Energy Systems – Time to "Get Real"
John C. Bean
University of Virginia, Charlottesville VA
Outline
Introduction
Current U.S. energy consumption and corresponding trends in climate?
Which energy choices now seem to make the most economic sense?
Including a short tutorial on different types of energy plants
A quick look at "carbon footprints"
Location, location, location (taking real estate into account)
The challenge of transmitting electrical power (a.k.a. "The Grid")
A final word about (the now near taboo) subject of nuclear energy
(version February 2014)
Origins of this talk
Like so many Americans, I am deeply concerned about our "energy future"
Based on declining reserves of fossil fuel
And on the possibility of major, or even catastrophic, climate change
To understand, I've tried to apply my personal science/engineering experience
Which falls in the area of "photonics"
A field that is closely related to (but distinct from) solar cells
But, when I dug into the literature on specific energy technologies,
All I seemed to find was arguments and confusion!
For example, I read that:
Concerning electric cars:
Electric cars are clean because they emit no exhaust
But they are dirty because in the U.S. their power is most likely produced
by polluting coal plants
But they are now becoming cleaner because we are shifting to cleaner
burning natural gas power plants
But they are actually still dirty if one takes into account the energy and
pollution associated with mining the rare metals used in their batteries,
and for their ultimate disposal
And these arguments were not just in the possibly ill-informed popular press
I found similar arguments raging in the national science and engineering
academies of several countries
Including in a recent study of electric cars by the U.S. Academies
What the heck is going on?
OK, in science & engineering I know we sometimes have our early disagreements
But this is ridiculous!
Eventually, however, I began to perceive a reason for all of this confusion:
We tend to focus on only the up front energy collecting technologies
And, as specialists, we often focus on only ONE such technology
But electrical energy is a unique product in that it cannot be efficiently stored!
In most cases it must instead be used within milliseconds of being produced
And this means you cannot just focus on how the energy will be produced
You have to be every bit as concerned about its distribution and use
It's also all about DIFFERENT energy technologies working together
Because studies I read say no single energy technology can replace fossil fuels
At least not in the foreseeable future!
So it is not only about energy production, distribution and consumption
Its about doing all of this using a mix of all sorts of energy technologies
In other words:
IT'S ABOUT COMPLETE ENERGY SYSTEMS
And the unique opportunities, synergies, and challenges that occur ONLY when
you try to put everything together
As well as the relevant economic, social, and political considerations
What follows:
For the last ~ 5 years, I've been trying educate myself about ENERGY SYSTEMS
As motivated by the preceding discussion
And facilitated by an NSF grant aimed at developing educational tools
In this talk I don't have time to share ALL that I have learned
But I can instead share things that surprised me and/or changed my perspective
Things that are stimulating my future research on energy
And things that might similarly influence you
So if it is about our WHOLE energy system, a good starting point might be:
What IS current U.S. energy production / consumption?
And what are the corresponding trends in climate?
"Energy Systems – Time to "Get Real"
How well informed are we about this?
In 2002, fifteen hundred U.S. adults were quizzed1 on their "Energy Literacy:"
They were pretty confident about their knowledge:
3 in 4 said they had "a lot" or "a fair amount" of relevant knowledge
But 90% of them failed the quiz!
But maybe the quiz slipped in all sorts of obscure questions! Not exactly:
- 36% believed that "clean" hydropower produces the majority of U.S. energy
The real answer is that only about ~ 1/20th of our energy comes from hydro
- 50% believed that the majority of U.S. energy comes from pollution-free sources
The real answer is that only ~ 1/5th of energy comes from non-fossil-fuel sources
1) NEEF: America's Low "Energy IQ:" A Risk to Our Energy Future (www.neefusa.org/resources/publications.htm)
From the U.S. Energy Information Agency's "Energy Report 2011:"
Total U.S. energy consumption: "98 quadrillion BTU's" (98 x1015 BTU =1.03 x 1020 J)
Use
Sources
Divided as follows (in those embarrassing antiquated units of "quadrillion BTUs"):
"Energy Systems – Time to "Get Real"
Converting this into a more readable form:
- Greenhouse gas producing fossil fuels shown in reds & oranges, ~ 80% of chart
- Imported fuels shown in oranges, ~ 33% of chart
- TOTAL renewables = 8.4% of chart, half of which is due to old hydroelectric
- Leaving only ~ 4% for wind + solar of all types + geothermal + biofuels + etc.!
"Energy Systems – Time to "Get Real"
U.S. energy use (in a more readable form):
Surprises?
- We turn around and export almost 8% of the energy we produce!
Charlottesville sees daily trains moving dirty coal to the coast for export to China
- Our very poorly sealed and insulated homes consume over 20% of our energy
Huge opportunity for savings as this is relatively cheap and easy to reduce!
- Transportation consumes fully 25%, almost as much as our total industry
Trends over time?
"Energy Systems – Time to "Get Real"
A Digression: California vs. U.S. energy use:
The difference made by modest California initiatives on efficiency & conservation:
(Source: www.energy.ca.gov)
What was economic impact of this efficiency & conservation?
California saved a LOT of energy while achieving a HIGHER GDP!
(Money NOT spent on energy can instead support investment, R&D, education . . .)
But returning to U.S. wide statistics:
"Energy Systems – Time to "Get Real"
Impact?
Trends, especially red "imports" line have huge negative economic consequences
As well as huge geopolitical consequences
Including dubious alliances and/or hugely expensive wars (in both $ & lives)
And then there is climate change
Which, bizarrely, has become an almost theological debate within the U.S.
But there IS now almost unanimous scientific agreement on the following:
The earth's climate is heating significantly
There WAS a lot of variation/noise in historical temperature data
To point that identifying trends required complex/controversial statistical analysis
Further, early detailed data only went back a few hundred years
And most of that data was from a few northern hemisphere cities (e.g. London)
Which were already known to have growing "urban heat bubbles"
Because of such weaknesses (and criticism from scientists such as Richard Muller):
Techniques for inferring historical temperatures have now been vastly expanded
Producing data from much wider selection of locations, over longer time span
For example, via tree growth ring data from around the world
And via gas bubbles taken from ancient glacial ice cores
Current temperature data (black line + brown scatter band):
Data from physics Prof. Richard Muller (U.C. Berkeley) - noted critic of earlier data
He was paid by U.S. billionaire "deniers" (the Koch brothers) to do in-depth study
That, to their dismay, concluded (in July 2012) that climate change is real
Versus widely accepted information about carbon dioxide:
2) CO2 is known to act as a heat-trapping greenhouse gas
Methane is an even more effective greenhouse gas (=> "Cow fart hypothesis")
CO2 rise correlates strongly with man's "industrial revolution"
New level as of May 2013
3) CO2 concentration is rising to historically unprecedented levels
Source: United Nations Environmental Project / GRID Arendal
http://www.grida.no/graphicslib/detail/historical-trends-in-carbon-dioxide-concentrations-and-temperature-on-a-geological-and-recent-time-scale_a210
With an excellent correlation between temperature and CO2
Again the data from Richard Muller (U.C. Berkeley)
But now note correlation between temperature (black) and CO2 (red)
In either case, it suggests that adding further to CO2 is a really bad idea
What energy choices now seem to make the most economic
sense?
"Energy Systems – Time to "Get Real"
Both climate sense AND economic sense
Because without the latter, there is unlikely to be any action on the former
And we need both viable short term options and long term options
Long term (?): In the distant future fusion might be a great
But after fifty years of research we still can't make it work!
Short term (?): Solar or biofuels might be great, but are they affordable?
"Affordable" in terms of both money and space
Because these technologies require huge chunks of real estate
And what about WATER?
1st world dependence on biofuel might require whole world's H2O
Conclusion of a Georgia Tech study "Biofuels Aren't Really Green"
It makes sense to START with discussion of power plants, right?
To design an energy system, you must to buy/build energy production plants
So you need data on what plants of different types would cost and produce
I would therefore have THOUGHT that such data would be very easy to find
After all, power companies have to make such choices all of the time
And "Public Utility Commissions" represent us in such decision making
Instead, I found such data to be almost "top secret"
Especially if I excluded data from sources pushing (or deriding) a single technology
How can we seriously discuss alternative energy without this information!
But I did, eventually, find comparative data from two objective sources:
The U.S. Congressional Research Service & the U.S. Energy Information Agency
Cost of energy by source? Typical plant capacities?
I first found Congressional Research Service report data (2008)
Its data was calculated from data on actual U.S. plants operating in 2007
Note wide range of total energy cost (I'll come back to the red numbers later)
Also note HUGE RANGE in the capacities of different types of plant
Did you REALLY note the range of power plant capacities?
FOSSIL FUEL POWER PLANTS:
~ 500 MW per plant
NUCLEAR PLANTS:
~ 1500-3000 MW per plant
SOLAR THERMAL:
< 250 MW per plant*
WIND:
< 200 MW per plant*
GEOTHERMAL:
< 150 MW per plant*
SOLAR PHOTOVOLTAIC:
< 75 MW per plant*
*And these are generally
rare (one or two of a kind
worldwide) super plants!
Existing sustainable energy power plants have small to tiny power outputs!!
Yet (I will show) they can require huge amounts of land
Why I said sustainable energy plans MUST have all sorts of plants working together
Adding in data from U.S. Energy Information Agency
The newer EIA data are projections for new plants coming on line in 2017
Adds data for many more types of power plants
Cost are generally higher (no surprise, costs would tend to rise over a decade)
But note last two columns – looks to me as if the CRS confused solar power types
Because I've read many claims that solar photovoltaic is "almost competitive"
A short tutorial on different types of energy plants
(as referred to by preceding mix of names an acronyms)
"Energy Systems – Time to "Get Real"
What IS difference between solar photovoltaic and solar thermal?
Solar Photovoltaic: Direct conversion of light to electricity
Based on light exciting electrons up out of bonds in semiconductor diodes
Source: http://jumpthecurve.net/energy/ashorter-road-to-our-energy-future/
Solar Thermal: Concentrate light > boil fluid > power boiler > turn turbine-generator
Source: http://blog.zintro.com/clean-tech-altenergy/page/2/
But I learned that CRS vs. EIA data discrepancy is even more worrying:
CRS and EIA reports ALL try to base models on EXISTING power plants
OK, but that sounds likes a GOOD idea!
NOT if existing plants are small or first-of-a-kind experimental plants
Costs of new technologies often fall rapidly
Costs also fall rapidly as plant sizes are ramped up
CRS and EIA TRY to correct by factoring in "learning curve" type corrections
But even these applied corrections can be very inaccurate:
I discovered that CRS based their solar photovoltaic projection
almost entirely on a single installation at one remote U.S. Air Force base
SO PROJECTIONS ON EMERGING TECHNOLOGIES ARE ALWAYS QUESTIONABLE!
What about the other acronyms used in the power plant data?
IG: Integrated Gasification:
Can burn coal as a pulverized solid
Or burn it more efficiently if first converted to a gas (via heat + moisture)
CC: Combined Cycle:
Combustion => hot expanding gases
Basic coal/gas/oil plants use expansion of gas to drive turbine generator
But hot exhaust can THEN be used to boil or preheat water into steam
To drive a SECOND turbine generator
Or, represented schematically:
So here is the schematic for an IGCC coal plant:
Integrated Gasification Combined Cycle:
Coal gasification =>
Combustion/expansion in 1st turbine =>
Electrical Power out
Exhaust gas heat from 1st turbine =>
Use this heat to boil water =>
To drive 2nd turbine =>
More electrical power out
IGCC is about increased efficiency
(= power out / fossil fuel in)
http://www.climateandfuel.com/pages/electrical.htm
"CC" in "IGCC" does NOT refer to carbon capture!
There is a LOT of confusion about this (including in governmental reports!)
To the extent that IGCC DOES produce more electrical power / fossil fuel in,
it would then reduce the net OUTPUT of carbon (for same power out)
But possibility of true carbon "capture" instead comes in here:
The gasified coal includes CO2
Which would add to the carbon output
Has been suggested that this CO2 could be
easily "captured" before combustion
Which would then reduce "carbon footprint"
But only if captured CO2 is not released later
Which leads to topic of "Sequestration"
Sequestration = long-term storage of "greenhouse gases" OUT of the atmosphere
How? By pumping into abandoned mines or wells:
(www.atlasobscura.com/articles/can-i-lick-it-yes-you-can)
But how "long" must this "long-term" storage be? Hundreds of years!
That is time atmosphere will need to purge greenhouse gases already present
Will high pressure CO2 STAY in abandoned mines or wells for hundreds of years?
I find that highly improbable (and almost akin to wishing away nuclear waste)
True sequestration of CO2 would require its conversion to a stable solid
(via some sort of as yet unproven mineralization or biological process)
Efficiency + Carbon Capture + Sequestration = "Clean Coal"
"Clean coal" has been promoted by a massive U.S. TV/print advertising campaign
Which environmentalists deride as nothing more than fantasy
Facts? 2008 Congressional Research Service Report to Congress:
Page 9:
"Coal-fired IGCC experience in the United States is limited to a handful of research and prototype plants,
none of which is designed for carbon capture. A commercial IGCC plant is being constructed by Duke
energy . . . and other projects have been proposed. However, some other power plant developers will not
build IGCC plants because of concerns over cost and the reliability of the technology"
Page 30:
"The estimates of the cost and performance effects of installing carbon controls are uncertain because no
power plants have been built with full-scale carbon capture" (emphasis added)
Page 31:
"Amine scrubbing (of CO2) is estimated to cut a coal plant's electricity output by 30% to 40% . . . cost for
building a coal plant with amine scrubbing is an estimated 61% higher"
Thus, while not quite fantasy, it is certainly NOT (commercial) reality!
We're about to dissect the economics of power plants
As you would expect, the construction of most power plants requires loans
Resembling our home mortgage with its monthly payments
But possibly also coming via utility or government bonds
But what if I, as a power company, squirreled away my past profits
So that I now have 100M$ (or 1B$) on hand, and don't need a loan?
Well, as the economics department and business school will tell you:
You could instead now invest that money elsewhere
And thus eventually reclaim your money PLUS interest
So if you instead now spend that money on a new power plant:
You have forgone the possibility of earning that added interest
Leading to "time value of money," "net present value," "levelized cost"
Typical power plant has ALL sorts of costs:
Construction (capital), fuel, operating, labor, decommissioning . . .
But any of this money COULD be invested elsewhere, earning interest
So economists compute effect of interest (earned or forgone) into all costs
They assume it is as if ALL power plant costs are paid via an up front loan
Where loan provides for not only for "non-recurring" costs of building plant
But also for recurring costs of fuel, maintenance, labor . . .
Then, in manner essentially the same as bank uses to figure out mortgage payments
They compute LEVELIZED annual costs, for each category
DATA TO FOLLOW are from such "levelized" cost computations
"Levelized" EIA data breaking down total costs:
(RED = particularly bad / high values
GREEN = particularly low / good values)
"Energy Systems – Time to "Get Real"
Analyzing contributors to EIA total cost, line by line:
Fuel & Variable Operating Costs (costs varying with the plant's output):
"Renewables" have zero to low costs (because nature provides fuel!)
EXCEPT for BIOMASS which does rack up substantial total fuel cost
Analyzing these data (continued):
Fixed Operating Costs:
Solar Thermal has unusually high fixed operating costs
Likely due to complexity:
1000's of steerable mirrors + boiler + turbine + generator
Analyzing these data (continued):
Capital Cost = Mortgage or bond payments on plant's construction loan:
THE MAJOR COST for almost every single technology
Exception? Natural Gas = gas powered jet engine connected to generator
This cost can vary HUGELY with government tax policies
Capital/mortgage/bond issues:
1) Don't mortgage/bond costs fall to zero once the loan is paid off?
Plants are financed such that duration of loan = likely duration of plant
So when loan is paid off, you scrap the plant and build a new one
POSSIBLE PROBLEMS WITH THIS ASSUMPTION:
2) There is now talk of operating nuclear plants beyond their planned lifetime
Doesn't that imply that the loan WOULD then be paid off in later years?
3) Have they assumed plausible lifetimes for very new types of plants?
For instance:
Single crystal silicon solar cells last longer than polycrystalline cells, last
longer than amorphous cells, last much longer than organic cells . . .
How do CRS or EIA reports deal with these issues?
THEY EFFECTIVELY IGNORE THEM!
In summer of 2013 I read through hundreds of pages of CRS/EIA/DOE reports
ONLY place they mentioned plant lifetimes was in sections modeling taxes
Sections on levelized plant costs instead referred to "standard 30 year model"
I couldn't believe that they'd make such an inappropriate assumption
So I e-mailed field expert Edward Rubin of Carnegie Mellon U.
He confirmed that they were indeed modeling ALL plants as lasting 30 years!
Even while solar and wind have not yet achieved such a track record
and existing nuclear plants are lasting longer!
Nevertheless, analyzing these data (continued):
Capacity Factor = Typical plant output / maximum possible output:
LOW for almost all of the renewables
Because the sun doesn't shine nor the winds blow all day
And water reservoirs run low in the summer
High biomass number suggests this refers only to plant that burns biomass (not produces it)
A quick look at the "carbon footprints"
"Energy Systems – Time to "Get Real"
Data from the UK Parliamentary Office of Science & Technology):
As noted earlier, I am skeptical about current carbon sequestration proposals
So focus just on CURRENT footprint data (rather than with proposed "CSS"):
Possible surprise #1: Footprint of natural gas power is ~ ½ that of coal (!)
Possible surprise #2: Renewables are all better, but some are strangely high
What is going on with things like photovoltaics (PV)?
Details (ibid):
PV does not PRODUCE carbon.
But PV manufacture requires a lot of heat (e.g. purification and crystal growth)
That heat is NOW supplied from largely "dirty" energy sources, thus
TODAY'S PV (in its manufacture) is responsible for a substantial carbon footprint
TOMORROW's PV (made with then cleaner energy) will contribute much less
But numbers depend on how/when ENTIRE energy system shifts to cleaner fuels!
Location, location, location - taking real estate into account
(The "elephant in the room" that has been largely ignored)
"Energy Systems – Time to "Get Real"
For renewables: Where to locate and how much space is required?
Conventional (coal, gas, oil) plants are not that large – say 2-5 hectares
Nuclear plants tend to be larger based on security and used fuel storage needs
Virginia's two reactors at Lake Anna occupy 4.35 km2 + cooling lake
Solar, wind, geothermal all tap into very dilute natural power sources
How much land is required to produce a given amount of electrical power?
And these "dilute natural power sources" vary widely with location
For a given type of natural power, where is it most concentrated?
Let's tackle these questions in reverse order:
Wind power: Average wind speed in Europe
Conclusions?
High mountains = Bad (block/lift wind)
Low hills = Fair
Low altitude plains = Poor (e.g. Veneto)
Offshore = Best
Especially at northern latitudes
But water cannot be too deep!
~ Excludes mountainous coasts
Wind power: Average wind speed in U.S
Same conclusion: Northern coast = Best
Different conclusion:
Low hills = Fair
High Mtns / Low plains = Poor
Abundant HIGH plains = Very good
What about sun exposure ("insolation")?
European Joint Research Centre:
http://re.jrc.ec.europa.eu/pvgis/countries/countries-europe.htm
Conclusion?
Look to the Mediterranean
Or to North Africa?
Insolation in the U.S.?
U.S. National Renewable Energy Lab map (by year, month, min, max or average):
http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook/atlas/
Conclusion? Build solar plants in the high deserts of the Southwest
And, for completeness: European Geothermal Potential
European Commission:
http://ec.europa.eu/research/energy/eu/research/geothermal/background/index_en.htm
Conclusion? Not much - Turkey, a bit of Spain, plus the Balkans . . .
And, U.S. Geothermal Potential
U.S. National Renewable Energy Lab (NREL) map:
http://www.nrel.gov/gis/images/geothermal_resource2009-final.jpg
Conclusion? Build geothermal plants in the West/Northwest
How much land would renewable energy plants require?
Start with solar cells (it's the easiest to figure out):
Solar cells try to collect ALL available sunlight
Means they can't share the land with farms
But could be placed on building or parking lot roofs
What is the total land area required, say for a 1 GW plant?
U.S. would require about 3000 such plants
(with mostly ~500 MW plants, current U.S. plant number is ~ 5800)
For photovoltaics, go back to the earlier NREL webpage on U.S. insolation
Select options of:
- Average annual insolation
- East to west tracking (tilting) solar cells
Map generated then gives total averaged solar energy striking surfaces:
NREL insolation map
Central Virginia: 3 kW-h/m2/day
3 kW-h/m2/day = 10 MJ/day/m2
= 10 MJ / 24*3600s/m2
= 125 W / m2
Assume a 20% efficient Si xtal cells
Occupying ~ 100% of surface area
Average energy harvested = 25 W / m2
Our plant target = 1 GW average
Land required = 1 GW / (25 W / m2)
= 40 million m2 = 40 km2
http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook/atlas/
(Only need half that if built in Arizona!)
What about alternative solar based plants?
Cheaper solar photovoltaic alternatives? Poly or amorphous Si, or organics?
Polycrystal Si solar cells ~ ½ as efficient > twice the land (80 km2)
Amorphous Si solar cells ~ ¼ as efficient > four times the land (160 km2)
Organic solar cells ~ 1/10 as efficient > ten times the land (400 km2)
Solar thermal? Might it not collect sun energy more efficiently?
"Energy and the Environment" – Fay & Golomb (page 186): "11.6-49 W/m2"
To get 1 GW need 20 to 86 km2, same ballpark as crystalline Si photovoltaic cells
Biofuels?
"Energy and the Environment" – Fay & Golomb (page 168): "0.42 W/m2"
To get 1 GW => 2.4 x 109 m2 => 2400 km2 (plus huge amounts of water)
What about technologies that CAN SHARE the land?
Geothermal: Unfortunately, for this, NREL map doesn't give quantitative data
But book "Sustainable Energy – Without the Hot Air" (page 99) gives:
Geothermal plant energy yield = 25 – 150 mW / m2
= 1/1000 to 1/166 of crystalline Si photovoltaics of two slides ago
So scaling, conclude 1 GW geothermal plant = 6600 – 40,000 km2
Wind: Must answer questions of how big turbines can be, and how closely spaced
In U.S. we tend to see single rows of turbines running along hill crests
Implying that turbines slow wind so much that next row must be far away
Is this correct?
"Energy Systems – Time to "Get Real"
Possible wind turbine spacings and sizes
No, wind speed is quickly replenished (from faster winds above):
Rule of thumb: Turbines should be separated by ~ 5 times their blade diameter
(Source: "Sustainable Energy – Without the Hot Air" – McKay, page 265)
Implying, number of turbines per plant area = 1 / (100 x blade-length2)
But then, are fewer large turbines better than more smaller turbines (per area)?
Decision, again, has to do with typical wind speed profile (above)
Few big turbines vs. more small turbines?
Taller turbines get blades up into faster moving air
So bigger but more widely spaced turbines are desirable
But what is the power produced per unit land area?
Should take turbine sizes, spacings, and wind maps into account
To simplify, am going to make use of some formulae drawn from the book:
"Sustainable Energy – Without the Hot Air" – David McKay (pages 263-5)
Calculation of wind energy => Wind farm power output
From basic physics (as explained in "Sustainable Energy without the Hot Air"):
Power of wind passing thru area (A) = ½ mv2 / (time for that mass to pass thru A)
= ½ (air density) x (air velocity)3 A
= ½ rho v3 A
where air density rho (ρ) is taken as 1.3 kg / m3
VERY IMPORTANT: Power does not increase as wind speed but as its cube!
Solving this for a windspeed of 8 m/s:
Power of 8 m/s wind passing thru area (A) = 332 (W / m2 ) x Area
For location with average wind speed of 8 m/s, would this be average wind power?
No! Because of that cubic dependence! To illustrate this:
Power of constant wind vs. averaged wind
Using formula from above, for two cases with SAME average wind speed of 8 m/s:
CASE 1: Constant daily wind speed of 8 m/s:
Wind speed over day:
Wind power over day:
8 m/s
½ ρ 83 A
Average Power = ½ ρ 512 A
CASE 2 : Variable wind speed averaging (over day) 8 m/s:
16 m/s
Wind speed over day:
Wind power over day:
½ ρ 163 A
8 m/s
Average Power = ½ ρ 1536 A
½ ρ 83 A
½ ρ 03 A
For same average speed, variable winds give 2-3 times more power!
Confirmed by numbers on earlier NREL Map:
Our formula: Constant wind speed of 8 m/s => Pwind = 332 W/m2 x A
Versus NREL figure: Average wind of 8 m/s => Pwind = 600 W/m2 x A
So to correct formula ~ double its results (rule of thumb I will use)
Then, for turbine with 25 m long blades, wind area intercepted = 1963 m2
P50m turbine = (50% efficiency) (wind power per area) (turbine blade area)
= (0.5) ( 600 W/m2) (1963 m2) = 589 kW
Finally, estimating power output of entire wind farm
Power / plant area = Power per turbine / turbine footprint (with optimum spacings)
Pper plant land area= P50m turbine / (5 turbine diameter)2
= 589 kW / (5 x 50 m)2 = 9.4 W / m2 = 9.4 MW / km2
For our target of a 1 GW wind plant, we would then need area of 106 km2
But only place with assumed 8 m/s average winds in VA is off our coast!
If same plant were located in central Virginia (as one class proposed):
NREL doesn't even bother to map low wind speeds there!
Guesstimate Richmond wind average of 4 m/s (off low end of NREL map):
One half of 8 m/s => (1/2)3 as much power per plant area
So near Richmond could require 8X land => ~ 800 km2
Summary of estimated 1 GW plant areas:
Central Virginia
Best National Site
Crystalline Si photovoltaic:
~ 40 km2
~ 20 km2
Polycrystalline Si photovoltaic:
~ 80 km2
~ 40 km2
Amorphous Si photovoltaic:
~ 160 km2
~ 80 km2
Organic photovoltaic:
~ 400 km2
~ 200 km2
Solar thermal:
~ 20-86 km2
Biofuel:
~ 2400 km2
Geothermal:
Wind:
6600-40,000 km2
~ 800 km2
~ 100 km2
These calculations contained MANY approximations and assumptions
So they are ONLY estimates, but they DO highlight the huge issue of land resources
NOT DISCUSSED: An equally large water consumption issue!!
Big takeaway messages:
Renewable energy sources are very dilute (i.e. average power / area)
So to capture nationally significant amounts of power NEED A LOT OF LAND!
Providing big incentive to build plants where energy sources are most intense
Which does not equal: My roof / back yard / town / or even my state
Instead requires: Very special locations (different for each type of energy)
Scale of geography required to get such locations?
A WHOLE CONTINENT!
Implying: Efficient long distance transport of energy will be VERY important!
And a bit about the challenge of transmitting electrical power
"Energy Systems – Time to "Get Real"
Preceding strongly suggests building at "best" sites rather than locally
And as seen above, in U.S. "best" sites can easily be 1000 miles away
Meaning that we must also build and maintain a network of TRANMISSION LINES
This is not just the current "grid" which serves mostly ~ local power plants
For distant renewables NEW GRID must be much longer/higher capacity
For these new transmission lines:
How much will THEY cost?
How much power will they loose?
Data from the American Electric Power Corp., for a single 765 kV power line:
Cost = 2.6 – 4 M$ / mile
Loss = 0.5 – 1.1 % / 100 miles
Then for a 1 GW power plant sited 500 miles away (requiring two 765 kV lines):
Transmission line Cost = (1000 mi) (3.3 M$/mi) = 3.3 Billion dollars
Power Losses ~ 1000 mi x (0.8% / 100 mi) x 1 GW ~ 8 MW
And even that calculation neglects a crucial limit
When sending electrical power over long (and short) distances, we use "AC"
"AC" = alternating current: first push electrons, then pull them back (at 60Hz)
Why? Electrical current => magnetic fields
Changing current / magnetic field in one coil of wire can "induce"
changing current / magnetic field in a second coil of wire
IMPORTANCE: By varying number of turns in each coil (in a "transformer")
High current / low voltage AC  Low current / High voltage
In our homes, lower voltage is safer (we thus use higher current for same power)
But transmission line losses of preceding slide were due to current flow
Hence reason for "transforming" it to low current / high voltage AC
The trap of long distance AC power transmission:
We don't just have one power plant transmitting its AC power outward
We instead have thousands, all connecting to grid at different points
So their AC power must all be synchronized, everyone pushing and pulling together
But the energy stored in magnetic fields makes that EXTREMELY difficult
Because as push goes to pull, the collapsing magnetic field pushes back
This tends to counter our intended AC push-pulling over distances
Meaning that while two side-by-side plants can be synchronized
the same plants moved away from one another will loose synchronization
(More precisely, current peaks may no longer come at same time as voltage peaks)
This loss of synchronization over distance introduces a whole new limit!
For AC transmission lines (due to "magnetic induction"):
Again using data from the American Electric Power Corporation (AEPC):
Say you had a 300 mi long line of capacity = 2.3 GW
Its capacity would drop sharply if its length were increased beyond 300 mi:
Capacity (at length X) ~ 2.3 (300 mi / X) GW (my formula from their graph)
So capacity falls to 1.15 GW at 600 miles, 575 MW at 1200 miles . . .
The (more expensive) alternative: HV DC Long distance transmission
That is, instead use steady ("direct") current and voltage
To minimize resistive losses use low current / EXTREMEY high voltages
Side advantages: Grid becomes much more stable (no synchronization issues)
And is much easier to integrate in myriad small solar, wind . . . plants
A final word about (the near taboo) subject of nuclear energy
"Energy Systems – Time to "Get Real"
All of the above suggests: This ain't going to be easy!
Prompting a lot of experts (including environmentalists) to reconsider nuclear plants
But they blow up!
Occasionally, but impact of those explosions was largely due to stupidity
Chernobyl core was built out of highly flammable graphite
At Fukushima, instead of storing piles of "spent" radioactive fuel elsewhere:
GE's design put it in a water pool on top of the reactor!
Where it vastly increased radioactive material available for release
reactor
Then they sited the emergency generators (essential for cooling the
and spent fuel pool) in the basement, a few meters away from a tsunami
prone beach
We don't HAVE to be that stupid and/or shortsighted!
My current take on nuclear?
I lived just downwind from Thee Mile Island's near "China Syndrome"
But, from above, I conclude its use looks unavoidable, with REAL ISSUES being:
- Safe long-term storage of radioactive spent fuel and reactor components
- Development of nuclear plant designs that are "walk away safe"
That is, plants where you DON'T have to spend days cooling them down
Requiring operation of complex equipment/pumps + fallible operators!
But can instead flick a switch to turn them off, and (safely) walk away
As you could for almost any other type of power plant!
New designs ARE being proposed that might be "walk away safe," plus:
Use more readily available or less easily weaponized fuels
Small enough to be made from cheaper factory-made modules
Credits / Acknowledgements
This note set, and the research upon which it is based, is part of our ongoing project on
energy system education, as funded by a 2011 NSF Research Initiation Grant in Engineering
Education (RIGEE).
Content is also drawn from our "Hands on Introduction to Nanoscience" class website
(www.virlab.virginia.edu/Nanoscience_class/Nanoscience_class.htm) as funded by an earlier
NSF Nanoscience Undergraduate Education (NUE) grant, and from our "UVA Virtual Lab"
science education website (www.virlab.virginia.edu) initiated under a NSF Course
Curriculum and Laboratory Improvement (CCLI) grant, and extended under NSF Materials
Science and Engineering Research Center (MRSEC) and Nanoscience Interdisciplinary
Research Team (NIRT) outreach programs.
Copyright John C. Bean (2014)
(However, permission is granted for use by individual instructors in non-profit academic institutions)