By Jo Twist
BBC News Online science and technology staff
Capturing sunlight to make enough hydrogen fuel to power cars and buildings has been brought a step closer by a British research company.
Turning sunlight into hydrogen could be the future
Hydrogen Solar says it has managed to convert more than 8% of sunlight directly into hydrogen with fuel cell technology it has specially developed.
For an energy source to be commercially viable, it must reach an efficiency of 10%, which is an industry standard.
Hydrogen power, a renewable energy, has the potential to replace fossil fuels.
"Over the last couple of years we have doubled efficiency.
"We are not yet in the hydrogen economy, but it has the potential to take over when the oil economy becomes untenable," Dr David Auty, chief executive of Hydrogen Solar told BBC News Online.
Depending on how it is produced, hydrogen fuel is a clean, green source of power that can be easily stored.
Its potential has been recognised for well over 100 years, but it requires energy to extract hydrogen from water, or any other source.
The Tandem Cell technology developed by Hydrogen Solar uses two photocatalytic cells in series which are coated with a nano-crystalline - extremely thin - metal oxide film.
Having a nanoscale coating makes the surface area far greater and means that hydrogen can be produced efficiently without the need for polluting fossil fuels.
The cells capture the full spectrum of ultraviolet light - the Sun's rays - and, via the novel coating, the electrons are captured and carried away on conductors.
This electrical current is then used to separate the hydrogen from water which is stored for use.
The key to the process has been the advances in novel coatings brought about by recent developments in nanotechnology.
The size of the molecules in the coating is 15 to 20 nanometres (a nanometre being a billionth of a metre).
A car could run for 11,000 miles on hydrogen
When they are stacked in layers, the property of the substance changes to produce large surface areas.
"It turns out these devices work because we are using nanocrystalline layers. It is the move to nanotechnology which has brought this technology forward," explained Dr Auty.
He added: "If we look five years ahead and we have a few square miles of hydrogen farm in a desert, we think we could produce hydrogen that is competitive with coal and oil."
Once production costs have been scaled down, large hydrogen cell farms could produce hydrogen, untaxed, at $1.80 to $3 a kilo.
That is equivalent to a third of the price of the same amount of power produced from untaxed gasoline, he thinks.
There has been huge amount of work in fuel cells for buses, cars, houses, and other buildings.
But Dr Auty envisages the car industry making the best use of the technology in modified combustion engines.
"Using a 10% cell, we say that a seven-metre squared array will power a Mercedes A class car for 11,000 miles a year [in LA sunlight conditions] without going to power station," said Dr Auty.
Hydrogen power can also be produced from hydrocarbons, like oil and gas, but these have downsides in their byproducts.
Pollution-free hydrogen cell technology is predicted to be the next wave in emissions-control after the hybrid electric motor, currently used in the automotive industry.
Research into hydrogen power has been pumped with funding in the US in particular.
In 2003, President George Bush announced an $1.7bn investment to turn the US into the world leaders of hydrogen-powered automobiles.
With increasing concern about the instability of the oil market, the development of a commercially viable alternative energy source has attracted interest.
"The potential lack of oil is the reason we are doing this," Dr Auty said.
"There are huge amounts of carbon released through coal and other hydrocarbons."
Last year, General Motors (GM) said it planned to be the first to sell a million fuel cell vehicles in the next decade.
Other automotive giants have also championed hydrogen fuel.
DaimlerChrysler, Ford and GM have spent about $2bn on fuel cell cars, trucks and buses. The first products came out last year, and many UK cities have deployed hydrogen buses.
Ford's Chairman William Clay Ford Jr went so far as predicting fuel cells would end the reign of the internal combustion engine.
But there have been a number of technical and financial stumbling blocks - including taxation - which have prevented its large scale adoption, and Dr Auty thinks there need to be more political will to push the technology forward.
"There is a chicken and egg issue here," he said.
"Who is going to build a car before they have filling stations, and who is going to build stations before we have the cars.
"It has to be strategically thought out and driven by government. There is a political will in US, but I think the UK is a bit behind the pace."
"The key about all of this is that all predictions about crude oil are pretty much going to be in our lifetimes," said Dr Auty.
"But if you talk about infrastructure change, these things don't happen overnight."
HOW TANDEM CELLS PRODUCE HYDROGEN POWER
1 Ultraviolet sunlight passes through glass skin of cell
2 Light is captured in glass coated with nano-crystalline film
3 Nano-coating properties enable the glass to conduct electricity, which is used to separate the water into oxygen and hydrogen
4 Hydrogen gas is stored for later use as a power source