subject: Safe Solar Power - Be Electrically Cute Not Electrocuted! [print this page] Electricity is funny stuff ...you know it's there, you can see its effect (your lights come on!), it's really useful but it just kind'a sits there, lurking behind the sockets, just waiting to jump out and 'get you'!
I realise I am being a bit flippant here but to me it makes sense to demystify 'stuff'. Mains electricity tends to frighten people because of a lack of understanding. Electricians like this because it means they can charge lots of money for their services and I think, like every subject, the people in the 'know' have the power (if you'll forgive the pun ...sorry!).
People who are techie with computers like to use terms that baffle everyone else and they always speak very quickly so you can never understand what they saying (I know 'cos I'm one of them :))!
I tend to think of electricity as an 'it', a live 'thing'. Its purpose in 'life' is to get to earth ...it will always try to find the lowest resistance path to get to the ground. If that path is through you, you've got a bit of a problem! The trick is not to give it that path!
If you treat with a healthy respect it can be worked with safely, complacency is dangerous, just do things carefully and methodically, thinking all of the time about what 'it' is trying to do and you will be safe.
If you are at all uncertain ALWAYS seek professional assistance.
Don't Do This At Home!
If you stick your finger into the live pin of a mains socket whilst standing on the floor, it has a path through you to ground and you will very probably die as a result. If, however you stick your finger in a socket (this is not recommended by the way ...it is purely for illustrative purposes!) and you are insulated from the ground; very thick rubber-soled boots, for example and you will suffer no more injury than does a bird sitting on an 11,000 volt power line!
This is because there is no path to earth. If the bird puts one of its claws across and touches the pylon supporting the cable it would instantly be fried.
The normal path for mains power is to flow through whatever device you connect between the live and neutral pins of a mains socket by plugging it in. If you provide that path by touching the live and neutral pins of a mains socket, you will have given it a path across your chest ...definitely not good!
Some materials are more resistant to the flow of electricity than others. Very highly resistant materials, like rubber for example, are called insulators and those that are least resistant, like copper wire for example, are called conductors. Resistance is measurable in units called 'ohms' (see Wikipedia for Ohms Law). The human body is a conductor, not as good as copper but good enough to allow electricity to pass through you if the voltage is high enough. Typical human resistance is between 300 and 1000 ohms.
Ohms Law defines the relationship between voltage, current and resistance.
The resistance of the path through your body if the electrical flow was from your fingers to your feet would be higher than from the fingers of one hand to the fingers of the other hand. Therefore the current would be higher, and more dangerous across your body, than down one side, with the right side (away from the heart) being slightly less dangerous.
You don't have quite the same level of concern with a 12 volt battery, if you touch the + and - terminals with each hand you will suffer no ill effect because the voltage is not high enough to provide enough current (amps) through your body to be a problem. Mains voltage at either 110v or 240v is definitely high enough to pass a current through you that is dangerous.
Having said that; voltages as low as 20v could prove fatal under the right (or wrong!) conditions e.g. if your fingers were wet, reducing the barrier resistance of your epidermis (skin).
Now let's get to the solar bit ...if you build a solar array with 36 solar cells, capable of supplying a current of 3.5 amps at an overall voltage of 21.5 volts you have the potential for a lethal shock. Of course the additional problem with a solar panel is that you cannot turn the sun and therefore the panel, off!
So there you are on the roof with a potentially dangerous electrical device that you cannot turn off!
There are a series of basic precautions that should be taken when working with solar panels:
1. The 'face' of the panel should be securely covered to prevent sunlight reaching the solar cells. This stops the generation of electricity while you are working.
2. Do not touch any of the terminations, especially if the panels are exposed to sunlight.
3. Use insulated tools to ensure you are isolated from any electrical connections.
4. Even though you might think it safer to work with solar panels in the rain, as mentioned above, your electrical resistance will be lowered by being wet, lowering the level of current at which you are in danger ...and as we know solar panels DO generate power on cloudy days! Plus working on a wet slippery roof isn't for the faint-hearted either.
5. You should also be aware of the danger of sparks being generated if the cells are exposed to sunlight and a trailing wire arcs against something metal. So do not work in an area with flammable gas.
