Green Energy Means Renewable Energy Environmental Sciences Essay

Green energy means renewable energy that is vast alternative for the use of fossil fuels such as petroleum. Other conventional method used to provide electricity is such as geothermal, biomass, ocean, solar, wind, hydro, hydrogen fuel cells and etc. Biomass energy is derived from the wastes and animal dung either by burning it or just leaving the wastes to lay off by itself to get biofuel or biogas. Ocean energy is gained from the sea and there are two types of them such as thermal energy and mechanical energy. Hydrogen must go through reformation process or electrolysis process to be able to use for the fuel cells to provide electricity. The objective of the project is to choose seven types of renewable energies and explain its applications and advantages in detail.

1. Introduction

Green energy is sustainable energy, which means meeting the needs of the present without compromising the future[2]. These alternative energy sources are said to be not harmful to humans and environment and also arenon polluting energy sources. It basically reduces pollution and the impact on the environment that the existing energy source is causing now and in the past by conventional energy sources such as fossil fuel, coal and wood. These are non renewable energy sources, also known as the brown energy[1]. These sources are mainly used in the production of electricity, heating and fuel for boilers. They cause excessive amount of pollutants, such as carbon monoxide and nitrogen oxides, together with particles that could harm humans. These pollutants are the main contributors to the greenhouse gases that cause global warning. Brown energy are also types of sources that are typically reducing on our earth, which means it could not be re-produced to be used in future. The main aim for this study on green energy is to literate the reader on what is green energy and the importance of these energy to substitute our current conventional energy resources. These report is also to identify the main types of green energies available for the current technology practised in our world today with the history of energy development that brought to the practice of green energy.

2. Green Energy

Sources of green energy come from the nature itself, being free to be harvested. They are mainly derived from the sun (solar power), wind and water. Wind turbines have been used since old times to grind grains, where the term “windmill” is derived from. A more expensive source would come from nuclear and bioenergy (biofuel and biogas).

Nuclear power is also categorized in green energy as it does not produce greenhouse gases. Waste from nuclear power plants are problematic and dangerous to be handled as it takes hundreds to thousands of years to decay before reaching the level that is not harmful to humans, plants and the animals. But in order to completely wipe out the usage of fossil fuels to produce electricity, the number of nuclear plants has to be increased so that greenhouse gases emissions can be cut down massively.[3] Energy from sun, wind and water are continuous but inconsistent. Rainy days that could affect solar power production and droughts that would affect water levels in dams are the main drawbacks of these energy sources.

As renewable energy is sometimes inconsistent, excellent storage capacity is needed to store energy that are produced. It is usually windier in the night time, but the demand would be lesser. Nuclear plants generate so much power at a particular time that they cannot be used at once. So large battery banks are required in order to mesh with the electricity system and provide a consistent power supply.

2.1 History of Energy Development

The history of energy consumption of human being dates back to 3000 BC where the Mesopotamians used petroleum to caulk ships and to build roads. Coals were used during the Bronze Age to heat up iron and shape them, as well as in the Roman culture. This long history of non-renewable energy usage has urged the emergence of green energy to replace them in order to keep the future generation safe.[4]

2000 B.C.

Crude oil was used to light lamps and heat up homes by the Chinese.

200 B.C.

Salt produced from brine using natural gas from underground by Chinese.

600 B.C.

Static Electricity found by Thales of Miletus by rubbing amber.

250 – 400 A.D.

First water-powered Mills built by the Romans

600 A.D.

Greek Fire was invented by the Persians and Arabs, a form of burning liquid used greatly in the Byzantine Empire as weapon.

500 – 900 A.D

Windmills were built to pump water and grind grains by the Persians.

Late 1500s

Coal was imported greatly by US, up to 108,000 tons until the 1800’s.

1700s

A kite that transmitted electricity through its wet cord was found by Ben Franklin. A breakthrough in electricity discovery.

1800-1826

US had the first electric utility.

Mid 1800s-1950

Wood as the primary source of fuel, but decreased after the shift back to coal.

1870-1880

Gas and alcohol using first combustion engine. First U.S. power plant to produce electricity opened (Thomas Edison’s Pearl Street Station)

1888

First wind turbine generating electricity in Cleveland, Ohio.

Early 1900s

Geothermal used to produce electricity commercially by the Italians

1938

Nuclear Fission discovered by the Germans.

1940-1950

The Atomic Energy Act implementation and the first electricity were produced by using nuclear power.

1950s

First silicon solar cell was invented (solar photovoltaic).

1960s

National Environmental Policy Act and Clean Air Act in US implementation to protect the environment and reduce pollution.

1970s

Department of Energy (DOE) were formed. Water from power plant was controlled with Clean Water Act in 1972.

1974

Development of renewable energy was initiated and supported by the National Renewable Energy Laboratory.

1980s

First wind farm built in the United States.2.2 Giga watts of power produced in California.

1990s

Natural gas was used in almost 50percent of homes in US for heating.

Towards the Greener Solution

Till 2007, 24 states adopted policies for increasing the production of renewable energy.

2.2 Importance of Green Energy

Research from scientific evidence are showing that what this present generation is doing will impact the environment in the next 50 – 100 years. The fact that only one earth is known by human being urges government and private sectors to find solutions to reduce pollution and having a lifestyle that is more eco-friendly. A few reasons on why green energy is important.

Non renewable fossil fuels burning are causing greenhouse gases that cause global warming. Carbon dioxide, methane and nitrogen oxides are released into the atmosphere, dissolving into raindrops and causing acid rains. Acid rains damages crops, plants and forests. Aquatic organisms are also affected by this as lakes and rivers pH levels are altered. Human built structures such as steel bridges, marble statues and limestone buildings are being eroded by acid rain.[10]

Figure 3 is a pie chart showing the anthropogenic greenhouse gas emissions in the U.S. by gas type.

Fossil fuels such as oil and coal are also supply that is not endless. Sooner or later the supply will vanish and unavailable for future generations.

Wind, water and solar energy are constant, sustainable and 100 percent clean energy. It does not cause negative impact on environment such as pollutant and waste. This energy type is free as well.

Humans would benefits in health as reduced pollutants would provide cleaner and more breathable air. Lands would be saved as waste management is not necessary. Cleaner water for domestic usage and aquatic organism a would be available.

Jobs opportunity would arise in rural areas as most renewable energy plants are located far from cities. Regional development also would benefit from this.[8][9]

3. Types of Green Energy

3.1 Biomass

Biomass is derived from farm wastes, animal wastes, plant oils, crops and some kind of garbage [11]. Energy that is generated from the wastes is called bio power or bioenergy [11]. Biomass can be processed further to obtain biofuels or burned directly to obtain bioenergy[11]. The energy obtained from burning the wastes can be converted into heat, electricity and mechanical energy [1].

3.1.1 Types of biofuels

Solid form – it’s obtained from the burning of organic material such as animal wastes, wood, grain and other types of garbage’s [11].

Liquid form- it’s obtained straight from the plant and does not involves any burning of material [1]. Biodiesel can be taken as an example for this type of form. It is extracted from vegetable oils or animal fats [11].

Gas form – it’s obtained from organic waste such as dead plant and animal wastes when the organic material breakdown naturally without the need of oxygen [12]. Biogases consist of methane that is essential in terms of natural gas [12].

3.1.2 Application of biomass

Widely used in transportation in the form of gases

Electricity generation plants

Gas produced from the biomass gasifier must be cleaned first before cooling it down and use it as a fuel to run an IC engine that is coupled together with the generator [13].

Heat application

Biomass is used as a fuel to provide energy for the fuel-fired furnace that is often used for high end outputs such as[13 ]:

Forging furnace

Ovens

Kilns

Dryers

Small boilers

Direct fire process heater

Re-rolling mills

3.1.3 Benefits of biomass energy

Biogases that are used as fuels gives more mileage for cheaper price compared to fossil fuels

Energy from biomass has got no ending to it since human throw wastes in daily basis and animals also constantly produce muck

Energy gained from burning the wastes releases carbon dioxide to the atmosphere and the carbon dioxide that is released from the burning is useful for the plants in terms of photosynthesis process.

Each country has their wastes in terms of plants, animals dung and garbage’s, these materials is available locally. This can reduce the need for foreign investors in the country thus improve the nation economically as well

Biomass in mass production can reduce the increase in global temperature significantly.

3.2 Ocean energy

Ocean energy is gained from the sea. There are two types of energy gained from the ocean such as thermal energy and mechanical energy [15]. Thermal energy is gained by the difference in temperature between the warmer surface of the ocean and the deep cold ocean water [15]. Mechanical energy is gained from tidal and wave that is used to rotate the turbine to provide electricity in most of the power plants available [15].

3.2.1 Types of energy gained

3.2.2 Thermal energy

The difference between the temperatures should be around 38 Degree Fahrenheit in order to build a power plant that can fully utilize this temperature difference to make energy [16]. There are 3 types of cycles involved in electricity conversion system from the heat energy such as:

Closed cycle – The heat at the surface of the ocean water is used to vaporize an ammonia type of fluid which has low boiling point and the vapor expands to turn the turbine to produce electricity [15].

Open cycle – The sea water in this case is kept at low pressure in order to force it to boil at low temperature and the steam produced from the sea water is then used to rotate the turbine to activate the generator to produce electricity[15].

Hybrid – The combination of both open and closed cycles is used to rotate the turbine in a most economical way [15]

3.2.3 Mechanical energy

Tidal energy – it’s gained as the earth rotates and the gravitational pull of the moon. The principle of tidal energy is when the tides is at high point the water is trapped in the dam and as the tides began to reach the low point, the trapped water is released to rotate the turbine at high speed to generate electricity[15]. The concept is similar to hydroelectric power plants [6].

Wave energy – Existing kinetic energy from the movement of the waves is used to power up the turbine [15]. The concept is simple that the waves from the ocean comes into the chamber from the right, as the rise of the waves will force the air to release from the chamber and the released air is the one that will rotate the turbine to provide electricity as shown in the figure 1 below[16]. The higher the waves, higher are the rotation of the turbine.

http://www.energyquest.ca.gov/story_old/images/chap14_wave_2007.gif

Application of wave energy [16]

3.3 Hydrogen and fuel cells energy

Hydrogen best identified as the simplest component [18]. One proton and one electron are the sub elements inside an atom of hydrogen [18]. It has a limitation is that it doesn’t appear by its own in the earth. Hydrogen atom always combined together with other elements such as water [17][18]. The molecular weight of hydrogen is 1kmol and the lightest weigh among all the other natural components available in earth. Hydrogen can be separated from hydrocarbon by heating process and this is called reformation process [18]. Electric current also used to separate hydrogen from water and the separation process is called electrolysis [18].

Fuel cells function is to convert hydrogen to electricity directly without any other processes in between [18]. Reformation of methanol, gasoline and natural gas can provide hydrogen for the usage of fuel cells [18]. Methanol can be used directly for some fuel cells without any reformation process [18].

3.3.1 Applications of hydrogen and fuel cells

NASA used liquid nitrogen as a fuel for the space shuttles and other rockets. Liquid nitrogen does not emit any harmful material after the combustion [18]. The product of the conversion by hydrogen fuel cells is pure water that is used as drinking water by the astronauts [18].

Hydrogen powered vehicles is among the growing applications of energy since hydrogen fuel cells capable of providing power for buses[21]. Fuel cells also can provide electricity for a residential housing area that is big as a traditional AC unit [21]. It can operate 24 hours a day and 7 days a week.

3.3.2 Advantages of fuel cells

Efficient conversion of energy from hydrogen to electricity without any combustion taking place and the byproduct is water[19][20]

The noise level created from an operation of a fuel cell relatively much more quiet than the conventional motors[20]

Easier maintenance since less moving parts[20]

Life span is longer than a battery since it has no memory effect when its refueled[10]

The source for fuel cells are hydrogen and it is available with water[20]

Can reduce the nation’s usage of fossil fuels since fossil fuels come at higher price than hydrogen that is naturally available in the earth [20].

3.4 Geothermal Energy

Geothermal energy is a form of thermal energy stored by generation of heat from radioactive decay of minerals occurring inside the earth (80 percent) and from the original formation of the planet (20 percent).[6] Due to the temperature differences between the earth core and surface, continuous heat transfer occurs from the core to surface. Radioactive decaying of natural materials such as uranium and potassium that occurs at the core creates a temperature reaching over 5000 degree Celsius and very high pressure.[7] This high temperature and pressure causes melting of surrounding cooler rocks and these results in the formation of magma. This magma then heats up the rocks and water in the crust which can go up tp 370 degree Celsius.[6] In the range of 10kilometers of earth surface contains heat energy that is 50000 times more than all the oil and natural gas sources in the world.[7] The typical place that usually spots geothermal activities is regions with active volcanic activities. This usually occurs at places where the earth crust is thin enough to let the heat out. Earthquake and magma movements breaks up the rocks covering and allows water to circulate, producing natural hot springs and geysers as the heated up water reaches the surface. As these hot and pressured water forms a reservoir type of containment underground, wells are usually constructed to harvest electricity or heat.

3.4.1 Applications

Steam produced from the reservoir containing pressured and hot water are usually used to power turbines in power plants that generates electricity (Steam Turbine), while other power plants uses the hot water in the reservoir to boil a working fluid that vaporizes and moves a turbine. Heat produced by hot water near to the earth surface can be directly used for heating purpose. The applications that utilizes these direct heat includes heating buildings and homes purpose, growing plants in greenhouses, drying crops, heating water at fish farms, and also in pasteurizing milk processes at milk industries. This is done by using geothermal heat pumps. There is also formation of hot dry rocks, usually 4-10kilometers from earth surface. Technologies is existing to inject cold water onto these hot dry rocks, circulating them through the cracks of the rocks and drawing back the heat from another well located at the end of the water circuit.[5]

http://www.bbc.co.uk/schools/gcsebitesize/science/images/131_geothermal_energy.gif

Water pumped down through injection well and collected at production well.

http://www.ucsusa.org/assets/images/ce/geopower3.gif

How geothermal heat used to power turbines.

3.5 Hydropower

Hydro means water, so hydropower basically is the power that derived from the force of moving water and generates electricity at damn by water falling throughout the turbines. [22] The fall of water and movement is part of a constant ordinary cycle known as water cycle. Water in the earth’s ocean and rivers evaporates by energy from the sun and draws it ascendant as water vapour. Once the water vapour reached the cooler air in atmosphere, it automatically abbreviates and forms as clouds. [23] Hence, the moisture fall to earth as rain and fill the water in oceans and rivers. The moving of water from higher ground to the lower ground with the gravitational force and it drives the water extremely powerful to assist generates electricity for daily usage of human being.[23] Hydropower is a one of the world’s biggest source of renewable energy and play important role or facing challenges during period of climate vary. [24] Hydropower also is considering clean energy source because it does not release any toxins to damage the environment. [25]

Figure 3.1: Water cycle diagram

3.5.1 Types of Hydropower

Hydropower is primarily used to generate electricity. There are few types of hydropower which is common usage in world.

Micro hydro: provide few hundred kilowatts to remote villages, homes and small industries.[26]

Pumped-storage hydroelectricity: stores the water that has been pumped during low demand and generates it when demand is high.[26]

Run-of-the-river hydroelectricity: it will capture the kinetic energy in rivers without using dams.[26]

Conventional hydroelectricity: power comes from the potential energy of dammed and water drives the turbine to generate electricity.[27]

The most common type of hydropower that has been used is conventional hydroelectricity known as hydroelectricity power plant which is uses a dam on a river to store water in a reservoir. This power station is usually placed in hill areas so can build dams easily and can obtain larger water reservoir and generate huge quantity of electricity. [28]

3.5.2 How is hydroelectricity power produced?http://cwc.gov.in/Kids%20Corner_files/hydropower.gif

Figure 3.2: Simple Hydropower station diagram

In hydropower station, the potential energy that stored in body of water at a given height is converted to kinetic energy which is used to rotate the turbine and produce electricity. [28]

In the generation of electricity by using hydroelectric power, water is accumulated or stock up at higher level and guide descending through large pipes to lower level known as penstock. [29] Once the water reaches the end of the penstock with higher pressure it will hits and drives the turbine to create mechanical energy from kinetic energy. Turbines rotate the connected to shaft which is turn the generator and change mechanical energy to electrical energy. [9] Inside the generator there is rotor that covers by turbine. Large electromagnets are attached to the rotor located within coils of copper wires called as stator. Flow of electrons is formed in the coils of stator when a generator rotor spins the magnets. [31] This produces electricity that can be step up in voltage through the station transformers and centre cross transmission lines. Therefore, transmission line conducts electricity from hydropower plant to the distribution system. There are certain advantages and disadvantages of using hydroelectric power station:

Advantages

It is constantly renewable remaining to the habitual nature of the hydrologic cycle.

The water that been used for generation of electricity can be utilize for irrigation, boating and fishing, kayaking and etc.

Fuel is not burned so there is minimal pollution and no waste is produced

Using water to run the power plant that provided free by nature

Disadvantages

Only at limited places hydropower plant can be constructed.

Dams are expensive to build.

Possibility of dam collapsing

3.6 Solar energy

Solar energy is the radiant energy emitted by the Sun that is converted into thermal or electricity energy for homes and industry usage. The amount of energy falling on the earth is given by the solar constant, but very little use has been made of solar energy. [32] Renewable and sustainable energy source such as solar energy make use of it around the world to produce electricity for number of different purpose and its use is both environmentally-friendly and cost-effective over the long term. There are varieties of technologies that have been used to take benefits of solar energy. Types of technologies such as photovoltaic system is common have been used to develop solar energy for daily and powering numerous applications. [33]

Photovoltaic system (PV) is solar cells or panels directly convert sunlight into electricity. [34] The conversion of sunlight directly into electricity (DC) will be done by solar cells. Electricity from solar cells is stored in the battery for instant or future usage and where an inverter is required to change the Direct Current (DC) to Alternating Current (AC) to power the most AC appliances. [35] Photovoltaic system solar cell made of semiconducting materials that related to those used in computer chips. Once the rays are engaged by these materials, the solar energy knocks electrons loose from the atoms, via allowing the electrons to flow through the material to produce electricity. This process of converting light (photon) to electricity (voltages) is called as photovoltaic (PV) effect. [36] The simple of photovoltaic (PV) system illustrated in figure below that can explain about it.A diagram of how the components of a PV system interact with each other.

Figure: Simple Photovoltaic (PV) system with components

The electricity that generated can be stored or directly utilize by photovoltaic standalone system, or a huge electricity grid powered supplied by central generation plants (photovoltaic grid-tied system), or else joint with single or numerous domestic electricity generations to supply into small grid (photovoltaic hybrid system). [37] Supplying of DC and/or AC electrical load that operate independently of the electric utility grid is designed by standalone photovoltaic system. Direct-coupled system is of the simplest type of standalone photovoltaic system that the DC output of a module or array is directly connected to a DC load (figure). [38] When there is no electrical energy stored in batteries in direct-coupled system, the load can operates during the sunlight. So, common applications that used for example water pumps, ventilation fans and small circulation pumps for solar thermal water heating systems are appropriate. [38]A diagram of a stand-alone photovoltaic system.

Figure: Direct coupled PV system

Hybrid system only integrates more than one generating source, which may use an engine-generator, wind, or utility power as a supplementary power source. Initially the battery store is recharged by the photovoltaic system once insufficient the generator charges the batteries.

Solar Hybrid System

Figure: Photovoltaic hybrid system

Grid tie photovoltaic system is deliberate to work with utility grid power. Direct Current (DC) power from the Photovoltaic array into Alternating Current (AC) power is converted by the inverter. AC appliances or local utility company can make use of the direct AC power.Solar Grid-Tie System

Figure: Photovoltaic Grid Tie system

3.7 Wind Energy

Wind energy is the renewable power or energy which comes from the air that flowing across the earth’s surface. Wind energy is a converted form of solar energy. [40] Wind is exist due to uneven heats of the atmosphere by sun, the irregularity of the earth’s landscape and rotation of the earth.[41] Movement of air from region of higher pressure level to region of lower pressure level is also known as wind. When hot air increases, the atmospheric pressure will reduce at earth’s exterior, and the cooler air will travel in to fill up the void. In fact, flow of wind patterns are personalized by earth landscape, vegetative cover and bodies of water. One of the fastest growing sources of electricity and fastest growing markets in the world today is wind energy because is green power, sustainable, affordable, and economic development. [42] In wind turbines there are consist of horizontal and vertical axis wind turbines been designed for rotation function.

3.7.1 How a wind energy or wind turbine is work?

Terms of “wind energy” or else “wind power” illustrate the generation of mechanical power or electricity by using wind. Air has mass when it is in motion, and it contains the energy of that motion, known as kinetic energy. [40] Therefore wind turbines are usually use to harvest the kinetic energy and convert it by using inverter into utilizable which can provide electricity for home, business applications and for sale to utilities. Wind turbine also produce mechanical energy that harvested from kinetic energy to drive machinery, for instance grinding grain and pumping water, the device called as windmill or wind pump in rural place. wind energy diagram

Most common method to generate electricity is by using wind turbines. Figure 1 is explaining the simple understand on working principle of wind turbines. Explanation from the figure 1, wind will turn the large turbine blades; the turning energy will spins a generator shaft and produces electricity. The electricity that produced by wind turbine is Direct Current (DC) and it cannot use because household appliances and use Alternating Current (AC). Hence, inverters connect to wind turbines to the mains power of a building and used to convert the DC electricity into useable AC electricity. [43] Small-scale of wind energy does not use inverters, as an alternative using the wind energy electricity can be charge batteries, connected to building’s main power or else connected to national power grid. [44]

Advantages

There are no fossil or fuels required to generate electricity [45]

Wind energy does not pollute at all so does not harm environment or discharge any toxic gases[7]

Wind energy directly can be used as mechanical energy[47]

Disadvantages

Once there is no wind, solar energy or geothermal energy use as alternative way to generate electricity [48]

Need expensive storage throughout peak production time.[49]

Requires large scale area to build wind farm.[49]

4. Conclusion

Green energy is the only visible solution so that the future generations are not compromised