What is a watt hour?
Before we figure out how to calculate watt-hours, it's helpful to get a better idea of the terminology. A watt-hour is equal to one watt of power used in one hour. You'll often see this term when talking about the energy output of electrical systems like generators and power supplies. Instead of using the full name, companies specify it as a Wh unit.
Units based on watt hours
1) Amperes
This is the amount of energy that passes through the device per second. The higher the amperage, the higher the current. This is a variable value, while the voltage is fixed.
2) Volt or voltage
This is the amount of energy delivered by the battery to an electronic circuit or device. Since batteries have a specific voltage, you should always know what you are working with. This can be as low as 12V or even as low as 6V. In any case, you must make sure that your device is compatible.
3) Watt
Wattage refers to the power a device uses at a specific time, while watt-hours cover power usage over a longer period of time. Both are useful metrics when dealing with solar power generators, but you still need to know the difference.
How do you calculate watt hours?
This all leads to an equation where energy equals power multiplied by time. In this case, you have your power in watts and time in hours, so your energy in watt-hours is watts multiplied by hours. For example, if you run a 150W solar panel for 4 hours, that's 150 x 4, or 600Wh.
To do this, you need to be clear about both numbers, which can be difficult depending on the device and the time period. For example, you may know the volts and amps of a battery, but not the wattage. If so, all you need to do is multiply the volts and amps together. Alternatively, you can multiply a battery's amp-hours by the voltage to get the watt-hours. More on this later.