System Function and Design Solar Photovoltaics System Function and Design

How does Solar PV work? Ted Talk on Solar Photovoltaic

Solar Cell N-type contains phosphorus with ‘extra’ electrons P-type contains boron with ‘extra’ holes

Solar Cell Photons provide energy for electrons to flow into circuit Photons provide energy for holes to move into position to accept electrons from circuit

Solar Systems Each cell = 1-2 Watts Cell connected together into modules/panels Modules/panels connected together into rooftop array Commercial cell = 8-22% efficient Current Max Efficiency = 46-48% (very expensive)

Solar Systems Modules/panels = 36-98 cells Residential usually 60 Commercial usually 72 Modules/panels connected together into rooftop array Rooftop array = 12-18 panels Average 2000 ft2 home Varies due to local conditions Latitude Weather/cloud cover

Solar Systems Electricity is produced ‘on demand’ Conversion from DC to AC is critical Storage is difficult and inefficient Not all systems have storage

System Design Solar cells are most efficient in direct light Photons more concentrated/less diffuse The sun does not stay in one position How to optimize for this discrepancy?

Optimizing System Design Sun’s angle varies and can’t be manipulated: Latitude Season Time of day Solar panel angle can manipulated: Maximize 90º relationship with sun Fixed or Tracking?

Optimizing System Design Measure maximum output At 90º light source to panel angle Vary source angles Sun altitude angle (between table top and center of light) Based on realistic changes Latitude, season, time of day Vary panel angles

Optimizing System Design Set angle based on latitude Larkspur = 37.9º N Determine angle for noon on: Summer solstice Winter solstice Spring/Fall Equinox Reduce angles (from above) to represent: Early morning/late afternoon Mid-morning/mid-afternoon