Electrical current is electrons flowing through a copper wire. Amps is the measurement of that current draw. Voltage or Volts is the force on those electrons. Power is a combination of both current (Amps) and voltage (Volts). To calculate the Power (Watts) you multiply the Amps by the Voltage:
Power in Watts = Amps * Volts.
So to increase the power, you can either increase the current or increase the voltage.
An analogy would be water flowing through a water pipe. Imagine you have a water tank with a garden hose connected to a sprinkler.
The volume of water in the tank = energy stored in a battery (Watt-Hours)
The water molecules flowing through the hose = electrons flowing through a wire. (Amps)
Water pressure in the hose = Voltage (Volts)
Diameter of the hose = Current (Amps)
Instantaneous volume of water flowing through hose per second = Power (Watts)
So a bigger diameter hose will carry more water than a smaller hose. To send the same amount of water through a hose, you can either use a small hose with a lot of pressure, or a big hose with less press pressure. That’s why you’ll want to step up the voltage when sending it long distances.
The size of the sprinkler head is like the electrical load or resistance (Ohms).
Big sprinkler holes = high electrical load (low resistor value (Ohms))
A sprinkler with big holes will draw more water than one with small holes. So a 50W light bulb and a 100W lightbulb draw different amounts of power even when plugged into the same power source.
Note: The above analogy fails to represent the fact that electricity flows in a circle or circuit (for brevity), so that should be noted.
Battery capacity is measured in Amp-Hours or Watt-hours. It’s the power output over a given time. To calculate the Amp-Hours you multiply the Amps by the hours. A typical car battery can store 55 Amp-hours of energy. That means it can power 10 Amps for 5.5 hours, 1 Amp for 55 hours, or 55 Amps for 1 hour. Then to calculate the Watt-Hours you multiply the Amp-Hours by the Voltage. (A 12V 20Ah battery has twice the capacity of a 6V 20Ah battery because 20 Amps at 12 volts is more Power than 20 Amps at 6 volts.)
Amp-Hours (Ah) = Amps * Hours
Watt-Hours (Wh)= Amps * Voltage * Hours
Kilowatt-Hours (kWh) = Wh * 1000
The capacity of solar panel arrays or battery banks can be increased by wiring them in a combination of series and parallel connections.
To add up the power consumption of appliances, you need to consider both the current and voltage. If appliances only give power consumption in Amps, then you have to calculate the Power in Watts by multiplying Amps * Volts. Then multiply it by the number of hours you'll be using it to get the Wh or kWh.
Microwave 1000W 0.2 Hours 200 Wh
Fridge 500W 6 Hours 3000 Wh
Lights 200W 5 1000 Wh