Before you can understand the difference between AC and DC, you might want to read my very short, easy-to-read article: 1. What Is an Electrical Circuit?
Then, come back to EASILY understand the bare-bone basics about AC and DC.
What’s the Difference Between AC and DC?
In a solar power system, you’ll usually have two signals, DC and AC.
DC: Direct current
AC: Alternating current
DC (the direct current) is an electrical signal that constantly moves in a single direction across the electrical circuit, from negative to positive.
An example of a DC power source is a 12-volt battery, which has a negative terminal and a positive terminal.
When you attach two wires to the positive and negative terminals of the battery, and you connect it to an appliance that is rated for 12 volts (like the 12-volt mini-fridge in the picture), the electrical force/charge will flow through these wires, from one side of the battery (negative) to the appliance, and then will flow out of the appliance back to the battery (positive).
You can think of the DC current like a river. The electrical force flow through the whole thing but can only go one way.
When you measure a DC voltage with a digital meter, the reading will be either entirely positive or entirely negative.
AC (the alternating current) is different than DC in that the electrical signal switches from positive to negative really fast and this causes the electrical force/charge to vibrate instead of flowing like a one-way river, like the DC current.
When I say “vibrate”, I don’t mean that the wires, battery, or appliances actually vibrate. It’s not a physical vibration. It’s the electrical force inside the wires that move back and forth at a regular speed (the technical term for this is oscillation).
In the United States, the electricity in an AC current switches back and forth 60 times per second.
In an AC system, there is no positive or negative.
AC and DC in a Solar System
Please Note: Before you can understand the difference between AC and DC in a solar system, you might want to read my very short, easy-to-read article: Solar Power for Beginners
In a solar power system, you will most likely have both AC and DC signals. The solar panels, the batteries, and the charge controller will always work in DC.
The inverter will transform the DC signal from the battery into an AC signal to power specific loads (computer, lamp, TV, etc).
So, when you test voltage or current in any part of the electrical circuit located before the inverter, you will have to measure it in DC. And, if you test anything after the inverter, you’ll have to measure it in AC.