Solar Lab: Assignment 1
How solar cells work
There are various different types of solar panels but I’ll describe the most commonly used type, p-n
junction silicon. Basically you array doped n-type silicon very close to p-type silicon. A p-n junction is
formed. I’ll spare the reader an extensive description of p-type and n-type doping, but it’s important to
note that the n-type side has an excess of unbonded electrons, and the p-type has an excess of “holes”,
which simply means there is an atom in want of an electron. At the junction, the electrons diffuse from
the n-type side to the p-type side until the resulting electric field prevents them from moving across the
junction. The junction is then in equilibrium. The electric field is oriented in such a way that the edge of
the n-type side is positive from the leaving electrons, and the excess of electrons on the edge of the ptype side cause it to be negative.
So at this point the solar cell is ready. A photon comes along and hits an electron with enough force to
knock it out of the valence band (an energy level where it is connected to the atoms sharing it) and into
the conduction band, where its high energy level allows it to move about without being bonded. This
electron leaving also creates a hole where it left. The electron being negatively charged and the hole
being positively charged, if they venture anywhere near the p-n junction’s electric field, the electron will
get sucked to the n-type side and the hole will get pushed further into the p-type side. This movement
of electron and hole is the same as a movement of electric charge and a current is formed.
Solar systems
A solar system is a group of solar cells connected together. Solar cells work act very similarly to batteries.
They can be combined in parallel to create a higher current or in series to create a higher potential. It
doesn’t seem necessary to point out, but a simple flow of electrons from point a to b in a circuit forms a
direct current. For this reason the use of solar systems in conjunction with an alternating current system
or devices which use alternating current, an inverter is required. An inverter is a fairly simple electrical
device which uses a switch and a transformer to convert direct current to alternating current and heat.
Renewable energy sources
1. Wind power. Wind power is happily becoming more and more widely used throughout the
world. Actually, my brother and I are currently developing a 175 million dollar 100MW wind
power facility in Oklahoma. We’re currently working on installing a $15,000 100 meter met
tower. Nice little after graduation project wouldn’t you say? Anyway, wind power is basically
being fed into power grids or stored in huge battery arrays and then fed into the electrical
system to supplement the amount of natural gas generation used. There are also small scale
uses such as powering your home or net metering or to run small devices such a windmill pumps
in the country.
2. Hydroelectric power. Hydroelectric power is used in places such as the Hoover damn where the
force of gravity acting on water can be used to run turbines. These generators are also used to
supplement the power grid. There are also historically smaller scale systems which operate on
rivers to transfer the kinetic energy of water to another physical system with no electricity
involved.
3. Biofuels. Biofuels are sortof an extension of solar energy in that plants use photosynthesis to
grow. These biofuels can be burnt to generate heat, and are now being converted to liquid for
use in automobiles.
Other uses for solar energy
There are a few obvious uses for solar energy besides photovoltaic generation of electricity. The most
obvious that jumps out is heating. Sun light makes me hot when I stand in it, so obviously everything it
hits gains some level of hit. In areas of the world where it’s cold and winters are harsh. Solar energy
heats buildings without any special equipment whatsoever. It may not be a great amount of heat, but
even the dinosaurs used it. Solar grills are small devices which use concave mirrors to direct sunlight at a
grill surface. This idea can be used to heat houses or pools but it is much more useful on a larger scale
where a huge array of mirrors can be used to focus the sun’s energy on a heat tower which can then run
a steam generator.
My new personal favorite use for solar energy is hybrid solar lighting. HSL is being developed at Oak
Ridge National Labs outside of Knoxville Tennessee. The way it works is similar to the way a solar grill
works except instead of a grilling surface the sunlight is focused on an optical fiber array and the fact
that the dish has GPS based sun tracking. An optical fiber is a glass or plastic fiber that carries light along
its length. Traditionally optical fiber is used for communication but since it efficiently carries light down
its length, ORNL decided to have to carry sunlight. The sunlight is then harvested of its infrared energy
and passed on to hybrid lighting elements which supplement it with electrically produced light
depending on the amount of sunlight available. The full spectrum sunlight is healthier and cheaper than
light produced electrically, and using the light in this manner is far more efficient than photovoltaic
methods. In addition the IR energy removed can be used to power high efficiency photovoltaic cells.
I’m not really sure why a second paragraph about HSL is necessary as the first described it so
comprehensively so this seems like a good place to say I’m pretty excited about finding it. In fact this
find has made the course worthwhile to me. I’ve already started planning the creation of my own HSL
system for lighting purposes. I’ve been a long time admirer of fiber optics and this use is just stunning. I
must have it.