July 26, 2021

I, Science

The science magazine of Imperial College

The sky went dark.  The clouds over our jumpers-for-goalposts pitch turned a turbulent brown; the light took on a cinematic quality.  There was a flash, a pause and then a long, deep rumble.

Rain came in great bands of grass-flattening deluge, a second lightning bolt crashed directly overhead, but it was the hail that had us running for cover.

Trudging soggily out of Hyde Park, I started to wonder: could there be a way to tap into all that energy?  Could we harness lightning as a renewable source of electricity?  Doc and Marty managed it in Back to the Future… Frankenstein had some success… could we do it for real?

Rocket Lightning

Well, according to a recent paper in Renewable Energy journal, harvesting power from storms – though still the stuff of science fiction – is not so far fetched.

Globally, there are around 2700 lightning strikes every minute.  Your average bolt provides around 1 terawatt (1,000,000,000,000 watts) in just 30 millionths of a second.  That’s as much power as a decent-sized wind turbine running at full capacity produces in 8 days.  The potential is huge.  However, to use it, you’ve first got to catch it…

Tall buildings are often struck by lightning – New York’s Empire State Building is hit 23 times a year on average – and one idea is to build towers in storm-prone areas.  They’d have to be tall enough to attract lightning and capped with large, highly-conductive metal ‘horns’ that would need to be replaced occasionally as the lightning vaporised the metal.  Once they were built though, there’d be very little to maintain.

A second option is firing rockets at storm clouds to trigger strikes: in 2002, researchers in Florida successfully directed several lightning bolts to the same spot on the ground using rocket-propelled copper wire.

Thirdly, as we all know, opposites attract and it seems lasers and lightning could make the perfect match.  Scientists can use extremely short bursts of high powered lasers to electrically charge air, creating what’s known as a plasma.  Lightning is usually negatively charged and strikes could be tempted by using the lasers to generate intense, positively-charged plasma above a lightning rod.   French and German researchers have already simulated this effect in the lab.

So we can catch it, what’s the problem?  It seems rapid, massive fluctuations of power are not all that easy to manage.  Cables, switches and capacitors – the devices used to store electricity – must be incredibly resilient.

The Catacumbo River, Venezuela, where lightning strikes several times a minute for 10 hours every night,150 nights per year.

So far, no engineering solution exists that can convert lightning into usable electricity.  Banks of capacitors large and hardy enough to store the huge amounts of charge would prove extremely expensive.  As is so often the case with promising renewable technologies, getting the money to build is the biggest obstacle.

However, climate change could mean more lightning; strikes are predicted to rise by forty percent with every one degree rise in global temperature.  Maybe now’s the time to invest.

James Pope.