Alternate Energy

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Alternate Energy

• Energy Efficiency and Renewable Energy

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Key Concepts

• Energy efficiency

• Solar energy

• Types and uses of flowing water

• Wind energy

• Biomass

• Geothermal energy

• Use of hydrogen as a fuel

• Decentralized power systems

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The Importance of Improving Energy Efficiency

• Energy efficiency

• Net energy efficiency

Least Efficient

• Incandescent lights

• Nuclear power plants

• Internal combustion engine

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Energy Efficiencies
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Ways to Improve Energy Efficiency

• Cogeneration

• Efficient electric motors

• High-efficiency lighting

• Increasing fuel economy

• Alternative vehicles

• Insulation

• Plug leaks

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Hybrid and Fuel Cell Cars

• Hybrid electric-internal combustion engine

• Fuel cells

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Hydrogen gas
H2
Cell splits H2 into protons and electrons.
Protons flow across catalyst membrane.
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1
O2
React with oxygen (O2).
2
Produce electrical energy (flow of electrons)
to power car.
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H2O
Emits water (H2O) vapor.
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Hybrid Car
Fuel
Electricity
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Fuel Cell Car
Fuel
Electricity
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Universal docking connection Connects the chassis
with the Drive-by-wire system in the body
Body attachments Mechanical locks that secure
the body to the chassis
Rear crush zone absorbs crash energy
Air system management
Fuel-cell stack Converts hydrogen fuel into
electricity
Drive-by-wire system controls
Cabin heating unit
Side mounted radiators Release heat generated by
the fuel cell, vehicle electronics, and
wheel motors
Front crush zone Absorbs crash energy
Hydrogen fuel tanks
Electric wheel motors Provide four-wheel
drive Have built-in brakes
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1.4
1.2
Energy useper capita
1.0
Index of energy use per capita andper dollar of
GDP (Index 19701)
0.8
0.6
0.4
Energy useper dollar of GDP
0.2
0
1970
1980
1990
2000
2010
2020
Year
12
30
25
Cars
Average fuel economy (miles per gallon, or mpg)
20
Both
15
Pickups, vans, and sport utility vehicles
10
1985
1970
1975
1980
2000
2005
1990
1995
Model Year
13
2.2
2.0
1.8
1.6
Dollars per gallon (in 1993 dollars)
1.4
1.2
1.0
0.8
1920
1930
1940
1950
1960
1970
1980
1990
2000
2010
Year
14
Using Solar Energy to Provide Heat

• Passive solar heating

• Active solar heating

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Net Energy Efficiency
Super insulated house(100 of heat R-43)
98
Geothermal heat pumps (100 of heating and
cooling))
96
Passive solar (100 of heat)
90
Passive solar (50 of heat) plus high- efficiency
natural gas furnace(50 of heat)
87
Natural gas with high-efficiency furnace
84
Electric resistance heating (electricity from
hydroelectric power plant)
82
Natural gas with typical furnace
70
Passive solar (50 of heat) plus high-efficiency
wood stove (50 of heat)
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Oil furnace
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Electric heat pump (electricity from coal-fired
power plant)
50
High-efficiency wood stove
39
Active solar
35
Electric heat pump (electricity from nuclear
plant)
30
Typical wood stove
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Electric resistance heating (electricity from
coal-fired power plant)
25
Electric resistance heating (electricity from
nuclear plant)
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1 ft2 of collector 1 gallon of hot water 1
person uses about 20 gallons/day
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Active and Passive Solar House in Belmont NY
(upstate west of Alfred NY)
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Passive Thermal Mass House
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Passive Solar Heater
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Summer sun
Heavy insulation
Super window
Winter sun
Super window
Stone floor and wall for heat storage
PASSIVE
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Heat to house (radiators or forced air duct)
Pump
Heavy insulation
Hot water tank
Super- window
Heat exchanger
ACTIVE
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R-60 or higher insulation
R-30 to R-43 insulation
Small or no north-facing windows or super windows
Insulated glass, triple-paned or super
windows (passive solar gain)
R-30 to R-43 insulation
House nearly airtight
R-30 to R-43 insulation
Air-to-air heat exchanger
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Direct Gain
Ceiling and north wall heavily insulated
Summer sun
Hot air
Super insulated windows
Winter sun
Warm air
Cool air
Earth tubes
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Greenhouse, Sunspace, or Attached Solarium
Summer cooling vent
Warm air
Insulated windows
Cool air
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Earth Sheltered
Reinforced concrete, carefully waterproofed walls
and roof
Earth
Triple-paned or super windows
Flagstone floor for heat storage
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Using Solar Energy to Provide High-Temperature
Heat and Electricity

• Solar thermal systems

• Photovoltaic (PV) cells

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Solar Energy Calculation

• We live at about 40o N and receive about 600 W
  /m2
• So over this 8 hour day one receives
• 8 hr x 600 W /m2 4800 W-hr /m2 4.8 kW-hr /
  m2
• 4.8 kW-hr / m2 is equivalent to 0.13 gal of
  gasoline
• For 1000 ft2 of horizontal area (typical roof
  area) this is equivalent to 12 gallons of gas or
  about 450 kW-h

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Photovoltaic Array
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Single Solar Cell
Boron-enriched silicon
Sunlight
Junction
Cell
Phosphorus- enriched silicon
DC electricity
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Roof Options
Panels of Solar Cells
Solar Cells
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Solar Cell Roof
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Trade-Offs
Solar Energy for High-Temperature Heat and
Electricity
Advantages
Disadvantages
Moderate net energy Moderate environmental Impact
No CO2 emissions Fast construction (1-2
years) Costs reduced with natural gas turbine
backup
Low efficiency High costs Needs backup or
storage system Need access to sun most of the
time High land use May disturb desert areas
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Solar Steam Generator Barstow, California
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Producing Electricity from Moving Water

• Large-scale hydropower

• Small-scale hydropower

• Pumped-storage hydropower

• Tidal power plant

• Wave power plant

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Trade-Offs
Large-Scale Hydropower
Advantages
Disadvantages
Moderate to high net energy High efficiency
(80) Large untapped potential Low-cost
electricity Long life span No CO2 emissions
during operation May provide flood control
below dam Provides water for year-round irrigatio
n of crop land Reservoir is useful for fishing
and recreation
High construction costs High environmental
impact from flooding land to form a
reservoir High CO2 emissions from biomass decay
in shallow tropical reservoirs Floods natural
areas behind dam Converts land habitat to lake
habitat Danger of collapse Uproots
people Decreases fish harvest below
dam Decreases flow of natural fertilizer (silt)
to land below dam
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Producing Electricity from Wind
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Gearbox
Electrical generator
Power cable
Wind Turbine
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Basics of Wind Energy

• Velocity measured in meters per second (m/s)
• Power is measured in Kilowatts (kW)
• 1 m/s is a little more than 2 mile/hr (mph)

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Basics of Wind Energy

• Kinetic Energy (of wind) is 1/2 mass
  velocity2
• KE 1/2 mv2
• The amount of air moving past a given point (e.g.
  the wind turbine) per unit time depends on the
  wind velocity.
• Power per unit area KE velocity or P mv2v
  mv3
• So Power that can be extracted from the wind goes
  as velocity cubed (v3)

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Basics of Wind Energy

• Power going as v3 is a big deal.
• 27 times more power is in a wind blowing at
• 60 mph than one blowing at 20 mph.
• For average atmospheric conditions of density
• and moisture content Power /m2 0.0006
  v3

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Sample Wind Problem

• How much energy is there in a 20 mph wind?
• 20 mph wind 10 m/s
• Power 0.0006 v 3
• Power 0.0006 (10) 3
• Power 0.0006 1000 0.6 kW/m2
• Which is equal to 600 W/m2
• This is identical to average solar power per
  square meter at our latitude.

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Sample Wind Problem

• Example calculation
• Windmill efficiency 42
• Average wind speed 10 m/s (20 mph)
• Power efficiency 0.0006 x 1000 x 0.42 250
  W/m2
• 250 W/m2 / 1000 W/kW 0.25 kW/m2
• Electricity generated is then 0.25 kW-h/m2
• If wind blows 24 hours per day then annual
  electricity generated would be about 2200 kW-h/m2
• (0.25 kW-h/m2 x 24h/d x 365d/yr 2190kW-h/m2 )

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Sample Wind Problem

• But, on average, the wind velocity is only this
  high about 10 of the time.
• Therefore a typical annual yield is about 220
  kW-h/m2

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Sample Wind Problem

• To Generate 10,000 kWh annual then from a 20 mph
  wind that blows 10 of the time
• Windmill area 10,000 kW-h/220 kW-h/m2 45 /m2
  
• Make a circular disk of diameter about 8 meters
• This is not completely out of the question for
  some homes
• Even a small windmill (2 meters) can be
  effective.

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Sample Wind Problem

• 20 mph 10 of the time      
• 2500 kW-h annually
• 40 mph 10 of the time      
• 20000 kW-h annually
• 20 mph 50 of the time      
• 12500 kW-h annually
• 4 small windmills at 20 mph 10 of the time
       
• 10000 kW-h annually

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Wind Farm
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Wind Farm
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Trade-Offs
Wind Power
Advantages
Disadvantages
Moderate to high net energy High
efficiency Moderate capital cost Low
electricity cost (and falling) Very low
environmental impact No CO2 emissions Quick
construction Easily expanded Land below
turbines can be used to grow crops or graze
livestock
Steady winds needed Backup systems when needed
winds are low High land use for wind
farm Visual pollution Noise when located near
populated areas May interfere in flights of
migratory birds and kill birds of prey
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Producing Energy from Biomass

• Biomass and biofuels

• Biomass plantations

• Crop residues

• Animal manure

• Biogas

• Ethanol

• Methanol

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Trade-Offs
Methanol Fuel
Advantages
Disadvantages
High octane Some reduction in CO2
emissions Lower total air Pollution
(30-40) Can be made from natural gas,
agricultural wastes, sewage sludge, and
garbage Can be used to produce H2 for fuel cells
Large fuel tank needed Half the driving
range Corrodes metal, rubber, plastic High CO2
emissions if made from coal Expensive to
produce Hard to start in cold weather
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Trade-Offs
Ethanol Fuel
Advantages
Disadvantages
High octane Some reduction in CO2
emission Reduced CO emissions Can be sold as
gasohol Potentially renewable
Large fuel tank needed Lower driving range Net
energy loss Much higher cost Corn supply
limited May compete with growing food on
cropland Higher NO emission Corrosive Hard to
start in colder weather
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Trade-Offs
Solid Biomass
Advantages
Disadvantages
Large potential supply in some areas Moderate
costs No net CO2 increase if harvested and
burned sustainably Plantation can be located on
semiarid land not needed for crops Plantation
can help restore degraded lands Can make use of
agricultural, timber, and urban wastes
Nonrenewable if harvested unsustainably
Moderate to high environmental impact CO2
emissions if harvested and burned unsustainably
Low photosynthetic efficiency Soil erosion,
water pollution, and loss of wildlife habitat
Plantations could compete with cropland Often
burned in inefficient and polluting open fires
and stoves
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Geothermal Energy

• Geothermal heat pumps

• Geothermal exchange

• Dry and wet steam

• Hot water

• Molten rock (magma)

• Hot dry-rock zones

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Geothermal Power Plant-Geysers, California
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The Geysers Geothermal Site

• Covers an area of 70 square kilometers
• Heat is recovered from the top 2.0 kilometer of
  crust
• In this region the temperature is 240 oC
• The mean annual surface temperature is 15 oC
• The specific heat of the rock is 2.5 J/cm3 oC
• (specific heat is usually expressed in J/g oC)
• Overall 2 of the total available thermal energy
  in this region heats water for steam.

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The Geysers Geothermal Site

• How many years can this source provide power for
  electricity generation at the rate of 2000 MW-yr?
  
• (Total Capacity required is rate divided by
  efficiency)
• Total Capacity required is 2000 MW-yr/0.02
  100,000 MW-yr
• 1 J/s 1 W 1 x 106 W 1 MW 1 yr 3.15 x
  107 s
• 100,000 MW-yr 1 x 105 MWyr
• 1 x 105 MW-yr 1 x 106 W/MW 1 x 1011 W-yr
• 1 x 1011 W -yr 3.15 x 107 s/yr 3.15 x 1018
  W-s
• 3.15 x 1018 W-s 1 J/ W-s 3.15 x 1018 J
  (each year)

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The Geysers Geothermal Site

• Volume of rock 70 km2 x 2 km 140 km3
• Change in Temperature (D T) 240 oC 15 oC
  225 oC
• Heat content (Q) Volume specific heat D T
• Q 140 km3 1015 cm3/km3 2.5 J/(cm3 oC)225oC
• 8x1019 J (Total Energy)

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The Geysers Geothermal Site
Hence the lifetime is Total Energy/ Energy
used in a year Lifetime of Energy Source 8x10
19 J / 3.15 x 1018 J/yr 26 yr This shows
that we can use this geothermal resource for 26
yr at that rate, after that it is used up.
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Geothermal Power Plants

• Dry Steam
• Flash Steam
• Binary Cycle

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Geysers dry steam field, in northern California
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Binary Plant Soda Lake, Nevada
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East Mesa, California Flash Steam Plant
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Hybrid Binary and Flash Plant Big Island of
Hawaii
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Trade-Offs
Geothermal Fuel
Advantages
Disadvantages
Very high efficiency Moderate net energy at
accessible sites Lower CO2 emissions than fossil
fuels Low cost at favorable sites Low land
use Low land disturbance Moderate environmental
impact
Scarcity of suitable sites Depleted if used too
rapidly CO2 emissions Moderate to high local
air pollution Noise and odor (H2S) Cost too
high except at the most concentrated and
accessible source
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Energy Density of Some Materials

• Material Energy Density (kW-h/kg)
• Gasoline 14
• Lead Acid Batteries 0.04
• Hydro-storage 0.3 / m3
• Flywheel, Steel 0.05
• Flywheel, Carbon Fiber 0.2
• Flywheel, Fused Silica 0.9
• Hydrogen 38
• Compressed Air 2 / m3

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The Hydrogen Revolution

• Environmentally friendly hydrogen

• Extracting hydrogen efficiently

• Storing hydrogen

• Fuel cells

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The Hydrogen Revolution
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Entering the Age of Decentralized Micropower

• Decentralized power systems

• Micropower systems

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Decentralized power systems
Easy to repair Much less vulnerable to power
outages Increase national security by dispersal
of targets Useful anywhere Especially useful in
rural areas in developing countries with no
power Can use locally available renewable energy
resources Easily financed (costs included in
mortgage and commercial loan)
Small modular units Fast factory production Fast
installation (hours to days) Can add or remove
modules as needed High energy efficiency
(6080) Low or no CO2 emissions Low air
pollution emissions Reliable
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Wind farm
Bioenergy Power plants
Small solar cell power plants
Fuel cells
Rooftop solar cell arrays
Solar cell rooftop systems
Transmission and distribution system
Commercial
Small wind turbine
Residential
Industrial
Microturbines
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Price Comparison from 1998 Study       Leveled
Costs (includes start-up costs)

• Wind 4.3 cents per kWh
• Coal 6.2 cents per kWh
• Photovoltaics 16.0 cents per kWh
• Advanced Gas Turbine 4.6 cents per kWh

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Solutions A Sustainable Energy Strategy
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What Can You Do?
Energy Use ad Waste

• Drive a car that gets at least 15 kilometers per
  liter (35 miles per gallon) and join a carpool.
• Use mass transit, walking, and bicycling.
• Super insulate your house and plug all air leaks.
• Turn off lights, TV sets, computers, and other
  electronic equipment when they are not in use.
• Wash laundry in warm or cold water.
• Use passive solar heating.
• For cooling, open windows and use ceiling fans or
  whole-house attic or window fans.
• Turn thermostats down in winter and up in summer.
• Buy the most energy-efficient homes, lights,
  cars, and appliances available.
• Turn down the thermostat on water heaters to
  43-49ºC (110-120ºF) and insulate hot water
  heaters and pipes.