Notes

Solar Energy
One of the reasons for the existence of life on Earth is the Sun. The Sun’s solar energy is necessary for plants to produce their own food. Most of the animals either depend on plants or the animals that eat plants for food. The Sun provides sunlight, which gives warmth to our planet. Without the Sun, our planet would freeze within few minutes. Plants cannot produce their food without the Sun. The sunlight received from the Sun varies from place to place. Areas near the equator receive more sunlight as compared to the areas away from the equator. This impacts the climate and weather of a place.

The energy that we receive from the Sun is solar energy. The process of energy formation begins at the Sun’s core. The process of nuclear fusion in the core results in the formation of solar energy. There is an incredible amount of heat and pressure at the core.

High temperatures cause fusion to occur. Fusion is the process by which nuclei of one element fuse with each other and form nuclei of another element. The Sun is primarily composed of hydrogen gas. At the Sun’s core, protons of hydrogen atoms fuse with each other and form helium atoms. This process is the proton-proton (PP) chain reaction. The PP chain reaction is the source of continuous heat and energy that we receive from the Sun. This process releases tremendous energy. The outward pressure of this reaction is balanced by the inward pressure that is created by the gravitational force of all the elements near the core.

Hydropower and Geothermal Power
Water is the most abundant natural resource on Earth. However, only one percent of it is freshwater. The water cycle, or the hydrologic cycle of evaporation, condensation, and precipitation, constantly recirculates and replenishes the Earth’s water supply. Hydropower is derived from the moving water or water cycle.

Like wind energy, water power has been used for centuries. Before the inventions of water turbines and hydroelectric dams for harnessing water power, farmers used water wheels for grinding grains.

A water wheel converts the kinetic energy of moving or falling water into mechanical energy. This mechanical energy is used for powering the mill. Water wheels have wooden or metal wheels that have buckets or blades attached around them. They are placed in a river or lake. The force of the water rotates the wheel. As the wheel moves, it turns an axle attached horizontally to the wheel. The axle in turn moves the system of gears that operate the functioning of mills. Waterwheels were used for preparing fiber and crushing ore.




Harnessing Solar Energy
There are various uses of solar energy. Solar energy is useful for generating electricity and for heating homes, swimming pools, or businesses. Every day the Earth receives enormous amount of solar energy. This energy is sufficient to meet the global energy demand. However, currently we use just a small fraction of the total solar energy received from the Sun.
Solar energy can be harnessed in three ways. They are photovoltaics, solar thermal systems, and solar heating.

Photovoltaics
A 19-year-old French physicist discovered photovoltaics. Photovoltaic cells in solar panels convert solar energy into electricity. These cells use silicon-based semiconductors. When these semiconductors are exposed to sunlight, the silicon atoms of the conductors transfer their energy to the loose electrons.

These loose electrons can be captured as an electric current. This current can power devices such as calculators, parking meters, or water pumps.

Solar panels on houses or on electronic road signs help to provide electricity.



Solar Thermal Systems
Solar thermal systems, including concentrated solar power systems, convert solar energy into heat. Lenses, mirrors, or reflectors are used for concentrating solar energy into a smaller area. The radiation concentrated in these areas heats up a specific kind of fluid that is a mixture of glycol and water. The heat from the fluid boils water and creates steam. This steam enables the generation of electricity by spinning turbines connected to generators. Solar thermal systems can be used for small applications, such as heating water in buildings or swimming pools, or can generate heat for equipment such as a solar cooker. On a large scale, solar thermal systems create heat to keep buildings warm during autumn and spring.

Passive Solar Heating
Soon after sunrise, the solar energy starts warming up materials on Earth. All through the day, these materials absorb solar energy. After sunset when the atmospheric temperature is low, these materials send back the absorbed heat into the atmosphere.

This mechanism of natural heating and cooling is used in passive solar heating. Materials used in our homes such as wood, metal, and clay help to absorb solar energy during the day. Through proper ventilation, hallways, and windows, the warm air is redistributed inside the house at night. This redistribution helps in maintaining a normal indoor temperature. Many buildings are design in way to utilize maximum solar energy. Large south-facing windows are an effective way to absorb solar energy. Moreover, architects should also take into account the latitude, altitude, and cloud cover in an area while designing buildings with passive solar heating systems.
Solar energy is an important source of energy. As it is a renewable source of energy it can be used indefinitely. However, a few points should be considered while harnessing or using solar energy.

Cloud cover in an area affects the amount of solar energy that area receives.
Solar energy is available only during daytime. Hence, it is necessary to use effective techniques to store this energy. Alternative sources of energy should be considered.
People who have installed solar panels to generate electricity can use less electricity from the utility companies. If they produce more energy than they use, they can sell their share of electricity back to the utility company.
Sometimes, it is expensive and impractical to connect power grids at remote locations. Solar energy is an attractive source of energy at these remote areas, provided they receive abundant sunshine.


There are few environmental implications of solar energy.

Solar power plants don’t release any type of pollutants. Thus, use of solar energy does not cause pollution.
However, the manufacturing of solar panels, photovoltaics, or devices used for harnessing solar energy can cause pollution.
Construction of solar power plants might result in land use changes. These changes impact the natural habitats of many species.
Moreover, concentrated sunlight can harm birds.

Wind Energy
The Sun unevenly heats the Earth and the atmosphere. The Earth consists of land as well as water. Due to these differences, the Earth absorbs solar energy at different rates at different places. The air above the land gets heated faster as compared to the air above water during day.

Warm air is less dense as compared to cold air. Less density creates less pressure. High density creates high pressure. Thus, the warm air rises and the cold air replaces it. Wind is the movement of air from high-pressure areas to low-pressure areas. Wind also arises as a result of the Earth's spin on its axis.

Wind energy has been in use for many years. The use of wind energy can be traced back to 5,000 B.C., when sailors used wind power to sail their ships. Wind energy was used to grind grains and for pumping water. As the importance of wind energy spread throughout the world, people started inventing methods for harnessing it.

Over the last century, the use of wind energy for creating electricity has become significant. Wind turbines are a modern equivalent of windmills. Wind turbines convert the kinetic energy of the wind to mechanical energy or electricity. The working of a wind turbine can be compared to the working of a fan. However, a fan uses electricity to produce wind while wind turbine uses wind to generate electricity.

The blowing wind has a similar effect on the blades of the turbine as it has on an airplane propeller.

The blades of the wind turbine rotate as the wind moves through them. This rotation causes an internal shaft to spin. This shaft is connected to the generator that produces electricity. This electricity is then transferred to a substation through transmission and distribution lines. The substation supplies electricity to homes, businesses, and the like.

Types of Wind Turbines
Horizontal Axis Wind Turbines
Horizontal axis wind turbines (HAWT) look similar to windmills. These wind turbines have either two or three blades. These blades look like propeller blades and spin on a horizontal axis. The main shaft and the generator are at the top of tower and the blades face into or away from the wind. Most of the horizontal axis wind turbines have the shafts connected to a gearbox that boosts the speed of the rotation and generates electricity. One of the biggest advantages of HAWT is the tall tower base that provides access to stronger wind. Moreover, the blades receive power through the whole rotation as they move perpendicular to the wind. However, the transportation and installation cost of wind turbines is high.

Vertical Axis Wind Turbines
A vertical axis wind turbine (VAWT) looks like an eggbeater. The shaft is arranged vertically. VAWT can thus be useful in areas having variable wind. Under this arrangement, it is not necessary for the blades to face the wind. A tower is not needed to support the shaft and the generator, as they are located near the ground.

Applications of wind turbines
Many wind turbines are built close to each other to form a wind plant. They are connected to utility power plants that provide electricity to their customers. Farmers and ranchers in windy areas can use stand-alone wind turbines for pumping water and grinding grains.

Electricity generated through wind turbines is increasing significantly. In the United States, electricity generated from wind energy increased from 6 billion kilowatt hours in 2013 (kWh) to 182 billion kWh in 2014.

Wind is a renewable energy resource because as long as the Sun shines, the wind will blow and we can reap the benefits of wind energy. However, a few points should be considered while harnessing wind energy.

Wind energy depends on the wind speed. The speed determines how much energy a turbine can generate.
Wind power is stronger over oceans as compared to land. Thus offshore wind turbines will have more consistent availability of wind.
Generally, wind power is stronger in areas with hills and valleys. However, these areas are less populated and thus the demand for electricity is low from such areas.
There are few environmental implications of wind energy.

Use of wind energy doesn’t produce air or water pollution.
As wind is freely available, the only cost involved in harnessing wind energy is that of installing the wind turbines. Due to technological advancements, the cost involved in maintaining and installing wind turbines is reducing.
Use of wind energy has very little impact on the environment. However, some believe that the noise produce by the turbines is affecting birds and bats.
For some, turbines or wind plants might spoil the beauty of aesthetic value of a place. However, this problem can be resolved by proper selection of sites.

Earlier, use of hydropower was limited to milling grains and other activities related to agriculture and mining. However, since the nineteenth century, hydropower has been used for generating electricity. Hydropower plants are set up for generating electricity.

A hydropower plant consists of three sections: a reservoir that stores water, a dam, and an electric plant. A dam is constructed on a large river. The dam creates a drop in elevation in the water surface. Water flows down from a higher height to a lower height. The hydropower plant uses turbines to convert the moving water into electricity. The water reaches the turbines through a penstock. This moves the turbines. A shaft attached to the turbine goes up in the generator. This generator produces electricity. The water continues to move into the river through the dam.

Nearly seven percent of total electricity of the United States comes from hydropower.

There are few implications of using of using hydropower for generating electricity:

Hydropower is a clean source for producing energy. It doesn’t produce pollutants or CO2 emissions.
The reservoirs at the hydropower plant provide recreational facilities for people.
There are few environmental implications of using hydropower:

It has been observed that dams constructed on rivers can disrupt aquatic ecosystems.
Dams prevent fish such as salmon to swim upstream to spawn. However, technologies such as fish ladders help the fish to pass though the dams.
Dams modify the natural flow of the river and can damage nearby habitats.

Geothermal Power
Did you know that energy can be found right in your backyard? Geothermal energy is generated from the Earth’s heat. The word geothermal comes from Greek words geo, which means Earth, and therme, meaning heat. Let’s see how heat is generated below the Earth’s surface.

The core is the innermost part of the Earth. Very hot molten iron makes up this part. Scientists estimate that the temperature in this part is approximately 5,500C. Some of the heat is the result of gravitational pull and friction caused when the Earth was formed more than 4 billon years ago. The majority of this heat is a result of decaying of radioactive isotopes in the core.

Elements that have same atomic number but different numbers of neutrons are isotopes. Carbon-12, for example, is an isotope that has six neutrons. But Carbon-14 has eight neutrons. In the Earth’s core the decay of radioactive isotopes is a continuous process where the temperatures rise above 5,000C. Some radioactive isotopes that contribute to the heating of Earth’s interior are uranium-238, thorium-232, and potassium-40.

The mantle surrounds the core. Rocks and magma make up the mantle. The crust is the outermost layer of the Earth and surrounds the mantle. Earth’s core acts like a giant burner, and the magma in the mantle acts like water in a pot. The heat from the core heats the magma in the mantle. As a result, this magma becomes less dense than the magma above it, and it rises. Unlike the shell of an egg, the Earth’s crust is divided into plates. Magma exists near the surface along plate margins. This magma heats rocks and underground aquifers. Hot water is released through geysers, hot springs, underwater hydrothermal vents, and mud pots. These features are sources of geothermal power. Geothermal energy can be found in underground reservoirs of steam and hot water.

Geothermal energy has been in use for thousands of years. Ancient cultures, including the Romans, Chinese, and American Indians, used hot springs for heating, cooking, and bathing. Some even believe that these hot springs have natural healing powers. Recently, water from hot springs has been used for heating buildings and for agriculture. Geothermal heat is useful for generating electricity, heating buildings, sidewalks, and for industrial purposes.

Geothermal Power Plants
Geothermal power plants are used to generate electricity from geothermal energy. At geothermal power plants, heat is converted to electricity by drilling water or steam wells, similar to the process of drilling oil. Hot water or steam is tapped to turn turbines, which in turn generate electricity.

Lets learn about the types of geothermal power plants.

Dry Steam Plants
Dry steam is the oldest geothermal technology. Dry system plants use steam to generate electricity. Dug 7,000 to 10,000 feet deep, wells tap the underground steam. In a dry steam reservoir, natural steam is taken out through pipes from the broken surfaces of the Earth. This steam powers a turbine that generates electricity. The steam is condensed in the plant’s cooling system and then flows back into the reservoirs. This cycle helps maintain water levels. The very first geothermal power plant, constructed in Larderello, Italy, in 1911, continues to supply electricity to millions of residents near that area.

Yellowstone National Park and the geysers in California are the only two known sources of underground steam in the United States. The geysers in California supply a dry steam power plant that provides nearly one fifth of the total renewable energy in California.



Flash-Steam Plants
These plants are the most commonly used plants for harnessing geothermal energy. Underground high-pressure hot water (hotter than 360F) is pumped out into cooler low-pressure areas. In the low-pressure areas, the hot water flashes, or evaporates into steam. The steam pushes the turbines. These turbines propel the generator that produces electricity.

Flash-steam systems provide almost all of the electricity in Iceland. The steam is also used to heat the snow-clad sidewalks and at parking lots. Remaining water flows back to the geothermal reservoirs.

Binary Power Plants
Binary power plants use a liquid organic compound with a lower boiling point than water. Hot water passes through a pipe and heats the other liquid. This liquid turns into steam and turns the turbines. The turbines power a generator and electricity is produced. The water in the pipe is allowed to flow back to the ground and can be used to reheat the other liquid again. The Beowawe Geothermal Facility in Nevada uses tetrafluoroethane, a greenhouse gas, that has a boiling point lower than that of water.

Geothermal Heat Pumps
Geothermal heat pumps take advantage of the heat that is just below the Earth’s surface. In this system, pipes are buried 10 to 300 feet below the Earth’s surface. A slinky loop arrangement of pipes is used in this system. These pipes contain water or other liquids such as glycerol. During winter, the liquid absorbs the geothermal heat. This heat moves through the pipes upward, enters the building through ventilation or duct systems, and provides warmth.

Conversely, during summer the liquid in the pipes absorbs the outside heat and passes it underground.

According to the US Environmental Protection Agency, geothermal heating is very energy efficient and environment friendly.

Over 20 countries in the world use geothermal power. The United States is the largest producer of geothermal energy. The geysers of California are the largest source of geothermal energy in the world.

A few implications of geothermal energy include the following:

Geothermal energy is a renewable source of energy. The Earth’s surface continuously radiates heat. Thus, geothermal energy will be available continuously.
Geothermal energy is a clean source of energy. It doesn’t produce any pollutants. However, some CO2 emissions from Earth’s surface may occur. Most of the systems emit only water vapor.
Geothermal energy is always available and is not affected by weather conditions. Availability of sunlight or wind doesn’t affect the geothermal energy. Unlike solar and wind energy, geothermal energy is available day and night throughout the year.
Geothermal power plants, if well managed, can function properly for decades.
Some processes might release noxious gases, such as hydrogen sulfide or sulfur dioxide.
Some of the fluids may contain toxic substances.

Biomass Energy
Biomass is organic matter from plants, animals, and other living things. Plants, wood, and waste are typical biomass materials used for energy. They are the biomass feedstocks. Other biomass feedstocks include agricultural residues, energy crops (high energy yield crops used for making biofuels), algae and organic wastes, and food and industrial waste. Methane, which a main component of natural gas, is produced from decaying of biomass and is a source of biomass energy.

Biomass is a renewable energy source that can be used as fuel. For example, you can burn trees and crops to produce heat. Because trees and crops can grow again, the source of the energy is renewable. Animal and plant waste, which is a type of biomass, exists in nature. Therefore, waste biomass is a renewable energy source as well.

Carbon is a major part of biomass composition. Biomass also contains oxygen, hydrogen, and nitrogen, and small amounts of alkali and heavy metals.

The environment produces biomass energy through a process called photosynthesis. It is a process by which plants utilize the energy from the Sun to create glucose, which is the main source of energy for plants. When animals consume plants, the energy from glucose is transferred into the animals and becomes animal biomass. The energy acts as fuel for animals. Thus, the ultimate source of biomass energy is the Sun through photosynthesis.

Biomass has been in use since the time the early humans discovered fire for heating and cooking. Biofuels, such as ethanol, were used as lamp fuel in the United States in the 1800s. Recently, biomass and biofuels have begun to replace fossil fuels such as gasoline.

Types of Biomass Energy
We can use biomass energy in different forms.

As per statistics, in 2014, biomass fuels provided nearly five percent of energy in the United States. Wood is the major source of biomass energy. It provided 46 percent of biomass energy in 2014. Biofuels such as ethanol provided 44 percent of biomass energy and nearly 10 percent energy was derived from municipal waste.

Let’s understand different types of biomass energy.

Wood
Burning of biomass such as wood or other agricultural products such as fruit pits and corncobs is a major source of biomass energy. Wood along with its by-products—logs, chips, bark, and sawdust—is most commonly used for generating electricity. Burning wood creates steam, which in turn produces electricity. Paper and saw mills use their wood waste to generate electricity for their use. Burning biomass such as wood can be use for heating homes. The fireplace in your home is an example of biomass energy received by burning biomass such as wood.

Biofuels
Biological processes such as agriculture produce biofuels. Ethanol and biodiesel are biofuels.

Ethanol: Corn and sugarcane are used for producing an alcohol fuel called ethanol. Fermentation and distillation of sugars and starches in crops and plants produce ethanol. Corn is the major source of ethanol in the United States. Ethanol is used in automobiles as fuel. Ethanol makes up around 10 percent of the total fuel in nearly all of the gasoline used in the United States.

Biodiesel: It is made from vegetable oils and animal fats. Chemical reactions between alcohol and vegetable oils or animal fats result in the formation of biodiesel. Currently, soybean oil is a major source of biodiesel. It can be used to power automobiles.

Methane
The stinky garbage heaps in landfills or dead plants and animals are definitely not a pretty sight. But they serve as an excellent source of energy. Bacteria and fungi eat the dead plants, animals, and garbage. This process results in rotting or decaying of the waste material. When this biomass rots, methane is produced. Methane gas is an important ingredient in natural gas. Burning methane gas heats buildings and produces electricity. Biogas plants primarily use methane. It is used for heating and cooking.

Solid Waste
People have been burning trash for years. However, burning trash also converts waste into a usable form of energy. Waste-to-energy plants burn trash to generate energy. These plants are a perfect alternative to coal-fire plants that use coal as a fuel. The waste-to-energy plants reduce landfill disposal costs, as they use garbage as a fuel to generate energy. However, they are more expensive than coal-fired plants.

One major advantage of using biomass energy is that it is easy to store. Biomass is a renewable source of energy that can replace non-renewable resources such as fossil fuels. However, there are certain environmental implications of using biomass energy.

Burning wood produces particulate matter and other pollutants such as carbon monoxide.
Sometimes trees are logged for fuel faster than they can grow. This logging disrupts the ecosystem. Excessive harvesting of wood for fuel can harm forests and result in loss of carbon stored in soils.
Burning of biomass emits carbon dioxide. However, it is the same amount of carbon dioxide that is consumed when the biomass was created.
Crops are grown especially for biofuels such as ethanol and biodiesel. Many oppose this practice as the resources such as land used for producing crops for biodiesel can be used for producing food.
Biodiesel produces higher amounts of nitrous oxide. Nitrous oxide can impact respiratory systems and can cause acid rains.
Methane gas causes explosions if it leaks and ignited.