You switched the lights on; traders made billions of dollars

BEFORE dawn on a recent autumn day, fog set in over large swaths of Eastern Europe. In any other financial market, the weather wouldn’t have mattered much. Perhaps a few delayed flights, maybe some traffic jams, most of little consequence. But in Europe’s electricity bazaar, bad weather equals money.

More than 1,000 kilometers away from the fog, a small group of largely anonymous trading firms based in Denmark was ready to pounce. As soon as the infrared picture from a Meteosat weather satellite arrived at their headquarters, computers automatically dissected it, feeding the data into complex trading algorithms.

With minimal human intervention, the machines bought millions of euros worth of electricity contracts. Their bet? Short-term power prices in Hungary would climb just after sunrise as the fog meant that solar electricity generation would be much lower than expected. It happened as they predicted. For a few minutes, until the fog lifted, electricity prices spiked, and the computers made money.