This is actually a sound engineering proposition. Simply usingsurplus energy to produce liquid air is an excellent first step andcan done generally at night when the cryogenic cycle can be operatedmost efficiently. Even better, the product of liquid air is easilystored for later use and easily transported.
As also noted here the product is a natural add on to every heatengine simply because it can scavenge the waste heat and convert itall directly into brake horsepower through expanders with a hugetemperature shift and resultant pressure.
We are looking at a 400 degree F transition whose energy will beequivalent to boiling water. This is an excellent solution for athermal power plant that already loses the residual energy from itsspent steam. This neatly captures that energy while drawingadditional energy out of the environment through the warming liquidair also.
I see a very efficient thermal plant resulting from this technologywith an excellent conversion of wind and solar energy into grid powerusing existing thermal stock.
Even better, all the hardware already exists and can be designed offthe shelf.
Liquid air 'offersenergy storage hope'
By Roger Harrabin 1 October 2012 http://www.bbc.co.uk/news/science-environment-19785689 Turning air into liquid may offer a solution to one of the greatchallenges in engineering - how to store energy.
The Institution ofMechanical Engineers says liquid air can compete with batteries andhydrogen to store excess energy generated from renewables.
IMechE says"wrong-time" electricity generated by wind farms at nightcan 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 theprocess to produce "right-time" electricity can achieve anefficiency of up to 70%.
IMechE is holding aconference today to discuss new ideas on how using "cryo-power"can benefit the low-carbon economy.
The technology wasoriginally developed by Peter Dearman, a garage inventor inHertfordshire, to power vehicles.
A new firm, HighviewPower Storage, was created to transfer Mr Dearman's technology to asystem 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 atthe back of a power station in Slough, Buckinghamshire.
More than hot air Theresults have attracted the admiration of IMechE officials.
"I get half adozen people a week trying to persuade me they have a brilliantinvention," head of energy Tim Fox told BBC News.
"In this case, itis a very clever application that really does look like a potentialsolution to a really great challenge that faces us as we increase theamount of intermittent power from renewables."
Dr Fox urged thegovernment to provide incentives in its forthcoming electricitylegislation for firms to store energy on a commercial scale with thisand other technologies.
IMechE says thesimplicity and elegance of the Highview process is appealing,especially as it addresses not just the problem of storage but alsothe separate problem of waste industrial heat.
The process follows anumber 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 thisprocess is only 25% efficient but it is massively improved byco-siting the cryo-generator next to an industrial plant or powerstation producing low-grade heat that is currently vented and beingreleased into the atmosphere.
The heat can be usedto boost the thermal expansion of the liquid air.
More energy is savedby taking the waste cool air when the air has finished chilling, andpassing it through three tanks containing gravel.
The chilled gravelstores the coolness until it is needed to restart the air-chillingprocess.Delivering durability
Highview believesthat, produced at scale, their kits could be up to 70% efficient, andIMechE agrees this figure is realistic.
"Batteries canget 80% efficiency so this isn't as good in that respect,"explains Dr Fox.
"But we do nothave a battery industry in the UK and we do have plenty of respectedengineers to produce a technology like this.
"What's more, ituses standard industrial components - which reduces commercial risk;it will last for decades and it can be fixed with a spanner."
In the future, it isexpected that batteries currently used in electric cars may play apart in household energy storage.
But Richard Smith,head of energy strategy for National Grid, told BBC News that othersorts of storage would be increasingly important in coming decadesand should be incentivised to commercial scale by government.
He said: "Storageis one of four tools we have to balance supply and demand, includingthermal flexing (switching on and off gas-fired power stations);interconnections, and demand-side management. Ultimately it will bedown to economics."
Mr Dearman, who alsoinvented the MicroVent resuscitation device used in ambulances, toldBBC News he was delighted at the success of his ideas.
He said he believedhis liquid air engine would prevail against other storagetechnologies because it did not rely on potentially scarce materialsfor batteries. "I have been working on this off and on for closeon 50 years," he told BBC News.
"I started when Iwas a teenager because I thought there wouldn't be enough rawmaterials in the world for everyone to have a car. There had to be adifferent way. Then somehow I came up with the idea of storing energyin cold.
"It's hard to putinto words to see what's happening with my ideas today."
John Scott, from theInstitution of Engineering and Technology (IET), added: "Atpresent, pumped-hydro storage is the only practical bulk storagemedium in the British grid.
"However,locations are very restricted," he told BBC News. "In thefuture, if new storage technologies can be deployed at a lower costthan alternatives, it would benefit the power system."
A spokesman for theDepartment of Energy and Climate Change (Decc) said it would shortlylaunch a scheme to incentivise innovation in energy storage. Othergrants are available from Ofgem.
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