480 - Safety Issues
Since we are designing a system that will be deployed in a school with no
preexisting power, and around people without much experience with electrical equipment
we need to take some extra precautions to make sure that the entire system is as safe as
possible. There will be solar panels that will either be mounted on poles outside of the
building or on the roof so we will have to make sure to protect these cables because they
will carry high currents. The battery bank also needs extra safety measures because it will
have the potential to unleash huge amounts of current should a short, or other low
resistance connection (ie. body) cross the terminals.
The solar panels will be mounted outside. If we mount them on the roof then we
need to make sure that the cable runs go into the structure through a watertight seal. Also
there will need to be an earth ground installed in case lightning hits the building. The
building itself must be structurally sound enough not only for the solar panels but also for
several people so that installation and maintenance is safe.
If the building is orientated in such a way that the panels can not face the sun
while they are on the roof then they will have to be mounted on a pole outside of the
school building. In this case extra precaution must be used to insure that a person is
unable to access any wire leads because the current can easily kill a person. Also the
cabling will have to be run underground so the wires will have to be enclosed in the
proper type of duct to that they cannot be cut by someone digging in the area. They also
must be completely weatherproof to avoid the wire insulation breaking down from the
elements. One advantage to this setup is that the structure that the panels hang on can be
used as an earth ground for the entire system.
Once inside the building all wiring outside of the case should be in ductwork.
This prevents a person from easily cutting the wires and also prevents animals from
chewing through the insulation. The system case must have a hole that is not sharp so that
the wires cannot fray over time. Also cabling should be secured to the case so that it
cannot easily be pulled out which could cause short circuits or broken hardware. Any
short unintentional short circuits have a large probability of destroying the expensive
equipment nearby or causing a fire.
The battery bank must be carefully installed so as to minimize any possibility of
short circuits. Each battery terminal should have a cover installed so that it is difficult to
touch the electrodes accidently. All batteries should also be secured to the casing so that
they cannot move if the whole case is tipped or moved.
There must be circuit breakers at several key points in the system to insure that if
there is a problem the system will cut off power to itself and hopefully save the
equipment from being ruined. There will be a circuit breaker between the solar panel
array and the Charge Controller and also between the Battery Bank and the Inverter.
These will trip if current exceeds expected ratings and will also allow the system to be
manually shut down if the need arises.
Following these simple precautions should allow the system to be safe from
prying fingers, weather, animals and equipment failure. Also in the case of a failure
troubleshooting should be easy because if our battery management system is running it
will provide feedback about which components are not working. If a breaker is reset then
it will also provide clues as to which part of the system failed.