Gigawatt hours per year (GWh/year) is a measure frequently used for electric generator output. To get the rate of electricity production for the year of your generator, you need to know the output capacity of the generator, whether it is a wind turbine, geothermal or other. The output will likely be in megawatts; a gigawatt is equal to 1,000 megawatts. A megawatt hour (MWh) is one megawatt of electricity produced for one hour.

Determine the generator production capacity in megawatts and translate that to a power production figure in MWh. If your generator capacity is 10 megawatts, it can produce 10 megawatts each hour, or 10 MWh.

Multiply the MWh figure from Step 1 by 8,760, the number of hours in a year. In this example, that would yield 87,600 MWh total annual power production.

Divide the annual MWh figure from Step 2 by 1,000 to get GWh. Thus, 87,600 MWh/year equals 87.6 GWh/year. This is the maximum annual power production for your generator.