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1 BTU = 1055.05585262 J energy

1 billion BTU = 0.000293 TWh

500 000 000 Billion BTU per year  = 5.275*10¹⁸ J = 527.5 exajoule = 146542 TWh

~ 16.7 TW (10¹² W) instantaneous power

So the total world average power consumption is approx. 17 TW (17*10¹² W)