Erik

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As far as cooling the working fluid, geo heat exchange could take care of that efficiently.

The stirling engine would be fine where more complex, more efficient systems would be impractical though.  Imagine a solar oven (that you can power with a campfire too) that had a fridge coil, cooking pot, and a stirling engine/generator and water pump/filter feeding off of the dual heat source.

That would be a very simple effective energy system for off grid living.  These could be mass produced and spread worldwide.

http://amazngdrx.blogharbor.com/blog John Schneider, Northern Wisconsin

Having lived on a biodigestor-equipped dairy farm in Costa Rica for awhile (the machine was set-up as a demonstration project by a nearby university), I will attest to the fact that they are very easy to use, and not only do they not require a central grid source and avoid a number of environmental externalities, but they also do wonders for their users' productivity. With such a low-cost energy source, the family I lived with on the farm was able to maintain the financial viability of their operation and to reject developers' proposals to buy up their land.      

The institution that set up the apparatus was EARTH University, in case you're interested, and information on the joint project between Infinia and EBI can be found at this address:

http://www.biobasednews.com/node/8908

("Infinia Announces Partnership to Develop Biomass Power Systems for Developing Nations")

This type of venture is definitely something to keep your eye on!

I know theres a lot of heat that goes out of that pipe, and its just wasted.

The stirling can be powered by a high range of biomass sources, from biogas to syngas.

Infinia partnership with Emergence Bioenergy.

They will use Grameen-type distribution models to reach millions of people. Since biomass is so widely available and dirt-cheap, this is probably the winner amongst small-scale energy systems.

(Provides reliable baseload, overall systems efficiency is very high because CHP, and the entire concept can even be turned carbon-negative, when the feedstock is gasified and a high char fraction sequestered in soils which get more fertile as a consequence.)

Others names investing in Infinia's stirling micro-engines coupled to biomass are Paul Allen, Vinod Khosla and Bill Gross.

I can imagine poor farmers in the poorest countries 'leapfrogging' us: they generate heat and power more efficiently than us, in a decentralised, offgrid manner, grow biomass to remove CO2 from the atmosphere, use gasification/slow pyrolysis to char it and sequester it in soils, receiving carbon money for doing so, and boosting crop yields...

It all seems to be coming together nicely.

But here's my beef with the manufacturers of said-terrific technology.  They've fallen in love the with the better mousetrap theory of technology development.

We would happily use stirling engines in lots of applications.  They have enormous inherent advantages over steam- and organic-rankine cycles by virtue of not needing boilers & condensers.  But all the manufacturers think that what the world really wants is a _ kW standard Stirling system.  Nobody wants that.

What the world really wants is a Stirling engine developer who says "you tell me how much waste heat you have, at what volume and at what temperature and I will build a Stirling engine accordingly."  It's the first lesson of cogen: size to the heat.  A 300 kW stirling engine sized for 1000 degree offgas is only helpful if you have 1000 degree gas and 300 kW of load.  On the other hand, if I have 750 F offgas and a big cooling sink, I'd love a stirling application, but none of the developers have taken a customer focus.

None of this is to diminish the technical glitches that remain with the technology.  But man, would I love to see a technology expert who approached the market with a customer focus.  There's a great opportunity awaiting those who do...

A great feature of this kind of biogas from manure, that ewould normally run off and emit methane, is that by converting the biogas to CO2, the GHG effect of the methane (21x the GHG of CO2) is canceled.  The net cancellation is 20 times the GHG effect of that CO2 emitted.

If biogas from waste provided 5% of our energy, the rest of our carbon footpront from CO2 would be offset.

Further more, the nitrous oxide emitted by chemical fertilizer is eliminasted by the use of the organic fertilizer from the biogas digestor.  

At 296x the GHG effect of CO2, that chemical (or raw manure) fertilizer nitrous oxide emission equals 2/3 the CO2 absorbed by the crops fertilized.  Biogas and organic farming together could reverse GHG climate change all alone.

Every long haul truck, train (not running on renewable electricity), and tractor should be running on biogas in the next 10 years.  Think of the huge reduction in oil and diesel fuel consumption.  That's economy and climate saving ag and energy policy.

High fuel and fertilizer costs are bankrupting  family farms leaving us at the mercy of corporate agripoisonous monopoly farming.

http://amazngdrx.blogharbor.com/blog John Schneider, Northern Wisconsin

Fact: Stirling Energy Systems (SES), which is working to develop Stirling-dish solar technology has contracted to provide a 300MW plant and options for two more of this size.  Each plant would be made up of 12,000 25kW Stirling-dish units.  The promised to deliver the first 300 MW phase by 2010.  

Fact: SES currently has only 6 hand-built prototypes of its dish technology undergoing testing at Sandia National Lab.

Fact: The US DOE in an April 15, 2008, research plan on page 107 said that it assumed a mean time between failure (MTBF) for the SES technology of only 200 hours. See:

http://www1.eere.energy.gov/solar/pdfs/solar_program_mypp ...

This means that each of the 12,000 dishes would be expected to break down about 18 times per year (assuming 10 hours of operation a day).  Do the math -- that's a lot of breakdowns.  In contrast reliable existing energy generators (wind, photovoltaic, natural gas, steam turbines) have a MTBF of less than once per year and they don't depend on so many individual units. SES touts its total run time and availability, but the reason it has high run time and availability, yet low MTBF, is because the machines are tended and repaired constantly by highly trained technicians, which is not commercially viable in a commercial setting. Also, the high conversion efficiencies of SES's technology don't compensate for reliability and cost problems.  Thus, despite over two decades of research, the SES technology is still no where near "utility grade" in terms of reliability.  Other companies using different technologies with less efficient and less problematic working gases are having different results, but lower efficiencies.  

Fact: The SES technology is not able to store thermal energy because it collects the energy via numerous dishes each of which is focused onto separate 4 cylinder Stirling motors/gen sets that are not connected to each other.  When the sun goes down, the motors turn off.  It's completely different technology from trough and tower.  

Fact: A 2007 report from Navigant Consulting, Inc. (NYSE: NCI), a firm with more than 1,900 global consultants, estimated that the SES technology would cost about $6/Watt installed capacity, whereas SoCal Edison is estimating that its recently announced roof top PV solar project in the LA region will cost about $4/Watt and would also not require spending money on a big power line.

The SES technology needs a lot of research money because it is simply not ready for utility-scale deployment. The US DOE doesn't think its engineers will even complete a design for a next generation prototype until June of 2011.  Assuming these engineers (who are actually operating SES's current equipment) are right, this means that construction and testing of these prototypes are very unlikely to be completed before the 2012-14 timeframe, which means that construction on a utility-scale 1 MW pilot plant wouldn't likely begin until the 2015 timeframe -- and that assumes that the scientists and engineers working on this technology can overcome the fundamental materials challenges that have kept this technology from being commercialized, and that research money is available.

NTR, a company that recently promised to invest $100 million in this technology, has not committed nearly enough money to build any sizeable project even assuming they can get the technology to stop breaking down, so hopefully they will invest their money in the basic research required to get this technology working.  The core problems with this Stirling engine technology has to do with basic materials challenges that have proved intractable for years.  NTR's investment in basic research may be particularly important because if the US economy tanks then the federal government may not have the money to pay for more research.

We need to be realistic about this technology, because doing so is more likely to ensure that money on it is spent wisely.  Hopefully, someday it will come to fruition, but don't hold your breath.  

ReGen Power Systems has designed a Stirling-type engine to operate at 250C, a temperature at which creep stress is not an issue and high cost materials unnecessary.  At 1000psi, 250C and 5hz, the difficulty of retaining the hydrogen is diminished.  We have also designed to recharge the engine automatically.  We will make a 500kW prototype and sell to the industrial waste heat market.

Dick