Solar Energy: The Ultimate Renewable Resource

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Solar Energy The Ultimate Renewable Resource
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What is Solar Energy?

• Originates with the thermonuclear fusion
  reactions occurring in the sun.
• Represents the entire electromagnetic radiation
  (visible light, infrared, ultraviolet, x-rays,
  and radio waves).

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How much solar energy?
The surface receives about 47 of the total solar
energy that reaches the Earth. Only this amount
is usable.
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Energy from the Sun

• About half the incoming solar energy reaches the
  Earth's surface.
• The Earth receives 174 petawatts (PW) (1015
  watts) of incoming solar radiation at the upper
  atmosphere. Approximately 30 is reflected back
  to space while the rest is absorbed by clouds,
  oceans and land masses.
• Earth's land surface, oceans and atmosphere
  absorb solar radiation, and this raises their
  temperature. Sunlight absorbed by the oceans and
  land masses keeps the surface at an average
  temperature of 14 C.
• By photosynthesis green plants convert solar
  energy into chemical energy, which produces food,
  wood and the biomass from which fossil fuels are
  derived.

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Putting Solar Energy to Use Heating Water

• Two methods of heating water passive (no moving
  parts) and active (pumps).
• In both, a flat-plate collector is used to absorb
  the suns energy to heat the water.
• The water circulates throughout the closed system
  due to convection currents.
• Tanks of hot water are used as storage.

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Heating Water Active System
Active System uses antifreeze so that the liquid
does not freeze if outside temp. drops below
freezing.
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Heating WaterLast Thoughts

• Efficiency of solar heating system is always less
  than 100 because
• transmitted depends on angle of incidence,
• Number of glass sheets (single glass sheet
  transmits 90-95), and
• Composition of the glass
• Solar water heating saves approx. 1000 megawatts
  of energy a yr, equivalent to eliminating the
  emissions from two medium sized coal burning
  power plants.
• By using solar water heating over gas water
  heater, a family will save 1200 pounds of
  pollution each year.
• Market for flat plate collectors grew in 1980s
  because of increasing fossil fuels prices and
  federal tax credits. But by 1985, when these
  credits were removed and fossil fuel prices were
  low, the demand for flat plate collectors shrunk
  quickly.
• Solar water heating is relatively low in the US,
  in other parts of the world such as Cyprus (90)
  and Israel (65), it proves to be the predominate
  form of water heating.

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Heating Living Spaces

• Best design of a building is for it to act as a
  solar collector and storage unit. This is
  achieved through three elements insulation,
  collection, and storage.
• Efficient heating starts with proper insulation
  on external walls, roof, and the floors. The
  doors, windows, and vents must be designed to
  minimize heat loss.
• Collection south-facing windows and appropriate
  landscaping.
• Storage Thermal massholds heat.
• Water 62 BTU per cubic foot per degree F.
• Iron54, Wood (oak) 29, Brick25, concrete22,
  and loose stone20

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Heating Living Spaces
Passive Solar
Trombe Wall
Passively heated home in Colorado
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Heating Living Spaces

• A passively heated home uses about 60-75 of the
  solar energy that hits its walls and windows.
• It is estimated that in almost any climate, a
  well-designed passive solar home can reduce
  energy bills by 75 with an added construction
  cost of only 5-10.
• About 25 of energy is used for water and space
  heating.
• Major factor discouraging solar heating is low
  energy prices.

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Solar-Thermal ElectricityPower Towers

• General idea is to collect the light from many
  reflectors spread over a large area at one
  central point to achieve high temperature.
• Example is the 10-MW solar power plant in
  Barstow, CA.
• 1900 heliostats, each 20 ft by 20 ft
• a central 295 ft tower
• An energy storage system allows it to generate 7
  MW of electric power without sunlight.
• Capital cost is greater than coal fired power
  plant, despite the no cost for fuel, ash
  disposal, and stack emissions.
• Capital costs are expected to decline as more and
  more power towers are built with greater
  technological advances.
• One way to reduce cost is to use the waste steam
  from the turbine for space heating or other
  industrial processes.

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Power Towers
Power tower in Barstow, California.
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Solar-Thermal ElectricityParabolic Dishes and
Troughs

• Focus sunlight on a smaller receiver for each
  device the heated liquid drives a steam engine
  to generate electricity.
• The more recent facilities converted a remarkable
  22 of sunlight into electricity.

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Parabolic Dishes and Troughs
Collectors in southern CA.
Because they work best under direct sunlight,
parabolic dishes and troughs must be steered
throughout the day in the direction of the sun.
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Solar Cells Background

• 1839 - French physicist A. E. Becquerel first
  recognized the photovoltaic effect.
• Photovoltaic convert light to electricity
• 1883 - first solar cell built, by Charles Fritts,
  coated semiconductor selenium with an extremely
  thin layer of gold to form the junctions.
• 1954 - Bell Laboratories, experimenting with
  semiconductors, accidentally found that silicon
  doped with certain impurities was very sensitive
  to light. Daryl Chapin, Calvin Fuller and Gerald
  Pearson, invented the first practical device for
  converting sunlight into useful electrical power.
  Resulted in the production of the first practical
  solar cells with a sunlight energy conversion
  efficiency of around 6.
• 1958 - First spacecraft to use solar panels was
  US satellite Vanguard 1

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Direct Conversion into Electricity

• Photovoltaic cells are capable of directly
  converting sunlight into electricity.
• A simple wafer of silicon with wires attached to
  the layers. Current is produced based on types
  of silicon (n- and p-types) used for the layers.
  Each cell0.5 volts.
• Battery needed as storage
• No moving parts?do no wear out, but because they
  are exposed to the weather, their lifespan is
  about 20 years.

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Single-Crystal Silicon Cell Construction

• The majority of PV cells in use are the
  single-crystal silicon type.
• Silica (SiO2) is the compound used to make the
  cells. It is first refined and purified, then
  melted down and re-solidified so that it can be
  arranged in perfect wafers for electric
  conduction. These wafers are very thin.
• The wafers then have either Phosphorous or Boron
  added to make each wafer either a negative type
  layer or a positive type layer respectively. Used
  together these two types treated of crystalline
  silicon form the p-n junction which is the heart
  of the solar electrical reaction.
• Many of these types of cells are joined together
  to make arrays, the size of each array is
  dependant upon the amount of sunlight in a given
  area.

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How Does A Cell Become A Module?

• A solar cell is the basic building block of a PV
  system.
• A typical cell produces .5 to 1V of electricity.
• Solar cells are combined together to become
  modules or if large enough, known as an array.
• A structure to point the modules towards the sun
  is necessary, as well as electricity converters,
  which convert DC power to AC.
• All of these components allow the system to power
  a water pump, appliances, commercial sites, or
  even a whole community.

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The Photovoltaic Effect

• The photovoltaic effect relies on the principle
  that whenever light strikes the surface of
  certain metals electrons are released.
• In the p-n junction the n-type wafer treated with
  phosphorus has extra electrons which flow into
  the holes in the p-type layer that has been
  treated with boron.
• Connected by an external circuit electrons flow
  from the n-side to create electricity and end up
  in the p-side.

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Photovoltaic Effect
                                                                                                                                      
A picture of an typical silicon PV cell
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• Sunlight is the catalyst of the reaction.
• The output current of this reaction is DC
  (direct) and the amount of energy produced is
  directly proportional to the amount of sunlight
  put in.
• Cells only have an average efficiency of 30

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Solar Cells Background

• First Generation Single Junction Silicon Cells
• 89.6 of 2007 Production
• 45.2 Single Crystal Si
• 42.2 Multi-crystal SI
• Large-area, high quality and
  
  single junction devices.
• High energy and labor inputs which
  
  limit significant progress in reducing
  
  production costs.
• Single junction silicon devices are
  
  approaching theoretical limit efficiency
  
  of 33. Achieve cost parity with fossil
  fuel
  energy generation after a payback period
  
  of 57 years. (3.5 yr in Europe)
• Single crystal silicon - 16-19 efficiency
• Multi-crystal silicon - 14-15 efficiency

Silicon Cell Average Efficiency
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Solar Cells Background

• Second Generation Thin Film Cells
• CdTe 4.7 CIGS 0.5 of 2007 Production
• New materials and processes to improve efficiency
  and reduce cost.
• As manufacturing techniques evolve, production
  costs will be dominated by constituent material
  requirements, whether this be a silicon
  substrate, or glass cover. Thin film cells use
  about 1 of the expensive semiconductors compared
  to First Generation cells.
• The most successful second generation materials
  have been cadmium telluride (CdTe), copper indium
  gallium selenide (CIGS), amorphous silicon and
  micromorphous silicon.
• Trend toward second gen., but commercialization
  has proven difficult.
• 2007 - First Solar produced 200 MW of CdTe solar
  cells, 5th largest producer in 2007 and the
  first to reach top 10 from of second generation
  technologies alone.
• 2007 - Wurth Solar commercialized its CIGS
  technology producing 15 MW.
• 2007 - Nanosolar commercialized its CIGS
  technology in 2007 with a production .
  capacity of 430 MW for 2008 in the USA and
  Germany.
• 2008 - Honda began to commercialize their CIGS
  base solar panel.
• CdTe 8 11 efficiency (18 demonstrated)
• CIGS 7-11 efficiency (20 demonstrated)
• Payback time lt 1 year in Europe

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Solar Cells Background

• Third Generation Multi-junction Cells
• Third generation technologies aim to enhance poor
  electrical performance of second generation
  (thin-film technologies) while maintaining very
  low production costs.
• Current research is targeting conversion
  efficiencies of 30-60 while retaining low cost
  materials and manufacturing techniques. They can
  exceed the theoretical solar conversion
  efficiency limit for a single energy threshold
  material, 31 under 1 sun illumination and 40.8
  under the maximal artificial concentration of
  sunlight (46,200 suns).
• Approaches to achieving these high efficiencies
  including the use of multijunction photovoltaic
  cells, concentration of the incident spectrum,
  the use of thermal generation by UV light to
  enhance voltage or carrier collection, or the use
  of the infrared spectrum for night-time
  operation.
• Typically use fresnel lens (3M) or other
  concentrators, but cannot use diffuse sunlight
  and require sun tracking hardware
• Multi-junction cells 30 efficiency (40-43
  demonstrated)

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World's largest photovoltaic (PV) power plants
(12 MW or larger)
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Name of PV power plant     Country      DCPeakPower(MW) GWh/year       Notes      
Olmedilla Photovoltaic Park Spain 60 85 Completed September 2008
Puertollano Photovoltaic Park Spain 50 2008
Moura photovoltaic power station Portugal 46 93 Completed December 2008
Waldpolenz Solar Park Germany 40 40 550,000 First Solar thin-film CdTe modules. Completed Dec 2008
Arnedo Solar Plant Spain 34 Completed October 2008
Merida/Don Alvaro Solar Park Spain 30 Completed September 2008
17 more 2 more Spain Korea Avg 20 Avg 20
Koethen Germany 14.75 13 200,000 First Solar thin-film CdTe modules. Completed Dec 2008
Nellis Solar Power Plant USA 14.02 30 70,000 solar panels
Planta Solar de Salamanca 6 more Spain, 1 US, 1 Germany Spain 13.8 Avg 12 n.a. 70,000 Kyocera panels

















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Waldpolenz Solar Park

• The Waldpolenz Solar Park is built on a surface
  area equivalent to 200 soccer fields, the solar
  park will be capable of feeding 40 megawatts into
  the power grid when fully operational in 2009.
• In the start-up phase, the 130-million-euro (201
  million) plant it will have a capacity of 24
  megawatts, according to the Juwi group, which
  operates the installation.
•  
• The facility, located east of Leipzig, uses
  state-of-the-art, thin-film technology. Some
  550,000 thin-film modules will be used, of which
  350,000 have already been installed. The direct
  current produced in the PV solar modules will be
  converted into alternating current and fed
  completely into the power grid.
• After just a year the solar power station will
  have produced the energy needed to build it,
  according to the Juwi group.

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Waldpolenz Solar Park
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Solar Panels in Use

• Because of their current costs, only rural and
  other customers far away from power lines use
  solar panels because it is more cost effective
  than extending power lines.
• Note that utility companies are already
  purchasing, installing, and maintaining PV-home
  systems (Idaho Power Co.).
• Largest solar plant in US, sponsored by the DOE,
  served the Sacramento area, producing 2195 MWh of
  electric energy, making it cost competitive with
  fossil fuel plants.

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World's Biggest Rooftop Solar Panels

• The largest rooftop solar power station in the
  world is being built in Spain. With a capacity of
  12 MW of power, the station is made up of 85,000
  lightweight panels covering an area of two
  million SqFt.
• Manufactured in rolls, rather like carpet, the
  photovoltaic panels are to be installed on the
  roof of a General Motors car factory in Zaragoza,
  Spain.
• General Motors, which plans to install solar
  panels at another 11 plants across Europe,
  unveiled the 50M (68M) project yesterday. The
  power station should be producing energy by
  September.
• The panels will produce an expected annual output
  of 15.1 million kilowatt hours (kWh) - enough to
  meet the needs of 4,600 households with an
  average consumption of 3,300kWh, or power a third
  of the GM factory. The solar energy produced
  should cut CO2 emissions by 6,700 tons a year.
• Energy Conversion Devices who makes the panels,
  said it would be the largest rooftop solar array
  in the world.

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World's Biggest Rooftop Solar Panels
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BREAKDOWN

• PV systems are like any other electrical power
  generating systems, except the equipment used to
  generate the power is different.
• Specific components required, and may include
  major components such as a DC-AC power inverter,
  batteries, auxiliary energy sources, sometimes
  the specified electrical load (appliances),
  wiring, surge protection and other hardware.
• Batteries are often used in PV systems for the
  purpose of storing energy produced by the PV
  array during the day, and to supply it to
  electrical loads as needed (during the night and
  periods of cloudy weather). Also to keep the
  system at full operational power

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Grid-connected or Utility-Connected

• Grid-connected or utility-interactive PV systems
  are designed to operate in parallel with and
  interconnected with the electric utility grid.
• These system contain an inverter, called a power
  conditioning unit (PCU) which converts the DC
  power produced by the PV array into AC power
  consistent with the voltage and power quality
  requirements of the utility grid.
• A bi-directional interface allows the AC power
  produced by the PV system to either supply
  personal electrical loads, or return power back
  to the grid when the PV system output is greater
  than the personal demand.

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Stand-Alone PV Systems

• Stand-alone PV systems are designed to operate
  independent of the electric utility grid
• Supply DC and/or AC electrical loads
• The simplest type of stand-alone PV system is a
  direct-coupled system, where the DC output of a
  PV module or array is directly connected to a DC
  load
• Since there are no batteries involved in direct
  load systems, stand-alone PV systems are suitable
  for such processes as heating and pumping water,
  ventilation fans, etcAlthough they can only work
  in the day.
• Stand-Alone systems may also power AC loads such
  as batteries. Like the AC adapter which powers
  your laptop.

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Efficiency and Disadvantages

• Efficiency is far lass than the 77 of solar
  spectrum with usable wavelengths.
• 43 of photon energy is used to warm the crystal.
• Efficiency drops as temperature increases (from
  24 at 0C to 14 at 100C.)
• Light is reflected off the front face and
  internal electrical resistance are other factors.
• Overall, the efficiency is about 10-14.

• Cost of electricity from coal-burning plants is
  anywhere b/w 8-20 cents/kWh, while
  photovoltaic power generation is anywhere b/w
  0.50-1/kWh.
• Does not reflect the true costs of burning coal
  and its emissions to the nonpolluting method of
  the latter.
• Underlying problem is weighing efficiency against
  cost.
• Crystalline silicon-more efficient, more
  expensive to manufacture
• Amorphous silicon-half as efficient, less
  expensive to produce.

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Final Thought

• Argument that sun provides power only during the
  day is countered by the fact that 70 of energy
  demand is during daytime hours. At night,
  traditional methods can be used to generate the
  electricity.
• Goal is to decrease our dependence on fossil
  fuels.
• Currently, 75 of our electrical power is
  generated by coal-burning and nuclear power
  plants.
• Mitigates the effects of acid rain, carbon
  dioxide, and other impacts of burning coal and
  counters risks associated with nuclear energy.
• pollution free, indefinitely sustainable.

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Advantages and Disadvantages

• Advantages
• All chemical and radioactive polluting byproducts
  of the thermonuclear reactions remain behind on
  the sun, while only pure radiant energy reaches
  the Earth.
• Energy reaching the earth is incredible. By one
  calculation, 30 days of sunshine striking the
  Earth have the energy equivalent of the total of
  all the planets fossil fuels, both used and
  unused!
• Disadvantages
• Sun does not shine consistently.
• Solar energy is a diffuse source. To harness it,
  we must concentrate it into an amount and form
  that we can use, such as heat and electricity.
• Addressed by approaching the problem through
  
• 1) collection, 2) conversion, 3) storage.

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The End