Power chips "can kill all engines"

Written by: Tom Shelley | Published:

Tom Shelley reports on the imminent commercialisation of a solid-state technology set to revolutionise the direct conversion of heat to electricity

Tom Shelley reports on the imminent commercialisation of a solid-state technology set to revolutionise the direct conversion of heat to electricity

Novel solid-state devices that convert heat directly to electric power have a claimed efficiency of 70-80% of the theoretical Carnot Cycle heat engine efficiency.
They rely on the thermionic emission of electrons across a very narrow gap between electrodes. The work functions of the electrodes have been optimised for maximum transfer by engineering the emitting surface to take advantage of a previously obscure quantum effect.
First commercial applications are expected to be in satellites, aerospace power generation, waste heat recovery from steel and aluminium mills, generators taking internal combustion engine waste heat and converting it to electricity, and geothermal power generation. Ultimately - if the work can be scaled up - they may replace internal combustion engines and industrial power generating equipment.
Numerous research groups are developing direct solid-state methods of converting heat to electric power with much higher efficiencies than conventional thermocouple-type devices (Seebeck effect) - and with potentially higher efficiencies than internal combustion engines and steam-raising systems coupled to electric generators (see box).
The crucial quantum effect in the latest devices was theorised, researched and discovered by Avto Tavkhelidze, who is based at the Tbilisi State University in Georgia. All his inventions are assigned to Borealis, which started out as a Canadian mining company, Borealis Exploration, but which is now an assembly of mainly US-financed technology companies headquartered in Gibraltar. Other researchers engaged in the project include Dr Alan Feinerman of the University of Illinois at Chicago, a team at Portland State University led by Dr Gertrude Rempfer, and Dr Marty Kordesch at Ohio University.
At the recent Clean Energy Investment Showcase in London, organised by the Centre for Sustainable Engineering in Peterborough, a Power Chips spokesman - who described himself as a "serious shareholder and business development consultant" - explained that it relies on electrons moving from a hot material with a low work function, across a gap less than 1 micron wide, to a cold material with a low work function. The work function is the amount of energy required to take an electron out of a solid material. The gap prevents heat flow and backflow of current, which is a problem that makes the best conventional thermoelectric devices less than 10% efficient.
The spokesman is a business angel, and asked to remain anonymous so as not to be 'bombarded' with funding enquiries.
He explained: "The Russians did a lot of the basic research in this field decades ago. We took on the principal scientists including Avto Tavkhelidze in Tbilisi - where the majority of the development work is still being done."
He showed Eureka a sample cell, with an active area about 10mm across, which appeared to have a textured internal silicon surface. He mentioned that, run in reverse, the same devices can be used for cooling - in which application they are referred to as "cool chips".
This Avto Metals texture, which consists of ridges and grooves about 250nm across, is crucial. The grooves reduce the number of possible standing wave energy states that electrons can occupy within the solid - making them less likely to stay in the material, and more likely to leave. The spokesman said that as regards work function: "We are heading towards 1eV, but we can play around with the surface structure. Gaps are 500nm to 1 micron and builds are getting down to 2 Angstroms [0.2nm] flatness and even smaller gaps."
However, he says there is no point making gaps smaller than 0.1 microns - and in many cases can be up to 5 microns. He claimed that a Power Chip diode with an Avto layer could be made in less than 20 steps, which was far fewer than for other technologies.
"Simpler technology leads to lower costs," he added.
In their current form, the devices have a projected power output of 10-40W per square centimetre when the work functions get low enough and can operate at up to 250ºC. Studies on lifetimes for the devices suggest that they should be of the order of 2 years at 1,600K (1,327ºC) and 10 years at 1,200K (927ºC).
The spokesman said: "The initial sale prices for Power Chips will go as high as tens of thousands of pounds per Watt."
While he declined to be drawn on which applications he had in mind, he did mention "applications out of this world" - and an obvious use would be converting heat from small reactors in military satellites and deep space probes into electric power - something currently done very inefficiently using Seebeck devices. The spokesman claimed that existing reactors relied on 78kg of plutonium because the power conversion efficiency is so poor.
He cited a study showing that geothermal resources using existing technology could support 35-70GW of worldwide electrical generating capacity. Currently, geothermal power stations use steam, heat or hot water to rotate turbine generators to produce electricity. With Power Chips, most of such plant would become redundant.
"Power Chips will competently make more geothermal resources viable," he said. "They won't introduce any additional energy or carbon emissions, and will extract energy from what are currently considered non viable sources of power."
Regarding internal combustion engines, he said: "Typically, they achieve 20% of maximum efficiency. Power Chips will eliminate the alternator by converting waste exhaust heat directly into electricity.
He said that a 100kW engine has 200kW of waste heat available. Power Chips could improve the efficiency and emissions of normal and hybrid vehicles by 75%, he claimed.
"In the future we expect Power Chips will be able to harness body heat, to power the likes of pacemakers," he said. "Many more uses will become feasible. We are working on solar power versions, to replace photovoltaics."

Lots of runners in heat-to-power race
We know of more than a few other developments aimed at producing solid state devices that can turn heat directly into electricity.
Most are coy about their technological basis, but of those willing to communicate, JX Crystals in Issaquah, Washington is a spin-off from Boeing - with licenses for patents on infrared-sensitive gallium antimonide photovoltaic cells.
The company's first commercial Thermo Photo Voltaic (TPV) product was what they called their "Midnight Sun Stove" which used the cells to produce 100W of electricity as well as 25,000 BTU/hour of heat. The company's Jim Avery says: "We are working on a residential TPV micro-CHP product that would provide all the heat, water and electricity for a home. The overall efficiency from fuel to heat and power is quite high. Fuel to electric will be about 10%."
Electric power output will apparently be 1.5kW. The company is headed by founder Dr Lewis Fraas. Funding for a new family of mirror-enhanced solar cells - also being developed by the company - has been provided by the Shanghai Science and Technology Committee. A 100kW demonstration unit is under construction in Shanghai with an additional 300kW now on order.
Also likely to end up in the Far East is a rival ex-Soviet Union solid state heat to power conversion technology being developed in St Petersburg. The technology, said to be derived from silicon photovoltaics, claims an efficiency of up to 80% of Carnot. All was to be revealed to Eureka until we heard they were in negotiation with Sharp Electronics, the world's largest manufacturer of conventional photovoltaics.
Professor Ted Sargent, at the University of Toronto, on the other hand, has invented a technology based on quantum dots - nano particles of semiconductor - combined with polymer that can be spun coated onto a glass substrate patterned with electrodes. We do not know what the polymer is but we do know his first experiments used oleic acid, the main ingredient in olive oil. The resulting cells respond to infrared light. Efficiencies are still very low but the manufacturing technology is very cheap. We have since heard that the same - or very similar - idea is being pursued by researchers in Thailand using straight olive oil as the dispersant.

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Centre for Sustainable Engineering


* Devices convert heat directly to electric power at efficiencies said to be 70-80% of theoretical maxima as defined by the laws of thermodynamics

* Projected power outputs are 10-40W per square centimetre

* Initial target markets with be high value applications - probably in space - but the long-term target is to replace internal combustion engines and steam-raising systems

* Run in reverse, the same devices can be used for cooling

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