ENGR 1315 Introduction to Engineering

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ENGR 1315Introduction to Engineering

• Making Solar Energy Economical

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Grand ChallengeMake Solar Energy Economical

• First of all what is solar energy?
• Actually, its all solar at the root
  petrochemicals started as green plants which used
  energy from the sun to create biomass
• All right, Ill concede geothermal and hydro but
  its arguable the energy that exists in the
  earths core comes from the creation of the earth
  out of the stellar mass, and you cant get the
  water uphill without the sun to create weather
• Never mind, leaving out petro, geo, and hydro,
  what do we have?

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Grand ChallengeMake Solar Energy Economical

• Ok, so what is solar?
• Look around you if I look around me I have 25
  m2 of black plastic microchannel to heat water
  over time will maintain about 5o C temperature
  differential in a 30,000 gallon reservoir
• And I can run out and buy photovoltaic panels
  that deliver 5 w for 50

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Grand ChallengeMake Solar Energy Economical

• Those are easy solar cells and passive heating
• Are they economical?
• What does economical mean?
• Whats useful?
• What else is solar, or what would we do with the
  things weve mentioned so far to make them useful?

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Grand ChallengeMake Solar Energy Economical

• We could certainly add wind to solar if the sun
  doesnt shine the wind doesnt blow
• Wind, like photovoltaic, is attractive because
  its high quality energy
• What makes petrochemicals so attractive?
• They are concentrated energy forms
• Sometimes thats good sometimes not so good

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Grand ChallengeMake Solar Energy Economical

• Lets make a solar toaster
• Approach 1 might be to string together enough
  photovoltaic panels to run my electric toaster
• Most toasters go about 1.5 2 kW is that
  right? My toaster is on the order of a go kart?
  Well, maybe a low end go kart2.5 hp
• Anyway, at 10/watt thats a 15,000 toaster
• Can that be right? Whats wrong with this
  picture?

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Grand ChallengeMake Solar Energy Economical

• Solar toaster
• First, it only takes about 5 minutes to make
  toast
• So maybe I could use the toaster to charge my car
  overnight when I wasnt making toast
• But the sun isnt shining at night
• So I have to figure out some way to store the
  energy the photocells are creating while the sun
  is shining and save that for when it isnt.

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Grand ChallengeMake Solar Energy Economical

• Well, that makes sensesort of
• Looks like I can have photovoltaic energy for
  about 10/watt right now
• Lets assume I can utilize that efficiently, that
  is store it without loss and that the sun shines
  half the day, every day, without fail
• What does my house cost me? Did I talk about the
  sustainable energy experts goal of 2 kW/person as
  a goal for sustainability?
• What is my energy usage currently?

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Grand ChallengeMake Solar Energy Economical

• Toasted by solar
• I did a little research because I couldnt
  believe the numbers
• The government (ours, that is) says that average
  consumption of electric power per household in
  the US is 920 kWh/month (http//www.eia.doe.gov/ba
  sics/energybasics101.html)
• Thats a little over 30 kWh/day or an average of
  1.2 kW continuous
• Hey, that means were right on track with that
  2kW, especially if its per person
• Well, it turns out that might be a spurious
  figure nobody seems to be able to resist
  quoting Al Gores mansion in Kentucky
  18,000-20,000 kWh/month. Woohoo thats living
  it up (http//www.tennesseepolicy.org/main/article
  .php?article_id367)
• I just dont understand how anyone could be so
  irresponsible

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Grand ChallengeMake Solar Energy Economical

• That looks like about 8,000 kWh in June
• As much as Id like to say thats a big month..

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Grand ChallengeMake Solar Energy Economical

• Toasted by solar
• So Im not quite in Al Gores league but Im
  still more than 10 kW continuous and its going
  to take me (gulp!) 100,000 worth of solar
  toasters to run my house
• Ack! 200,000 unless I turn everything off at
  night (12 hours a day)
• Somehow that doesnt seem economical to me
• But, to be fair, I spent 800 in June, and 800
  the month before andugh,not a great picture but
  if I saved that money I might be able afford the
  toasters, or service the debt on their purchase

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Grand ChallengeMake Solar Energy Economical

• Plan B
• What are my alternatives?
• 10 kW for 30,000 (wind) (http//www.bergey.com/P
  roducts/Prices1.htm)
• I have to keep my neighbors happy, but the last
  one I talked with offered to go in on the capital
  investment in return for some of the output
• I still have to figure out the batteries, and it
  doesnt include site prep but sounds a lot better
  than 200,000
• I could go direct solar to toast my bagel and
  solar ovens are cheap - 200, (http//www.solarove
  ns.org/buy.html)
• Next question air conditioning..

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Grand ChallengeMake Solar Energy Economical

• Is that really reasonable? Every home has a
  windmill?
• Here it might be, but lots of places dont have
  the reliable wind we have
• Or the reliable insolation the way the southwest
  does
• So maybe we should be looking at commercial or
  industrial solutions
• And assume that we could achieve economies of
  scale
• If were looking at a national or global problem
  we could probably afford to invest in some
  research
• Like increasing the efficiency of photovoltaics
  to the theoretical 40
• And reducing manufacturing costs to the point
  that wed be looking at only 2x what we currently
  pay

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Grand ChallengeMake Solar Energy Economical

• If we were looking at national or global
  solutions we could assume a network or grid of
  power distribution that would accommodate calm
  conditions
• And by the same thinking a global network of
  photovoltaic generators would solve the problem
  at night
• But for a global solution how much money is that?
  In 2007 the total world energy consumption was
  about 140,000 TWh
• Over a year thats an average of
  140x1015/(365x24)1.6x1013W
• For the photovoltaic numbers we used thats about
  1014, or about 10 x the US GDP in the same year
• And, realistically, RM on that, estimated at
  10/year would only cost about what the total GDP
  of the US is to sustain the system
• Yeah, thats the same problem I had with my
  toaster
• Wind? Cheap at only 3/W, or about 1/3 of those
  figures
• We have to figure out how to get to 1/10 to 1/100
  of these numbers

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Grand ChallengeMake Solar Energy Economical

• What else can we do with solar?
• Back to the toaster, without the photovoltaics
• How about concentrators (mirrors or lenses) that
  would collect thermal energy and transfer it to
  water, say
• Then use the hot water to run turbines as in
  conventional generators (oil, coal, nuclear)
• That turns out to be a fairly large industry,
  with solar thermal concentrators returning more
  than 300,000 hits, http//www.energylan.sandia.gov
  /sunlab/snapshot/overview.htm is typical

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Grand ChallengeMake Solar Energy Economical

• This trough concentrator is under test at Sandia
  National Labs
• The tube in the focus of the cylindrical
  parabolic mirror is filled with water or oil
• Temperatures approaching 1000 degrees are
  possible
• Steam runs conventional turbines, molten salt is
  under consideration as an overnight energy
  storage reservoir

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Grand ChallengeMake Solar Energy Economical

• Other solar thermal concentrator configurations
• Pictures from http//www.energylan.sandia.gov/sunl
  ab/snapshot/overview.htm

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Grand ChallengeMake Solar Energy Economical

• These configurations are under investigation
• http//www.energylan.sandia.gov/sunlab/snapshot/ov
  erview.htm

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Grand ChallengeMake Solar Energy Economical

• Fairly inexpensive photovoltaics can be used to
  decompose water electrolyically into hydrogen and
  oxygen
• Some of the products could be burned to drive
  compressors to achieve higher energy densities
• And standard internal combustion engines can be
  adapted to run on gaseous hydrogen
• Issues here include the difficulties in
  containing hydrogen, its volatility, and
  embrittlement
• There are other possibilities for hydrogen.

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Grand ChallengeMake Solar Energy Economical

• Fuel cells how do they work?

A catalyst separates protons and electrons from
the incoming fuel A proton exchange membrane
allows the protons to diffuse to a cathode The
electrons are required to pass through a
conductor where they do work The protons and
electrons recombine with an oxidant at the
cathode Fuel cells are thermodynamically more
ef- ficient than Carnot cycle engines (2x) but
significantly more expensive (figure from
Wikipedia)
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Grand ChallengeMake Solar Energy Economical

• Fuel cells

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Grand ChallengeMake Solar Energy Economical