By Roger Harrabin
Environment analyst
Renewable power generation, such as wind turbines, can produce electricity when it is not in demand
Turning air into liquid may offer a solution to one of the great challenges in engineering - how to store energy.
The Institution of Mechanical Engineers says liquid air can
compete with batteries and hydrogen to store excess energy generated
from renewables.
IMechE says "wrong-time" electricity generated by wind farms
at night can be used to chill air to a cryogenic state at a distant
location.
When demand increases, the air can be warmed to drive a turbine.
Engineers say the process to produce "right-time" electricity can achieve an efficiency of up to 70%.
IMechE is holding a conference today to discuss new ideas on how using "cryo-power" can benefit the low-carbon economy.
The technology was originally developed by
Peter Dearman, a garage inventor in Hertfordshire, to power vehicles.
A new firm, Highview Power Storage, was created to transfer
Mr Dearman's technology to a system that can store energy to be used on
the power grid.
The process, part-funded by the government, has now been
trialled for two years at the back of a power station in Slough,
Buckinghamshire.
More than hot air
The results have attracted the admiration of IMechE officials.
The energy storage technology has been tested for two years at a power station
"I get half a dozen people a week trying to persuade me they have a brilliant invention," head of energy Tim Fox told BBC News.
"In this case, it is a very clever application that really
does look like a potential solution to a really great challenge that
faces us as we increase the amount of intermittent power from
renewables."
Dr Fox urged the government to provide incentives in its
forthcoming electricity legislation for firms to store energy on a
commercial scale with this and other technologies.
IMechE says the simplicity and elegance of the Highview
process is appealing, especially as it addresses not just the problem of
storage but also the separate problem of waste industrial heat.
The process follows a number of stages:
- "Wrong-time electricity" is used to take in air, remove the CO2 and water vapour (these would freeze otherwise)
- the remaining air, mostly nitrogen, is chilled to -190C (-310F)
and turns to liquid (changing the state of the air from gas to liquid
is what stores the energy)
- the liquid air is held in a giant vacuum flask until it is needed
- when demand for power rises, the liquid is warmed to ambient
temperature. As it vaporizes, it drives a turbine to produce electricity
- no combustion is involved
IMechE says this process is only 25% efficient but it is
massively improved by co-siting the cryo-generator next to an
industrial plant or power station producing low-grade heat that is
currently vented and being released into the atmosphere.
The heat can be used to boost the thermal expansion of the liquid air.
More energy is saved by taking the waste cool air when the
air has finished chilling, and passing it through three tanks containing
gravel.
The chilled gravel stores the coolness until it is needed to restart the air-chilling process.
Delivering durability
Highview believes that, produced at scale, their kits could be up to 70% efficient, and IMechE agrees this figure is realistic.
"Batteries can get 80% efficiency so this isn't as good in that respect," explains Dr Fox.
"But we do not have a battery industry in the UK and we do
have plenty of respected engineers to produce a technology like this.
"What's more, it uses standard industrial components - which
reduces commercial risk; it will last for decades and it can be fixed
with a spanner."
In the future, it is expected that batteries currently used in electric cars may play a part in household energy storage.
But Richard Smith, head of energy strategy for National Grid,
told BBC News that other sorts of storage would be increasingly
important in coming decades and should be incentivised to commercial
scale by government.
He said: "Storage is one of four tools we have to balance
supply and demand, including thermal flexing (switching on and off
gas-fired power stations); interconnections, and demand-side management.
Ultimately it will be down to economics."
Mr Dearman, who also invented the MicroVent resuscitation
device used in ambulances, told BBC News he was delighted at the success
of his ideas.
He said he believed his liquid air engine would prevail
against other storage technologies because it did not rely on
potentially scarce materials for batteries. "I have been working on this
off and on for close on 50 years," he told BBC News.
"I started when I was a teenager because I thought there
wouldn't be enough raw materials in the world for everyone to have a
car. There had to be a different way. Then somehow I came up with the
idea of storing energy in cold.
"It's hard to put into words to see what's happening with my ideas today."
John Scott, from the Institution of Engineering and
Technology (IET), added: "At present, pumped-hydro storage is the only
practical bulk storage medium in the British grid.
"However, locations are very restricted," he told BBC News.
"In the future, if new storage technologies can be deployed at a lower
cost than alternatives, it would benefit the power system."
A spokesman for the Department of Energy and Climate Change
(Decc) said it would shortly launch a scheme to incentivise innovation
in energy storage. Other grants are available from Ofgem.
Follow Roger Harrabin on Twitter:
@RogerHarrabin
Source