Solar Electricity Beginner's notes
Direct Current, Series, Parallel
Solar cell electricity is direct current (DC)
electricity - it flows in one direction. When a solar panel is attached to a
motor, the motor can be made to spin in the reverse direction by reversing the
connections at the back of the motor.
No harm will result if the clips are "shorted" on a single solar panel. While
electricity will flow, according to the amount of sunlight, no damage results
to the cell, nor will the wires wear out. These solar panels will not harm each
other if hooked together in any combination.
Solar cells and panels can be hooked up in series
(positive to negative - adds voltages together) or parallel (positive
to positive, negative to negative - adds amperages together) circuits.
The solar cell reaction has an electrical potential of approximately
0.5 volts. If we add two cells together in series, we get 1 volt. Higher
voltages are obtained by linking many cells in series. Voltage is the
measure of potential energy each electron has in the electrical field formed
within the electrical circuit. Amperage is a gross measurement of how
many electrons are flowing. Together they are like a waterfall, with voltage
being like the height of the water fall, and amperage being like the amount
of water flowing over the waterfall's edge. At the bottom, where the water splashes
down, we have power according to how far the water fell into
the gravity field, and how much of it fell each moment (time).
volts x amps = watts (power)
Normally we must turn an electromagnetic
generator with physical force to obtain electrical energy. Or, discharge a
chemical battery.
Solar-generated electricity is different - the power comes
from light, and the reaction in the cells is not chemical, but electrical
only. The atoms remain the same, and are not involved in chemical reactions.
What are affected are the electron clouds of the silicon crystals, as photons
of light energy are absorbed. When two layers of differently doped purified
silicon are joined, immediately an electrostatic field with a potential of
0.5 volts
is formed
at their junction. Because it is rather tricky to achieve in our three-dimensional
world - having a photon strike an electron on the P-side of the electrical
junction of two layers of differently doped purified silicon - and very close
to the junction to boot - solar cells are only about 12 - 15 % efficient
in
changing light energy into electrical energy. That is, only about 1/8 of
the solar energy striking the panel gets converted to electricity.
The photovoltaic panels supplied by SunWind
generate 1 volt 400 mAmp in full sun. They are comprised of two 400 mAmp cells
wired in series (positive to negative) to make 1 volt. Increasing the voltage
will generally increase the speed at which an attached motor will spin.
If cells, or panels, are wired in parallel, their amperages
are added together. The amperage of a solar cell is determined by the cell
quality and area of the cell, and the amount of sunlight striking the cell.
If two of these 1 volt 400 mAmp panels are connected in parallel, 800 mAmps
of 1 volt electricity could flow through a connected device, which might be
useful if the device needs some low-end power. And, if it is a cloudy day,
the motor would still be getting SOME electrons to run on. There is a generally
direct relationship between the amount of sunlight (number of photons) striking
the cell, and the amount of electricity (number of electrons) produced.
Try shading the panels in different ways and observe
what sort of shading lets the motor run, and what stops it completely. Clue:
if the voltage of one cell is brought to zero, can the voltage of the other
cell pass through it?
In larger photolvoltaic panels, where many individual
cells are added together to achieve voltages of 18 or more, what might happen
if leaves shaded just some of the panels?
http://www.sunwindsolar.com