Earth’s Changing EnvironmentEnergy Options

Review of Concepts

Reducing fossil fuel consumption alleviates environmental problems

Conserve fossil fuel resourcesReduce air pollutionReduce CO2 emissionsReduce extraction impacts Reduce use of water and other resources.

US Residential Energy Consumption(21 Quad)

Electricity 67%

Natural Gas 21%

Oil 7%

US Commercial Energy Consumption(17 Quad)

Electricity 76%

Natural Gas 18%

Oil 4%

US Industrial Energy Consumption(32 Quad)

Electricity 33%

Natural Gas 23%

Oil 28%

US Transportation Energy (27 Quad)

Oil 100%

US Electricity Generation (38 Quad)

Coal 52%

Nuclear 21%

Gas 15%

Renewable 10%

Ways to reduce fossil fuel consumption.

Increase energy efficiency.

Use renewable energy.

Alter lifestyle to lower energy needs.

Energy Efficiency

Energy Efficiency = Useful Energy Output / Energy Input

Power Plant Capacity

Consider a 1000 MW Capacity PlantW = Watt = unit of powerSo, a 1000 MW plant could provide a maximum of 1000 million watts of power or 1,000,000 kW of power

Power Plant Energy Output

Energy = power x timeExpress power in kilowatts (kW) and time in hours; so, energy will be in kWh or “kilowatt hours”During a 24 hour day, a 1000 MW plant could provide 1 million kW x 24 hours = 24 million kWh

Power Plant Annual Output

A typical coal-burning plant will operate at 70% capacity.Energy produced by a 1,000 MW plant =:

0.70 x 1x106 kW x 24 hours/day x 365 days =6.13 billion kWh (annual)

A typical residential customer consumes 12,000 kWh annually; so a 1000 MW plant can supply 0.5 million customers.

Power Plant Energy Efficiency

A typical 1000 MW plant burns enough fuel to release 3333 MW of thermal power.

Efficiency = output power / input power= 1000 MW / 3333 MW= 30 %

First Law of Thermodynamics

Energy must be conserved; so, the other 2,333 MW is dumped as waste heat.

Second Law of Thermodynamics

Efficiency is always less than 100%.Some energy is always dumped as waste heat.Typically coal plant efficiency is 30%, but new plants may be 50% efficient.High efficiency plants conserve energy and reduce CO2 emissions.

Power

Power (watts) = I (amps) V (volts)

Compact Fluorescent Bulbs

Efficiency is 4X incandescent bulb.14 W bulb produces light level corresponding to 60 W bulbLast 10X longer, 10,000 hours

Space Heating

The amount of heat that flows through a wall or window may be calculated by the following formula:

Heat Loss (Btu/hour) = Wall Area • in - Tout) R-value

R-value of insulation indicates its resistance to the flow of heat.R-20 has twice the resistance to heat loss as R-10.

How do we lower energy consumption for space heating?

Increase R-value of walls, ceiling, and windows.Increase efficiency of furnace. Use heat pump.Use natural gas rather than electric heater.Better home design and construction.Lower Tin. (Easy lifestyle change)Decrease wall size. (Major lifestyle change)

How do we lower energy consumption for Air-Conditioning?

Increase R-value of walls, ceiling, and windows.Increase efficiency of Air-Conditioner. Use heat pump.Better home design and construction.Raise Tin. (Easy lifestyle change)Decrease wall size. (Major lifestyle change)

Air-Conditioner Efficiency

Regulated by the U.S. DOE.

Efficiency rating -SEER (seasonal energy efficiency).

SEER is defined as the annual cooling output (Btus) divided by its total energy input (Watt-hours) during the same period.

Air-Conditioner Efficiency - SEER

The minimum SEER allowed for a central A/C is 9.7.The best available SEER is 18.Older units have SEER ratings of 6 or less. Consumers should look for a SEER of 12 or higher when buying a new A/C system.

Cars and Drivers210 million cars and light trucks

191 million licensed drivers

140 billion gallons gasoline/year

2.7 trillion vehicle miles

US Automobile Culture Transportation consumes18% of Household Expenses

91% travel by private vehicles vs. 2% by mass transit

76% rides to work are solo

2.7 trillion vehicle miles per year

Carbon Emissions

US Automobiles add 1.3 billion metric tons of CO2 to atmosphere annually. (23% of US total emission)

Efficiency of cars is 20 miles/gallon

Drivers travel 14,000 miles annually

How do we reduce global impact of US transportation?

Raise CAFE Standards

Reduce Miles Traveled

New Technologies

Raise CAFE Standards

• Corporate Average Fuel Economy

• Established in 1975 to set U.S. mileage standards.

Current CAFE Standards

• 27.5 mpg for passenger automobiles

• 20.7 mpg for light trucks & SUVs

How can cars be more efficient?

• Smaller & more streamlined (wind resistance)

• Lighter (starting & stopping)• Less powerful (lower acceleration)

Internal Combustion Engine

Engine – 20% efficientHighway driving – Energy lost to air drag. City driving – Energy lost during braking

Electric Car

Batteries are heavy and limit range to 100 miles.Vehicles don’t have enough acceleration for traffic.Not a practical solution.

Why do hybrids get better mileage?

Smaller engine. Electric motor boosts gas engine for acceleration.Regenerative braking. Electric motor runs at low speed where gas engine is very inefficient.Electric motor shuts off when stopped.

Fuel Cells and the Hydrogen Economy

Fuels Cells use hydrogen to produce electrical energy2H2 +O2 2H2O + energyFuel cells could be used to power cars with hydrogen as the fuel.Clean fuel

Barriers to Hydrogen Cars

Availability of hydrogen fuel.Storage of hydrogen fuel.Expensive.Infrastructure

Fuel Cells

In development stage.Currently very expensive.Are not a source of energy.Hydrogen must be supplied.

Hydrogen Sources

Steam reforming of natural gas:

CH4 +2H2O CO2 + 4H2

Electrolysis:

2H2O + energy 2H2 + O2

Energy Source for Electrolyzer

Electrolysis requires energy. Energy could come from Solar, Nuclear, or Wind.In the short term, it would probably come from coal.

Nucleus

Composed of protons and neutrons239Pu94 or Pu – 239

94 protons

145 neutrons

Isotope of Plutonium

Radioactivity

Some isotopes are unstable

Spontaneously Decay

Decaying isotopes emit particles

Half-life

Pu-239 decays to U-235 with the emission of an alpha particle:The time for half of the Pu-239 nuclei to decay is called the half-life. 24,000 years is half-life for Pu-239 decay

Fission

By bombarding a nucleus with neutrons, a stable isotope can be induced to fission or split. U-235 is an example of a fissionable material.The release of neutrons in this reaction means that we can set up a chain reaction

Fission Releases Energy

When the fission is controlled, as in a nuclear reactor, it can be a practical source of power.

When the fission is uncontrolled it can be the basis for weapons of mass destruction.

Fusion

Two light nuclei combine to form a heavier nucleus.

The fusion of deuterium (a hydrogen isotope) with tritium (another hydrogen isotope) to form a helium nucleus can release a great deal of energy.

Nuclear Reactors:Boiling Water Reactor (BWR)

Similar to coal plant: boils water, makes steam, steam drives turbine, turbine turns electrical generator Fissioning of U-235 is the fuel.

BWR Components

Containment building prevents release of radiationWater is needed as coolant and to prevent meltdown.

Nuclear Reactor is a Heat Engine

Efficiency is similar to a coal burning plant, about 33%So, 2/3 of the released energy is waste heat.

Uranium Fuel

Only 0.7% of natural U is U-235. U-238 is not fissionable.U must be enriched to 2.8% U-235.

Uranium Fuel Supply

Worldwide U-235 resource does not offer a long-term energy solution. Breeder reactor consuming U-235 can convert U-238 into Pu-239.

Plutonium Economy

Breeder reactors would greatly increase the availability of weapons-grade Plutonium.

Nuclear Power in the US

104 nuclear plants Produce 20% US ElectricityNo new plants since 1973Why?

Nuclear Accidents

1979 Three Mile Island partially core melt1986 Chernobyl explosion and fire, release of radiation

Waste Disposal

WIPP near Carlsbad, NM. Stores hi-level waste associated with nuclear weaponsYucca Mountain, Nevada. High-level waste from commercial reactors.

Three forms of solar energy.

Passive Solar

Active Solar

Photovoltaic

Passive Solar Energy

Sensible architectural design Use sun in the winter Avoid in the summer. Cold climates- large glazing which may be insulated at night and opened during the day. Hot climates - blocking the sun and providing good ventilation.  

Passive Design

Another interesting design.

The wall is down and the passive collector is collecting solar energy

Passive Design

In this mode, the wall is up and the building is storing solar energy or blocking summer heat gain.

Active Solar Energy

Use pumps and solar collectors to provide energy.

Two types of solar collectors: flat plate concentrating

Flat Plate Collector

Made of a black absorbing plate with water running through it or air blowing past it.

Usually a flat plate collector has a glazing to stop heat from escaping.

Efficiency 50% or better.

Flat Plate CollectorHot Water Heater

Solar water heater system has four components:

Collector

Tank

Pump

Controller

Concentrating Collector

A concentrating collector includes some kind of lens or mirror.

Tracks the sun.

High temperature.

 Efficiency near 50%.

Concentrating Collector

Components:

Optics

Glazing

Absorber

Insulation

Tracking

Photovoltaics

Photovoltaic systems convert solar energy directly into electricity. They have efficiencies near 10%.

Photovoltaics

A complete system has an array, a battery, an inverter and a load.

The system can supply either DC or AC loads.