because some green power sources have no fuel costs, green power can help protect your power portfolio from volatile prices of fossil-fuel-generated electricity.
  • Power reliability – On-site renewable generation can be a more reliable source of power than power distributed through the electric grid.

The market for renewable energy technologies has continued to grow. Climate change concerns and increasing in green jobs, coupled with high oil prices, peak oil, oil wars, oil spills, promotion of electric vehicles and renewable electricity, nuclear disasters and increasing government support, are driving increasing renewable energy legislation, incentives and commercialization. New government spending, regulation and policies helped the industry weather the economic crisis better than many other sectors. It is the right time that we too start investing for a better future and a better environment.

All this was about renewable energy. Read in particular about one of the major sources of renewable energy – wind energy!

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