The output capacity (power) of an energy source is measured in Watts. 1GigaWatt (GW) = 1000 MegaWatt (MW) = 1,000,000 kiloWatts (kW).

The energy generated over a period is in Watt-hours or Joules.  1GigaWatt-hour (GWh) = 1000 MegaWatt-hours (MWh) = 1,000,000 kiloWatt-hours (kWh).  1kWh=3.6 MegaJoules.

Australian coal-fired power stations are typically 1-3GW in "nameplate" capacity and average about 80% of that.  Our wind farms are 20-500MW nameplate, with a factor of 35-40%, and our solar farms 100-200MW at 16% (because the sun don't shine at night).  So it takes about 50 solar farms to match the average output of one coal fired.

Total Australian power demand is around 200,000 GWh per year, or 23GW average.