The calm, blue waters of Lake Kivu in the west of Rwanda belie the energy powerhouse it stores deep underwater.

Hundreds of meters down in the inky blackness, the lake is holding enough unexploited energy to meet Rwanda’s needs for 200 years.

Rotting vegetation which has been deposited for millions of years at the bottom of the lake is giving off a constant regenerating supply of methane gas.

Some of that gas bubbles to the surface where it is carried away and dispersed on the wind, but much of it, under massive pressure, is dissolved in the water at the bottom of the lake, which is in places more than 600m deep.

Methane is a combustible gas ideal for use in electricity generation and heating, it is the main component of “natural gas“ fed to cookers all over the world.

Huge Pressure

The challenge at Lake Kivu is getting the methane out of the water and that process is not too complicated.

A number of engineering companies have been looking at ways of “harvesting“ the gas and one company EcoEnergy is in the process of finalizing a deal with the Rwandan government to get the gas to the surface and establish an electrical power generation facility.

Put in simple terms, all that is needed to release the dissolved gas is to bring water up from close to the bottom of Lake Kivu, to a depth of about 70m.

Because of the huge pressure at a depth of several hundred meters, no pumping is required to get the water up.

All that needs to be done is to “agitate“ the water a bit and the pressure will force it up.

At 70m the reduction of pressure will allow the dissolved methane to bubble out of the water.

Other gases like carbon dioxide and hydrogen sulfide will remain dissolved in the water, which is then pumped back down to the depths again, leaving a chamber gradually filling up with methane.

The gas can then be piped away for storage and use.

Cheap, Accessible, Plentiful

At purities of more than 80%, the methane can be burnt.

Isaac Gitoho, the Projects Director of Eco Energy, says they are aiming for purity above 95%.

The technology is moving on all the time, but methane has been taken out of lake for the past 25 years.

Bralirwa Brewery on the banks of Lake Kivu had been using methane for most of its energy needs until a couple of years ago.

A small pilot methane plant intended to produce methane for just five years, kept going for 18 years until it packed in 2004.

The director of the brewery, Anand Chaurasia, says it was the perfect solution for him. Methane was cheap, accessible and plentiful.

Now he has to import very expensive petroleum oil to run his generators and heat the water needed in a brewing operation.

The oil has to be driven into land-locked Rwanda from the East African coastal ports of Mombassa and Dar es Salaam.

“It has put up my costs up threefold in the past two years,“ he said. Mr Chaurasia showed me the yellow pipes which used to feed methane into the brewery.

“If we could get our hands on methane again it would be perfect,“ he said.

Crying Out for Power

There are billions of cubic meters of methane at the bottom of the lake and recent studies have shown that enough is regenerated every year to supply all of Rwanda’s energy needs.

So this is a resource that could cut the country’s reliance on oil, and potentially bring in huge foreign earnings--Uganda to the north and the Democratic Republic of Congo to the west are crying out for power.

Plus, of course, there are the environmental benefits; methane in this form is renewable and relatively clean.

It is a powerful greenhouse gas, at least 20 times more harmful than carbon dioxide.

Getting it out of the environment will be very beneficial.

So the methane operation ticks all the right environmental boxes.

It may in the long term even reduce the wanton tree-cutting that is going on all over Rwanda.

Massive forests have disappeared to be used for firewood and charcoal.

Cataclysmic

There is another benefit as well.

Lake Kivu is what is known as a “turnover lake“.

Geological evidence from around the lake shows that every 1,000 years or so there have been cataclysmic events which have wiped out all animal life in a huge radius surrounding the lake.

What happens is that gradually so much methane and carbon dioxide is dissolved in the water that it begins to acquire buoyancy.

Instead of this being released gradually there is a sudden huge explosion, where the lake effectively turns over.

The gas laden water from the bottom of the lake surges to the surface, releasing billions of cubic meters of gas; this settle like a huge toxic blanket over the surrounding area.

It is heavier than air so all the oxygen is forced out and all life is suffocated.

This is what happened at Lake Nyos in Cameroon in 1986, when 1,700 people were killed.

Lake Kivu is hundreds of times bigger than Lake Nyos and it is estimated that more than two million people would die.

Extracting methane from the lake will help to mitigate this cataclysmic eventuality.

PIN/ BBC