SOLAR ELECTRICITY

1
SOLAR ELECTRICITY

• Solar Energy Applications
• EnvS 116
• Asim Zia
• Department of Environmental Studies
• San Jose State University

2
Overview

• Solar Cell Design
• Solar cell efficiency
• PV System applications
• Residential PV system design
• Economics of residential PV systems
• Uncertainties in cost estimation of system life
• Solar electricity through concentrators
• Haydens perspective on solar electricity

3
Solar Cell Design

• Edmund Becquerel (in 1839) discovered
  photovoltaic effect (i.e. light falling on some
  materials created electric charge, proportional
  to intensity and amount of light)
• Materials for solar cells include silicon, and
  other advanced semi-conductor alloys
  
• A four-inch silicon cell can produce 1 watt of
  electricity
  
• Cells Modules Panels Arrays

4
Solar cell efficiency

• Currently solar cells are 12 to 20 efficient
• Solar thin films are 4 to 11 efficient
• Efficiency is measured by the amount of sunlight
  used to measure electricity divided by the
  sunlight that fell upon the cell.
  
• Or Efficiency Sunlight used/ Insolation100

5
PV system applications

• Solar powered house numbered lights
• Solar electronics (watches, calculators etc)
• Solar battery charger (cars, boats)
• Solar lightening systems (including security
  lights)
  
• Solar charged attic vent fans
• Residential power

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Residential PV system design

• Determine your power demand
• Quality, reliability and timing of power demand
• Quantity (KW) demand
• Output of energy (Voltage)
• Storage (mandatory if off the grid)
• Inverters from DC to AC (mandatory if off the
  grid)
  
• Calculate the number of solar panels needed to
  meet the quantity/output of the demand

7
Economics of residential PV systems

• Find out the demand for power per day (in
  KWH/day)
  
• Average home needs 30 KW/day, which can be met by
  installing 3x 2 kwh/day PV systems (assuming 5
  hours of sunlight, 6 x 200 sq feet 1200 sq feet
  space).
• 3x2 kwh/day PV systems average around 72000/-
  (which includes all the related mounting,
  inverter, controller, storage costs)
  
• Calculate system lifetime costs in per KWh units
  System costs, 72000/30 kw/d x 365 d x 20
  years 0.3287/KWh

8
Uncertainties in cost estimation of system life

• Amount of sunlight per day (if 10 hours/day, then
  system costs reduce by half as compared to 5
  hours/day)
  
• Intensity of sunlight per day
• Storage requirements add 50 to the total cost
• PV panel mounting requirements vary
• Local interconnection requirements vary
• Power disruptions with traditional supply
  systems
  

9
Solar electricity through concentrators

• Conventional power plant design is used except
  that steam is produced by solar concentrators
  
• Pilot projects have limited success, but critics
  found overwhelming problems (including low
  efficiency, cost-ineffectiveness and space
  requirements)

10
Haydens perspective on solar electricity

• Solar 2 project generating electricity through
  concentrators is inefficient, and it needs more
  space due to the shading problem
  
• The Solar Two site occupies 52.6 hectares (130
  acres) and produces 10 MWe peak. Its capacity
  factor is about 16. For a Solar Two installation
  to produce as much energy as a typical 1000-MWe
  power plant does in a year, it would have to
  cover about 33,000 hectares (127 square miles).
  That is environmental imapct! Page 187

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Haydens Perspective (Continued)

• Limitations on the efficiency of photcells (pages
  192-195) also Quantum limitation
  
• We ask a broad spectrum sunlight, ranging
  from infrared to ultraviolet to do a quantum
  job, causing electrons to transit between
  well-defined states. No matter whether the
  transition involves 1.1 eV or 2.8 eV or any other
  number of your choosing, some light will always
  be useless because its energy is too low. Other
  light will always have too much energy, and the
  excess will be wasted as heat. For that reason,
  PV cells are inherently limited as their
  efficiency. As a matter of practical concern, the
  best solar cells available on a large scale have
  an efficiency of about 10.

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Haydens Perspective (Continued)

• The output power of a PV cell varies with the
  amount of sunlight.What sorts of electrically
  powered things might be consistent with this
  property? page 195
• Electrolysis of water to generate hydrogen for
  fuel cells
  
• Battery charging
• Exotic materials That sand is not a PV cell,
  nor is the silicon that is extracted from the
  sand. But the availability of the sand is not the
  limiting factor. To make a PV cell means to
  dope the silicon with other elements to cause
  the device to have semiconductor properties. When
  all is said and done, the Si-based PV cell has an
  efficiency of 10 or less.To make PV cells of
  higher efficiency requires exotic materials,
  including germanium, gallium, antimony, indium,
  and cadmium, possibly with gold or platinum for
  conductors. page 196

13
Haydens Perspective (Continued)

• The PV price will fall through the floor!
• It is wrong to say that PV prices will fall as
  the prices of transistors and computers fell. In
  the 1989-2002 interval while PV prices dropped
  20 to 30, the price of transistors in CPUs has
  dropped by over 99. page 199
• Putting PV systems in desert retains the problem
  of transmitting electricity
  
• Urban/suburban rooftops are mostly covered with
  trees on the south side to provide shades
  
• Layered PV cells can attain more efficiency, but
  researchers have not gotten there yet!