Solar Power isn't Feasible!

Solar Power isn't Feasible!
This cartoon was on the cover of the book "SolarGas" by David Hoye. It echoes the Sharp Solar slogan "Last time I checked nobody owned the sun!"

Saturday, September 22, 2007

Setting up a home solar electric system: Simplicity itself!

To get started in solar all you need are four basic pieces of equipment:
  1. A Photovoltaic Solar Panel
  2. A Charge Controller
  3. A Battery
  4. An Inverter
This table gives you the basic components of a stand-alone do-it-yourself solar electric power system.

Here are the things you need to buy:
Solar Panel

Rechargeable Battery
Charge Controller


Note: you can get away with just having a solar panel, a charge controller and a battery if you are running DC appliances. However, if you want to run regular AC appliances, an inverter is required (but notice that the Xantrex rechargeable battery depicted above contains IT'S OWN INVERTER). You can also get away without having a charge controller, but you would have to monitor the charge state of your battery to make sure it doesn't overcharge. I have done this by connecting a simple volt meter to the battery and watching it over the day, but you run the risk of ruining your batteries if you aren't vigilant. Our advice is, buy a charge controller and then you can simply leave the whole thing hooked up without worry!)

Hooking the system up is so simple a child can do it (and probably do it better than you!!). It takes the same skills as hooking up a home stereo system -- if you are familiar with connecting speaker wires (red being positive, black negative) to your amp, you already have the know how!

You connect the positive wire coming from the solar panel to the place with the + on it on the charge controller, and the negative wire from the solar panel to the place with the - on it. You then run a positive wire from the charge controller to the + terminal of the battery, and a negative wire from the charge controller to the - terminal of the battery (note, if you are using a "cigarette lighter" type plug, the center is usually positive and the sleeve negative). Then, if you are using regular rechargeable batteries without a built in inverter, you just connect the + terminal of the battery with a wire to the + terminal of the inverter, and the - terminal of the battery to the - terminal of the inverter.

Voila, you are done!

Since you have a charge controller, you don't have to worry about overcharging your batteries. The inverter also shuts down when the battery voltage is too low, so you don't have to worry about draining your batteries. Leave the solar panel in the sun (facing south is best in the northern hemisphere) and keep the rest of the system indoors to protect from moisture (the solar panel can get rained on, so don't worry about that) and you are set.

To get more power and recharge your batteries faster, you can simply add more solar panels IN PARALLEL. That means simply that you run all the positive wires to the same place (the + input on the charge controller) and all the negative wires to the same place. You can add as many solar panels as you like, of whatever shapes and sizes and wattages, as long as you add them in parallel, but you have to make sure you don't exceed the AMPERE RATING of the charge controller. The one shown above is a 7 AMP controller, so it can take up to 7 Amperes of Current.

How do I know how many amps my solar panel puts out?

Most solar panels have the amp rating listed, but a good rule of thumb is to take the wattage of the panel and divide by the voltage, since Volts x Amps = Watts. Most solar panels produce a peak voltage of about 19 volts. Thus, the 15 watt panel shown above is approximately 15/19 = .8 amps. This means that you could hook up 8 of these panels, giving yourself 120 Watts of charging power!

(I should mention here, however, that this would not be cost efficient since the prices of solar panels are highest when you buy the smaller ones -- around $10 a watt! Once you have learned how to set up your own PV system using the components shown above, I recommend you invest in a single 120 Watt panel, costing around $600. The rule of thumb in PV is to try not to pay over 5 bucks a watt, and you can do that by buying the bigger panels.

Hope that helps!

Have a sunshiny day,

T.H. Culhane
Solar Cities
Cairo, Egypt/Essen, Germany/Los Angeles, CA

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