Energy Systems – Time to "Get Real"

John C. BeanUniversity of Virginia, Charlottesville VA

OutlineIntroduction

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 usedin 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)

Divided as follows (in those embarrassing antiquated units of "quadrillion BTUs"):

"Energy Systems – Time to "Get Real"

Sou

rces

Use

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:

(Source: www.energy.ca.gov)

The difference made by modest California initiatives on efficiency & conservation:

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")

3) CO2 concentration is rising to historically unprecedented levels

CO2 rise correlates strongly with man's "industrial revolution"

Source: United Nations Environmental Project / GRID Arendalhttp://www.grida.no/graphicslib/detail/historical-trends-in-carbon-dioxide-concentrations-and-temperature-on-a-geological-and-

recent-time-scale_a210

N

ew

level as o

f M

ay 2

013

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)

So remaining scientific debate (if any) is: "Are we are responsible for that CO2?"

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*

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

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

*And these are generally rare (one or two of a kind worldwide) super plants!

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/a-shorter-road-to-our-energy-

future/

Solar Thermal: Concentrate light > boil fluid > power boiler > turn turbine-generator

Source: http://blog.zintro.com/clean-tech-alt-energy/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:

http://www.climateandfuel.com/pages/electrical.htm

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)

"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:

"Energy Systems – Time to "Get Real"

(RED = particularly bad / high values GREEN = particularly low / good values)

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 Low hills = Fair High Mtns / Low plains = Poor

Different conclusion: 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

(Only need half that if built in Arizona!)

http://rredc.nrel.gov/solar/old_data/nsrdb/1961-1990/redbook/atlas/

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?

"Energy Systems – Time to "Get Real"

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?

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:

CASE 2 : Variable wind speed averaging (over day) 8 m/s:

Wind speed over day: Wind power over day:

8 m/s

8 m/s

16 m/s

½ ρ 83 A

½ ρ 163 A

Average Power = ½ ρ 1536 A

½ ρ 83 A

Average Power = ½ ρ 512 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: 6600-40,000 km2

Wind: ~ 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

Then they sited the emergency generators (essential for cooling the reactor

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)