Thunderstorms are surely powerful, but quantifying their electrical potential is challenging. A new study, however, was able to look deep within one giant storm using a telescope designed to study cosmic rays, finding that it contained a shocking 1.3 billion volts, according to a new study in the journal Physical Review Letters.

Matteo Rini at Physics reports that in the past researchers have flown airplanes or released balloons into storm clouds to try and measure their electric potential. The largest reading taken with those methods clocked in at 130 million volts during a storm over New Mexico in the 1990s.

But researchers at the Tata Institute of Fundamental Research in Mumbai, India, decided to probe thunderclouds using something more sophisticated than a balloon: muon detectors. Muons are charged particles produced in the upper atmosphere of the Earth when cosmic rays that constantly bombard our planet interact with various particles. That means there’s a steady rain of these energetic muons constantly falling across the earth. When something gets in their way, however, muons lose energy, and the loss of energy can be detected using special equipment.

The GRAPES-3 telescope at The Tata Institute tracks muons, detecting over one million muons per minute. But George Dvorsky at Gizmodo reports that the team added electric field monitors to the detector and began watching storms passing overhead. By looking at the reduction in energy of the muons passing through the cloud, the team can calculate the amount of electrical potential within the storm.

Between 2011 and 2014, the team captured data on 184 storms. They narrowed that list to the seven largest storms. Six of those, however, were complex storms and computing their electrical potential had various problems. A massive storm in December 1, 2014, however, had the right profile for a calculation.

The storm moved along at 40 miles per hour at an altitude seven miles above the Earth’s surface and and covered about 146 square miles. Calculations based on the number of muons the storm repelled show it had a potential of 1.3 billion volts, 10 times more than the previous highest reading for a thunderstorm.

“Scientists estimated that thunderclouds could have gigavolt potential in the 1920s," co-author Sunil Gupta of Tata tells Tia Ghose at LiveScience. “But it was never proven — until now. The amount of energy stored here is enough to supply all the power needs of a city like New York City for 26 minutes. If you could harness it.”

Gupta says the chances of finding a way to use all that electrical potential is unlikely—the energy is so intense it would melt anything we used to conduct it.

Michael Cherry, a cosmic and gamma-ray researcher at Louisiana State University in Baton Rouge tells Rini at Physics that the muon-detecting technique is a good start, but that it relies on some simplified models of storms to derive its calculations. In the future, he says, sending drones or balloons into storms in combination with the muon detector could help refine the readings.

The fact that storms can climb into the gigavolt range does help solve one mystery. Since the 1990s satellites have recorded gamma-ray flashes emanating from the higher reaches of the atmosphere known as Terrestrial Gamma Ray Flashes. If thunderstorms do have electrical potential in the gigavolt range, it means they are powerful enough to accelerate electrons to speeds that can smash certain atoms to pieces, producing the flashes.