25.0 Review of Renewable Energy

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

Some of the more important points

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)

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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 marketChina and India increasing demand; price up

Key issues affecting the economy are the prices of gasoline and natural gasGasoline 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 pollutantsRoad traffic caused by oil truck transportation, and

resultant exhaust fumes, which cause more ailments

Renewable energies usually cause less or no pollution than conventional fuelsMaking the converter also uses energy and may

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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 coolingOn 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 fuelsSee Amory Lovins, Rocky Mountain Institute for early

espousal of the concept; Romm for the oppositeThere are no hydrogen wells, so hydrogen isn’t a fuel

in the usual sense, but an energy carrierTo get hydrogen, electrolysis of water, pyrolysis of

fossil fuels, or bacterial action is requiredNuclear and fossil fuel base-load power plants

produce energy to support the lowest daily load or moreThis 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 unneededBright local lighting is better than bright general

lighting since less power is needed to produce itCompact fluorescent lights (CFLs) produce good

light intensity with about 1/4 the powerTimers or motion detectors can turn off lights

when they are not neededBetter 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 plantsMany 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

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Note declines are getting steeper!

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 truckSome complain that storage must last 250,000

yearsHuman failure remains the largest concernMore 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 dateSolstices are at the extremes of angular sun

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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 understandingEvaluate intended loads closelyUse spreadsheets to change system parameters

readilyMake 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 peakNot 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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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

25.12.2 Wind Energy 2

080415 www.pnl.gov/ces/analysis/ sum3fly.htm http://www.weibull.com/Articles/RelIntro/data_a3.gif

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/eda362.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 wellThe 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 energy080415

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 wattFlorida 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 countriesEurope 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

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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 entry2 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

25.13 Bioenergy

Biomass collects solar energy to build more biomassEnergy crops that maximize the energy absorption

can be grown for biomass combustors or reactorsBiomass has less pollution than fossil fuels but still

emits pollutionBiomass is CO2 neutral since it absorbs CO2 in

growingThe Southeast US has more biomass energy than

other kinds of renewable energyBiomass can yield fuels like ethanol, or with still

more processing, methane gasMethane 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

070424 http://www.eia.doe.gov/cneaf/electricity/st_profiles/florida/fl.html#t1

25.14 Hydropower

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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

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 developedHydropower 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

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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

25.16 Geothermal Energy

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Geothermal energy is categorized into three (3) qualities:Low: 0 to ~250 degrees F

Air conditioning or heatingMedium: ~250 to 450 degrees F

Industrial or processing industryHigh: ~450 or higher degrees F

High temperature energy generation, testing, cutting, missile nosecone testing

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]

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25.17 Transmission of Energy

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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 = I2RThis 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 sideThe 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

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 pointsThe 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

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25.18 Energy Storage

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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

25.18 Energy Storage Batteries

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Storage batteries are rated differently for starting engines (continuous cranking amperes, CCA) than for powering lesser loads like lightsReserve 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

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 vehicleSpecial 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

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25.19.1 Transportation Energy

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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

25.19.1.1 Transportation Energy

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Florida voters changed the state constitution to mandate high-speed trains to service the major citiesWhile the cost wasn’t specified to distract them,

maglev trains reaching 300 mph were impliedThe 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 waysA just fare might be $2000 for Tampa to Orlando

Public subsidy will be required indefinitely, so the nonpassengers can pay for the few passengers!

25.19.1.1 Transportation Energy

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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 energyA 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

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

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25.19.2 Transportation Energy: Cars, Etc.

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Alternative fuel vehicles (AFVs) use ethanol, methanol, compressed natural gas, propane, or hydrogen

The alternative is other than gasoline or dieselSome hydrogen-fuel-cell cars are being tested in

Los Angeles, California; the manufacturer furnishes the hydrogen

Electric cars use utility energy stored in batteriesWhere did the electricity come from?Electric cars are being discontinued since

hybrid electric cars are more widely accepted by the public

25.19.2 Transportation Energy

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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 Cocoahttp://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

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

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25.19.2.3.1 Conclusion: Transportation 2

Current hybrid vehicles are user-friendly, thus will be rapidly accepted by the market if price fallsIn 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

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25.20 Distributed Generation

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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

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 attackCritical loads are better protected when nearby

multiple sources are availableComputer 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

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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

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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

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25.22 Tradeoffs and Decisions

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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 totalWeighted scoring allows the importance of

various parameters to be adjustedAdjustment of the weights will greatly affect the

outcomeBe wary of forcing the outcome to be what you

want it to be

25.22 Conclusion: Trades

Renewable energy is faced with the same types of problems that affect other areas of daily livingGetting 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

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25.23 Legal Considerations

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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

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

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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

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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 kmEarth 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)”

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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.)

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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 reflectionAltitude of the sun = 90º -latitude + sun declination;

azimuth is the horizontal angle clockwise from north (declination is the varying solar latitude+/-23.45

degrees)

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Olin Engineering Complex 4.7 kW Solar PV Roof Array

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Questions?

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. 0-262-02349-0, 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. PetersSustainable Energy Choosing Among Options. Boston: MIT Press, 870 pp. July 2005 ISBN-10:0-262-20153-4

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References: Websites, etc.

awea-windnet@yahoogroups.com. Wind Energy elistawea-wind-home@yahoogroups.com. Wind energy home powersite elistgeothermal.marin.org/ on geothermal energymailto: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 Commissionwww.hawaii.gov/dbedt/ert/otec_hi.html#anchor349152 on OTEC systemstelosnet.com/wind/20th.htmlwww.google.com/search?q=%22renewable+energy+course%22solstice.crest.org/dataweb.usbr.gov/html/powerplant_selection.html

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