Assumptions:-
Population = P = 100000
Average energy consumption per person per year = E = 77,028 kWh (thanks
@CNBA3 for the reference)
Calc:
P*N*300 = 2.31084e+12 kWh
In joules this would be = 8.319024e+18 Joules
Which is
High 7-A
Edit: Assuming the character output this much energy in one second or in one attack. If not then divide the yield by the timeframe of the character outputting this much energy to get AP or sumn.
Edit 2: I used 100000 as the population. For 50000 just divide the final number by 2. Still should be around baseline High 7-A.