Electricity types

Electron flow in a cross-section of wire: Top- In a direct current circuit, the electrons only flow in one direction from positive to negative. Bottom- In an alternating current circuit the electrons flow in both directions as positive and negative alternate.

Voltage over time: Direct current maintains a steady voltage (red). Alternating current switches back and forth (blue).

There are two types of electricity – alternating current (AC) and direct current (DC). These two terms describe the way in which the current flows in a circuit. In a DC circuit, the current only flows in one direction, meaning that they have a constant positive (+) and negative (-). This relationship of positive to negative charge is referred to as polarity. In an alternating current circuit, current flow changes direction regularly, switching the polarity (positive (+) and negative (-)) each time. This back and forth switching of polarity in an alternating current circuit is reffered to as frequency and is measured in Hertz (Hz).

Each one has different characterstics that make it useful for certain applications. Nearly all electronic devices run on DC as does anything that uses a battery without an inverter as batteries can only store energy in DC form. Cell phones, radios, televisions all run on TV internally, meaning that if they are connected to the grid or an inverter, they will use electronics to convert the AC to DC. Why not just use direct current for every circuit then? AC has important properties that make it useful in the electrical grid. It is cheaper to transmit AC over long distances as it is easier to change between high and low voltages. High voltages are ideal for long distance transmission as they require less current, which means you can use smaller wires.

All PV systems include DC as PV modules can only produce DC. Many small scall systems are DC only and work well for lightning and the charging of small electronic devices like cell phones. Larger systems require an inverter to convert from DC to AC. In any electrical system, whether AC or DC, all components or appliances must be rated to function with the characteristics of the electrical system - voltage, current, and frequency if AC. If they are used improperly it can lead to a failure that results in fire or injury.