STM Power, Clean Power from Stirling Engines

STM Power Inc., produces Stirling cycle generators that produce electricity from almost any form of heat or fuel: waste gases from landfills or sewage treatment plants, biomass, solar energy and paint fumes.  STM Power was originally organized as a research and development company that did experiments and demonstrations showcasing a variety of energy-related technologies, including engines based on the Stirling Cycle, a technology invented in 1816. The Stirling is an external combustion engine, somewhat like a steam engine, that burns fuel to heat a liquid or gas in a sealed system -- hydrogen in the case of STM's Power Units. That heated hydrogen is then used to drive pistons that are in turn connected to an electrical generator.

The STM engine is a four-cylinder, double-acting Stirling engine with a swash plate drive. At the heart of the engine are four independent gas enclosures each comprised of the volume under a piston (compression volume), the volume above the adjacent piston (expansion volume), a series of three heat exchangers connecting these two volumes, a cooler adjacent to the compression volume, a heater adjacent to the expansion volume and a regenerator between the heater and the cooler.

The four pistons are arranged symmetrically around a swash plate that forces the reciprocating motion of any two neighboring pistons to be 90º out of phase. The gas enclosures are charged with high-pressure hydrogen that serves as a working fluid. The reciprocating motion of the pistons causes the volume of hydrogen to increase and decrease alternately. The expansion spaces are maintained at a high temperature by continuous combustion of fuel or some other source of heat (waste heat) outside the tubes of the heaters. The compression spaces are maintained at a low temperature by liquid cooling of the coolers. Therefore, the temperature and the pressure of the hydrogen during expansion is higher than during compression. The hydrogen absorbs heat from the combustion process, converts a portion of it to mechanical power, which it delivers to the pistons, and rejects the balance to the liquid coolant. The mechanical power delivered by the hydrogen to the pistons is aggregated and converted to rotating shaft power by means of the swash plate drive. The regenerator, which is the third heat exchanger, does not exchange heat with the outside. It alternately absorbs heat from and releases heat back to the hydrogen in order to improve the engine efficiency. The engine’s output shaft is connected to a generator to make three-phase electrical power.

Their Stirling cycle engine has several advantages:

• Scalable - Competitively priced 55 kW modules.
• Fuel Versatility - Can utilize a broad variety of liquid and gaseous fuels.
• High Efficiency - 30% electrical efficiency our up to 80% overall efficiency in CHP applications
• Quiet and Low Vibration - The engine is extremely smooth, quiet and produces negligible vibration. This makes it possible to install units without vibration isolation or external sound attenuation, thus lowering installation costs.  The engine generally requires maintenance once a year in full time operation.
• Low Maintenance - The engine has half the moving parts of reciprocating internal combustion engine and is not exposed to any of the products of combustion.
• Can operate using an external heat source instead of fuel.

Ford Motor Co. runs one of STM's generating systems on paint fumes from the automaker's Michigan Truck Plant in Wayne.   STM estimates the annual landfill gas business to be about $1.5 billion. But with few companies using the methane gas that landfills give off to generate electricity, STM sees a largely untapped market.

STM has 32 units in the field, including China, Singapore and Britain and a backlog of orders for more.  Consisting of an engine and generator, the units are about 9 feet long, 3 feet wide, 4 1/2 feet high and weigh 2 tons.

STM Power, Inc. is a privately held Ann Arbor, Michigan based company that designs, develops and sells ultra-low emission, external combustion (Stirling Cycle) engine products.  STM Power holds 34 active patents, 57 worldwide patents and has patents pending.

Resources:

STM Power, Inc., Ann Arbor, MI, USA
STM Power, The Clean Power Choice, online brochure
Energy company uses waste fuel, old engine, Detroit Free Press, November 19, 2005
Ten Eco-Friendly Companies, 5-A Stirling Solution, Newsweek, November 21, 2005

More blogs about electrical generation, alternative energy, energy

Comments

[Engineer-Poet]

So that's what happened to Stirling Thermal Motors.  (Some of their checks used to get mis-debited from an account of mine.  Kinda funny, actually.)

[Bill Quinn]

I'm building a $2,433 s.f. house on 2.5 acres in the Mohave desert, CA & incorporating manyinnovative & energy saving devices. Is it possible to buy your engine? If so, please contact with price, etc.

[hermans Koelingen import]

Please sir,

we have some questions about the stirling engine can we adjust our solar heat pipes (www.zonnecollector.net) on the stirling engine so we can make electric energie from these heat pipes? what is the size of the stirling engine? can we also connect from our refrigeration compressor the hot gas pipe and the cold gas pipe?
if you have a question about our question please ask.

with kind regards,

paul(from holland)

[Walter Hurst]

We have a factory with a process which generates a lot of waste heat, which is presently just vented to the atmosphere.
Can this be harnessed to generate electricty using one of these engines

[Bob Wallace]

Stirling engines with stored hot water/salts?

We're seeing thermal solar beginning to use stored heat to shift solar electricity production to the non-sunny hours.

Nights in the high desert can be quite cold and Stirling engines operate off of temperature differentials.

Would it make sense to install Stirling engines at altitude for late afternoon/evening electricity production?

--

Does it make sense to locate thermal solar at higher altitudes in order to take advantage of atmospheric cooling?

[Cyril R.]

Nights in the high desert can be quite cold and Stirling engines operate off of temperature differentials.

Dry cooling makes sense in the desert anyway (water scarcity) so a standard Rankine steam cycle with an air cooled condenser would also have that advantage. Too bad there's little electric demand during nighttime when it's really cold in the desert. Ice storage could be useful here.

The problem about Stirlings is that they are very expensive compared to Rankines, especially the saturated steam Rankines.

The advantage of a Stirling would be small size and modularity, and very low maintenance (at least the free piston ones). So it's nice for a parabolic dish. Still I think a microturbine would have better economics for a parabolic dish.

But if you're talking about really large solar thermal plants in the desert, then troughs, CLFR, LFR, and power towers have much better land efficiency and one or two large Rankines have clear advantages over many tiny Stirlings as well.

[Kit P]

“Too bad there's little electric demand during nighttime when it's really cold in the desert.”

Idiot!!! Many in California have no concept of winter heating demand on the electric grid. It is hard to explain to those were flip flops that electricity is more than a luxury allowing Starbucks the ability to make you a low fat coffee drink.

[Bob Wallace]

"Too bad there's little electric demand during nighttime when it's really cold in the desert."

Actually, if you look at cities like Las Vegas and Salt Lake ....

Right now we're shipping a lot of power out of Lake Mead/Hoover Dam. With the dropping water levels it is going to be necessary to reconfigure Hoover to keep the power flowing.

Apparently some utility companies think that Stirlings can be cost competitive. Southern California Edison is contracting for 500MW from Stirlings.

And if the economics support it then there's the HVDC grid. The Pacific Intertie swings through western Nevada on its way to LA.

Other systems might be more cost effective. I'll let the market make that decision. ;o)

[Cyril R.]

Idiot!!! Many in California have no concept of winter heating demand on the electric grid.

I was clearly talking about the NIGHTTIME electric load, and dit not even mention WINTER at all.

Kit P does not understand the difference between NIGHTTIME and WINTER.

Somehow, this doesn't even surprise me.

For what it's worth, there is a winter peak but it is much smaller than the summer peak.

[Cyril R.]

Actually, if you look at cities like Las Vegas and Salt Lake ....

Bob, I was taking an aggregated system view. Powering Las Vegas and Salt Lake City with solar thermal looks like a no-brainer, maybe a good place to start implementing it as well.

But, when the entire aggregated load on the Californian grid is considered, there is little demand for power during nighttime. Ice storage for A/C could be really helpful here.

[Kit P]

Cyril you are an idiot because you do not know there is a large demand when it is 'really cold' at night in the winter time.

I have been in the SW desert many nights in the summer. Cold is not a word that I would use. Warm is how I would describe it. While is is cooler that during the day, from the stand point of providing a temperature differential for a heat engine, not very cool at all.

[Gianluca Lezzi]

In Italy, where I live, 1 Kwh costs about $0.22(0.12 euro). To produce energy is very important for us. If you can sale a microgenerator for any fuel, I think it will be very appreciated in Italy. If you have same price or same address to find it please answer to me. Thank you.

[Praveen Kumar]

I am a mechanical engineering student.I am doing a project regarding the solar energy.I want to buy 10KW stirling engine from STM power.Can you please tell me how i can buy this engine.And cost of the engine.

[jaymart]

What ever happened to STM? I've been trying to contact them lately but you only get an answering machine when you call and their website is down. Have I missed the news about them lately, or what's going on?

[dave]

they reorganized under the name stirling biopower... http://www.stirlingbiopower.com/

[Arquitect. Fernando Rey Farías]

Plase; coud you send me information about how can I do to contact a Sales Manager to bring me prices and technical datas for bring them to my clients.
I´ve very interesed to offer our unit in Hospitals of my country.

[husky air compressor]

I'm working on a green house project. I'm really interested by this Stirling Engines.
thanks a lot!
Husky air compressor
Husky air compressor parts