This is actually a sound engineering proposition. Simply using
surplus energy to produce liquid air is an excellent first step and
can done generally at night when the cryogenic cycle can be operated
most efficiently. Even better, the product of liquid air is easily
stored for later use and easily transported.
As also noted here the product is a natural add on to every heat
engine simply because it can scavenge the waste heat and convert it
all directly into brake horsepower through expanders with a huge
temperature shift and resultant pressure.
We are looking at a 400 degree F transition whose energy will be
equivalent to boiling water. This is an excellent solution for a
thermal power plant that already loses the residual energy from its
spent steam. This neatly captures that energy while drawing
additional energy out of the environment through the warming liquid
air also.
I see a very efficient thermal plant resulting from this technology
with an excellent conversion of wind and solar energy into grid power
using existing thermal stock.
Even better, all the hardware already exists and can be designed off
the shelf.
Liquid air 'offers
energy storage hope'
By Roger Harrabin
1 October 2012
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.
"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.
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