Lana Intl Home and Garden

So you are interested in installing some solar panels to try and help out with your ever increasing fuel bills. This may be to a shed, garage or outhouse that is too far away from your main building to effectively have an extension laid out or maybe you just wish to try out solar power on a small scale first before perhaps moving onto a large scale project.

Ok, first lets start with a very basic solar power system. You buy a 20 Watt solar panel, an 8 amp charge controller, a 75 amp/h leisure battery and a few low wattage lights (2 x 16 watt flourescent) just to ensure your workshop has enough light for those late nights. At present prices (Summer 2008) this will set you back approx $350 or 200GBP or 300Euro.

But what does this all mean…
Lets start easy, your 12V 75amp/h battery will supply (12 x 75)watts = 900 watts of energy according to the basic electric law (Volts X Current = Power), BUT this is not necessarily the case. Losses are introduced that will remove around 20% of this figure, so your 75amp/h battery will supply 720 Watts before losing all of its energy.
It is best to think of the battery as a water tank, with the solar panel as the flow coming in, and your lights as the flow leaving the tank.

You start with 720 Watts in your “tank”, if you have no solar panel or way of topping up you will find that your 2 x 16 watt lights will empty your battery in about 20 hours of use. By using a way of refilling your tank (your solar panel) the practical hours of use of your lights will be increased.

Lets say that each day you have 4 hours of “useful” sunlight a day, with a 20Watt solar panel this will mean that you will refill your “tank” by 80 watts a day. If you use your two lights for 3 hours a day this will mean a defecit into your battery of 12 Watts a day, so a few weeks down the line you will find your lights will no longer work as your tank (battery) has been drained completely. Never a good thing to have in front of you.

The simple way around this is to either use your lights less, difficult to do when you need them to see, or to add another solar panel. An extra panel of 20 Watts would supply you with enough extra energy to supply your lighting needs and also allow you to use extra electrical sytems on occasions as needed.

Always remember that a fully charged battery off load (i.e. nothing attached to it) will be at a voltage of 12.79V and above, a battery at a voltage of 12v is effectively worthless and unless it is a gel or discharge resistant type of battery you might as well discard it and buy a new one as it is unlikely you will be able to charge it effectively.

It is useful to remember that although your solar panels may be out in sunlight from 6am to 10pm there is only 5 or 6 hours of “useful” sunlight within these hours. A simple way to see how this happens is to connect your voltmeter to your solar panel and take readings from dawn to dusk, you will find readings from 8v to 15 volts and back down to 8v during these hours. Your battery will only be charged when the output from your panel is 13.2v and above.

This is where your charge controller comes in. This vital piece of equipment will stop your battery from being overcharged and also will stop your solar panel from discharging the battery when the power form the sun is not enough to charge your “tank”

This is just a simple overview of the electrical basics and there are so much more considerations to consider before you embark on a major solar power sytem