Solar CellsSolar Cells
David AllenDavid AllenAlex BearAlex Bear
Zack EasonZack EasonDennis Dennis OgbeOgbe
How a solar cell worksHow a solar cell works Solar cells are electrical devices that convert Solar cells are electrical devices that convert
the energy of sunlight into electricitythe energy of sunlight into electricity
Photons are absorbed by semiconductor Photons are absorbed by semiconductor materials (such as silicon)materials (such as silicon)
Electrons are knocked loose from atoms, which Electrons are knocked loose from atoms, which creates electricitycreates electricity
It takes a series of solar cells to create usable It takes a series of solar cells to create usable amounts of DC electricityamounts of DC electricity
http://http://www.youtube.comwww.youtube.com//watch?vwatch?v=x2zjdtxrisc=x2zjdtxrisc
Silicon type solar cellsSilicon type solar cells MonocrystallineMonocrystalline Solar CellSolar Cell
A silicon crystal is produced (silicon can be A silicon crystal is produced (silicon can be prepared either intrinsic or doped)prepared either intrinsic or doped)
Semiconductors are imbedded in the disk, Semiconductors are imbedded in the disk, which has + and which has + and –– leads that serve as leads that serve as connection points to tie cells in series. connection points to tie cells in series.
Higher efficiency than most solar cells, but Higher efficiency than most solar cells, but come at a higher costcome at a higher cost
ArraysArrays Many linked solar cells are called modules Many linked solar cells are called modules
(or panels)(or panels)
Many linked panels make up solar arraysMany linked panels make up solar arrays
Panels alone produce between 100Panels alone produce between 100--400 400 WattsWatts
Solar arrays can produce into the megawatt Solar arrays can produce into the megawatt rangerange
TrackingTracking Option when building solar array is tracking Option when building solar array is tracking
the sunthe sun
Panels tilt different ways throughout the day, Panels tilt different ways throughout the day, getting peak sunlightgetting peak sunlight
Can be 20Can be 20--25% more efficient during 25% more efficient during morning and afternoonmorning and afternoon
If not equipped with tracking, cells face high If not equipped with tracking, cells face high noonnoon
InvertersInverters Solar arrays produce DC electricity, but most Solar arrays produce DC electricity, but most
systems need ACsystems need AC
DC to AC inverters are used to convert the DC to AC inverters are used to convert the DC into AC that can be fed into a DC into AC that can be fed into a commercial electrical grid, or a local off grid commercial electrical grid, or a local off grid networknetwork
This allows the use of ordinary commercial This allows the use of ordinary commercial appliancesappliances
Very efficient, usually 93Very efficient, usually 93--96%96%
Maximum Power Point Maximum Power Point TrackingTracking
Solar cells have a Solar cells have a non linear output non linear output efficiencyefficiency
MPPT applies MPPT applies optimal load to optimal load to produce maximum produce maximum powerpower
Typically integrated Typically integrated into DC to AC into DC to AC inverterinverter
ConnectivityConnectivity Ways to connect solar panelsWays to connect solar panels
OffOff--grid without battery (arraygrid without battery (array--direct)direct) OffOff--grid with batterygrid with battery GridGrid--tie with batterytie with battery GridGrid--tie without tie without batterybattery
Grid connection usually works as consumer Grid connection usually works as consumer selling electricity back to electric utilityselling electricity back to electric utility
Output must match the grid frequency, be Output must match the grid frequency, be lower than grid voltage, and disconnect if lower than grid voltage, and disconnect if grid is turned grid is turned offoff
ShadingShading Panels lose efficiency when partially shadedPanels lose efficiency when partially shaded
Short circuiting occurs when electrons Short circuiting occurs when electrons reverse direction through the preverse direction through the p--n junctions n junctions of shaded cellsof shaded cells
Panels use bypass diodes (diode opposite Panels use bypass diodes (diode opposite biased) to prevent shaded cells absorbing biased) to prevent shaded cells absorbing power generated by neighboring cellspower generated by neighboring cells
Pros and ConsPros and Cons ProsPros
Less fossil fuels usedLess fossil fuels used Flexible usage (such as rooftops)Flexible usage (such as rooftops) Long lifetime and little required maintenanceLong lifetime and little required maintenance
ConsCons High initial costHigh initial cost Not good in bad weather areasNot good in bad weather areas
Future ImprovementsFuture Improvements One main complaint of solar cells is that One main complaint of solar cells is that
they are not very efficient (around 27%)they are not very efficient (around 27%)
More efficient semiconductors could make More efficient semiconductors could make solar cells bettersolar cells better
As energy demand grows, solar technology As energy demand grows, solar technology and research will increaseand research will increase