Transcript Sustainable Energy Systems Engineering

Sustainable Energy Systems Engineering
Peter Gevorkian
Ch 1: Solar Power Technology
Brevard Community College
EST1830
Bruce Hesher
Solar Cells
Solar cells are diodes also called PN junctions. They
directly convert solar radiation into electricity with no
moving parts, no water, no pollution, and no !
They do not work at night and their output decreases
when cloudy. They do not store any energy.
There are various
ways to make them
and a lot of research
being done.
Intersil, Sematech, UCF
History of Photovoltaics
The photovoltaic effect was first recognized in 1839 by
French physicist A. E. Becquerel. In 1883 the first solar
cell was built, by Charles Fritts, who coated the
semiconductor selenium with an extremely thin layer of
gold to form a PN junction, it was only 1% efficient.
Albert Einstein explained the photoelectric effect in 1905
and received the Nobel prize in Physics in 1921. Russell
Ohl patented the modern junction
semiconductor solar cell in 1946,
Modern highly efficient solar cells were
first developed by Chapin, Fuller, and
Pearson in 1954 using a diffused silicon
PN junction.
Solar Cell Physics
Carbon, silicon, and germanium are
semiconductor elements.
This means they have 4
valence electrons and form
covalently bonded crystal
masses. Silicon can easily
be doped to make P and N
type silicon.
P-N Junction
Solar cells are P-N junctions, also known as diodes.
Free electrons can only from the N-type to the P-type.
A PN junction is a one way current valve similar to a
check valve in a water pipe.
How a Solar Cell Works
A solar cell converts light energy to electrical energy and is
a current source. When a photon at a frequency with energy
that equals to the bandgap of the impurity used to dope the
silicon enters the PN junction, it frees both an electron and a
hole. These opposite electric charges attract and want to get
back together but the electron can’t go back through the PN
junction. So, it goes the long way around through wiring
attached to the cell (circuit) thereby doing useful work.
How a Solar Cells Works
The electrons flow through the circuit
and the holes stay in the P-type material
waiting for electrons.
The voltage only increases a little
with increasing insolation while the
current increases a lot! Predictable
stable voltage is good; it allows us to
match the voltage ranges of different
pieces of equipment so we can
connect them.
Types of Solar Cells
Mono-crystalline silicon: The most efficient, and
most expensive, solar cells are made of single
crystal integrated circuit grade silicon wafers.
Poly-crystalline silicon: Slightly less efficient
and less expensive.
Thin film: The least expensive and gaining
ground in efficiency. Flexible and can be
applied to curved and bending surfaces like
backpacks or clothing.
Solar Cell Efficiencies
Solar Modules
Cells are wired in series in modules and modules are
connected in series in strings.
Cells -> modules -> Strings - > Array
Cells are connected in series to make modules; modules
are connected in series to make stings. String are
connected in parallel to make an array.
PV System Overview
The array is connected to a PCU (Power Conditioning Unit)
which is in turn connected to the buildings electrical
distribution panel. The PCU performs many functions
including:
MPPT
DC to AC inversion
Charge control of batters (if present)
US Insolation Map
Central Florida
gets about 5.2 Sun
hours per day.
“Sun hours” is
synonymous with
KWH/m2/Day.
Germany is leading
the world in
deployed PV and
they get the same
insolation as Alaska!
http://www.nrel.gov/gis/solar.html
Solar PV Applications
• Utility Scale Power plants: FPL’s Next Generation PV
plant on KSC M.I.
• Mobile: RV’s, Boats, Cars
• Commercial: Electric car recharging stations (like WalMart), road signs, school zones, etc.
• Residential: Utility Interactive (“grid tied”)
Off-grid (stand-alone)
Further Study
EETC2550 Photovoltaic Systems:
 Technology
 Design
 Mechanical integration
 Electrical integration
 Permitting and Licensure
 NABCEP certification