Right now - energy radiating from the sun
is making me sweat
Fortunately solar power technology allows
me to
also use the sun’s energy to cool off a
bit.
Your move … sun.
Right - anyway!
Solar panels were first used to power satellites
back in the 1950s,
but since then they’ve become much more
efficient & widely used.
A panel like this one converts light into
electricity
using an array of solar or “photovoltaic”
cells -
These cells are surprisingly simple devices
- quite similar to diodes.
As you may recall, a diode uses two types
of silicon stacked together
to allow electrical current to flow in a single
direction -
negative-type silicon,
which has an excess of electrons
and positive-type silicon
which has an excess of electron holes or vacancies
waiting to be filled.
Each photovoltaic cell uses a wide, flat layer
of p-type silicon
covered by a thin layer 
of n-type silicon.
When light hits the surface of the cell,
photons pass through the top layer
and hit the junction between the negative
and positive layers.
These photons knock electrons out of their
holes
and toward the top layer of the cell…
while those empty holes are pushed toward
the bottom.
The positive layer of the cell is connected
to a single flat metal conductor,
while the negative side is connected to thin
metal finger-like conductors
which leave most of the surface exposed to
light.
When we connect a circuit to these conductors,
electrons leave the negative layer and travel
through the circuit
in order to reach those available holes down
on the positive layer.
All the while, more photons are knocking electrons
out of holes,
and the cycle continues.
Hmmm.
Well that’s quite a bit different from what
a diode does, eh?
I mean, a diode can’t generate electricity
or even respond to light …
… or can it?
Ok - here we have a bunch of silicon diodes,
They’re the “small signal” type so they
have glass packages -
which should allow light to pass directly
to the silicon.
By wiring them all up in parallel and exposing
them to light
We can see that in fact they do produce a
voltage of x.xx volts
Wow.
Ooh - and what about Light Emitting Diodes?
A row of 8 LEDs produces a voltage of x.xx
These little tests won’t produce much current
-
still it’s sort of bizarre that common LEDs
and diodes can act as solar cells.
But I digress …
A single photovoltaic cell can provide one
half of a volt.
My panel here has …
2-4-6-8-10-12 cells -
So at half a volt each that means it can provide
a total of 6 volts.
It’s much more practical to use a solar
panel to charge a battery -
and then use the battery to power … well,
whatever needs powering.
In order to charge this 3.7V LiPo battery
from the panel,
I’ll need a specialized charging circuit
…
Which will manage the unstable output from
the panel
to provide a steady charge to the battery.
This small power boost circuit will convert
the battery’s 3.7 volts to a standard 5
volts
suitable for use with USB devices, microcontrollers
and what have you …
In any case - even after understanding how
it works,
the ability to convert light into electricity
is still a bit mind blowing to me.
So go make something solar powered - but umm,
don’t wear a black suit on the roof.
Can I get a towel from somebody?
