About 1 gigajoule per typical bolt

Photo from Wikimedia Commons
Total Lightning Strikes Per Year
About 1.4 billion bolts slamming into Earth every year/Collective & Conceptual
Earth experiences roughly 1.4 billion cloud-to-ground lightning strikes per year, plus many times more cloud-to-cloud bolts that never touch the surface. At any given moment, about 1,800 thunderstorms are active worldwide. Each bolt heats the surrounding air to roughly 30,000 K, five times the surface temperature of the Sun, and carries a current of about 30,000 amperes. The total energy is staggering, but unfortunately too brief and unpredictable to harvest for electricity.
Measurements
1.4 billion bolts at ~1 GJ each
Five times the surface of the Sun
About 0.2 milliseconds for the main stroke
About 8 km cloud to ground
About 44 strikes per second worldwide