The world’s economy can be seen as a giant heat engine. It consumes energy, mainly in the form of fossil fuels, and uses it to produce services and goods. No matter how fine-tuned and efficient the engine is, it still needs energy to run. So, if we want to do the big switch that we call the “energy transition” from fossil fuels to renewables, we can’t rely just on efficiency and on energy saving. We need to feed the big beast with something it can run on, energy produced by renewable sources such as photovoltaics (PV) and wind in the form of electric power.
Here are a few notes on the kind of effort we need in order to move to a completely renewable energy infrastructure before it is too late to avoid the double threat of climate disruption and resource depletion. It is a tall order: we need to do it, basically, in some 50 years from now, possibly less, otherwise it will be too late to avoid a climate disaster. So, let’s try a “back of the envelope” calculation that should provide an order of magnitude estimate. For a complete treatment, see this article by Sgouridis et al.
Let’s start: first of all, the average power generation worldwide is estimated as around 18 TW in terms of primary energy. Of these, about 81% is the fraction generated by fossil fuels, that is 14.5 TW. This can be taken as the power that we need to replace using renewable sources, assuming to leave everything else as it is.
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