Solar:
.1% of the electricity in US produced through solar panels.
Constant, free energy supply
-Amount of solar energy reaching the earth's surface is 10,000 times all the commercial energy used each year.
-Until this century it was too diffuse and low in intensity to use except for environmental heating and photosynthesis.
-Passive Solar Heat
Much of passive solar heat is simply orientating your home toward the sun and absorbing the heat- naturally.
- Indirect gain: Absorption-using natural materials or absorptive structures with no moving parts to simply gather and hold heat.
-Old Method: Thick-walled stone and adobe dwellings that slowly collect heat during the day and gradually release heat during the night. After cooling at night, they maintain a comfortable daytime temperatures while still absorbing external warmth.
-New Method: glass-walled "sunspace" or greenhouse on the south side of a building. Uses massive energy-storing materials such as brick walls, stone floors, or barrels of heat-absorbing water to collect heat to be released at night.
-Direct gain: Use a roof overhang that blocks the direct sunlight in the summer, but lets the sun in when its at a lower angle in the winter.
-Active Solar Heat
-Solar panels-Photovoltaic Cells-capture solar energy and convert it directly to electrical current by separating electrons from their parent atoms and accelerating them across a one-way electrostatic barrier formed by the junction between two different types of semiconductor material. This is known as the photovoltaic effect.
-They used to be too expensive for practical use but prices are falling.
-In 2001 prices were approaching $5 per watt.
-By 2020 it will be down to about $1 per watt and nuclear energy will cost twice as much.
-World market for solar energy is expected to grow rapidly in the near future, especially in remote places where conventional power isn't available.
-Already used in watches, solar-powered calculators and toys
-Solar energy could mean being able to build a house anywhere and have a cheap, reliable, clean, quiet source of energy with no moving parts to wear out, no fuel to purchase, and little equipment to maintain.
Pro:
No pollution, unlimited resource, can store energy during the day and release it at night, cost going down- decreased by a factor of ten in 2 years!
Con:
Needs a storage system like deep cell batteries, not efficient if climate too cloudy, high costs for purchasing solar panels and have limited life span, Visual pollution, efficiency between 10 and 25%.
-Solar water heaters- generally pump a heat-absorbing, fluid medium through a relatively small collector instead of passively collecting heat.
-Can be located next to or on top of buildings.
-Flat, black surface sealed with a double layer of glass makes a good solar collector.
-A fan circulates air over the hot surface and into the house through ductwork, like standard forced-air heating.
-A simple flat panel of 5 square meters can provide enough hot water for an average family of four.
-What about when it's not sunny?
1) For climates where sunless days are rare- small, insulated water tank makes a good solar energy storage system.
2) For winter months-A large, insulated bin containing a heat-storing mass, such as stone, water, clay provides solar energy storage.
Fuel Cells:
- Devices that use an ongoing electrochemical reaction to produce an electric current.
- Discovered by William Grove in 1839 during his study of electrolysis.
- Fuel cells consist of a cathode (positive electrode) and an anode (negative electrode) and are separated by an electrolyte.
- an electrolyte is a material that allows ions (positively charged atoms) to pass through but not electrons.
How a fuel cell works: hydrogen passes over the anode and a catalyst on the anode takes an electron from each hydrogen atom, creating a positive hydrogen ion. The ion can pass through the electrolyte to the cathode, but not the electron. The electron then passes through an external circuit going into the cathode creating an electrical current. Then, at the cathode the electrons and positive ions rejoin and combine with oxygen creating water.
Pro:
-Emits water as waste! no pollution, minimal environmental impact, easily transported, not explosive when stored in compounds
Con:
- takes energy to produce hydrogen, changing from fossil fuels to hydrogen would take a lot of money to build the infrastructure, hydrogen gas is explosive which is inconvenient- how could we store it in a car?
Biofuels:
-Biofuels produce 15% of the world's energy, 4% of that energy is used by the U.S (.1% electricity).
-Types of biofuels include switchgrass, woodchips, sawdust, wood residue, any kind of wood or plant material. Maybe we should use all the paper we throw into the dumps... if I were queen...- Biomass (plants, wood, etc.) converted into a liquid form making storage and transportation easier.
Pro:
-It is a renewable resource if used in moderation; biofuel could produce 1/2 of the world's electrical needs if managed properly; many marginal areas of the world could support biomass plantations with plants like cottonwoods, populars, sycamores and shrubs; its inexpensive, and the burning of biofuels produce less SOx and NOx then coal.
Con:
-Deforestation and soil erosion occur, requires fertilization and water. It is expensive to transport and can cause the loss of wildlife and habitats. Some methods of burning biomass causes air pollution such as CO2 emission. Also the use of corn to produce ethanol takes more energy than it creates and is driving the price of corn up for the poor who depend on it for food (ex. Mexicans).
-When biofuels are converted to electricity, 70% of the energy is lost!
Hydroelectric Power:
-Dams trap water which is then released and channeled through turbines which generate electricity.
- 9% of USA's electricity, 3% worldwide. There are 2000 dams in the US.
Pro:
- Good because there's no pollution, low operation costs and they control flooding. They also have a high to moderate energy yield and a long life span.
Con:
Dams create large floods, which uproot people, destroy habitats, and disrupt natural soil fertilization of agricultural land downstream. Sediments eventually need to be dredged from the reservoir. Also dams upset fish migration patterns (salmon!) andthe natural beauty of rivers. Also dams are extremely expensive to build.
Tidal and Wave energy:
The natural movement of tides spin turbines which generate electricity. Very few plants exist- only in US, France and Scotland.
Pro:
No pollution, moderate energy yield, minimal environmental impact, cheap to maintain.
Con:
Costs a lot to construct, few suitable sites. Plants get hurt by corrosion from salt and storms.
Wind Power:
Large blades of wind mills spin create electricity. Now make less than .1% of electricity in US but growing!
Pro:
-Fastest growing renewable energy resource today- no pollution
-Very promising
-Unlimited source (quick fact: all electrical needs of the US could be met by wind in North Dakota, South Dakota and Texas!)
-Wind farms can be built quickly
-Maintenance is low and automated
-Moderate to high net-energy yield
-Production of wind turbines would be a boost to economy
-Land underneath turbines can be used for agriculture
Con:
-Steady wind is required to make it economical. Back up systems needed when wind is not blowing
-Visual Pollution- ugly
-Noise pollution
-May interfere with communications (radio, TV, Microwave)
- may kill some birds if on migrational pattern
Geothermal Power:
-Two kinds: Heat contained in underground rocks and and fluids from magma are used or just the stable subsurface ground temperature is used to heat air in winter and cool it in summer.
-Geothermal energy supplies less then 1% of energy needs in the U.S.
-It is being utilized in Hawaii, Iceland, Japan, Mexico, New Zealand, Russia and California
Pro:
-Moderate net-energy yield
-Limitless and reliable source if managed
-Little air pollution
-Competitive cost
Con:
-Reservoir sites for hot geothermal power are scarce
-Source can be depleted if not managed
-Non-renewable
-Noisy
-Odor
-Local climate changes
-Land damage involved for pipes and roads- can cause land sinks.
-Can degrade ecosystems due to hot water wastes and corrosive or saline water
