Coming up:

• Quiz Friday: EFP chapters 9,13,15(minus section on Hydrogen)

• Test 2: Monday, October 29

US Geothermal Resources

Advantages• Geothermal power requires no fuel, is emissions free and is not

susceptible to fluctuations in fuel cost. • geothermal power stations don’t rely on transient sources of

energy (wind, sun)• It is considered to be sustainable because the heat extraction is

small compared to the size of the heat reservoir.– individual wells may need to recover, geothermal heat is

inexhaustible and is replenished from greater depths. The long-term sustainability of geothermal energy production has been demonstrated at the Lardarello field in Italy since 1913, at the Wairakei field in New Zealand since 1958, and at The Geysers field in California since 1960.

– However, there has been a decrease in output noted at The Geysers• Geothermal has minimal land use requirements

Disadvantages• The geothermal fluid is corrosive and, worse, is at a low temperature compared to

steam from boilers, this limits the efficiency of heat engines in extracting useful energy during the generation of electricity. Much of the heat energy is lost, but could be used for co-generation purposes

• Construction of the power plants can adversely affect land stability in the surrounding region. This is mainly a concern with Enhanced Geothermal Systems, where water is injected into hot dry rock where no water was before.

• Dry steam and flash steam power plants also emit low levels of carbon dioxide, nitric oxide, and sulphur, although at roughly 5% of the levels emitted by fossil fuel power plants. However, geothermal plants can be built with emissions-controlling systems that can inject these substances back into the earth, thereby reducing carbon emissions to less than 0.1% of those from fossil fuel power plants.

• Hot water from geothermal sources will contain trace amounts of dangerous elements such as mercury, arsenic, and antimony which, if disposed of into rivers, can render their water unsafe to drink.

• Locations may eventually cool down

Biomass• Plant matter grown to generate electricity or

produce biofuel• Examples: trash such as dead trees and branches,

yard clippings and wood chips, plant or animal matter used for production of fibers, chemicals or heat.

• Biomass may also include biodegradable wastes that can be burnt as fuel.

• It excludes organic material which has been transformed by geological processes into substances such as coal or petroleum.

Energy from Biomass

• Comes initially from the sun• Solar energy is stored as chemical energy in

the plants• This chemical energy is released when the

biomass is burned or converted to another fuel that is burned.

• Process starts with the conversion of sunlight to chemical energy in the plant – we call this photosynthesis

Review of Photosynthesis

• Plant takes in water and carbon dioxide. The energy in visible light excites atoms in the water and carbon dioxide which allows bonding to take place. As a result, compounds with hydrogen, carbon and oxygen are formed (called carbohydrates), along with oxygen and water.

• The simplest carbohydrate formed is sugar, and these compounds are the plant’s fuel.

Biomass

• About 30% of the energy in the incident sunlight is stored in biomass.

• Not a new idea, remember way back in the semester when we looked at sources of energy production in the US? Wood was a primary source of energy until 1880.

• If you look at the average crop yield for all the harvested land in the US, you find that nearly all our energy needs could be furnished from biomass.

Municipal Waste

• Our solid waste (garbage) needs a home-we normally put it in a landfill (polite name for a dump!)

• Landfill sites are diminishing for a variety of reasons, but our waste production is increasing.

• Unfriendly to the environment:– Can contaminate groundwater– Nasty smell– Harbor diseases and disease carrying rodents– Can contain toxic chemicals– Emit methane (produced in the decay of organic materials

and is not only toxic, but a greenhouse gas)

Municipal waste• This waste has energy

stored in it, which can be released of the waste is burned.

• Energy produced is modest, but this solves another environmental problem.

• Plants are expensive to construct and maintain, most cities do not have the money to get one started. Rely on private investors or companies

Creating Fuel from Biomass• Ethanol – common form of alcohol, it is an

oxygenated hydrocarbon (a hydrocarbon with oxygen added).

• Also known as ethyl alcohol, pure alcohol, grain alcohol, or drinking alcohol,

• volatile, flammable, colorless liquid.• type of alcohol found in alcoholic beverages and

in modern thermometers.• Fermentation of sugar to ethanol is one of the

earliest organic reactions employed by humanity

Ethanol• Usually produced from corn,

though other grains can be used. (Brazil is a major user of Ethanol, and uses sugar cane to produce their ethanol)

• Entire plant is ground up and mixed with water.

• Cooked to convert starch to sugars via enzymatic action.

• Sugars are converted to alcohol via fermentation.

• Distillation removes the rest of the material from the alcohol.

Ethanol as a Fuel additive• Ethanol increases the oxygen content of gasoline, and

leads to more complete combustion and reduces CO2 emissions.

• Mixtures are defined by E#, where # is the percent of ethanol in the fuel.

• So E100 is 100% ethanol• E10 (10% ethanol) is a particular type of mixture called

gashol – most cars can run on this with no adverse effects

• Current gasoline engines cannot run on pure ethanol since to maximize its energy conversion efficiency, higher compression ratios are needed, which won’t work for gasoline engines.

Debate rages

• Will it really solve all our problems?• Is it cheaper? Government tariffs and lower mileage• Is it cost effective?• What about the issue of using a food source (corn)

for fuel?-note current research has made progress on a second generation of ethanol made from the non-edible parts of plants

• Potential damage to engine components with high ethanol content(> E15) fuels(engines run hotter).

Methane from Biomass• Methane makes up 85% of the natural gas extracted from the

ground.• In the presence of water and absence of oxygen, organic material

will ferment naturally.• Such organic materials include:

– Crops– Agricultural waste (animal or vegetable)– Waste from lumber mills– waste from breweries– Algae– Sludge from sewage treatment plants– Municipal waste

• Fermentation by bacteria in the absence of oxygen is called anaerobic fermentation

Methane from Biomass

• Same heating value as natural gas• High conversion efficiency(50-70% of the

useful energy is converted)• High cost• Useful in systems that can generate their own

power - for example sewage plants

Biodiesel• Diesel fuel made from

vegetable oil, recycled cooking grease or oil and animal fat

• Used as a fuel additive, designate the same way we designate ethanol fuels-i.e B# where # is the amount of biodiesel in the diesel fuel.

• B20 widely used in trucks and school buses

Nuclear Energy

• Nuclear Fission - the splitting of two atoms• Nuclear fusion – the combining of 2 atoms• Both processes release energy

Atomic structure• Atoms are composed of protons , neutrons and

electrons – discovered in the 1930’s• Protons – positively charged– q=1.602176487×10−19 C– m=1.67262158 × 10-27 kg

• Neutrons – no charge– m=1.6749 x 10-27 kg

• Electron –negative charge– q =−1.602176487×10−19 C– m= 9.10938215×10-31 kg

Atomic structure• Protons and neutrons make up the

nucleus• Electrons orbit the nucleus at specific

distances known as energy levels• Atomic number = number of

protons=Z• Atomic mass number = A = Z+ N,

where N is the number of neutrons• Atomic mass = total mass of the

electrons, protons and neutrons• Atomic weight = the ratio of the

average mass of an atom to 1/12 of the mass of an atom of carbon-12.

• Ion –if an atom loses or gains an electron and has a net charge

• Isotope-atom has the same number of protons but different number of neutrons

Atomic Structure

• Atoms are held together by forces• There are four forces in nature– Gravity -force between masses– Electrostatic forces-like charges repel, unlike

charges attract– Strong nuclear force - causes an attraction

between protons and neutrons– Weak nuclear force – causes protons to transform

into neutrons and neutrons in to protons

Atomic Structure

• In atoms, the electrostatic force is holding the electrons to the nucleus, since the electrons are negatively charged and the protons are positively charged.

• The protons in the nucleus are being pushed apart by the electrostatic force since they have the same charge, but the strong nuclear force overcomes this repulsion on the atomic size scales and holds the protons together.

Fission

• In the late 1930s, it was discovered that if a uranium nucleus was bombarded by neutrons, it absorbed the neutron and became an unstable isotope of uranium, which then spilt into 2 separate atoms (Krypton and Barium) and emitted more neutrons and gamma rays

Is mass conserved?

• Now the mass of the fission products plus the excess neutron should equal the mass of the initial incident neutron and the uranium. But it doesn’t.

• Where did the mass go?• Well, remember E = mc2 - mass cannot be

created or destroyed, only converted to and from energy, so the missing mass must be converted into energy.

How much energy

• 200 MeV is released per fission event• The fission of 1 g of uranium or plutonium per

day liberates about 1 MW. • This is the energy equivalent of 3 tons of coal

or about 600 gallons of fuel oil per day• No CO2 emissions!

• Vastly superior in terms of energy per amount of fuel