Knowing how to relate energy and power together is a very important concept, but it is also important to have a more in-depth understanding of electricity as well. This section will go over what electricity is made up of along with different forms of application.
Current, Voltage and Watts are all related to electricity. Current is measured in amps. You can imagine current as the amount of electrons. Voltage is measured and volts. You can image the voltage being the amount of pressure pushing those electrons. More electrons or more pressure pushing electrons means more energy, just like more mass or more velocity for an object means more energy.
Just like you will need mass and velocity to calculate the power or energy of an object, the same is true with current and voltage. Just having one is not enough. Wattage is a measure of power in an electrical system, and is made up of amps x volts. Watt-Hours is a measure of energy in an electrical system and is made up of amps x volts x time.
Electricity by default will travel in one direction, which is called Direct Current, or DC. In a direct current circuit, electrons flow continuously in one direction from the source of power through a conductor to a load and back to the source of power. Originally electricity traveled by these means. The problem is, DC is not sustainable as it is hard to transfer electricity over large differences without power loses due to the low voltage level.
Eventually Alternating Current, or AC was discovered. An AC generator makes electrons flow first in one direction then in another. In fact, an AC generator reverses its terminal polarities many times a second, causing current to change direction with each reversal. AC can create a higher voltage level depending on how you utilize it. This provides advantages for utility companies to transfer electricity over hundreds of miles with little loss by utilizing over a million volts at times, since voltage travels easier than current. Eventually when the power reaches back to your house it is outputted to 100-120VAC, or sometimes 200-240VAC. Because of this, most household appliance are AC, and when you read the specification sheet, you will see the voltage in these ranges.
Now that you know the general differences, it is important to understand the difference of Power in Direct Current (DC) and Alternating Current (AC). Ignoring efficiency loses from either, power should remain relatively constant in both. For example, we can take a 200W TV and look at it in terms of DC (12V) or AC (110V). In terms of direct current the TV would produce 200W/12V = 16.6 Amps. In terms of alternating current the TV would produce 200W/110V = 1.8 Amps. Although the amp and the voltage values differ, the overall power is the same, so the rate of energy consumption, not counting efficiency loses, would be the same.