25.0 Review of Renewable Energy
Some of the more important points
Frank R. Leslie,
B. S. E. E., M. S. Space Technology
2/23/2010, Rev. 2.0
fleslie @fit.edu; (321) 674-7377
www.fit.edu/~fleslie
In Other News . . .
 Crude oil continues at ~$50/bbl
 LAGOS (AFP) — Shell cannot meet its contractual obligations on the
delivery of crude after a fire on a key pipeline in Nigeria that caused a
major production loss, a spokesman said on Thursday.
 "We have declared a force majeur for the remainder of April and the
month of May. The force majeur took effect from noon on April 14,"
Precious Okolobo told AFP, using the term that releases the company
from its contractual obligations.
 "We have stopped the fire. We are investigating its cause while the
repair of the pipeline is about to start."
 The 180,000 barrels per day crude production loss in the volatile
southern Niger Delta involves a range of companies: 130,000 for Shell,
30,000 barrels for French group Total and another 20,000 barrels from
various other operators, an industry source told AFP.
 President Obama announced an $8B down payment of
stimulus money to build/improve ten high-speed rail lines in the
Northeast and California (AMTRACK costs more than airlines)
090416
25 Overview of the Review
 These slides are intended to provide the most important
aspects of each of the sessions of the course
 Equations should be provided at the end, but you are
responsible for knowing how to find them and how to
use them
 Some sections may not be fully complete at this time
when other lecturers used transparencies
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25.1 Introduction
 The introduction at RE01 has a synopsis of the general
content of the whole course and should be studied for
the test
 Not all sessions are treated equally here, but reflect
what I believe to be most important in the renewable
energy field and with general energy issues
 I have concentrated on the conclusions of each session
and may not have completed the one or two pages of
the “condensed” version from the original files
 Look at
http://my.fit.edu/~fleslie/CourseRE/ClassPres/classpresentations.htm
to select those files
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25.2a Current Events
 “Light sweet” crude oil futures rose from $26/42-gallon
barrel (4/26/2003) to about $112/bbl (4/15/2008)
OPEC production cut-backs affect the global market
China and India increasing demand; price up
 Key issues affecting the economy are the prices of
gasoline and natural gas
Gasoline affects the price of goods delivered by
truck, and diesel oil for trains and ships tends to
parallel this price, also affecting farming and food
Natural gas is used for home heating and for the
large utility plants built for natural gas or being
converted to use it (lower pollution)
Hydrogen made from NG will increase that price
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25.2b Pollution
 Air and water pollution continue to drive the costs of
energy production
 There are other costs outside of the cost to consumers
known as “externalities”
Military defense of oil sources (Kuwait; Iraq?)
Public health costs of respiratory and other diseases
caused by pollutants
Road traffic caused by oil truck transportation, and
resultant exhaust fumes, which cause more ailments
 Renewable energies usually cause less or no pollution
than conventional fuels
Making the converter also uses energy and may
cause pollution during production
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25.2b Conclusion: Pollution
 Combustion energy sources emit pollutants NOx, SOx,
VOCs, etc. plus CO2, a green house gas (GHG)
 Nuclear plants might rarely emit accidental releases of
radioactivity, but safe designs reduce this chance
 Wind and solar energy doesn’t pollute, but there may
have been pollution from the making of the equipment
 Laws effect and enforce plant changes to reduce
pollution; they remove economic incentives to pollute
 Emissions credit trading may help reduce pollution since
there is an economic incentive to clean up
 During the Iraq War, Hussein did not have time to set oil
wells on fire as in the Persian Gulf War of 1991
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25.3 Climate Change
 Climate change is controversial, as many or most
scientists believe that increased combustion of fuels by
civilization and industry releases green house gases (like
CO2) that change the earth’s temperature balance
 The level of atmospheric CO2 and population have both
grown over the last 150 years; is one the cause of the
other?
A classic statistics example is that the sales of liquor
and the number of Baptist ministers (who presumably
claim to eschew alcohol) are positively correlated
They are correlated to the increasing population, not
necessarily to each other! Be wary of those who say
correlation proves cause and effect!
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25.3 Climate Change
 An argument is made that most of the World’s scientists
agree that global warming is caused by mankind
 In somewhat earlier days, “most” scientists agreed that
the earth was flat, and only “extremists” thought
otherwise! Koreshans thought Earth was hollow!
 Science is not democracy, and “most” doesn’t make
right! Public opinion doesn’t determine science
 About 1950, there was concern about global cooling
 On the other hand, now glaciers are melting and
receding over a period of years indicating a warmer
average weather change
 Solar dimming due to pollutants reduces global
warming; do we need more pollution to fight GW?
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25.4 Fuel: Hydrogen
 There is much talk of the “Hydrogen Economy”, where
hydrogen (an energy carrier) will replace fossil fuels
See Amory Lovins, Rocky Mountain Institute for early
espousal of the concept; Romm for the opposite
There are no hydrogen wells, so hydrogen isn’t a fuel
in the usual sense, but an energy carrier
To get hydrogen, electrolysis of water, pyrolysis of
fossil fuels, or bacterial action is required
Nuclear and fossil fuel base-load power plants
produce energy to support the lowest daily load or
more
This cycle peaks in mid-afternoon and/or
dinnertime and is lowest at 3 a.m.
If the electrolysis is done off-peak, is the resultant
hydrogen clean? Depends upon energy source
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25.4 Fuel
 Fossil fuels are of limited extent: known, suspected, and
possible
 Hubbert predicted the depletion of US oil about 1970 (it
peaked in 1974)
 World oil production may peak about 2005 to 2020
 After the peak, lots of money chasing a diminished
supply increases the price (has the price increased
lately?)
 When fossil fuel prices exceed the cost of renewable
energy, a shift will occur, slowly at first, then
accelerating
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25.4.3 Fuels Conclusion
 Fuel usage is
determined by cost and
convenience
 Fuel density is critical
for transportation
 Cost of fossil fuels and
nuclear energy will
keep these in
predominance for
several decades
 Renewable energy
provides small
contributions now, but
diversity is critical as
transition occurs
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25.5 Conservation and Efficiency
 Conservation of energy is the cheapest way to cut
energy costs, but there is a tradeoff against the benefits
of using the energy
 Automatic air conditioning thermostats can manage
temperatures without human intervention, simplifying
life while saving energy
 Motion-sensor lights only use electricity when someone
is moving in the field of view
 The time to pay off the investment is zero, and savings
begin immediately
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25.5 Conservation and Efficiency
 Efficiency means getting the desired result for less
money; effectiveness means doing the right thing
 Lighting must be bright enough for the task and yet not
present when unneeded
Bright local lighting is better than bright general
lighting since less power is needed to produce it
Compact fluorescent lights (CFLs) produce good light
intensity with about 1/4 the power
Timers or motion detectors can turn off lights when
they are not needed
 Better building insulation conserves heating in winter
and keeps summer heat out
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25.5.3 Cons. & Efficiency Conclusion
 Conservation by reducing loads or shortening duration
of use will save money, reduce pollution, and extend
the time that fossil fuels last
 Greater efficiency in generating, transmitting, and using
energy will yield the same utility for lower cost
 Energy not used reduces the need for utility plant
construction or delays it
 Efficient use of fuels will save still more money and
prolong their economical use
 While conservation and efficiency are valuable
practices, they only delay the depletion of fossil fuels
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25.6 Prof. Odum, EROEI, and Emergy
 Emergy addresses the amount of energy that is required
to make energy conversion systems and to obtain and
process the fuel for them
 Energy Return on Energy Invested (EROEI) shows worth
of an approach or product
 This subject is “well-known, but only to a few” --- Miles
E. Hall, 1958
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25.7 Thermal Systems
 Steam boiler systems require fuel to heat the water,
making steam for turbines that spin generators that
produce electricity
 Solar parabolic and paraboloidal collectors have been
developed to heat water into steam or to power Stirling
engines
 Simple flat plate collectors moderately heat water or air
for household or industrial use
 Thermocouple systems generate very-low-voltage
electricity from heat on metals of different types
 Used in radioactive thermal generators (RTGs) for
space probes or undersea work
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25.7.3 Conclusion
 Thermal energy conversion remains the predominant
use of fuel
 Since fossil fuels are still perceived as cheap, there isn’t
much clamor to change to renewables, which are still
more expensive
 As the price of conventional fuels increases and
renewable energy decreases, a shift will occur
 There must be a long overlapping period of the two
technologies to permit development of renewable
resources before conventional fuels become difficult to
obtain at a reasonable price
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25.8 Coal
 The most available and least expensive fuel in the US,
coal has many pollution issues
 The so-called “Clean Coal” program reduces pollution by
washing the coal first, controlling burn temperature, and
then cleaning the stack gases afterwards; sequestration
is next
 Powerful marketing forces and lobbies clamor for
maintaining coal predominance in the energy market
 Utilities say coal diversifies their “fleet” of plants
 Many union jobs depend upon coal production and
transport, thus many block-votes drive politicians to
retain coal rather than fund the renewable energy area
 There aren’t many renewable energy unions
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25.8.3 Conclusion: Coal
 Coal is the most abundant fuel in the United States and is
estimated to last about 100 to 200 to 400 years
 Coal will last several hundred years longer than oil or NG
 Coal will continue to be a primary fuel close to coal mines
 Coal is most suited to fixed energy plants; while mobile
use requires oil or natural gas for density and
convenience
 Coal is cheap, and may be chemically processed to yield
natural gas, liquids, or hydrogen, but taking heat and
water to do so
 Is hydrogen clean (green) if it is processed from coal or
coal-generated electricity? No, really dirty
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25.9 Oil and Natural Gas
 Oil and the natural gas often found with it are of limited
extent; NG aids oil production by its pressure
 Estimates of the remainder vary greatly since detection
of more deposits is somewhat limited
 Production in the United States peaked in 1974,
resulting in oil imports as demand increased
 World production will possibly peak in 2005 to 2010 as
China and India develop needs
 Natural gas is a relatively clean-burning fuel and is the
choice for new fossil-fuel power plants, but the price is
volatile
 Competition for the diminishing supply will drive prices
still higher
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25.9 Natural Gas Decline
Note declines are getting steeper!
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http://www.eogresources.com/investors/stats/us_decline_curve.jpg
25.9.3 Conclusion: Oil & Natural Gas
 Oil is energy-dense and easy to transport and use, and
thus it works well in vehicle tanks
 Many chemicals and materials are made from oil, thus
burning it may restrict or prevent a better, higher use
 Choices are made from the economics and cost of doing
business in the short term
 The future value of oil in ANWR is difficult to predict, but
it will be far more valuable in constant dollars a hundred
years from now than it is right now
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25.10 Nuclear Energy
 Nuclear energy is not well understood by many; the
mysteriousness leads to fear (and loathing)
 Nuclear energy has many radioactive concerns in
mining, preparation, transportation and disposal
 At the end of the fuel cycle, the “spent” fuel must be
dealt with to avoid a concentration of plutonium in the
fuel that might be misused by terrorists
 Yucca Mountain AZ will eventually be a storage site for
spent fuel, yet the fuel must be taken there from many
locations by rail or truck
Some complain that storage must last 250,000 years
 Human failure remains the largest concern
 More outcry is raised about the possibility of nuclear
contamination than about the statistical health problems
caused by fossil fuel plants
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25.10 Nuclear Energy
 Future hydrogen may be produced by nuclear energy for
electrolysis of water; is this what we want?
 In many cases, what “we” want is instant gratification
and cheap, not-a-care energy – it’s just there for us
 The Age of Terrorism brings a new level of uncertainty
to the problem, as the potential of attacks on nuclear
plants cause widespread anxiety and outcry
 The first nuclear truck bomb exploding in the US will
bring incredible social changes
 If there were $1 billion of lawsuit payouts per year for
plant errors, that much would have to be set aside each
year $risk = $consequence * prob(consequence)
Money spent to reduce the risk would cut the amount
needed as insurance premiums
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25.11.1 Solar Energy
 Available solar energy changes with the seasons, thus
collectors may need adjustment to receive maximum
energy
 There are four important astronomical epochs or
transitions:
The vernal equinox about Mar. 21 (equal day and
night hours; equi nox  night equals day)
The summer solstice about Jun. 21 (longest day)
The autumnal equinox about Sep. 23 (equal day and
night hours)
The winter solstice about Dec. 22 (shortest day)
These sometimes drift into an adjacent date
Solstices are at the extremes of angular sun travel
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25.11.1 Solar Energy
 Since the earth axis is tilted 23.45 degrees from the
plane of revolution, the Northern Hemisphere is tipped
towards the sun in summer, which occurs because the
sun’s rays strike more directly than in winter
 Since the direction of the sun at solar noon changes
throughout the year, a fixed collector works best if
aimed parallel to the equatorial plane (latitude angle)
The sun is too high in summer; too low in winter
 Setting the collector angle to the latitude angle thus
allows the sun angle to be equal and opposite at the
solstices
 To heat water in the winter, an extra tilt to the south
(north) of ~15 degrees may be added since the cold air
around the collector cools the collector in winter
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25.11 Conclusion: Solar Energy
 Received solar energy varies widely as evidenced by
climate records and vegetation (deserts and rain
forests) that average growth to match solar energy
 This variability affects the economic viability of a system
 Solar energy systems are simple, robust, and easy to
install
 Solar modules are still expensive, approximately
$3.50/W for large arrays to $16/W for small modules,
depending upon size
 Organic process might yield $0.20/W!?!?
 Installation adds another ~$5 per watt of cost
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25.11.2 Solar Electric
 A PV module may produce 30 volts with no load, yet
produce maximum power at ~17 volts
 If it produces 17 volts and 5 amperes, the power is 17 *
5 = 85 watts (instantaneous power; not per day, etc.)
 Typical sun-hours might be only 5 hours/day
 If it does this for 5 hours, the energy produced is 85
watts * 5 hours = 425 watt-hours (both the values and
the units are multiplied)
 If it produces 425 watt-hours in one day (24 hours), the
average power is 425 watt-hours / 24 hours = 17.7
watts over that day including nighttime
 Clearly (or cloudily), the average power varies with the
weather
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25.11.2 Solar Electric: Batteries
 Batteries are comprised of primary (nonrechargeable like dry cells)
and secondary (rechargeable) types
 Primary batteries don’t recharge well; but chargers are sold since
people will buy them
 Only secondary batteries (groups of cells) are used for renewable
energy storage
 A battery with a 300 ampere-hour capacity based upon 25 hours
specified time can deliver 300 ampere-hours/25 hours = 12
amperes current to a load for 25 hours
 For 30 hours, 10 A; for 100 hours, 3 A; 300 hours, 1 A, etc.
 But these aren’t quite linear relations, and lower currents yield
even more ampere-hours
 Engine-cranking currents of ~500 A are for 30 seconds periods and
then the alternator recharges the auto battery
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25.11.2 Conclusion
 Solar PV cells tend to lose capacity (~10%) due to some
darkening of the cover glass; use more area than
needed to compensate
 While PV is expensive at $3.50/W to $14/W, the low
installation costs (~$5/W) reduce the overall cost as
compared to a diesel generator
 Research similar installations to gain understanding
 Evaluate intended loads closely
 Use spreadsheets to change system parameters readily
Make these into a report format
 Isolated remote sites have no alternative utility power,
and some assumptions are warranted
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25.11.3 Solar Thermal
 Solar thermal energy for water heating is simply done
with uncomplicated materials
 To get higher temperatures (>180 degrees F), the sun’s
rays must be concentrated on the collector
 Parabolic single-curved surfaces are inexpensive and
increase the energy by the ratio of the sunlight
interception area to the collector pipe area
 Paraboloidal (dish) surfaces are more expensive to make
but increase the temperatures still further
 The SEGS solar thermal plants near Barstow CA use long
rows of parabolic reflectors to heat oil to ~700F, which
then heats water to steam to spin a turbine
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25.11.3.3 Conclusion: Solar Thermal
 Solar thermal systems are cost effective at low
temperatures
 Solar water heaters are energy savers, but initial cost
dissuades many from using them
 Power tower (Solar Two) electricity cost is at $6/W peak
Not competitive
 Massive power tower yields 10 MWe, while a typical
utility plant is 500 MWe
 Power towers aren’t likely to be economically practical
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25.12.1 Wind Energy
 Expensive wind turbines require good assessment of the
local site winds to determine where to place the turbine
 A 10% increase in wind speed can yield a 33% increase
in power
 Obstructions that interrupt a smooth laminar flow of
wind will greatly hamper power production
 Long-term local wind studies ensure an optimal
positioning of a turbine
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25.12.1.1 Wind Energy
 Distant forests will have little influence on wind speed
while a nearby building will have a great influence
 The width and height of a blocking object determines
how much wind-slowing effect will occur
 A flagpole upwind is cylindrical and narrow, thus the
wind stream will reconverge ~5 to 10 pole diameters
behind the pole to resume smooth, fast flow as before
 A rule of thumb is that the wind turbine should be ~500
feet from the nearest large object and at least 15 feet
above it; rules vary
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25.12.1 Conclusion: Wind Resources 1
 Wind resources vary greatly with latitude, season, and
terrain
 Extensive data and wind maps exist for wind prospecting
 At the mesoscale level, topographic information is being
used to create predictions of wind speed from widely
scattered measured data
 Anemometers can be erected to obtain wind speeds in a
likely locale
 An alternative is to erect a small wind turbine to sample
the energy and to help determine where a large turbine
should be placed
 Wind resources may be excellent, but there is much more
to installing a turbine
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25.12.2 Wind Energy 2
 Wind energy is a statistical variable that is usually much
more time-variable than sunshine
 We traditionally quantify wind energy in “bins” or ranges
of various speeds
 A probability density function (p.d.f.; left) and
cumulative distribution function (c.d.f.; right) define
these variations and make revealing graphs
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http://www.weibull.com/Articles/RelIntro/data_a3.gif
www.pnl.gov/ces/analysis/ sum3fly.htm
25.12.2.1 Wind Energy 2
 The probability of a certain wind speed times the energy of
that speed yields the probable energy; add each of these
products to get the 100% probable energy
 Proportional averaging means multiply the percent of time a
value occurs by the value, sum each of these products to get
the overall average (all of them =100%)
Average = (A + B)/2 = (0.5 * A) + (0.5 * B) = (50% *A)
+ (50% * B)
So 20% * 10 + 80% * 40 = 2 + 32 = 34
 For a wind problem, winds under ~6 mph cause zero output
and don’t turn the rotor because of bearing resistance
 The top 30% of the winds likely produce the majority of the
energy, but too much requires turbine shutdown
 http://www.itl.nist.gov/div898/handbook/eda/section3/eda36
2.htm is a good statistics reference
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25.12.2 Conclusion: Wind Theory
 The theory of wind energy is based upon fluid flow, so it also
applies to water turbines; water density is 832 times more
 While anemometers provide wind speed and usually direction,
it’s data processing that converts the data into information
 Because of the surface boundary drag layer of the
atmosphere, placing the anemometer at a “standard” height of
10 meters above the ground is important for comparisons
 Turbine anemometers are often placed at 150 meters above
ground --- anticipated hub height is ideal
 The erroneous average of the speeds is not the same as the
correct average of the speed cubes!
 The energy extracted by a turbine is proportional to the
summation of (each speed cubed x the time that it persisted)
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25.12.3 Wind Turbines
 Vertical axis turbines are simple but don’t work very well
The wind forces reverse on the blades with each half
turn of the rotor and cause mechanical stress failure
 Three-bladed horizontal axis turbines have good
performance and appear to have the best future
chances of success (this common style works!)
 The turbine power is proportional to the cube of the
wind speed, thus a 20 mph wind has eight times the
power of a 10 mph wind
 This means a wind speed of 20 mph (eight times the
power as 10 mph wind) for an hour yields the same
energy as a 10 mph wind for eight hours!
 The longer gusts are very important for high energy
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25.12.3.1 Wind Turbines
 Large companies investing in renewable energy usually
choose wind or solar as offering the best return on
investment
 Wind power is about one-fifth the solar cost per watt
 Florida doesn’t have very high winds (ignoring
hurricanes), yet GE Power Systems builds wind turbines
near Pensacola, while FPL (formerly known as Florida
Power and Light) is the largest owner of utility size wind
turbines in the US, all elsewhere
 Many turbines were developed in Nordic countries
 Europe has good ocean winds and strong incentives for
renewable energy, thus many turbines
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25.12.3.2 Conclusion: Wind Turbine Theory 1
 The turbine rotor must be matched to the generator or
alternator to maximize the extracted power at lowest cost
 Although most turbines won’t rotate until the wind speed
reaches 6 mph, there is no significant energy lost below
this speed; remember the cube law?
 If better placement (siting) can increase the wind speed
by just 10%, the power increases by 33%
 All parts must be designed to survive high winds, say 140
mph
 Large turbines use yaw motors to aim the nacelle into the
wind; small turbines steer by wind forces on the tail
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25.12.4 Wind Turbines 2
 The exact site determines the annual power available
 Rows of turbines are placed at right angles to the usual
“power” wind direction so they don’t block each other
 Rows are spaced some eight rotor diameters apart to
allow wind speed to re-increase between rows
 Turbines are often remotely controlled from a central
operations site
 Offshore turbines have free access to the unhindered
wind from any direction and yield high energy over a
year
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25.12.4.3 Conclusion: Wind Turbine Siting and Installation
 Turbine siting is somewhat of an art, but science is
providing tools that speed that site selection
 Accurate siting strongly determines the economic and
energy success of the system
 Energy storage is likely to be in batteries for the
foreseeable future; more exotic methods are slow in
reaching a cost-effective market entry
2 MW batteries for wind farms are available
 Since wind energy is the fastest developing energy
source, the economic fall of prices will speed its
adoption where the wind is powerful
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25.13 Bioenergy
 Biomass collects solar energy to build more biomass
 Energy crops that maximize the energy absorption can
be grown for biomass combustors or reactors
 Biomass has less pollution than fossil fuels but still emits
pollution
 Biomass is CO2 neutral since it absorbs CO2 in growing
 The Southeast US has more biomass energy than other
kinds of renewable energy
 Biomass can yield fuels like ethanol, or with still more
processing, methane gas
 Methane also can be produced from agricultural wastes
and manure
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25.13.3 Conclusion: Biomass
 Renewables are a very small contributor to current
Florida energy sources
 Biomass energy is the predominant renewable energy
source available in Florida
 Unfortunately, most of present production is from
municipal solid waste (MSW) that should be avoided or
phased out due to heavy metal contaminants
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http://www.eia.doe.gov/cneaf/electricity/st_profiles/florida/fl.html#t1
25.14 Hydropower
 The large hydroelectric dams of the US West were built
to bring the economy out of depression, put people to
work, and provide cheap energy to spur (pun intended)
the development of the West
 Once installed, the hydro plants had a short time to pay
off and produced cheap energy that attracted high users
of electricity (aluminum plants)
 Boulder Dam (now Hoover) was built to supply Los
Angeles, where many of the dam-haters live
 The Columbia River of Washington State has many
dams, raising the controversy of fish migration and kills
 Some extremists want to breach dams to “let the river
run free” – this would cause extensive economic
damage to the Nation as power systems fail
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25.14 Conclusion: Hydropower
 The majority of logical, large US hydropower sites were
developed in the 1930s
 Hydropower provides inexpensive electricity in the US
Northwest, primarily from the huge Columbia River
 There are still some in construction, like China’s Three
Gorges 18 GW dam
 Africa has only 7% hydro potential developed
 Hydropower in the US West was a result of President
Roosevelt’s work program to increase employment
during a depression and also to provide cheap electricity
to spur commerce
 Small hydropower on the scale of remote home energy is
still developing
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25.15 Ocean Energy
 Because of water density, energy is ~826 times more
dense than for wind energy (power is directly
proportional to density)
 Momentum of water flow can stabilize the flow speed,
so the range of variation is not as great as for wind
 Tidal energy is primarily lunar driven; it’s not renewable
but the time to depletion is when the earth-moon
angular momentum decays a great deal; the moon is
receding about 3.8 cm per year per NASA laser ranging
 Wave energy varies more than tidal energy and thus
requires greater strength in extraction
 Current flow requires deep water work that increases
the cost
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25.16 Geothermal Energy
 Geothermal energy is categorized into three (3)
qualities:
Low: 0 to ~250 degrees F
Air conditioning or heating
Medium: ~250 to 450 degrees F
Industrial or processing industry
High: ~450 or higher degrees F
High temperature energy generation, testing,
cutting, missile nosecone testing
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25.16 Conclusion: Geothermal
 Geothermal energy is limited in extent as extracting the
heat usually exceeds the replenishment rate
 Hot, dry rock (HDR) is widespread and offers new
resources in areas where geyser activity is unknown
 Direct low-temperature heat transfer for home heat
pump systems is practical as long as low maintenance is
designed into the system
 Sources of high temperature water or steam are limited
and the cost of extraction, maintenance, and operation
will remain high in comparison with other sources of
energy
 Geothermal energy likely to remain at 1% world energy
[Kruger, 1973]
030327/080415
25.17 Transmission of Energy
 Electric currents flowing through wires lose energy as
heat, and there may also be leakage currents across
insulators (especially when it rains)
 Power lost in the wire is P = I2R
 This power loss can be reduced by sending the power at
high voltage and low current; P = V times I
 A step-up transformer has heavy windings on the
primary input and many more windings of lighter
conductor on the secondary or output side
The turns ratio of 10:1 will increase voltage 10 times
and reduce current to 1/10 of the input (for an ideal
transformer)
The process is reversed at the distribution end
080415
25.17 Conclusion: Energy Transmission
 Installation of new power lines and pipelines is usually
met with opposition by NIMBYs
 Doubling of conductors on an existing line doubles the
possible current flow and is not met with vocal
opposition
 The “Hydrogen Economy” will require hydrogen-grade
pipelines to bring the gas from wherever it is made to
the sales points
The only alternative is to carry the hydrogen in tank
trucks in groups of bottles like those used for welding
gases
 Direct radiation of electrical power is unlikely despite
Nikola Tesla’s experiments due to radio interference
080415
25.18 Energy Storage
 Energy may be produced when not needed or be
needed when not available
 Storage of energy allows use at a different time than
when it was produced
 Electricity is more valuable during “prime time” than
during the middle of the night
 The most common form is the storage battery, but other
types are flywheels, compressed air, hydraulic lifting,
chemical storage (like hydrogen), high temperature oil,
or ultracapacitors
080415
25.18 Energy Storage Batteries
 Storage batteries are rated differently for starting
engines (continuous cranking amperes, CCA) than for
powering lesser loads like lights
Reserve capacity (RC) is defined as the time in
minutes to supply a 25 ampere load until the voltage
falls to 10.5 volts for a nominal 12 volt battery
Lesser loads can receive energy longer, while heavier
loads drain the battery faster
The battery capacity (BC) is approximately 25
amperes * RC; if RC = 180 minutes, then BC = 25 *
180 = 4500 ampere-minutes or 75 ampere-hours
As an approximation, multiply the RC by 25A and
divide by the actual current drain: say 180 minutes *
25 A/20 amperes = 225 minutes until 10.5 V
030427
25.18 Conclusion: Energy Storage
 Energy storage is to be avoided due to the losses of
energy storage and removal, but may be economic when
load time-shifting is possible
 Energy must be stored in vehicles since they cannot
obtain sufficient power from wind or sun on the vehicle
Special student SunRayce PV cars are fragile and light
(built about as strongly as a model airplane), and
cannot be used at normal highway speeds without a
significant death rate
 Newer technologies may increase energy storage density
at a lower cost; both are needed for a viable product
040415
25.19.1 Transportation Energy
 Transportation by steel wheel on steel rails is most
efficient because of the low deformation of steel
 These vehicles can only go where the rails are located
 Car and truck are less restricted, and the low cost allows
people to move wherever they desire
 Changing from rail to cars requires extensive road
systems that form an area of transport instead of the
linear corridors of rail systems
 As population growth expanded, service of the people
by train was more difficult since they still had to get to
the station
 High-speed rail is touted as a better way to move people
medium distances
040415
25.19.1.1 Transportation Energy
 Florida voters changed the state constitution to mandate
high-speed trains to service the major cities
While the cost wasn’t specified to distract them,
maglev trains reaching 300 mph were implied
The cost of such systems was so great that a first link
from Tampa to Orlando is projected to cost nearly $4
billion dollars and will likely be conventional rail
running at a speed just over 100 mph
The fares can’t be made high enough to pay off such
a system or passengers would seek other ways
A just fare might be $2000 for Tampa to Orlando
Public subsidy will be required indefinitely, so the
nonpassengers can pay for the few passengers!
040415
25.19.1.1 Transportation Energy
 Airline travel requires jet fuel to power the engines
 Some experiments with hydrogen and even electric/fuel
cell engines are possible
 The high energy density of liquid fuels cannot readily be
replaced by highly compressed gas
 Compressing gas costs energy
 A return to synfuel made from coal may be necessary
(the Germans did this during World War II), or possibly
transcontinental flights will require more stops for
refueling
040415
25.19.1.3 Conclusion: Transportation
 Changes in lifestyles have led to a highly mobile US
society
 Public transportation declined as more people drove a
car and were disinclined to wait for a bus or a train
 In high density areas, exorbitant parking charges
($20/day at New York City Days Inn), traffic delays, and
convenient trains or light rail shift public use back to
public transportation
 Long-haul trains, ships, and barges carry freight, having
a decline in passenger travel
 Still, short-term ships carry tourists, as do AMTRAC
trains
 The heavily congested Northeast US has the most use
of fast trains for commuting to work or school
030412
25.19.2 Transportation Energy: Cars, Etc.
 Alternative fuel vehicles (AFVs) use ethanol, methanol,
compressed natural gas, propane, or hydrogen
 The alternative is other than gasoline or diesel
 Some hydrogen-fuel-cell cars are being tested in Los
Angeles, California; the manufacturer furnishes the
hydrogen
 Electric cars use utility energy stored in batteries
Where did the electricity come from?
Electric cars are being discontinued since hybrid
electric cars are more widely accepted by the public
030427
25.19.2 Transportation Energy
 The DOE Clean Cities Program has a local group, the
Florida Space Coast Coalition, that is based at the
Florida Solar Energy Center (FSEC) in Cocoa
http://www2.fsec.ucf.edu/env/fsccities/spccst.htm
 About “twenty-six years after the energy crisis, we’re
still sending money – about a billion dollars a week –
somewhere else” – Dan Reicher, Assistant Secretary for
Energy Efficiency and Renewable Energy, DOE
030427
25.19.2.3 Conclusion: Transportation 2
 Introduction of alternate fuel vehicles will require a long
period of adjustment by the public
 At one time, “full service” gas stations seemed
necessary, but most people now found they could pump
their gas in order to pay a lower cost
 Perhaps CNG stations will need “full-service” at first
030409
25.19.2.3.1 Conclusion: Transportation 2
 Current hybrid vehicles are user-friendly, thus will be
rapidly accepted by the market if price falls
In transition over 10 years, they may be the common
vehicle before some other type dominates the market
Now, the Plug-in Hybrid Electric Vehicle (PHEV)
seems the most likely in the future
 Vehicle changes are driven by cost above all else; if
costs increase due to government pollution or carbon
taxes, an economic shift will begin to occur
070424
25.20 Distributed Generation
 Distributed generation (DG) is diffuse and consists of
many small sources interconnected by the power grid
 Central utilities plants are often rated at 800 MW per
section, and they often have two or three sections
 Distributed plants are perhaps 3 kW to 30 MW, but there
are many of them
 Since the plants feed the grid as well as supply their
own loads, there is a robust energy supply that resists
outages
030427
25.20 Conclusion: Distributed Generation
 Distributed generation is less vulnerable to outages since
there are so many local sources of supply
 Winter ice storms can stop electrical power over a much
wider area than a terrorist attack
Critical loads are better protected when nearby
multiple sources are available
 Computer and industrial processes require backup power
to prevent secondary problems caused by loss of power
 Independent energy systems can use failure-resistant
sources like multi-day fuel tanks or natural gas pipelines
 Islanding of multiple power sources is a concern for
power line workers, yet this robustness ensures power
stability
040415
25.21 Economics of Energy
 Sustainable energy is essentially renewable energy
 If an amount of coal took a million years to form, using
a millionth of that amount each year would be
sustainable (that amount would be pathetically small)
 Great amounts of solar energy strikes the earth each
day, and recovery would satisfy human needs without
depleting it
 Ethically, we should use only enough energy that we are
neither better off nor worse off than some distant future
generation
 The present value of money can be computed to
evaluate the risk of a project
030427
25.21 Conclusion
 The cost of money must be included in economic
decisions since, generally, inflation will occur in the
future
 Limited resources should be used with an amount set
aside for future generations
 While the use isn’t sustainable, the result and benefit to
a future period should be equivalent to that for this
period
 Eventually, costs will rise until a different type of
renewable energy becomes a better choice
030419
25.22 Tradeoffs and Decisions
 Tradeoffs provide a systematic way to evaluate choices
and select the “best” one
 Uncertainty in various estimates may tend to be
forgotten but should not be!
The square root of the sum of the squares of
uncertainties yields the uncertainty of the total
 Weighted scoring allows the importance of various
parameters to be adjusted
 Adjustment of the weights will greatly affect the
outcome
 Be wary of forcing the outcome to be what you want it
to be
030427
25.22 Conclusion: Trades
 Renewable energy is faced with the same types of
problems that affect other areas of daily living
Getting permission to do something different than
what is codified in law or local ordinances (variance)
Convincing the public or government officials that the
project is not a nuisance and will be beneficial to the
community
 Trade studies that produce a well-written report
documenting the situation, goals, choices, and selections
may help to sway those with the power to approve or
disapprove your proposal
 Practice these trade studies on small projects to be
prepared to do the large projects
040415
25.23 Legal Considerations
 Energy projects are constrained by laws, regulations,
and ordinances
 Compliance is mandatory to avoid fines or imprisonment
 Design of an energy project must include the costs of
licensing, inspection, and pollution prevention, etc.
 Comprehensive plans define the uses for various
geographic areas or districts
 Code compliance is necessary for the public good
Codes written by professional organizations are often
recognized in law or ordinances by reference “shall
comply with Sect. Xxx of the National Electrical Code
. . . “ phraseology
030427
25.23 Conclusion: Legal
 Legal restrictions enforce many things that people should
do, but perhaps would not due to cost or bother
 The public good is protected by these laws and
regulations
 Without legal requirements, there would be no possibility
of recovery for loss or injury
 Renewable energy installations should be designed to
comply with these restrictions
 Oh, yes --- ethics is what you do when no one is
watching and no one will ever know but you
070424
24 Conclusion: Review
 This review synopsizes the key points of the Renewable
Energy course, ENS4300
 Study of this presentation provides a good starting point
for mastering the final test, but you will find study of the
original presentations also is helpful
 Where additional presenters assisted, you may need to
study your class notes if no PowerPoint slides were
available
 Good luck on your exam and in your career!
Frank Leslie
040415
25.1 Some Interesting Facts
 Earth’s axial tilt = 23.5 degrees (23.45)
Earth-sun distance = 92 M miles = 92,955,820.5 miles = 149,597,892 km
Earth Equatorial Radius = 6378137 m (WGS-77)
 Wind Turbine Power, P = ρ/2·A· U3 watts, where ρ (rho) is 1.225 kg/m3, A is
area = π r2 m2, r= blade radius in m, U = wind speed in m/s.
 “P = 0.5 · ρ · A · Cp · V3 · Ng · Nb
 where:
P = power in watts (746 watts = 1 hp) (1,000 watts = 1 kilowatt)
ρ = air density (about 1.225 kg/m3 at sea level, less higher up)
A = rotor swept area, exposed to the wind (m2)
Cp = Coefficient of performance (.59 {Betz limit} is the maximum
theoretically possible, .35 for a good design)
V = wind speed in meters/sec (20 mph = 9 m/s, or 2.24 mph =
1 m/s)
Ng = generator efficiency (50% for car alternator, 80% or possibly
more for a permanent magnet generator or grid-connected
induction generator)
Nb = gearbox/bearings efficiency (depends, could be as high as
95% if good)”
 (from AWEA, the American Wind Energy Association)
030419
25.2 Some Interesting Facts
 Average wind power density, P/m2 = 6.1x10-4 v3 watt/m2, where v is
m/s
 Locations: Arctic Circle is 66.55º N; Big Blow, Texas is 31º N,
103.73º W; Colon, Panama is 9.7º N, 80º W; Cicely, Alaska is 66.55º
N, 145º W; Florida Tech, Melbourne FL, 28.2º N, 80.6º W; Panama
City, Panama 8.97º N, 79.53º W; Paris, France is 48.8º N, 2.33º E;
 Area of sphere = 4 π r2
Volume of a sphere is 4/3 π r3
P=E*I=E2/R=I2R; E or V=IR
 Typical computer/monitor power is 150 watts. “Standard” 40 W
fluorescent ceiling lamps were/are being replaced by newer T8, 32 W
lamps.
 The Link Building power meter (SE corner) indicates a typical
weekday power load to be 60 kW, and nights/weekends, it is 35 kW.
 A copy machine is on only during office hours (8 to 5) weekdays and
usually draws 190 W. When copying, it draws 900 W.
 FPL charges $0.10/kWh for electricity (ignore demand charge and
billing charge, taxes, etc.)
080415
25.3 Some Interesting Facts
 Melbourne FL, Dec. 24-hour radiation on a horizontal
surface is 150 W/m2 (?) and annual direct normal energy
is 2.5 to 3.0 kWh/m2. Direct normal often is 1000W/m2
 Air density is 1.225 kg/m3;
Kinetic energy = 0.5 mv2
joules, where v is in m/s
 K.E. also = p / (R·T), where p = pressure, T = Kelvin, and
R = gas constant = 287.05 Joule/Kg/K for air
 Snell’s Law: Angle of Incidence = Angle of reflection
 Altitude of the sun = 90º -latitude + sun declination;
azimuth is the horizontal angle clockwise from north
 (declination is the varying solar latitude+/-23.45 degrees)
040415
Olin Engineering Complex 4.7 kW Solar PV Roof Array
Questions?
080116
References: Books
 Boyle, Godfrey. Renewable Energy, Second Edition. Oxford: Oxford
University Press, 2004, ISBN 0-19-26178-4. (my preferred text)
 Brower, Michael. Cool Energy. Cambridge MA: The MIT Press, 1992. 0262-02349-0, TJ807.9.U6B76, 333.79’4’0973.
 Duffie, John and William A. Beckman. Solar Engineering of Thermal
Processes. NY: John Wiley & Sons, Inc., 920 pp., 1991
 Gipe, Paul. Wind Energy for Home & Business. White River Junction, VT:
Chelsea Green Pub. Co., 1993. 0-930031-64-4, TJ820.G57, 621.4’5
 Patel, Mukund R. Wind and Solar Power Systems. Boca Raton: CRC
Press, 1999, 351 pp. ISBN 0-8493-1605-7, TK1541.P38 1999, 621.31’2136
 Sørensen, Bent. Renewable Energy, Second Edition. San Diego: Academic
Press, 2000, 911 pp. ISBN 0-12-656152-4.
 Tester, Jefferson W. , Elisabeth M. Drake, Michael J. Driscoll, Michael W.
Golay and William A. Peters
Sustainable Energy Choosing Among Options. Boston: MIT Press, 870 pp.
July 2005 ISBN-10:0-262-20153-4
090404
References: Websites, etc.
awea-windnet@yahoogroups.com. Wind Energy elist
awea-wind-home@yahoogroups.com. Wind energy home powersite elist
geothermal.marin.org/ on geothermal energy
mailto:energyresources@egroups.com
rredc.nrel.gov/wind/pubs/atlas/maps/chap2/2-01m.html PNNL wind energy
map of CONUS windenergyexperimenter@yahoogroups.com. Elist for
wind energy experimenters
www.dieoff.org. Site devoted to the decline of energy and effects upon
population
www.ferc.gov/ Federal Energy Regulatory Commission
www.hawaii.gov/dbedt/ert/otec_hi.html#anchor349152 on OTEC systems
telosnet.com/wind/20th.html
www.google.com/search?q=%22renewable+energy+course%22
solstice.crest.org/
dataweb.usbr.gov/html/powerplant_selection.html
090416