Now that we have our PV module, what do we do with it? What would
you have to do to power your house with solar energy? Although it's
not as simple as just slapping some modules on your roof, it's not
extremely difficult to do, either.
First of all, not every roof has the correct orientation or angle
of inclination to take advantage of the sun's energy. Non-tracking
PV systems in the Northern Hemisphere should point toward true south
(this is the orientation). They should be inclined at an angle equal
to the area's latitude to absorb the maximum amount of energy year-round.
A different orientation and/or inclination could be used if you
want to maximize energy production for the morning or afternoon,
and/or the summer or winter. Of course, the modules should never
be shaded by nearby trees or buildings, no matter the time of day
or the time of year. In a PV module, even if just one of its 36
cells is shaded, power production will be reduced by more than half.
If you have a house with
an unshaded, south-facing roof, you need to decide what size system
you need. This is complicated by the facts that your electricity
production depends on the weather, which is never completely predictable,
and that your electricity demand will also vary. These hurdles are
fairly easy to clear. Meteorological data gives average monthly
sunlight levels for different geographical areas.
This takes into account rainfall and cloudy days, as well as altitude,
humidity, and other more subtle factors. You should design for the
worst month, so that you'll have enough electricity all year. With
that data, and knowing your average household demand (your utility
bill conveniently lets you know how much energy you use every month),there
are simple methods you can use to determine just how many PV modules
you'll need. You'll also need to decide on a system voltage, which
you can control by deciding how many modules to wire in series.
You may have already guessed a couple of problems that we'll have
to solve. First, what do we do when the sun isn't shining? Certainly,
no one would accept only having electricity during the day, and
then only on clear days, if they have a choice. We need energy storage
Unfortunately, batteries add a lot of cost and maintenance to the
PV system. Currently, however, it's a necessity if you want to be
completely independent. One way around the problem is to connect
your house to the utility grid, buying power when you need it and
selling to them when you produce more than you need.
This way, the utility acts as a practically infinite storage system.
The utility has to agree, of course, and in most cases will buy
power from you at a much lower price than their own selling price.
You will also need special equipment to make sure that the power
you sell to your utility is synchronous with theirs -- that it shares
the same sinusoidal waveform and frequency.
Safety is an issue as well. The utility has to make sure that if
there's a power outage in your neighborhood, your PV system won't
try to feed electricity into lines that a lineman may think is dead.
This is called islanding.
If you decide to use batteries, keep in mind that they will have
to be maintained, and then replaced after a certain number of years.
The PV modules should last 20 years or more, but batteries just
don't have that kind of useful life. Batteries in PV systems can
also be very dangerous because of the energy they store and the
acidic electrolytes they contain, so you'll need a well-ventilated,
non-metallic enclosure for them.
More information: http://science.howstuffworks.com/solar-cell8.htm