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