Photovoltaics are the simplest form of alternative energy. There
are no moving parts in photovoltaic modules and little maintenance
is required. A photovoltaic module converts the suns energy
into electricity which is either used immediately (grid intertie
or water pumping) or is stored for future use (batteries). Solar
electric systems are modular, allowing you to start with a small
system. As your power requirements grow, you can easily add more
Types of solar cells
Single crystal silicon cells are extremely thin wafers of
silicon cut from a single silicon crystal. These are the most
efficient type of silicon cells and have a life expectancy exceeding
25 years. The cells are fragile and must be mounted in a rigid
frame. You can tell it is a single crystal due to the uniform,
rounded individual cells.
Multi crystal silicon cells are also extremely thin wafers of
silicon but are cut from multiple crystals grown together in an
ingot. They are similar to single crystal cells in life expectancy
and fragility. However, they are slightly less efficient than
single crystal cells and require more surface area to produce
a given amount of electricity. These types of cells are usually
square and will have a varied appearance.
Amorphous silicon cells are made by depositing a micro thin layer
of silicon directly onto a sheet of stainless steel. Because amorphous
absorbs light more efficiently than its crystalline counterpart,
the amorphous solar cell thickness can be 100 times less, thereby
significantly reducing cost of materials. By utilizing a flexible,
stainless steel substrate and polymer-based encapsulates, products
utilizing this technology can be very lightweight, flexible, and
durable. No parts are broken during shipping and units are easy
to transport to remote rural areas, thus saving on shipping costs.
Innovative new technologies that will allow us to capture energy
from the sun will undoubtedly be hitting the market in years to
come. Energy Alternatives is constantly reviewing new technologies.
How to Choose
There are many different considerations when selecting a specific
type of solar panel. Energy Alternatives only sells PV modules
that have an extensive, proven track record and a solid company
backing the product. Generally speaking, the larger the module,
the better the cost per watt. Crystal type panels are most common
for stationary applications. Amorphous cells are approximately
twice the physical size as crystal type cells but are much more
durable and shade tolerant. Their unique construction makes them
Sunshine and Shading
PV modules produce electricity in proportion to the amount of
sunlight falling on them. In full overhead or peak
sun (1000 Watts/m2) they will produce their rated power. Reduced
sunlight caused by clouds or location will diminish the amount
of electricity generated. Modules will produce electricity even
when there is no direct sunlight. A cloudy sky with an occasional
blue patch will often be equivalent to approximately 50% peak
sun. A cloudy day with rain in the forecast will produce approximately
10% to 20% peak sun. Reflected sunlight from snow or water can
also increase the output of solar panels.
It is very important to note that shading even one cell of a module
will reduce the output of the entire module. The only exception
to this found in the Uni-Solar modules which have built-in diodes
between the cells to reduce the effect. However, it is better
to mount solar modules so shading is avoided.
It is a common misconception that heat is required for PV modules
to produce electricity. High temperatures actually decrease the
power output. Warmer climates require PV modules with a higher
maximum voltage than those used in cold climates. Cold temperatures
decrease resistance and increase voltage. Modules with a lower
voltage rating are ideal in colder climates such as Canada.
Size and cost
There are two primary factors that determine the size of your
The daily power consumed by your electrical loads.
The sunlight levels (insolation) available at your particular
Insolation or sunlight intensity is measured in peak sun hours.
A full sun hour is equal to the amount of sunlight striking the
earth in one hour when the sun is directly overhead in a clear
sky. Bright sunshine hours do not equal peak sun hours. Bright
sunshine first thing in the morning or just before sunset is not
the same as bright sunshine at noon from a PV modules perspective.
The lower the sun is in the sky, the more atmosphere the light
must pass through. Water molecules and other gases in the atmosphere
reflect and absorb some of the light passing through it, reducing
the insolation. Smog or other pollutants will also block or reflect
sunlight. Most of the suns energy is delivered between 10
a.m. and 3 p.m. when the sun is highest in the sky.
Location - getting the best sun
Your PV array is a valuable investment. To achieve the best performance
from your array it should be aimed in the direction of the most
sunlight and angled correctly for the season. The array should
be adjusted to the latitude plus or minus 15° from summer
to winter for optimal output. If your mounting structure is not
seasonally adjustable the modules should be mounted to achieve
maximum output during the period of highest usage. For example,
if you use your cottage during the summer months your array should
be angled accordingly.
PV modules should always be aimed in the direction where they
receive full exposure to sunlight. In areas with little or no
shading, modules should face true south (not magnetic). True south
is calculated by using the magnetic declination information for
your site (available on most maps) and adjusting your compass
New technology allows for PV arrays to be located much further
away from the battery bank. If your site dictates a longer transmission
distance, please contact your local dealer or Energy Alternatives
for design details.
Purchase Products Online:
Mortgage and Housing Corporation) guide to Photovoltaics. This excellent
publication covers off-grid and on-grid PV systems and is essential reading
for those who are new to PV.
introduction to Photovoltaic Systems
Every day, the sun delivers energy to the earth free of charge. You can
use this free energy thanks to a technology called photovoltaics, which
converts the sun's energy into electricity.
Systems : A Buyer's Guide
Systems Simplified - HomePower
Article. Whether you are the rookie who wants to understand how solar-electric
systems work, or that better describes your spouse, friend, or prospective
this article explains the guts and bolts of the three most common options
in solarelectric systems: grid-intertied, grid-intertied with battery
backup, and off-grid.
Energy Society of Canada, Inc.
Solar Industries Association
Department of Energy Photovoltaics Program
National Renewable Energy Laboratory