The presence of strange balls of light hovering over a valley in central Norway has baffled scientists for years.

Known as the Hessdalen Phenomenon, the flashing orbs can be as large as cars and have even attracted attention from ufologists.

But now scientists think the unusual lights could be formed by a natural ‘battery’ buried deep underground, created by metallic minerals reacting with a sulphurous river running through it.

 Great balls of fire? Flashing balls of light that can be as large of cars are known as the Hessdalen Phenomenon (pictured). They have attracted attention from ufologists, but now scientists think the unusual lights could be formed by a natural ‘battery’

If the theory is proven correct, it could open up a new way of storing energy.

Some of the lights drift gently through the sky for up to two hours, while others flash white or blue and streak through the valley, disappearing in seconds, New Scientist reported.

A computer engineer called Erling Strand from Ostfold University in Norway, has been looking for the physics behind the natural phenomenon since 1982, when frequent light shows captured the attention of the press and scientists alike.

He set up Project Hessdalen in a bid to unite experts trying to unravel the mystery of how the mysterious orbs are formed, and was able to quickly rule out theories that the lights came from planes, vehicles or buildings.

The researchers noticed a small fluctuation in the areas’ magnetic field before the formation of the lights, but when they measured radioactivity and seismic activity – both of which could cause such a phenomenon – there was nothing unusual at the site 248miles (400km) north of Oslo.

An international team of experts then measured the size, shape and speed of the orbs using radar and spectral analysis to examine the elements that make up the light.

Fully charged: One expert has studied the Hessdalen site since 1996 and has found that rocks in the valley are rich in zinc and iron on one side of the river running through it, and rich in copper on the other side. The sulphurous water in the river creates a giant battery

They revealed that the lights make no sound, appear to be cool and do not leave any scorch marks on the ground, unlike ball lightning. They do however sterilise an area upon contact, killing the soil microbes.

Jader Monari of the Institute of Radio Astronomy in Medicina, Italy, has studied the Hessdalen site since 1996 and found that rocks in the valley are rich in zinc and iron on one side of the river running through it, and rich in copper on the other side.

‘If there is sulphur in the water in the middle, it makes a perfect battery’ he said.

Together with a colleague from the University of Bologna, the scientists used rock samples to create a miniature valley and dunked them in river sediment. They found that electricity flowed between the two rocks and that this could light a lamp.

Dr Monari believes that bubbles of ionised gas are created when sulphurous fumes from the River Hesja react with the humid air of the valley. The geology also forms electromagnetic field lines in the valley, which could explain why the orbs of light move around.

‘This electrical field creates a path that could be the ‘main road’ of the lights inside the valley,’ Dr Monari told Caroline Williams.

Bjorn Gitle Hauge, an electrical engineer at Ostfold University, thinks that the energy needed to make the clouds glow could come from the charge building up.

There are many other competing theories as to how the light may be formed, although the battery theory seems to be the most probable based upon current evidence.

Scientists revealed that the lights of Hessdalen – which lies 248miles (400km) north of Oslo – make no sound, appear to be cool and do not leave any scorch marks on the ground, unlike ball lightning. They do, however, sterilise an area upon contact, killing soil microbes

Some experts think some sort of plasma causes the light as when a gas ionises it forms a cloud of ions and electrons – plasma – that produce light. Plasmas can be cool to touch and can also kill microbes, but they require incredibly high temperatures and a huge supply of energy to be produced.

Others believe the lights are a type of ball lightning because similar balls of light spotted and analysed in China showed they were formed of silicon, iron and calcium – which are present in the Hessdalen lights, along with the addition of an element called scandium.

But the Hessdalen lights do not appear when there is lightning, leading Dr Hauge to suggest another idea.

He proposed that the valley’s shape, climate and geology generate a massive electric charge and that static electricity on the mountains were whipped up by strong winds.

Other experts believe the lights are powered by radioactivity and the decay of radon in the atmosphere. They think the lights are made from ‘dusty plasma’ containing ionised dust particles.

They will search for the presence of radon in the valley to test their idea that bubbles of the gas could erupt from the ground, pick up dust and enter the air as a glowing orb.

Whatever the reason for the lights’ formation, the answer could lead to a new way of storing energy.

‘If we have some kind of installation that we could pick up charged particles and lock them inside, then you can store energy,’ Dr Hauge said.