The Solar Scholars Program and Fundamentals of PV Design

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The Solar Scholars Program and Fundamentals of
PV Design

• Prepared by
• Colin Davies Eric Fournier
• Sept 2007

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Outline

• Renewable vs. non-renewable energy
• The science of photovoltaics
• Principle design elements
• System configurations
• The Solar Scholars program at Bucknell

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Whats wrong with this picture?

• Pollution from burning fossil fuels leads to an
  increase in greenhouse gases, acid rain, and the
  degradation of public health.

• In 2005, the U.S. emitted 2,513,609 metric tons
  of carbon dioxide, 10,340 metric tons of sulfur
  dioxide, and 3,961 metric tons of nitrogen oxides
  from its power plants.

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Making the Change to Renewable Energy

• Solar
• Geothermal
• Wind
• Hydroelectric

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Harnessing the Sun

• Commonly known as solar cells, photovoltaic (PV)
  devices convert light energy into electrical
  energy
• PV cells are constructed with semiconductor
  materials, usually silicon-based
• The photovoltaic effect is the basic physical
  process by which a PV cell converts sunlight into
  electricity
• When light shines on a PV cell, it may be
  reflected, absorbed, or pass right through. But
  only the absorbed light generates electricity.

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The Science of Photovoltaics

• http//www1.eere.energy.gov/solar/video/solarcell1
  .mpg

Source Olympus Microscopy Resource Center
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Crystalline Structure

• Single Crystal Silicon Very efficient but
  expensive manufacturing process

- A single seed crystal is place atop a crucible
of molten silicon. As this seed crystal is slowly
raised a large single crystal ingot is formed.
This ingot is then sliced into several sheets for
solar panel manufacturing.
                      
Source U.S. Dept of Energy
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Other options

• Multicrystalline Silicon Less efficient than
  single crystalline silicon but also less
  expensive to produce

• Amorphous Silicon Non-crystalline structure
  (even less efficient) very inexpensive
  depositional manufacturing process

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Electricity Basics

• The power produced by solar arrays is in the form
  of direct current or DC power.

• The outlets in our homes provide alternating
  current (AC).
• Questions?

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Design Elements Going from DC to AC power

• The DC power generated by the array must first be
  converted to AC before it can be used in the home
  or sold back to the utility

• An Inverter converts DC power to AC power

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Wiring

• Efficiency penalty associated with DC power over
  long distances
• AC line losses are minimal
• Resistance depends on conductor gauge, length,
  material, and temperature

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Getting Desired Voltage and Amperage

• Series Voltages are additive, current is equal
• Parallel Currents are additive, voltage remains
  the same

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IV Curve - MPP
Power (Watts) Current (Amps) X Voltage (Volts)
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IV Curve Cell Temp Irradiance Response
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Site Selection - Shading

• Shading effects important to site selection

• Orientation of shaded region on module is
  critical to output

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Site Selection Panel Direction

• Face south
• Correct for magnetic declination

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Site Selection Tilt Angle
Max performance is achieved when panels are
perpendicular to the suns rays

• Year round tilt latitude
• Winter 15 lat.
• Summer 15 lat.

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Mounting Options

• Fixed
• Roof, ground, pole
• Integrated
• Tracking
• Pole (active passive)

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Configurations

• Grid-tied
• Grid-tied with battery backup
• Stand-alone

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Grid-tied

• When grid goes down, you also lose power

• Excess power can be sold to grid
• Electricity can be bought from grid at night or
  on cloudy days

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Grid-tied with battery backup

• More independence
• Batteries add complexity and cost

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Stand-alone

• Remote locations
• Road-side

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Energy Consumption

• Air conditioner (1 ton) 1500W
• Blow dryer ....... 1000W
• Refrigerator/freezer (22 ft3) .. 540W
• Washing Machine ...... 1450W
• Incandescent light (75W) .. 75W
• Compact fluorescent (75W equiv.) .. 20W
• Cell phone charger .... 24W

Avg U.S. home 25 30 kWh per day
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Energy Efficiency

• Home energy audit
• Insulation, windows
• Compact fluorescent lights
• Appliances
• Phantom loads
• 45 billion kWh annually
• 3.5 billion per year
• 10 power plants
• 18,000,000 tons of CO2
• More pollution than 6 million cars
• TVs and VCRs alone cost the US 1 billion per
  year in lost electricity

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Solar Scholars Overview

• Solar Scholars is an innovative, solar-energy
  education program for university students
  throughout Pennsylvania, created by The
  Sustainable Energy Fund of Central-Eastern
  Pennsylvania (The SEF-CEPA).
• Its goal is cultivating the solar and renewable
  energy leaders, policy-makers and entrepreneurs
  of tomorrow.

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Solar Scholars Workshop
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BUEC Installation

• Twelve 200 W GE panels (2.4kW)
• Ground mounted
• Fronius Inverter with Datalogger
• Grid-tied

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Mod Installation

• Two pole mounted arrays Eight 200 W GE panels
  per pole (3.2kW total)
• Fixed
• Passive tracker
• Two Fronius Inverters
• Grid-tied

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Mod Installation (cont)
All in a good days work
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Ready for a field tour?

• Questions?
• If you are interested in anything you have seen
  today and would like to get involved, please
  contact any member of the Solar Scholars team
• Colin Davies, Eric Fournier, or Jess Scott
• (cjdavies, efournie, jpscott)