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Chapter 16: Renewable Energies

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Green-collar jobs
design, installation and management required to develop technologies and rebuild our society's energy infrastructure will be major source of employment
What is todays economy powered by?
Largely by fossil fuels; 81% of our energy comes from oil, coal and natural gas
Rapid growth in renewable energy sectors seems...
likely to continue as population and consumption grow, global energy demand expands, fossil fuel supplies decline and people demand cleaner environments.
Why can't we switch overnight to renewable energy sources?
There are technological and economic barriers. but rapid technological advances in recent years now suggest that most remaining barriers are political so public steps can help accelerate our societal transition to renewable energy
Bioenergy/biomass energy
energy obtained from biomass; biomass consists of organic material derived from living or recently living organisms and it contains chemical energy that originated with sunlight and photosynthesis. comes from diverse sources
What still accounts for 35% of energy use in developing nations?
Fuelwood, charcoal and manure; and it can go as high as 90% of use in the poorest nations
Biomass is renewable only if?
Only if it is not over harvested.
Bio power and bio fuels
biopower is using a variety of materials to provide innovative types of energy and burning them in power plants for power and generates heat or electricity. other sources can be converted to biofuels which are liquids that are used primarily to power automobiles
Biopower generates electricity from...
Biomass!
Can you use livestock manure to generate electricity?
yes; at small scales, farmers, ranchers or villages can operate modular biopower systems that use livestock manure to generate electricity. At large scales, power plants built to combust biomass operate like those fired by fossil fuels
Co-firing
in some coal fired power plants, wood chips, wood pellets or other biomass is combined with coal in a specialized boiler
Gasification
a way to harness biopower; biomass is vaporized at high temps in the absence of oxygen, creating a mixture of hydrogen, CO, CO2, methane and other gases
What is the benefit of biopower?
by enhancing energy efficiency and recycling waste products, biopower helps move utilities and industries in a sustainable direction. biopower also helps mitigate climate change by reducing CO2 emissions; capturing landfill gas reduces emissions of methane, which is a potent greenhouse gas. when biomass replaces coal in co-firing and direct combustion, biopower rescues emissions of sulfur dioxide b/ plant matter contains no appreciable sulfur
What is a disadvantage of biopower?
when we burn crops or plant matter for power we deprive the soil of nutrients it would have gained from the plant matter's decomposition
Ethanol
the alcohol that is in beer, wine and liquid. produced as a biofuel by fermenting biomass
Can automobiles run on gas blended with ethanol?
yes; any vehicle with gasoline engine can run on gasoline blended with up to 10% ethanol; some are producing flexible fuel vehicles that run on E-85 which is a mix of 85% ethanol and 15% gasoline
Why is growing corn for ethanol not the best solution?
Environmental scientists not huge fan of it because growing the corn for ethanol also requires substantial inputs of fossil fuel energy
Biodiesel
drivers of diesel-fueled vehicles can use biodiesel, which is a fuel produced from vegetable oil, used cooking grease or animal fat. cuts down on emissions compared with petrodiesel. waste oil as a biofuel is sustainable but most biodiesel comes from crops grown specifically for this purpose
Scientists have been experimenting with variety of other crops from wheat, sorghum, cassava, sugar beets, hemp, jatropha and miscanthus. What is one promising next-generation biofuel crop?
Algae
Cellulosic ethanol
relying on any monocultural crop for energy is not a sustainable strategy so researchers refining techniques to produce this; using enzymes to produce ethanol from cellulose, which gives structure to all plant material.
Is bio energy carbon neutral?
in principle, energy from biomass is carbon neutral, releasing no net carbon into the atmosphere. international climate change policy so far has failed to encourage sustainable bioenergy approaches.
modern hydropower uses three approaches. what are they?
storage technique; run of river technique; pumped storage approach
Hydroelectric power/hydropower & storage techniques
we use kinetic energy of moving water to turn turbines and generate electricity. most of it today comes from impounding water in reservoirs behind concrete dams that block the flow of the river water and then letting that water pass through the dam. b/c immense amounts of water are stored behind dams this is called the storage technique
Run of river technique
generates electricity w.o greatly disrupting the flow of river water
pumped storage approach
water is pumped from a lower reservoir to a higher reservoir during times when demand for power is weal and prices are low; when demand is strong and prices are high, water is allowed to flow downhill through a turbine, generating electricity.
What are two clear advantages of using hydropower over fossil fuel generated electricity?
Hydropower is renewable; as long as precipitation falls from the sky and fills rivers and reservoirs we can use water to turn turbines. And no carbon compounds are burned in production of hydropower so no CO2 or other pollutants rate emitted into the atmosphere. Hydropower is also efficient
Although hydropower is efficient, renewable and produces little air pollution, it has some negative impacts. What are they?
Need to dam rivers; which destroys the habitat for wild lie as riparian areas above dam sites are submerged and those below are starved of H2O. also water D/C is regulated to optimize electricity generation so the natural flooding cycles of rivers is disrupted. sediments become trapped behind dams where they begin filling the reservoir.
What are some other negative impacts of hydropower?
causes thermal pollution by changing water temps and this along w/ habitat alteration has diminished or eliminated many fish populations. it also generally blocks the passage of fish and other aquatic creatures which fragments the river and reduces biodiversity in each stretch.
Hydroelectric power is widely used but may not expand much more. Why?
Nations today obtain large amounts of their electricity from hydropower. But not likely to expand b/c worlds arrest rivers are already dammed and people have grown more aware of the ecological impacts of dams and some residents are resisting construction
Solar energy
energy from the sun. each ay, earth receives enough to power human consumption for a quarter of a century.
Passive solar heating
buildings are deisnge and building materials are chosen to maximize the absorption of sunlight in winter and keep the interior cool in the heat of summer. one design technique involves installing low, south facing windows to maximize the capture of sunlight in the winter.
Thermal mass
in passive solar heating; the use of construction materials that absorb heat, store it and release it later.straw, brick, concrete or other materials often makes up floors, roofs and walls or can be used in portable blocks. anoth
Planting vegetation around a building to buffer the structure from temperature swings is what type of approach?
Passive solar approach
Active solar energy
makes use of devices to focus, move or store solar energy. one common method involves installing flat-playe solar collectors on rooftops. Concentrating solar rays magnifies energy; we can magnify intensity of solar energy by gathering sunlight from a wide area and focusing it on a single point
CSP/Concentrated solar power
in one approach, numerous mirrors concentrate sunlight onto a receiver atop a tall "power tower".
Photovoltaic/PV cells
convert sunlight to electrical energy directly by making use of the photovoltaic effort or photoelectric effect. PV cells generate electricity directly. PV cells of all types can be connected to batteries that can store the accumulated charge until it's needed or PV electric can sell power to their local utility if they are connected to regional electric grid.
What is the fastest growing power generation technology today?
PV technology; it has doubled every two years. As production of PV cells increases, prices fall and at the same time efficiencies are increasing, making each unit more powerful.
What are the benefits to solar energy?
sun is an inexhaustible energy source for human civilization; solar systems allow local, decentralized control over power; development and deployment of solar systems is producing many new green solar jobs
what is a major advantage of using solar energy over fossil fuels?
it doesn't polite the air with greenhouse gas emissions or other pollutants
What are some drawbacks to using solar energy?
location, timing and cost can be drawbacks. Not all regions are sunny and the up front cost of investing in the equipment is high
Wind energy
energy derived form the movement of air. indirect form of solar energy b/c it is suns differential heating of air masses on Earth that causes wind to blow. we harness power from wind using wind turbines, which are mechanical assembles that convert wind's kinetic energy or energy of motion into electrical energy.
What is a wind farm?
when turbines are erected in groups; happens often
Why has wind power growth in the US been haphazard?
Congress has not committed to a long term federal tax credit for wind development but instead has passed a series of short term renewals leaving the industry uncertain about how to invest
Which areas hold more promise for wind energy?
Offshore sites. Wind speeds on average are roughly 20% greater over water than over land. There is less air turbulence over water.
What are some benefits to wind power?
no emissions once necessary equipment is manufactured and installed. more efficient under optimal conditions than conventional power sources in the energy returned on investment. Can be used on many scales from single tower for local use to a fair to supply large regions. Farmers and ranchers can also lease their land for wind development and it can create job opportunities
What are some downsides to wind power?
wind is an intermittent source and we have no control over when wind will occur. it varies from time and place b/c some areas are windier than others. Good wind resources are not always near population centers that need the energy.
Geothermal energy
thermal energy that arises from beneath Earth's surface. we harness geothermal energy for heating and electricity. power plants harness energy of naturally heated underground water and steam to generate electricity.
Ground source heat pumps/GSHPs
provide heating in the winter by transferring heat from the ground into buildings and they provide cooling int he summer by transferring heat from buildings into the ground. heat pumps make use of temp differences above and below the ground.
What is the greatest limitation of geothermal electric power?
it is restricted to regions where we can tap the energy from naturally heated ground water.
Tidal energy
can be harnessed by erecting dams across the outlets of tidal basins. as tidal current pass through the dam, water turns turbines to generate electricity. can also use the motion of ocean currents to try and harness marine kinetic energy
Wave energy
people are working to harness the motion of ocean waves and convert their mechanical energy into electricity
Ocean thermal energy conversion/OTEC
oceans sun warmed surface is warmer than its deep water and OTEC approaches based on this temp gradient.
One approach of OTEC
warm surface water is piped into a facility to evaporate chemicals, such as ammonia, that boil at low temps. These evaporated gases spin turbines to generate electricity. Cold water piped in from ocean depths then condenses the gases so they can be reused.
Another approach of OTEC
warm surface water is evaporated in a vacuum and its steam turns turbines and then is condensed by cold water. Because ocean water loses salts as it evaporates, the water can be recovered, condenses and sold as desalinized fresh water for drinking or agriculture.
Hydrogen economy
basing an energy system on hydrogen could alleviate dependence on foreign fuels and help fight climate change.
electrolysis
electricity is input to split hydrogen atoms from the oxygen atoms of water molecules. hydrogen fuel may be produced from water or from other matter. produces pure hydrogen and does so without emitting the carbon or nitrogen based pollutants of fossil fuel combustion
What is one major drawback of hydrogen and fuel cells?
major drawback of hydrogen at this point is the lack of infrastructure
What are other concerns about the use of hydrogen and fuel cells?
some research suggests that leakage of hydrogen from its production, transport and use could potentially deplete stratospheric ozone and lengthen the atmospheric lifetime of the greenhouse gas methane. it is energy efficient and a fuel cells are silent and nonpolluting.
What are some benefits to using hydrogen fuel cells?
we will never run out of it b/c its the most abundant element. can be clean and nontoxic to use and may produce few greenhouse gases and other pollutants. water and heat are the only waste products from a hydrogen fuel cell. although hydrogen can catch fire and explode during transport and storage, if its kept under pressure it is probably no more dangerous than gasoline int ants.
Describe the feed in tariff being utilized in places like Germany, which is the country that producers the most solar power.
utilities are mandated to buy power from anyone who can generate power from renewable energy sources and feed it into the electric grid. under this sytsem utilities must pay guaranteed premium prices for this power under long-term contract. as a result, german homeowners and businesses have rushed to install more PV panels each year and are seelin their extra solar power to the utilities at a profit
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