**DC** means Direct Current. It's the kind of electrical current produced by batteries. 12-volt DC batteries are the kind found in cars, trucks, RVs, and boats.

**AC** means Alternating Current, the kind of electrical current found in wall sockets in buildings.

In buildings, we can replace any amount of AC electricity, from a small fraction to 100 percent, with energy collected by solar panels and stored in 12-volt DC batteries. Direct current from the batteries can be changed to AC by means of an inverter, or it can be used directly to run equipment designed for DC; for example, a car vacuum that plugs into a cigarette lighter socket.

On this website we talk about very basic 12-volt concepts and systems. If you would like to replace a bit of your AC requirement with energy derived from the sun -- get your toe in the water for a minimal investment -- this will be a good place to start. If you'd like to get involved with solar energy in a serious way, try www.findsolar.com.

Now, on to more basics. Note that these are utterly rudimentary definitions. There's much more to know, but you don't need to know much more in order to get involved.

**Voltage/Volts** = the amount of potential energy available to push electrical current. Think of it as pressure in a water system. For a battery-powered system, think of a water tower with a big tank on top. It's drained by gravity, and the way water flows out of it depends on the diameter of the pipe, the length of the pipe, and the weight of the water in the tank at any given time.

**Amperage/Amps** = the flow of electrical current through conductors like wires. Think of it as the amount of water current flowing through a pipe.**Wattage/Watts** = the amount of energy expended, or used. Think of it as the water that fills a glass (a few watts) or a swimming pool (lots of watts).

**Ampere-hours (Ah)** = the current in amperes multiplied by the amount of time it flows. Deep-cycle batteries, the kind used for solar-power storage, have ampere-hour capacity ratings that give a general idea of how many amps can be drawn from the battery for how long. In a perfect world, a battery rated for 90 amp-hours would be able to give you 90 amps for one hour, 45 amps for two hours, one amp for 90 hours, and so on. In reality, you can and would use only a portion of those amp-hours before the battery should be charged again.

**Ohm** = a measure of resistance in a wire or other conductor. Resistance is determined both by the wire's length and its thickness, or gauge. The thicker the wire, the more easily current will flow through it. In a

simple 12-volt solar panel arrangement, resistance can exist between the solar panel and the battery, and between the battery and whatever it's supplying power to. Resistance always creates heat, and the greater the resistance, the more heat. Try to put too much current through too small a wire, and you can create enough resistance to start melting things and causing fires. This can happen even in a simple 12-volt system, so always use common sense and generous wire gauges. See 12-Volt Safety for more.

Now, here are some of the easiest equations you'll ever have to use:

- Volts x Amps = Watts
- Watts / Amps = Volts
- Watts / Volts = Amps

If you read the owner's manual for any electrical appliance, or the stamped electrical infomation on the appliance itself, you can usually discover what it needs for energy input and how much energy it uses. Then it's a matter of arithmetic to find out if your 12-volt system can handle the task. Bear in mind, though, that sometimes there's more to the story than simple volts, amps, watts, and ohms. For example, an inexpensive automotive-grade DC-to-AC inverter can be used for a myriad of tasks that are electrically simple, like running an incandescent light bulb, but some appliances that are sensitive to interference, like TVs, often need to be run through a better, more expensive inverter.

For starters, we'd recommend one of the simpler inverters. A 400-watt model from an auto-parts store or online retailer will cost about $35. If you find that you need a more sophisticated inverter later, you won't have too much of an investment in the simpler ones. See our Inverters section for more detailed information.

~ Doug Logan, *New Energy Watch*

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