Transcript of "Multivariate Analysis Of Energy Policy Options Using Lindo"
A Multivariate Analysis of Energy Policy Options for
the United States of America using Lindo.
Brian D. Bissett, Member, IEEE
Abstract—The eventual depletion of fossil fuels was first While petroleum contributes a nearly insignificant amount
modeled by geophysicist M. King Hubbert, who predicted using a toward electric power generation in the United States, it
left skewed Gaussian curve in 1956 that U.S. oil production would provides 96% of the energy required for the United States
peak in the year 1970 and decline thereafter. While initially
transportation needs. The remaining 4% is divided evenly
ridiculed, the Hubbert analysis has proven to be remarkably
accurate, with the prediction of peak U.S. oil production off by between natural gas which is used to power some busses in
only one year. Hubbert also predicted using the same model that large metropolitan areas, and electric which is used to power
world oil production would peak in 2000 . The peak of world some rail systems, most notably Amtrak along the entire
oil production is a topic of much debate with some experts northeast corridor . The world currently produces 82.5
predicting peak production has already occurred, while more million barrels a day, of which one fourth is consumed by the
optimistic projections suggesting the peak will not occur until
United States. The United States consumes 20.7 million
2030 or beyond . The inevitability of an eventual decline in the
production of oil is generally accepted at this point in time, but barrels of oil a day, of which only one quarter is produced
the question of how to make up for the loss of energy generated domestically. Of this 20.7 million barrels of oil, 9.3 million
by oil and other non renewable energy sources has yet to be barrels (or 390 million gallons of gasoline) are utilized solely
answered. With the GDP heavily influenced by the price of crude for motor vehicle use. When diesel and all other motor fuels
oil , the future economic health of the United States is in peril are allocated for, 70% of the oil consumed in the United States
without a sound energy policy. In addition, the effect of high
energy prices on the economy is underreported by the U.S.
is utilized for transportation needs. The shortfall in US oil
Federal Reserve as both energy and food prices are not included production is made up for by imported oil, of which the OPEC
in the core inflation index . This paper will present one cartel provides nearly a third of US energy needs. The single
potential method of modeling how to allocate energy generation country which supplies the largest chunk of US oil imports is
methods for the future energy requirements of the United States. Canada, which provides a total 4.25 million barrels of crude
oil and petroleum products per day. Saudi Arabia is the top
Index Terms - energy, “energy policy”, “fossil fuel”,
producer of crude oil generating 10.6 million barrels of oil per
electricity, “electric power generation”, “electric power plant”,
power, “power generation”, “power generation efficiency”, coal, day. Even if Saudi Arabia were to supply the output of all its
oil, “natural gas”, petroleum, “nuclear power”, geothermal, oil fields to the United States, it could supply only one half of
hydroelectric, “tidal power”, solar, “solar power”, “wind power”. the oil the United States requires .
I. INTRODUCTION Percentage of Non-Renewable Resources Located in the United States
E lectric power generation in the United States comes
principally from three sources: coal, natural gas, and
nuclear power plants, none of which are renewable power
sources, yet produce nearly 90% of the electricity consumed in 35
the United States. The largest renewable power generation 30
source in the United States is hydroelectric power at (7.1%), Percentage 25
but the contribution of renewable power sources toward
current national needs is minimal and in fact under 10 percent. 10
(See Figure 1) 5
Petroleum Natural Gas Coal Nuclear
United States Electrical Power Generation Sources
Figure 2: United States “Ownership” of Non-Renewable Resources .
At the present time the United States is clearly dependant on
four nonrenewable sources of energy to supply nearly all of its
19.6% Coal Oil energy needs. Coal, natural gas, nuclear power, and petroleum
provide the energy required for the country to function on a
daily basis. Figure 2 shows the world resource allocation of
Oil these nonrenewable resources relative to the United States. In
descending order, the United States has the greatest supply of
coal, nuclear fuel (U3O8 – “yellow cake”), natural gas, and
petroleum. A comparison of Figure 1 with Figure 2 shows that
Figure 1: Electrical Power Generation in the United States . US energy requirements are not met in proportion to access
and control of resources. This subjects the United States CO2 emissions into deep underground reservoirs for long-term
economy to the whims of geopolitical instability, as the control storage. Pumping CO2 into oil reservoirs is an established
of energy prices and energy access are not entirely within its method to enhance oil recovery over the conventional method
means. The most precarious situation is that the United States of pumping water into an oil reservoir. The Weyburn
owns less than 2% of the world’s supply of the resource that Enhanced Oil Recovery Project in North Dakota and Canada
provides 96% of the energy for its transportation needs has used CO2 from an area coal-gasification plant to enhance
(petroleum). The situation is not much better for natural gas oil extraction since 2000. Long-term sequestration methods
where the United States owns 3.36% of a resource that may evolve from these methods but according to a report from
provides nearly a fifth of its electrical power. It is hardly the Massachusetts Institute of Technology, CCS is not yet
surprising if there is the slightest disruption in natural gas guaranteed to work on the scale necessary to contain 90% of
production that the price skyrockets. the emissions from a major power plant, a Department of
Table 1 lists the four most prevalent nonrenewable energy Energy (DOE) goal .
resources along with the known reserves in both the United Integrated gasification combined cycle (IGCC) provides
States and the entire world. improved energy recovery from coal as opposed to burning the
coal to drive an electricity-generating turbine with pressurized
Global Reserves United States Reserves
Known Units Known Units
steam. By heating the coal under an oxygen and water
1,237.64 Billion Barrels
6,288.57 Trillion Cubic Feet
20.97 Billion Barrels
211.09 Trillion Cubic Feet
atmosphere (no nitrogen), the gasification process generates
Coal 998.00 Billion short ton 491.00 Billion short ton selected combinations of product, including heat energy,
Nuclear 5,469,000.00 U3O8 tons 445,000.00 U3O8 tons
carbon monoxide, hydrogen, methane, and carbon dioxide.
Table 1: Known Reserve Levels for Nonrenewable Resources.  The carbon monoxide or methane can serve as a chemical
feedstock, or burn completely to carbon dioxide. Similarly, an
II. NONRENEWABLE ENERGY SOURCES IGCC plant can collect hydrogen as an added fuel product or
power an additional gas-driven generator to produce
A. Coal electricity. Remaining solids can find use in a conventional
Coal has the distinction of being the most abundant coal-burning furnace as a low-grade fuel. The leftover mineral
nonrenewable energy source in the United States. As of components are often recovered as useful industrial materials,
October 22, 2007, there are 1,493 coal fired electrical power an example being fly ash which is recovered from coal-burning
plants operating in the United States . Coal is frowned upon plants for use in concrete .
in many circles as an energy source because of the high In addition to (CO2), oxides of nitrogen (NOx), and sulfur
amounts of CO2 and pollutants coal burning energy plants (SOx), are pollutants emitted in large quantities by coal fired
release into the atmosphere. Each year coal burning plants power plants. Air quality legislation and regulations under the
release 9.3 billion metric tons of CO2 into the atmosphere . Environmental Protection Agency’s Acid Rain Program focus
Coal as a resource however is simply too viable of a on reducing the emissions of oxides of nitrogen (NOx) and
commodity to ignore. The United States has enough coal to sulfur (SOx).
supply its energy needs for an estimated 1,500 years . The
coal seam running under Pittsburgh, Pennsylvania alone could
provide 250 years worth of power to the United States .
In recent years, a number of new technologies have emerged
to reduce the levels of emissions generated by burning coal.
Clean coal is a marketing term often utilized to describe a
group of technologies and industry practices that significantly
increase coal-derived energy generation efficiency (including
coal gasification), while reducing coal power plant emissions.
Due to dramatic advances in pollution control technology,
emissions from coal plants, with the exception of CO2, can be
Table 2: NOx Reduction Technologies 
reduced to about the same level as natural-gas electricity
generation. These pollution control measures however also
The Clean Coal Technology Demonstration Program is a
adversely impact the economics of coal power generation .
partnership of the DOE and US industry that has the goal of
The two most widely utilized pollution control technologies
successfully demonstrating advanced coal based pollutant
for coal burning power plants are carbon capture and
reduction technologies. Its intent is to move the most
sequestration (CCS), and Integrated gasification combined
promising technologies into the domestic and international
cycle (IGCC). These technologies do not come cheaply, each
adds about 50% to the cost of electricity generated by a coal
The Clean Coal Program demonstrations were developed
power plant .
with the intention of retrofitting existing coal power plants to
Coal power plants equipped with CCS pressurize and pump
reduce NOx and SOx emissions independently, and for
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technologies that achieve combined SOx and NOx emission Burner (LNB)/SNCR wet scrubber and the fluidized bed
reductions. Tables 2 through 4 identify the technology or absorber. The incomplete status of the latter projects is the
process and present data pertinent to the environmental and reason that capital costs are not available .
economic performance of each.
Table 2 identifies NOx reduction technologies and presents
environmental and economic data pertinent to each. Two
projects presented in Table 2, advanced over fire air 1 generis
NOx control intelligent system (GNOCIS) and reburning
micronized coal, have not been completed and, therefore, do
not have final data available. Additionally, levelized busbar
costs and retrofit market estimates were not available for the
advanced tangentially fired boiler technology.
The Clean Air Act Amendments of 1990 (CAAA) and
proposed regulations require significant reductions of NOx
emissions from electric utility plants. The Ozone Transport
Table 4: Dual NOx & SOx Reduction Technologies 
Assessment Group recommends a NOx emission reduction of
85 percent compared to the 1990 rate in the designated fine
One potential pitfall to increasing the use of coal is that one
grid areas (areas of most serious air pollution). This translates
of the most widely utilized pollution control technologies for
to an emission limit of 0.15 pounds of NOx per million British
coal burning power plants, carbon capture and sequestration
Thermal Units of coal burned. 
(CCS), has yet to have any long term studies done. It remains
It is apparent from Table 2 that no single technology can
to be seen if carbon capture and sequestration can be done
achieve the required percentage reductions, with the possible
safely at a large scale for a long period time.
exception of selective catalytic reduction (SCR). This may
The scale of sequestration required for large coal power
mean that combinations of two technologies will be required to
plants could cause unknown changes in soil chemistry. The
achieve emission standards, thereby increasing the cost of
possibility also exists that stored carbon dioxide could leak,
compliance. Because SCR treats post-combustion stack gases,
causing other unforeseen problems.
it can be retrofitted on any coal-fired boiler. Its market
The U.S. Department of Energy's current Clean Coal
potential includes all coal-fired boilers.
program does not have sufficient funds to meet to commit to
large-scale projects to store carbon dioxide underground at
coal-fired power plants as suggested by the Massachusetts
Institute of Technology.
While utilizing more coal as an energy source represents a
challenge in terms of minimizing the harmful effects upon the
environment, the challenges to do so do not seem
insurmountable given the variety of existing pollution
controlling options available. Given the sheer volume of
domestically available coal, it would be irresponsible to not
investigate the potential exploitation of this proven energy
source for future energy needs.
Table 3: SOx Reduction Technologies 
B. Natural Gas
SOx constitutes another pollutant emitted in large quantities Natural gas was at one time heralded as the best solution to
by coal fired boilers. Together with NOx, SOx creates acid rain the energy needs of the United States. Electric generation by
deposition, causing acidification of lakes and rivers leading to natural gas has many advantages over oil, nuclear power, and
fish kills. It also results in the killing of trees, particularly coal. Natural gas has essentially zero waste disposal costs.
above 2,000-foot elevations. Emission standards are also being Unlike coal and nuclear plants, the cost of electricity from
tightened for SOx, and it is assumed that many power plants natural gas plants is not highly sensitive to interest rates .
will need to retrofit new technology in order to achieve the Non-fuel operation and maintenance expenses strongly favor
newly legislated standards. Table 3 displays the SOx reduction natural gas combined cycle plants as they require smaller staffs
technologies funded by the Clean Coal Program together with to operate, have less boiler tube wastage, and lower
pertinent data for each. Each of the projects listed in Table 3 component replacement costs when compared to coal, oil, and
has been completed. nuclear power plants . Natural gas plants are the cleanest
Combined SOx and NOx Reduction Technologies (Table 4) commercial fossil fuel fired powerplants, emitting essentially
lists the technologies in the Clean Coal Program that can zero SO2 and particulates, and the lowest levels of NOX and
achieve reductions in both SOx and NOx. All the projects listed CO2 . In addition, natural gas plants emit half of the CO2
in Table 4 are completed, with the exception of the Low NOx
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of coal-gasification plants . Natural gas plants also have repealed the sections of the Powerplant and Industrial Fuel
short lead times and can be constructed quickly, allowing gas Use Act that restricted the use of natural gas by industrial users
fired power plants to more closely track electric demand and electric utilities .
growth and preventing electricity rate shock . Natural gas The current shortage of natural gas is due to more ominous
plants are economic at a much smaller size (in MW) than their reasons. The United States is a large producer of natural gas,
coal, nuclear, and oil brethren . second only to Russia, and 85 percent of the gas used here
In spite of all its advantages, natural gas has one hurdle it is comes from domestic wells . Canada, with large reserves
unlikely to overcome – dwindling supplies in the United States and geographic proximity, provides more than 90 percent of
and Canada. Shortages of natural gas are now occurring in the the natural gas exported to the United States, satisfying the
United States and have occurred in the past during the 1970s. bulk of the United States’ 15 percent shortfall. Canada
In 1956, Hubbert used an estimated ultimate recovery however has continued to produce natural gas faster than it
(EUR) of 850 trillion cubic feet (an amount postulated by replenishes its reserves. Canada’s production/reserves ratio
geologist Wallace Pratt) to predict a US production peak of (the number of years of proven reserves remaining at existing
about 14 trillion cubic feet per year to occur in approximately production levels) has declined from 35 years in 1985 to 9
1970 . years in 2006 . Canadian imports to the United States are
US natural gas production reached a peak in 1973 at about now slowing, as demand for natural gas grows at home.
24.1 trillion cubic feet, and declined through 1976. New
discoveries in the Gulf of Mexico, development of
"unconventional reserves", and new gas discoveries in
Prudhoe Bay, Alaska proved Pratt's EUR estimate to be too
low, as US gas production rose again .
Hubbert revised his peak gas estimate in 1971 based on
updated reserve information. He revised his estimated ultimate
recovery upward to 1,075 trillion cubic feet for the lower 48
states only, and predicted: "For natural gas, the peak of
production will probably be reached between 1975 and 1980"
. Gas production for the lower 48 states in fact did peak in
1979, and declined for several years, but then began rising
again, principally from new gas discoveries.
The direct cause of the natural gas shortages in the 1970s
was price regulation by the Federal Power Commission. By Figure 3: Canada's Ability to Supply US Natural Gas Shortfalls is
maintaining an artificially low price, the FPC made natural gas Diminishing .
the choice fuel (for those consumers who could obtain it), so
its demand grew rapidly. At the same time, the low prices For many years the price of natural gas oscillated within a
depressed supplies. This occurred for two reasons. First, the narrow corridor, rising and falling slightly with respect to
incentive was removed for the exploration and discovery of supply and demand. From roughly 1984 to 1993, this price
new natural gas reserves, and as a result, total U.S reserves of corridor was upper bounded at about $7.00 per thousand cubic
gas fell by about a third between 1967 and 1976. This feet, and lower bounded at about $5.00 per thousand cubic feet
dwindling reserve base made it impossible for producers to (Figure 4) . From about 1994 to the present day, natural
satisfy the demand for new long-term contracts. Second, low gas prices have been rising in an exponential fashion. At the
prices removed the incentive to produce gas out of existing current utilization rates, natural gas supplies are being utilized
higher cost reserves, so production from these sources fell faster than they are being replenished by exploration. The
irrespective to their level of reserves. This situation of rapid consequence of much tighter supplies of natural gas makes it
growth in demand combined with dwindling supplies led to a much more difficult for the market to supply large quantities of
shortage of natural gas during the 1970s . excess natural gas needed during times of peak consumption,
In response to the 1973 oil crisis and natural gas such as excessively cold winters. This accounts for the greater
curtailments of the mid-1970s, the U.S. Congress restricted peak to peak variation in the oscillations of the price of natural
construction of power plants using oil or natural gas with the gas. In today’s current market, price variations of $5.00 per
Fuel Use Act of 1978. The Fuel Use Act of 1978 also thousand cubic feet are not uncommon whereas decade ago
encouraged the use of coal, nuclear energy, and other they were half that amount. If this trend continues, the price of
alternative fuels, while restricting the industrial use of oil and natural gas will reach ≈ $93.00 per thousand cubic feet in 2025
natural gas in large boilers. In the early 1980s, the demand for and ≈ $155 per thousand cubic feet in 2030. Unless vast new
natural gas declined significantly, resulting in price declines reserves of natural gas are discovered in the United States and
. Canada, the percentage of natural gas fired power plants in the
Enactment of the Natural Gas Utilization Act in 1987 United States should be frozen if not reduced. At current
consumption rates, Canada will be unable to make up for the
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shortfall in United States production by the year 2015.
Because no long term repository currently exists for HLW,
currently existing waste from operating nuclear power plants is
being stored at the various reactor sites where it was generated.
This was not the planners’ intent. When most US reactors were
built, it was assumed that spent fuel would be stored only
briefly on site, and would then would be sent to a central
facility for reprocessing (removal of fission products and
recovery of fissionable elements for reuse). For economic
reasons and because of concerns about control of weapons-
grade materials, reprocessing has not become an option in the
United States, and electric utilities have found ways to extend
their on-site storage capacity .
The United States has approximately 56,000 tons of high
Figure 4: Natural Gas Prices have begun to Grow Exponentially . level nuclear waste stored in cooling pools and dry casks at
over 100 sites in 39 states . If no new nuclear plants are
C. Nuclear built, the total spent fuel accumulation is projected to be about
As of December 31, 2007, there are 104 commercial nuclear 85 thousand metric tons by 2030 . This exceeds the
power plants licensed by the U.S. Nuclear Regulatory capacity of the Yucca Mountain Repository by 15,000 tons.
Commission (NRC) to operate in the United States. Of these The Yucca Mountain repository is already over a decade
104 reactors, 69 are categorized a pressurized water reactors behind schedule (its opening has been delayed twice,) and
(PWRs) totaling 65,100 net megawatts (electric) and 35 units probably will not open until about 2020 . Construction of
are boiling water reactors (BWR) totaling 32,300 net the Yucca Mountain facility is challenging because the deep
megawatts (electric) . Sixteen utilities have expressed geological repository must be designed to meet exacting
intentions to build 25 new nuclear power plants in the United performance requirements set forth in regulations written by
States while Senator John McCain is calling for the the Environmental Protection Agency and the Nuclear
construction of 45 new nuclear reactors by 2030 . Nuclear Regulatory Commission. Specifically, the repository must:
power is very much in vogue because its methods of power isolate the high-level waste (HLW) from the biosphere for
generation do not generate greenhouse gas emissions. 10,000 years , have multiple barriers with waste packages
While nuclear power lacks some of the pollution problems that can provide “substantially complete” containment of
of other methods of nonrenewable electricity generation, it has wastes for 300 to 1,000 years , have an engineered barrier
some problems that are uniquely its own. Nuclear reactors system which will prevent the rate of release from the waste
produce high level waste (HLW), which contains fission packages from exceeding one part in 100,000 per year ,
products and transuranic elements generated in the reactor constrain groundwater movement by virtue of its geology from
core. It is highly radioactive, and often thermally hot. Twelve the repository disturbed zone to the environment for at least
of the most common radioactive isotopes commonly found in 1,000 years , have integrity such that its system must be
spent nuclear fuel (HLW) are graphed verses their half life in internal, i.e., it must work by virtue of its own properties and
Figure 5. There is not a single facility in the world built for not rely on human monitoring or intervention, or even the
safe long term storage of high level nuclear waste. The United existence of government .
States is the most advanced in this regard, and is in the process Yucca Mountain’s capacity has been artificially constrained
of building a waste repository at Yucca Mountain, Nevada for to 70,000 tons of waste by statute. This was decided nearly
this purpose . three decades ago when most believed that nuclear power had
Biologically Significant Long-Lived Radioisotopes in Commercial Spent little future in the US. The actual capacity of Yucca Mountain
is in reality much larger. Numerous bills have been offered in
recent years to repeal the artificial 70,000 ton capacity
1,000,000.0000 restraint and replace it with a more scientifically calculated cap
. The Department of Energy believes that the Yucca
Half Life (Years)
Half-life repository could safely hold 120,000 tons of waste .
10.0000 Even if Yucca Mountain could expand its capacity to hold
120,000 tons of waste, it would not be able to hold all of
0.0100 America’s spent fuel if the U.S. adds nuclear capacity.
9 According to one analysis, assuming a 1.8 percent growth in
m m m m ne m m um um um t iu
iu di iu iu it i
tr on c hn America’s nuclear capacity after 2010, the U.S. would fill a
Am Ne Ne Pl Pl Pl
Isotope 120,000-ton Yucca by 2030. At this growth rate, the U.S.
Figure 5: Life of Radioisotopes in Commercial Spent Nuclear Fuel .
would need nine Yucca Mountains by the end of the 21st
Page 5 of 24
century . uncertain how much oil is left in Saudi Arabia’s reserves,
If the United States wishes to expand its energy capacity because the kingdom will not allow an independent auditing of
using nuclear power, the numbers clearly show that the United its reserves . This should be of great concern because
States will need to embrace reprocessing of high level nuclear Saudi Arabia is the world’s top producer of crude oil.
waste in some fashion. The current policy of disposing of all There are two schools of thought with respect to the peak of
spent fuel permanently is a monumental waste of resources. oil supplies. Some continue to believe in the validity of
To create power, reactor fuel must contain between 3 to 5 geophysicist M. King Hubbert’s original prediction that oil
percent enriched fissionable uranium (U-235). Once the production has already peaked and did so in about the year
enriched fuel falls below that level, the fuel must be replaced. 2000 . Others, like Ben Witten of Stanford University,
argue that Hubbert’s prediction was flawed because it failed to
Yet this “spent” fuel generally retains about 95 percent of its
model the asymmetric nature of the oil production over its life
original content, and that uranium, along with other byproducts
cycle, and the model does not account for the possibility of
in the spent fuel, can be recovered and recycled .
multiple production peaks. Witten argues that when Hubbert’s
Many technologies exist to recover and recycle different original model is improved, a more realistic figure for peak oil
parts of the spent fuel. The French have been successful in production is 2018 .
commercializing a process. They remove the uranium and The interesting thing about this debate is that it is somewhat
plutonium and fabricate new fuel. Using this method, irrelevant. The difference between the two opinions as to
America’s 56,000 tons of spent fuel contains roughly enough when the peak of world petroleum supplies occurs are only
fuel to power every U.S. household for 12 years. Some eighteen years apart. This does not leave a very large window
recycling technologies show even greater promise, and would of opportunity to find a suitable replacement resource for
leave virtually no high level waste at all, which would lead to transportation and home heating needs. Unless vast new
the recovery of an almost endless source of fuel. However, reserves of crude oil are discovered, petroleum fired power
none of these processes has been successfully commercialized plants should not be part of the United States future energy
. generation matrix.
Most of the reprocessing technologies, including the process
used in France, were developed in the United States. They III. RENEWABLE ENERGY SOURCES
were abandoned during the Carter administration because of
The need to switch to non-fossil fuels is apparent for two
concerns that a byproduct of reprocessing, plutonium, could be
reasons: eventually the economically recoverable fossil fuel
stolen by a terrorist group and used to make a nuclear bomb. It
resource base will be depleted, and the conversion of
is difficult to imagine that any form of chemical reprocessing additional large quantities of naturally sequested carbon to
would be more proliferation resistant in the short term than not atmospheric carbon dioxide could result in an unprecedented
reprocessing at all, and leaving the plutonium mixed in with rapid global climate change.
the highly radioactive fission products in the solid fuel matrix. Renewable energy power plants all share some common
Proponents of reprocessing however, argue that burying traits. They require a great deal of starting capital to build.
plutonium containing spent fuel creates an unacceptable long- The large up front costs of renewable energy power plants are
term hazard, since the half-life of the most important offset however by low variable costs and no fuel costs. In a
plutonium isotope, 239Pu, is 24,000 years . paradigm where fuel is essentially free, efficiency
If nuclear power is to play a greater role in the future energy improvements are far less critical factor for renewable energy
needs of the United States, it will be imperative to power plants.
commercially develop some form of HLW reprocessing. This
is probably why the Department of Energy has proposed that
geological storage of spent fuel be kept open for possible
retrieval for at least 100 years after emplacement begins .
The Fuel Use Act of 1978 restricted the construction of oil
fired industrial power plants using large boilers. In addition to
the legal restrictions in place for new applications of oil fired
electric power plants, high demand for oil in the
transportation sector and for household heating applications
has limited the continued utilization and replacement of
existing oil fired electric power plants. Today oil fired power
plants provide only about one percent of the electric power Figure 6: Geothermal Resources in Continental United States .
used in the United States. A. Geothermal
In addition to the above obstacles, oil has another hurdle it Although estimates of available geothermal resources are
cannot overcome. Petroleum is becoming scarce not just in the
uncertain until exploratory work is done, the Northwest Power
United States, but throughout the entire world. It is even
Planning Council has identified eleven specific areas in the
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western United States where it expects there are about 2,000 Lardarello, Italy, in 1904 .
megawatts of developable geothermal resources. Geothermal Current exploration activities in the U.S. typically concern
areas in the western United States are usually found where 10 to 50 MW projects. Recent interviews with geothermal
there has been relatively recent volcanic activity. Alaska also developers provided exploration cost estimates averaging
has approximately 30 low to moderate temperature geothermal $150/kW . Most lending institutions require 25% of the
systems located in the interior of Alaska . total project capacity to be confirmed prior to lending money
Most geothermal electrical plants use either flash or binary to a geothermal developer . The confirmation phase of
technologies. Generally, flash technologies are utilized when a geothermal development consists of drilling additional
geothermal resource has temperatures of 350°F and higher, production wells and testing their flow rates until
and binary technologies are utilized when temperatures are approximately 25% of the resource capacity needed by the
below 350°F. In both technologies, the geothermal fluids are project is confirmed. Production rates of 1000 gpm are
returned to the underground reservoirs and naturally reheated typically required for the geothermal power plants .
for reuse . Confirmation cost estimates for commercially viable
In a flash steam process, water from underground wells is projects average $150/kW . In order to secure steam
separated (flashed) into steam and water. The water is directly delivery, developers usually drill over 105% of the brine
returned to the geothermal reservoir by injection wells, or requirements for the power plant, and have at least one spare
utilized for other processes such as agriculture prior to productive well available to compensate for any steam supply
reinjection. The steam is utilized to drive a turbine and problem. In some cases, financial institutions may require
generate electricity. Any gases in the steam are removed and development of 125% of required flow to the plant. Interviews
treated to remove any dissolved pollutants if necessary. The of geothermal developers revealed that total drilling costs
steam is then cooled to liquid form, and re-injected into the (confirmation + site development drilling) range from
geothermal reservoir. For very high temperature resources, the $600/kW to over $1200/kW, with average drilling costs close
water can be controlled to flash more than once to recover to $1000/kW .
even more energy from the same resource. The temperature of the resource is an essential parameter
influencing the cost of the power plant equipment. Each power
plant is designed to optimize the use of the heat supplied by
the geothermal fluid. The size and thus cost of various
components is determined by the resource's temperature. As
the temperature of the resource goes up, the efficiency of the
power system increases, and the specific cost of equipment
decreases (more energy can be produced with similar
equipment). The temperature of the resource will also
determine the technology choice, steam or binary.
High temperature resources utilize steam power systems,
which are simpler and less costly. The cost of steam plant
equipment rises quickly however as brine temperature
Figure 7: Common Geothermal Power Plant System Configurations . decreases, as a result of efficiency losses. Binary systems
become competitive at temperatures close to 350°F. Despite a
A binary power plant is utilized for moderate-temperature more complex design, binary power systems are generally less
resources. The hot water from a geothermal source is used to expensive than steam systems for temperatures below 350°F.
heat a secondary working fluid with a low boiling point, such The specific cost of binary systems also rises as temperature
as ammonia or isobutane, in a closed-loop system. The drops.
working fluid is vaporized in a heat exchanger and is then used
to drive a turbine generator. A cooling system is used to
condense the vaporized working fluid back into liquid form to
repeat the process. The hot water extracted from the
geothermal resource is then injected back into the reservoir.
The hot water and the working fluid are kept in separate closed
loop systems, so that environmental issues are minimal.
Dry steam is another less commonly utilized method of
geothermal power generation. Dry steam power plants use
very hot steam (>455 °F) and little water from the geothermal
reservoir. The steam goes directly through a pipe to a turbine Figure 8: Geothermal Power Plant Costs vs. Well Temperature .
to spin a generator that produces electricity. This type of
geothermal power plant is the oldest, first being used at The chemistry of the brine is another essential parameter
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that may significantly affect the cost of the power system. The nature, energy content, water content, and permeability of the
four major chemical characteristics that are of concern are: the reservoir. Shallow production wells run the serious risk of
brine scaling potential, corrosiveness, non-condensable gas rapid cooling without proper pressure support, which is
(NCG), and hydrogen sulfide (H2S) content. Each of these obtained by utilizing a suitable barrier formation or separation
characteristics may require additional equipment that can deal distance between cooler and hotter waters in shallow wells
with specific problems or may influence the size of some .
power plant components. Chemicals can cause scaling, and it “Make-up drilling” is utilized to compensate for the natural
is necessary in some geothermal installations to inject a productivity decline of the original geothermal wells by
surfactant into the hot water supply . drilling additional production wells. An Interview of
A TS Cycle Diagram for a typical geothermal power plant is geothermal developers revealed that annual make-up drilling
shown in Figure 9. On the preheater/evaporator side of the costs approximately correspond to 5% of the initial drilling
ORC system, 530 gpm of 164 °F hot water (point A in Figure costs .
9) enters the unit and is cooled to 130 °F (point B), Operation and Maintenance (O&M) costs are not constant
transferring 2.58 MW of thermal energy to the refrigerant. during the lifetime of a geothermal power plant. During the
This energy preheats the 26.8 lbm/s refrigerant mass flow rate first years of operation, O&M costs are expected to be
from 54 °F (state point 4) to 136 °F and subsequently boils the relatively low but will climb progressively as equipment ages
working fluid at this temperature before slightly superheating and requires more maintenance or replacement. Major
it (state point 1). The high-pressure refrigerant vapor is parameters affecting O&M cost are: the plant labor
expanded in the turbine that extracts 270 kW of mechanical requirement, the amount of chemicals and other consumables
power . used during operation, the extent of make-up drilling
requirements, and the cost of the equipment that has to be
replaced throughout the years.
Another important factor that affects the cost of power is the
"capacity factor" (CF) of the power plant. The capacity factor
of a geothermal power plant corresponds to the ratio between
the amount of energy actually delivered to the grid, and the
potential energy that it could have delivered during the period
of time considered. Geothermal plants typically have a CF
around 90% , which is higher than most other power
production technologies. This means that geothermal power
plants typically deliver power at full capacity 90% of the time,
while outages (planned and unplanned events) prohibit power
delivery during the remaining time.
Geothermal power plants do not need external fuel to
Figure 9: Typical Temperature-Entropy (TS) diagram for Geothermal
operate. Once the power project is built, most of its power
Power Plants .
With a typical staffing requirement of 40 employees, the production costs are known, and extremely few market
operating cost of a 50 MW power plant is $7/MWh . The parameters can modify them. Market prices can only impact
size of the power plant is another important parameter that labor and consumables costs, which are minor components of
affects labor costs. Geothermal power plants are advantageous the cost of geothermal power.
because the number of operators needed to run a geothermal B. Hydroelectric
plant is relatively independent of its size. Therefore, most Hydroelectric power currently provides about 7 percent of
existing power plants ranging from 15 to 100 MW require the electric energy needs of the United States . The
similar crews of 5 to 7 employees (working on 24-hour/7-day mechanical power of falling water is an age-old tool. As early
shifts). Thus, significant economies of scale apply, and smaller as the 1700's, Americans recognized the advantages of
plants have substantially higher labor costs than larger plants. mechanical hydropower and used it extensively for milling and
In 2001, the estimated annual cost of power plant pumping. By the early 1900's, hydroelectric power accounted
maintenance was 5% of the initial capital costs . An initial for more than 40 percent of the United States’ supply of
investment of $1400/kW was considered, and maintenance electricity, and in the West and Pacific Northwest sections of
costs were estimated to average $9/MWh . the country during the same time period hydropower provided
The productivity of geothermal wells declines with use and about 75 percent of all the electricity consumed . While
is a complex phenomenon which is caused by pressure and/or other forms of electric power generation have increased in
temperature drops in the reservoir. The productivity decline development, hydropower generation has remained nearly
rate of a well is directly related to its capacity to supply energy constant, resulting in a decline of its total power contribution
to the power plant. The long-term capacity of the resource to to the power requirements of the United States .
deliver energy to the power plant depends on the size, rock A hydropower resource assessment by the Department of
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Energy’s Hydropower Program has identified 5,677 sites in the One of the greatest challenges to provide for our national
United States with acceptable undeveloped hydropower energy needs is the ability to not only provide the energy, but
potential. These sites have a modeled undeveloped capacity of to provide it when it is needed. Renewable energy sources
about 30,000 MW. This represents about 40 percent of the often provide excess energy when it is not needed, at which
existing conventional hydropower capacity . point it can either be stored or wasted. Building infrastructure
A variety of restraints exist on the development of this to store excess energy is costly and problematic, so excess
potential energy source, some natural, and some imposed by energy is often unutilized.
society. The primary natural restraint is terrain unsuitable for Using a process termed pump storage, it is possible for
the construction of a dam. Societal restraints include hydroelectric plants to store power much like a battery.
disagreements about who has the legal right to develop a Pumped storage is a method of keeping water in reserve for
resource, or the impact of changes on environmental peak period power demands. When consumer demand for
conditions from development of a resource. Often, an area power is low, such as during the middle of the night, some of
suitable for a hydroelectric power facility would require a dam the excess energy generated by a hydroelectric plant can be
and reservoir to be built, which would result in the destruction utilized to pump water up to the storage pool above the
of preexisting developments. powerplant (typically the dam.) The water is then allowed to
Finding solutions to the problems imposed by natural flow back through the turbine-generators at a time when
restraints often demands extensive engineering efforts. energy demand is high. The reservoir then acts much like a
Sometimes a solution is impossible, or so expensive that the battery, storing power in the form of the potential energy of the
entire project becomes impractical. Solution to the societal water when demands are low, and producing more power
issues frequently exceeds the costs of solving the problems during peak periods. In addition, excess energy created from
imposed by nature . Because of these factors, the full other renewable energy sources such as wind can be utilized to
potential of hydropower will probably never be realized. pump more water into the hydroelectric reservoir for storage,
where it can later be released to generate power for use during
peak demand times .
A common misconception about hydroelectric power is that
projects must be large like the Grand Coulee Dam in order to
be economically viable. Economically viable hydroelectric
plants have been constructed with water drops of less than 65
feet and generating capacities less than 15,000 kW .
Termed low-head dams, the usefulness of such units is tied to
their ability to generate power close to where it is needed,
reducing the amount of power inevitably lost during
While larger dams produce more power at lower costs than
low-head dams, the number of suitable sites for the
construction of large dams is limited. In contrast, there are
many existing small dams and drops in elevation along canals
Figure 10: Undeveloped Hydroelectric Power Amounts and Locations in the United States where small generating plants could be
Hydroelectric power plants offer some unique advantages
In hydroelectric power generation, two basic types of over other methods of electricity generation. Since
turbines are utilized, but each has many possible variations hydroelectric generators can be started or stopped almost
. Reaction turbines are the type most widely used. A instantly, hydropower is more responsive than most other
reaction turbine is a horizontal or vertical wheel that operates energy sources for meeting peak power demands. In addition,
with the wheel completely submerged, a feature which reduces hydroelectric plants have low failure rates and operating costs.
turbulence. In theory, a reaction turbine works like a rotating The average annual capacity factor of all U.S. hydroelectric
lawn sprinkler where water at a central point is under pressure plants however is only 50%, with larger plants having better
and escapes from the ends of the blades, causing rotation . utilization rates . Hydroelectric plants can be adversely
An impulse turbine is a horizontal or vertical wheel with affected by droughts, as happened during the year 2000 when
buckets or blades which are utilized to cause rotation. The the capacity factor for all Hydroelectric plants fell to 39.6%
wheel uses the kinetic energy of water striking its buckets or due to drought conditions across the country .
blades to cause rotation. The wheel is covered by a housing, Hydroelectric plants also pose environmental concerns as the
and the buckets or blades are shaped so they turn the flow of turning blades on the turbines have the potential to harm
water about 170 degrees inside the housing. After turning the marine life.
blades or buckets, the water falls to the bottom of the wheel
housing and flows out .
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C. Solar (HVDC) power transmission backbone would have to be built
According to Lawrence Berkeley National Laboratory, the .
sun bathes the Earth with enough energy in one hour (4.3 x The presence of clouds, which scatter and absorb solar
1020 joules) to provide for all of humanity's energy needs for a energy, is the predominant atmospheric condition that
year, which is estimated at (4.1 x 1020 joules) . In spite of determines the amount of solar energy available for conversion
this fact, solar power is currently only used to generate one to other energy forms at any particular location. Thus, as
tenth of one percent of the electricity utilized in the United Figure 11 illustrates, the annual average daily solar radiation in
States . The reason for this is that in the past solar energy the United States is highest where the atmosphere is very dry.
was much more expensive than energy generated using For example, in the western desert regions of Arizona,
nonrenewable means. This however is about to change. Nevada, and California, the annual average daily direct solar
In the year 2000, the average residential cost of electricity radiation ranges from 8.5 to 9.0 kWh/m2 at some locations.
was 8.2 cents per kW/hr . In 2006, the U.S. Department However, in most locations along the Pacific coastline, where
of Energy announced that Boeing-Spectrolab with DOE moisture levels in the atmosphere are likely to be higher, it
funding had produced a solar cell which achieved a world- drops to less than 6.0 kWh/m2, even without latitude changes.
record conversion efficiency of 40.7 percent . The
consequence of this breakthrough is that solar power systems
can now be built with a cost of only $3 per watt, producing
electricity at a cost of 8-10 cents per kilowatt-hour, making
solar electricity cost competitive with energy produced from
nonrenewable sources .
As this paper was being written, the largest solar
photovoltaic system ever to be built in North America was
under construction at Nellis Air Force Base. When complete,
the plant will provide 25 percent of the power used at Nellis
Air Force Base, and will occupying 140 acres of land leased
from the Air Force at the western edge of the base. The plant
will utilize an advanced tracking system which will follow the
sun, enabling the solar panels to capture up to 30 percent
more energy than an equivalent ground-mounted fixed-tilt
system . Solar power, which produces energy at the
source of consumption, alleviates stress and vulnerability on
Figure 11: Solar Resources of the United States in kWh/m2/day.
the nation’s power grid. It also ensures continued power to
Nellis Air Force Base should transmission facilities or A great advantage of solar power is that in most parts of the
generating stations fail due to terrorism, accidents, or natural United States there is a concordance between when peak
disasters. electricity demand occurs and when solar electricity generation
The United States has the best solar resources of any is near optimal efficiency (9 AM – 6 PM). Currently this
developed country in the world. Proportionally, U.S. solar demand load is almost exclusively served by natural gas or
energy resources exceed those of fossil, nuclear or other other fossil fuels that can be easily cycled on and off to meet
renewable energy resources . Despite this tremendous changing demand conditions . Given the high price of
advantage, the U.S. has failed to capture and harness this free natural gas to key industrial sectors and consumers, the United
and readily available energy. Germany, by comparison, has States would be ill advised to neglect its abundant solar
solar resources no better than those of Alaska, but has installed resources.
seven times as much solar energy than the entire United States
It has been estimated that a desert area in the southwestern
United States that measures 161 km on a side (0.3% of the
land area of the United States) could theoretically meet the
electricity needs of the entire country if the solar radiation in
that area could be converted to electricity with 10% efficiency
(Sandia National Laboratories 2001) . The only
drawback to such an idea is that the existing system of
alternating-current (AC) power lines is not robust enough to
carry power from the southwest to consumers throughout
North America, as it would lose too much energy over long
distances. To be viable, a new high-voltage, direct-current Figure 12: Utility Load and PV Output versus Time of Day .
Page 10 of 24
using electrolyzers available in 2004, electricity prices would
One of the big arguments against solar power is that it have to be less than $0.01/kWh .
generates less electricity when skies are cloudy, and none after What is most exciting, is that if both solar and wind sources
the sun has set. For solar power to be utilized in a manner are utilized, there is sufficient potential to generate enough
other than for supplemental purposes during peak demand hydrogen fuel to provide for the transportation needs of the
times, excess power produced during the daytime will need to entire country. In 2000 the gasoline consumption of the
be stored for use during dark hours. Most energy storage United States as a whole was 128 billion gallons of gasoline.
systems such as batteries are expensive or inefficient. To date The potential for hydrogen production from photovoltaic (PV)
there are three viable technologies that allow storage of solar and wind for the entire country is 1,110 billion kilograms of
power for utilization during times when generation is hydrogen. As a kilogram of hydrogen is roughly equivalent to
impossible due to darkness. a gallon of gasoline in energy content, the ability to generate
Compressed air energy storage has emerged as a successful 8.6 times the fuel needed by the United States can be met
means of storing solar energy for later use. Electricity from using hydrogen produced from PV and wind sources .
photovoltaic plants compresses air and pumps it into vacant The state with the highest potential production of hydrogen
underground caverns, abandoned mines, aquifers, and depleted from PV and wind sources is Texas, with 106,000 million
natural gas wells. The pressurized air is released on demand to kilograms of hydrogen. The state with the lowest potential
turn a turbine that generates electricity, which can be production of hydrogen from PV and wind is Rhode Island,
supplemented by burning small amounts of natural gas if with 213 million kilograms of hydrogen .
necessary. Compressed air energy storage plants have been
operating reliably in Huntorf, Germany, since 1978, and in
McIntosh, Ala., since 1991. Studies by the Electric Power Tidal energy is one of the oldest forms of energy used by
Research Institute in Palo Alto, California, indicate that the humans. Tide mills on the Spanish, French and British coasts,
cost of compressed-air energy storage today is about half that date back to 787 A.D . Tide mills consisted of a storage
of lead-acid batteries. The research indicates that these pond, filled by the incoming (flood) tide through a sluice and
facilities would add three to four cents per kWh to emptied during the outgoing (ebb) tide through a water wheel.
photovoltaic generation . The tides turned waterwheels, producing mechanical power to
Another technology that has the ability to store solar energy mill grain.
is known as concentrated solar power. In this design, long Despite its historical use for other purposes, the use of Tidal
metallic mirrors focus sunlight onto a pipe filled with fluid, Energy to produce electricity is still in its infancy, and
heating the fluid as a huge magnifying glass would. The hot techniques for building and deploying turbines are currently
fluid runs through a heat exchanger, producing steam that turns being shaped .
a turbine. Traditional tidal electricity generation involves the
To store this energy, the pipes can run into a large, insulated construction of a dam across an estuary to block the incoming
tank filled with molten salt, which retains heat efficiently. Heat and outgoing tide. The dam includes a sluice that is opened to
can then be extracted at night, creating steam. The molten salt allow the tide to flow into the estuary, and once filled the
does slowly cool however, so the energy stored must be tapped sluice is closed. As the sea level drops when the tide goes out,
within 24 hours. Nine concentrated solar power plants with a the captured elevated water in the dam is utilized to drive
total capacity of 354 MW have been generating electricity turbines to generate electricity using traditional hydropower
reliably for years in the United States. A new 64 MW plant in technology. Tidal energy can also potentially be exploited by
Nevada came online in March 2007. These plants, however, harnessing the energy from offshore tidal streams. Known as
do not have heat storage. The first commercial installation to tidal in-stream or hydrokinetics, the process is a far cry from
incorporate heat storage is a 50 MW plant with a capacity of old-style tidal barrages that are more akin to dams and cost
seven hours of molten salt storage, which is currently being much more to build. The best-known plant of that type, built
constructed in Spain. Similar plants are in the design phases on France's La Rance estuary, has been producing power for
around the world . more than 40 years.
The last and most exciting technology is using sunlight Tidal energy offers some significant advantages to other
during the day to produce hydrogen, which can then be stored forms of renewable energy generation. While winds can turn
and utilized as fuel to generate electricity in either fuel cells or calm and clouds can obscure the sun, the immutable tides
turbines at night. Hydrogen is produced via electrolysis by however will turn twice a day no matter what, and can provide
passing electricity through two electrodes in water. The water a steady and predictable source of power. In addition, due to
molecule is split and produces oxygen gas at the anode and water's greater density, tidal power requires fewer turbines to
hydrogen gas at the cathode via the following reaction: H 2O → produce the same amount of electricity as wind . Perhaps
½ O2 + H2. However, when hydrogen is produced in this even more important is that underwater turbines are unlikely to
manner, hydrogen prices are highly dependent on electricity draw opposition from coastal residents about new energy
prices. For example, to produce hydrogen at $2/kilogram, projects spoiling their views.
Tidal energy schemes have some drawbacks as well. Tidal
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energy typically has low capacity factors, usually in the range The SeaGen system uses two rotors that are 16 meters in
of 20-35% . Since there are two high and two low tides diameter, and can each produce 600 kilowatts of power. Two
each day, electrical generation from tidal power plants is rotors are used because the depth of the seas limits the size of
characterized by periods of maximum generation every twelve the rotors, forcing tidal systems to in effect grow sideways.
hours, with no electricity generation at the six hour mark in The SeaGen system also has complete control over the
between, resulting in low capacity factors . rotors. They are pitched like the propeller on an aircraft. The
The demand for electricity on an electrical grid varies with rotor can be optimized by changing its angle, which also
the time of day. Due to the fact that the tides typically come in dictates how much force is produced by the blades. The rotors
early in the morning or late in the evening, the supply of can be made to start and stop, and go faster or slower .
electricity generated from a tidal power plant will never match This is very important because turbines operate at maximum
the demand placed on a system by consumers, which typically efficiency over a very narrow range of speed . The use of
peaks during the early afternoon . variable speed turbines is also important as it results in a 2.3%
Some tidal power, like its hydroelectric cousin, can be increase in power production than nonvariable turbines
stored for later use by utilizing the turbines to pump extra operating under the same conditions . In order to prevent
water into the basin behind the dam during periods of low damage to the ecosystem, it is important that the speed of the
electricity demand . rotors not exceed 14 revolutions per minute, a speed that is too
Tidal dams can be designed to generate electricity on the slow for marine life to run into the blades or to alter tides
ebb side, the flood side, or both. Tidal deltas vary over a wide .
range, typically from 4.5m to 12.4m. A tidal range of at least Passamaquoddy Bay and the Bay of Fundy between the U.S.
7.0m however is required for economical operation of a and Canada are prime proving grounds for tidal power, and
traditional tidal electricity plant . tests are also being run at other sites. Clean Current Power
There is a high capital cost for any tidal energy project, with Systems of Vancouver, Canada also announced plans to build
a construction period lasting up to 10 years. The major factors a system that generates two megawatts of power from the tidal
in determining the cost effectiveness of a tidal power site are currents in the Bay of Fundy in 2009. Marine Current
the size (length and height) of the dam needed, and the Technologies has teamed up with a German utility company to
difference in height (delta) between the high and low tide. build a 10.5-megawatt project off the coast of North Wales.
These factors can be expressed in what is called a site's Marine Current Technologies has already started working on
"Gibrat" ratio. The Gibrat ratio is the ratio of the length of the the system, which should be developed within three years
barrage in meters to the annual energy production in kilowatt .
hours. The smaller the Gibrat site ratio, the more desirable the Another developer, Verdant Power, has placed turbines in
site. Examples of Gibrat ratios at existing or under New York's East River to test delivery of tidal power to a local
construction tidal plants are La Rance at 0.36, Severn at 0.87, supermarket and parking garage. The test was a success, but
and Passamaquoddy in the Bay of Fundy at 0.92 . the project experienced problems with broken blades and has
Only a handful of sites in the Lower 48 states lend since installed new ones. Another urban site being explored is
themselves to utility scale tidal generation, including Eastport, beneath the Golden Gate Bridge in San Francisco .
ME, and a few areas along Washington's Puget Sound. Alaska, During the great depression, under Roosevelt's
however has 95 percent, of U.S. tidal resources and Canada Passamaquoddy Bay Tidal Power Project, a model was
also has huge potential, but a big challenge lies in transmitting developed by the Army Corps of Engineers to harness the
that power to markets where it can be utilized . powerful tides in the Eastport, ME region. The project was
The waters off the Pacific Northwest are ideal for tapping suspended however after the United States Congress refused
tidal power, as the tides along the Northwest coast fluctuate further funding, thus the actual barrier dams were never built
dramatically, as much as 12 feet a day. The coasts of Alaska, .
British Columbia, and Washington, in particular, have The technology to harness Tidal Power is available,
exceptional energy-producing potential. On the Atlantic however it needs to be engineered for the lowest cost, the
seaboard, Maine is also has excellent tidal characteristics highest reliability, and the longest survivability in the hostile
. and corrosive environment of the ocean. The current standard
The world's first commercial tidal-power system was to simplify maintenance of tidal power equipment is to mount
connected to the power grid in Northern Ireland in November the turbines on a crossbar of a large steel beam that is held in
2008. Built by the British tidal-energy company Marine place by four legs cemented into the seabed. The crossbar can
Current Technologies (MCT), the 1.2-megawatt system be raised above or lowered below the surface of the water for
consists of two submerged turbines that are harvesting energy easy assess to the turbines.
from Strangford Lough's tidal currents. The company expects
that once the system, called SeaGen, is fully operational, it will
be able to provide electricity to approximately one thousand In the United States it is estimated that sufficient wind
homes . energy is available to provide more than one trillion kilowatt-
hours of electricity annually, or about 27% of the total used in
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