One megawatt-hour is equivalent to 3.6 gigajoules. Here's how you do the conversion:

1 MWh = 3.6 GJ

So, if you have 82,457 MWh (cell E18, Worksheet SFDR PAI Indicators), you would convert it as follows:

82,457 MWh * 3.6 GJ/MWh = 296,845.2 GJ