Renewable Energy Sources
10.1 The Status of Renewable Energy
Currently, renewable energy sources supply about 13.5% of the world’s total energy.
The price of energy from renewable energy sources is competitive with fossil fuel sources.
Response to climate change is stimulating investment in renewable energy.
Renewable energy sources include:
Biomass conversion.
Hydroelectric power.
Solar energy.
Wind energy.
Geothermal energy.
Tidal power.
Some studies suggest alternative energy sources could provide half of the world’s energy needs by 2050.
Biomass Conversion
All biomass is produced by green plants that convert sunlight into plant material through photosynthesis.
Biomass fulfilled almost all of humankind’s energy needs prior to the Industrial Revolution.
Biomass is still the predominant form of energy used by people in less-developed countries.
Major Types of Biomass
Fuelwood.
Municipal and industrial wastes.
Agricultural crop residues and animal wastes.
Energy plantations.
Fuelwood
In less-developed countries, fuelwood has been a major energy source for centuries.
Fuelwood is the primary energy source for about 30 percent of the world’s population.
Wood smoke is a significant air pollutant.
Wood Use for Cooking
Many people in the developing world use wood as a primary fuel for cooking, often over open fires.
Efficient stoves reduce the need for fuel, reduce the time or money needed to obtain wood, and reduce air pollution.
Waste
Waste is a major source of biomass and other burnable materials produced by society.
The burning of municipal solid waste to produce energy only makes economic sense when the cost of waste disposal is taken into account.
Using municipal solid waste as a source of energy makes economic sense when landfill costs are high.
Crop Residues and Animal Wastes
Materials left over following the harvest of a crop (e.g., straw and stalks) can be used as biomass fuel.
Animal dung is dried and burned or processed in anaerobic digesters to provide a burnable gas.
Negative impacts of using crop residues and animal wastes:
Removing crop residues reduces a supply of organic matter for soil.
Removing crop residues in the field exposes the soil to erosion.
Energy Plantations
Many crops, including sugar beets, sugar cane, corn, grains, kelp, and palm oil, can be grown for the express purpose of energy production.
Two factors determine whether a crop is suitable for energy use:
Good energy crops have a very high yield of dry material per unit of land.
The amount of energy that can be produced from a biomass crop must be more than the amount of energy required to grow a crop.
Biomass Conversion Technologies
Direct combustion:
Burning biomass in fires to cook food or heat homes.
Biofuels production:
Fermentation converts plant sugars to ethanol, which is used as an energy source.
Anaerobic digestion:
Green, wet biomass and animal waste is broken down by anaerobic bacteria, producing methane and .
Pyrolysis:
A controlled combustion process that converts biomass to a more useful fuel such as charcoal, burnable gases, and burnable liquids.
Environmental Issues related to biomass use for energy
Habitat and biodiversity loss:
1.3 billion people cannot obtain wood or must harvest it faster than it grows.
Much forest has been destroyed in Asia and Africa.
Desertification has increased in these regions.
Air pollution:
Burning wood produces air pollution.
Smoke, particulates, carbon monoxide, and hydrocarbons contribute to ill health.
Burning municipal solid wastes produces toxic products.
Climate change:
Burning biomass releases carbon dioxide in the short term.
Removal of carbon dioxide by plants is a long term process.
Food production:
Using crops to provide energy reduce the amount of land available for food production.
Millions of people do not have enough to eat.
Use of crop residues and animal manure for energy diverts them from use as fertilizer.
Hydroelectric Power
Hydroelectric power is created when the kinetic energy of flowing water is converted to electrical energy.
Damming a river and storing water in a reservoir is the most common method for generating electricity.
Water released from the reservoir flows through a turbine, to produce electricity.
The potential for developing hydroelectric power is best in mountainous regions and large river valleys.
Hydroelectric power currently supplies about 16% of world’s electricity.
In South and Central America, 56% of electricity comes from hydroelectric power.
Norway gets 95% of its electricity and nearly 60% of all its energy from hydroelectric power.
Hydroelectric Power Environmental Issues
Building dams for hydroelectric production causes significant environmental and social consequences.
Loss of farmland or forest land due to flooding.
Community relocation.
Alter fish migration patterns.
Trapping of silt fills in reservoir and stops flow of nutrients downstream.
Mercury accumulation.
Solar Energy
Daily energy from the sun is 600 times greater than energy produced each day by all other energy sources combined.
The major problems with solar energy are its intermittent and diffuse nature.
Solar energy is utilized in three ways:
In passive heating, the sun’s energy is converted directly to heat and used at collection site.
Using the sun to illuminate the interior of buildings is also a passive process.
In an active heating system, the sun’s energy is converted into heat but transported elsewhere to be used.
Solar energy is also transformed into electrical energy.
In a passive solar system, light energy is transformed to heat energy when it is absorbed by a surface.
Buildings designed for passive solar heating in the Northern Hemisphere usually have large, south-facing windows.
Floors and walls, made of materials that absorb and store the sun’s heat during the day, slowly release heat at night when it is needed most. This feature is called direct gain.
Solar-Generated Electricity
Solar energy can generate electricity in two different ways:
The sun’s energy can be used to create steam to drive a turbine.
Currently the most successful design is the parabolic trough which heats oil in pipes. The heat is transferred to water to make steam and run a turbine.
Photovoltaic (PV) cells can generate electricity directly.
Generating electricity from coal and nuclear power is rising, while electricity from photovoltaics is now less expensive in some places than electricity from the grid.
In recent years, the amount of PV power installed worldwide has been increasing dramatically.
Photovoltaics
Photovoltaic (PV) solar cells are a sandwich of materials that contain a semiconductor that releases electrons when light is absorbed.
The released electrons flow from one place to another, thus a solar cell can convert sunlight directly to electricity.
Originally the semiconductor material used in solar cells was silicon, and it is still the most widely used material.
New varieties of semiconductors have been invented that are beginning to be used in solar cells, particularly in thin- film technology.
Thin-film technology has made it possible to build solar cells into roof shingles and tiles, building facades, and the glazing for skylights and atria.
Huge photovoltaic arrays are being constructed by utility companies to provide electricity.
Worldwide, during 2019, about 98,000 megawatts of photovoltaics were installed, an increase of 20 percent over 2018.
Solar Energy (Environmental Issues)
Since solar energy is renewable, it has minimal environmental impact.
However, the manufacture of the silicon or other materials that make up the units requires large amounts of energy.
Thermal or photovoltaic power plants require large amounts of land to position mirrors or solar collectors.
Installation of photovoltaics or water heating systems on buildings does not require additional space and is often incorporated into the design of the building.
Wind Energy
For centuries, wind has been used to move ships, grind grains, pump water, and do other forms of work.
In more recent times, wind has been used to generate electricity.
In 2008, the U.S. Department of Energy published a report that stated that it was technically feasible to generate 20 percent of electricity in the United States from wind by 2030.
Because winds are variable, wind must be coupled with other, more reliable sources of energy.
Since the technology to generate electricity from wind is relatively easy to install, sizable increases in capacity occur each year.
In 2019, there were about 622,000 megawatts of installed capacity worldwide. This was an increase of 10.5% over 2018
The United States, Germany, and China constitute about 60 percent of the installed capacity.
Total electrical energy produced by wind today is still only 2 percent of total worldwide energy consumption.
Moving blades are a hazard to birds and bats.
Newer designs have slower-moving rotors that many birds such as the golden eagle find easier to avoid.
A study done in Norway found that painting one of the blades of wind turbine black, reduced bird deaths by 70%
Some people consider the sight of a large number of wind generators to be visual pollution.
Geothermal Energy
In geologically active areas hot magma moves to the surface and heats water.
The hot water can heat buildings or generate electricity through a steam turbine.
Wells are drilled to obtain steam trapped underground, and the steam powers electrical generators.
The U.S. produces about 25% of world’s geothermal electricity.
However, geothermally produced electricity is less than 1% of total U.S. electrical consumption.
Heat pumps can be used in areas that are not geologically active.
The pump extracts heat from the Earth and deposits it in a building.
Geothermal Energy Environmental Issues
Steam often contains hydrogen sulfide gas, which smells like rotten eggs.
Minerals in the steam corrode pipes and equipment.
The minerals are toxic to fish.
There are few environmental issues with heat pumps.
Tidal Power
Certain coastal regions experience higher tides than others.
To produce practical amounts of power, a difference between high and low tides of at least 5 meters (16 feet) is required.
A dam or “barrage” is built across a tidal bay or estuary.
Number of suitable sites is very small.
Tidal Current System
Changing tides create strong ocean currents in some locations.
Wind turbine-like machines are placed on the seafloor.
Only one such system is in operation north of Scotland.
Tidal Power Environmental Issues
The barriers and turbines will affect the migration of fish and other marine species.
10.3 Energy Conservation
Energy conservation can be thought of as a “source” of energy since it reduces energy demands and thus makes it easier to meet future energy needs.
Many cultural or lifestyle factors have been shaped by the availability of relatively low-cost energy, such as:
Large homes.
Outdoor lighting.
Large lawns.
If the cost of energy were higher, people would be likely to make different choices about what is essential and would evaluate energy efficiency more carefully.
There is typically a relationship between the cost of an item and its energy efficiency.
Often, poorly designed, energy-inefficient buildings and machines can be produced inexpensively.
The short-term cost (purchase price) is low, but the long-term cost for upkeep and energy utilization is high.
Typically, the cost of more efficient buildings or machines is higher, but the difference in initial price is made up by savings in energy cost over several years. This is known as the payback period.
The United States and Canada have about twice the per capita energy consumption than other countries with similar economic status.
Many conservation techniques are relatively simple and highly cost-effective:
LED bulbs use about 20 percent of the energy and last 25 times longer than incandescent bulbs.
Government Incentives
The shift to more efficient use of energy needs encouragement.
Most U.S. government incentives provide economic rewards in the form of tax incentives or impose economic penalties (taxes and fines):
Higher fuel economy standards for automobiles and trucks.
Tax incentives for those who upgrade insulation, windows, doors, heating and cooling systems, and other appliances.
2014 incandescent light bulb phase-out.
Higher energy efficiency standards for appliances.
Investment in more efficient electricity distribution.
Improvement in high speed rail transportation.
Summary
Fuelwood is the major source of energy in less-developed countries.
Biomass can be burned to provide heat or electricity or can be converted to alcohol or used to generate methane.
Hydroelectric power can be increased significantly but may displace people.
Solar energy can be collected and used in either passive or active systems and can also generate electricity.
Geothermal and tidal applications are limited by geographic locations.
Wind power may be used to generate electricity but requires wide, open areas and a large number of wind generators.
Energy conservation can reduce energy demands without noticeably changing standards of living.