U.S. Energy Consumption
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Energy use in the future will not be dominated by a single source
The most important aspects of most alternative energy sources is that they promise clean, pollution-free energy
- The four primary consumers of energy in the U.S. in 2007 were
- Industrial 32%
- Transportation 28%
- Residential 22%
- Commercial 18%
- 93% of the energy generated and used in the U.S. are from nonrenewable resources
- World-wide, with the exception of coal, which has known reserves that will last a couple of centuries, the known reserves of oil are expected to be exhausted in your lifetime...
- Clearly, alternative energy sources are needed for the future
- The Sun is free (nobody owns or controls it)
- In principle, the amount of solar energy that reaches the Earth’s surface could provide for all human energy needs forever
- The distribution of solar energy over the continental U.S. in watts per square meter
- The desert regions of the southwest U.S. receive the most sunlight
- Solar energy is clean energy
- It produces no hazardous solid, liquid or gas wastes
- It does not create water or air pollution
- The two areas in which solar energy can make the greatest contribution are in space heating and in the generation of electricity
- These are uses that account for two-thirds of U.S. energy consumption
- The simplest approach to solar heating is passive-solar heating
- The building design should allow the maximum amount of sunlight to stream in through south and west windows during the cooler months
- This heats the house and materials inside
- Trees can be positioned to shade the house in summer
- Wide eaves can shade windows in summer, but allow winter sunlight to enter
- Drapes and shutters can insulate window areas in winter
- It has been estimated that 40 to 90% of most homes’ heating requirements could be supplied by passive-solar heating systems
- 100% solar homes have been built, but such homes usually cost many tens of thousands of dollars more to build
- Retrofitting older homes to be solar efficient can be too costly
- Over insulation can aggravate indoor pollution
- Direct production of electricity using sunlight is accomplished using photovoltaic cells, also called solar cells
- They have no moving parts and are “clean” energy
- They are used to power the space station and to provide electricity in remote areas on Earth
- A major limitation is cost, which greatly exceeds the cost of producing electricity using fossil fuels or nuclear power
- The best solar cells are only 20% efficient and only provide 50 watts of electricity per square meter of cell size
- A 100 watt light bulb would require 2 square meters of solar cells
- And a 100-megawatt power plant would require 2 square kilometers (0.78 square miles) of solar cells
- This represents a major use of land and resource, which would use far more steel and concrete than a fossil fuel power plant
- In a solar energy home, extra electricity is stored in batteries for later use
- This work well for one house
- Unfortunately, no wholly practical technology has been developed to store large amounts of electricity, despite advances in batteries
- Some possible schemes for storing the energy of solar generated electricity include breaking up water into oxygen and hydrogen to burn later as fuels
- Also pumping water to an elevated reservoir for later use as hydroelectric power generation
- Currently, solar energy provide less that 0.5% of the U.S. power needs, but even with existing technology, it could provide up to 15%
- In summation, to make solar energy truly useful for large-scale power generation:
- We need more efficient solar cells
- We need a means of better storing electricity
Advantages
- Energy is free
- Net energy is moderate (active) to high (passive)
- Quick installation
- No CO2 emissions
- Very low air and water pollutions
- Very low land disturbance (built into roof or windows)
- Moderate cost (passive)
- Need access to sun 60% of the time
- Sun can be blocked by trees and other structures
- Environmental cost not included in market price
- Need heat storage system
- High cost (active)
- Active system needs maintenance and repairs
- Active collectors unattractive
- Magma rising from the mantles brings unusually hot material near the surface
- Heat from the magma, in turn, heats any groundwater
- This is the basis for generating geothermal energy
- The steam and/or hot water is used to create electricity or for heating
- Worldwide, there are now about 40 geothermal power plants, especially in Japan, Mexico and the Philippines
- Note that most geothermal power plants are built along plate tectonic boundaries
- How the geothermal energy is used depends on the temperature of the water
- Three types of power plants are used to generate power from geothermal energy:
- Dry steam
- Flash
- Binary
- Dry steam plants take steam out of the ground and uses the steam to turn a turbine that spins a generator
- This was first done in Italy in 1904
- Iceland, a volcanic island, has many geothermal areas that produce steam and are tapped to generate electricity
- Flash plants take super heated water, usually at temperatures over 200°C, out of the ground, allowing it to boil as it rises to the surface, then separates the steam from the water and uses the steam to turn a turbine generator
- In binary plants, the hot water flows through heat exchangers, boiling an organic fluid that spins the turbine
- For all three types of power plants, the condensed steam and remaining geothermal fluid are injected back into the hot rock to pick up more heat
- This is why geothermal energy is viewed as sustainable
- It is also very “clean”
- Only produces steam
- The largest U.S. geothermal power plant is The Geysers in California (it uses dry steam)
- By 1989, a total of 10 billion watts of electricity was being produced by The Geysers and six other plants in the U.S.
- By the end of 2005 worldwide use of geothermal energy for electricity had reached 9.3 billion watts, with an additional 28 billion watts used directly for heating
- In 1999, it was estimated that the U.S. could produce 100 billion watts of geothermal energy by 2050
- Even if the geothermal water is not as hot as steam, the warm water can be used to heat buildings, home and even greenhouses
- This is routinely done in Russia and Iceland
- In fact, using geothermal energy to heat is about 2-3 times as common as using it to create electricity
- Each geothermal field can only be used for a period of time, a few decades, before heat extraction is seriously reduced
- Simply put, you can take hot water out of the ground faster than it can be renewed (even if you pump the water back into the ground)
- For example, steam pressure at The Geysers has declined rapidly over recent years
- It peaked at over 2 billion watts by 1991, but now in 2011 produces about 0.7 billion watts
Advantages
- Very high efficiency
- Moderate net energy at accessible sites
- Lower CO2 emissions than fossil fuels
- Low cost at favorable sites
- Low land use and disturbance
- Moderate environmental impact
- Scarcity of suitable sites
- Can be depleted if used too rapidly
- Environmental cost not included in market price
- CO2 emissions
- Moderate to high local air pollution
- Noise and odor (H2S)
- High cost except at the most concentrated and accessible sources
- One-third (33%) of all power plants in the U.S. are hydroelectric, but they only generate 6% of U.S. electricity needs
- A cross-section of a typical hydroelectric dam
- Water flows down the penstock, turns the turbine blades which power the generators
- Water use for generating hydroelectric power is totally dependent on the available water (duh!!)
- The Glen Canyon Dam in Utah is the classic example of building too big of dam for not enough water
- Hydropower is a very clean, pollution-free, renewable energy source
- The water is not consumed, but rather simply passes thru the generating equipment, and since several dams may occur along the same river, the water can be reused and reused
- If every stream and river in America was dammed to generate power, you still only provide 20% of current U.S. power needs
- There are about 1000 dams in the U.S. and there is very little prospect of building any new ones
- In fact, some older dams have been removed, such as the 162 years old Edwards Dam in Maine
Advantages
- Moderate to high net energy
- High efficiency (80%)
- Large untapped potential
- Low- cost jelectricy
- Long life span
- No CO2 emissions during operations in temperate areas
- Can provide flood control below dam
- Provides irrigation water
- Reservoir useful for fishing and recreation
- High construction costs
- High environmental impact from flooding land to form a reservoir
- Environmental cost not included in market price
- High CO2 emissions from rapid biomass decay in shallow tropical reservoirs
- Danger of collapse
- Uproots people
- Decreases fish harvest below dam
- Decrease flow of natural fertilizers (silt) to land below dam
- All large bodies of water, including the oceans and large lakes, have tides
- Tidal power captures the energy contained in moving water mass due to tides
- Two types of tidal energy can be extracted:
- Kinetic energy of currents between ebbing and surging tides
- Potential energy from the difference in height (or head) between high and low tides
- You can use the flowing water between low and high tides to generate electricity, similar to hydropower
- Turbines can be place on the ocean floor, for example at the entrance of a bay, where the flowing water can turn the fan to generate electricity
- Another option is to use under water turbines, which is like an underwater wind farm
- This is currently being tested offshore of Scotland’s Orkney Islands
- The ebbing and surging tidal flows turn 100 foot propellers, which each produce 1 megawatts of electricity
- Ocean energy thermal conversion (OTEC) is a new, clean technology that is still in the developmental stage
- It exploits the temperature difference between warm surface water and the cold water at depth to run a “heat engine”
- A heat engine is a device placed between a high temperature reservoir and a low temperature reservoir that produces energy
- Either the warm water is used directly to run a turbine, or the heat is used to vaporize a working fluid (ammonia) which runs the turbine
- The cold water is used to chill down the water or vapor
- Drinkable, distilled fresh water is a by-product
- The temperature difference must be at least 40oF (22oC) year round, which is only found near the equator
- So this emerging technology is best for tropic islands
- A test plant is currently being constructed at Keahole Pointe on the Kona coast of Hawaii and should become operational in 2013
- Wind energy has been utilized for thousands of years
- The wind is free, commonly available and can provide clean, pollution-free energy
- Today’s wind-turbines are very high tech
- In most places, the cost of commercial wind power on a large scale is not now economically competitive with conventionally generated electricity
- One important factor is that with a doubling of wind speed, power output increases by a factor of 8
- The numbers indicate the percentage of 1990 regional electricity demand that full utilization of wind energy could meet
- Clearly, the great plains have significant wind energy potential
- The U.S. remains the world leader in wind energy, but Europe has embarked on an very ambitious wind-power development program
- It is predicted that by 2030, wind energy will supply at least twice the electricity it does now
- It would take about 1000 one-million watt windmills to equal the energy output of one sizable fossil fuel power plant
- The windmills can be noisy
- And they are hard on migrating birds
Advantages
- Moderate to high net yield
- High efficiency
- Moderate capital cost
- Low electricity cost (and falling)
- Very low environmental impact
- No CO2 emissions
- Quick construction
- Easily expanded
- Can be located at sea
- Land below turbines can be used to grow crops or graze livestock
- Steady wind needed
- Backup systems needed when winds are low
- Plastic components produced from oil
- Environmental cost not included in market price
- High land use for wind farm
- Visual pollution
- Noise when located near populated areas
- Can kill birds and interfere with flight of migratory birds
- Biomass energy is derived from organic matter
- Stoves that burn wood are the classic example
- In fact, there had been a 20-25% increase in the use of wood stoves over the past several decades
- Biofuels differ from other renewable energy sources, such as wind, hydroelectric, geothermal and solar, as they are primarily used in the transportation sector and are derived from recently living matter, both plant and animal
- Ethanol fuel is a biofuel alternative to gasoline, which is gaining popularity world-wide
- Car engines can be designed to run on 10%, 50% even 100% pure ethanol
- It is cleaner burning than gasoline
- Worldwide, the use of ethanol is rapidly increasing
- Ethanol fuel mixtures have "E" numbers which describe the percentage of ethanol in the mixture by volume, for example, E85 is 85% ethanol and 15% gasoline
- Low ethanol blends, from E5 to E25, are also known as gasohol, though internationally the most common use of the term gasohol refers to the E10 blend
- E10 gasohol is becoming more commonly found at gas stations in the U.S. (Tennessee is way behind)
- As the “10” indicates it is made from a mixture of gasoline (90%) and ethanol (10%)
- Gasohol has higher octane, or antiknock, properties than gasoline and burns more slowly, more cooler, and more completely, resulting in reduced emissions of some pollutants
- Automotive ethanol capabilities vary widely country to country, but most spark-ignited gasoline style engines will operate well with mixtures of up to 10% ethanol
- Brazil is the world leader in ethanol fuels
- In Brazil, ethanol-powered and flexible-fuel vehicles are manufactured to be capable of operation by burning hydrated ethanol, an azeotrope of 93% ethanol and 7% water
- Ethanol fuel is produced from sugar cane in Brazil, which is a more efficient source of fermentable carbohydrates than corn as well as much easier to grow and process in the tropical climate
- The UT Biofuels Initiative has started testing the use of switchgrass, which is believed to offer a greater ethanol yield than corn in a temperate climate, such as in Tennessee
- The project represents the culmination of years of corporate research and development and a highly touted $40.7 million investment from the state of Tennessee to build a plant for demonstrating technology developed by DuPont Danisco Cellulosic Ethanol
Advantages
- Reduce CO emissions
- Reduce CO2 emissions (78%)
- High net energy yield for oil palm crops
- Moderate net energy yield for rapeseed crops
- Reduce hydrocarbon emissions
- Better gas mileage (40%)
- Potential renewable
- Increased NO2 Emissions and more smog
- High cost than regular diesel
- Environmental cost not included in market price
- Low net energy yield for soybean crops
- May complete with growing food on cropland and raise food prices
- Loss and degradation of biodiversity from crop plantations
- Can make engines hard to start in cold weather
Advantages
- High octane
- Some reduction in CO2 emissions (sugarcane bagasses)
- High net energy yield (bagasse and switchgrass)
- Reduced CO emissions
- Can be sold as E85 or pure ethanol
- Potentially renewable
- Lower driving range
- Lower net energy yield (corn)
- High CO2 emissions (corn)
- Much higher cost
- Environmental cost not included in market price
- May compete with growing food and raising food prices
- Higher NOx emissions and more smog
- Corrosive
- Can make engines hard to start in cold weather
Energy use in the future will not be dominated by a single source
The most important aspects of most alternative energy sources is that they promise clean, pollution-free energy