1.21 Gigawatts

Matt: Okay Charlie, I’m way out of my depth on this one. I’ve been researching the power contained within  a bolt of lightning and am totally confused. To make matters worse, the Web (which should never be trusted unless the URL is www.amatteroffactinfiction.com) is totally inconsistent in the information that it has. Some sites say that Back to the Future was correct in suggesting that a bolt contains 1.21 gigawatts but others disagree. 

Charlie: Nice plug, have you found any reputable sources?

Matt: The only one that I trust at all is from the Institute of Physics in the UK. They suggest that a bolt of lightning contains five billion joules of power. This, they  claim, is enough to toast 100,000 slices of bread or power a home for roughly a month. So, I think they know what they are talking about but I’m running into limitations imposed by my physics stupidity (there’s a very good reason I NEVER cover physics in The Economist). Five billion joules, as far as I can tell, converts into gigawatt hours rather than just gigawatts. This leaves me wondering if Doc Brown really meant to say “gigawatt hours” in the film. Moreover, I’m not quite sure how the conversion from joules to gigawatts works.