New Stirling Engine with Higher Temperature, Efficiency

The Stirling engine is a piston engine that can operate with a variety of external heat sources (i.e., “external combustion”, when a fuel is burned to supply the heat). A contained gas, typically helium, is cyclically heated to high temperatures and pressures to provide force on a piston, which then drives an electric generator. The difference in temperature between the heat source and a heat sink (typically the atmosphere) and the effectiveness of the transfer of heat into and out of the working gas is what determines its performance. Stirling engines are operating today with fuels as diverse as natural gas, fuel oil, and biomass (e.g., wood chips) and also with concentrated solar energy. Stirling engines typically have low maintenance and high reliability, and when paired with clean fuels can be an environmentally friendly way to generate power.

There have been many attempts over many decades to develop a commercially viable stirling engine, and recently there has been renewed interest and progress. (Try putting “stirling engine” in to a search engine like google, and stand back.)

Here are a few of the current players:
– STM Power Inc., Ann Arbor MI, has attracted industry and investor interest with their four-cylinder “swash-plate” design.
– Stirling Energy Systems, Phoenix AZ, plans to use the Swedish Kockums engine in solar dish concentrator developed with Boeing (actually Northrup). Rumor has it the company may be shortlived, having not been able to raise funding.
– Whisper Tech is a recent entrant from New Zealand, focused on residential cogeneration (aka micro combined heat and power – MCHP).
– Sigma PCP developed in Norway ( is now a wholly owned subsidiary of Ocean Power (; also directed at MCHP.

Alternative Designs, Inc. (ADI) has developed an advanced “Dual Shell” Stirling engine which permits operation at higher temperatures and thus higher efficiencies. They believe that this “Dual Shell” system and other improvements will allow the company to achieve a fuel to electricity conversion efficiency as high as 50%. They estimate that their costs could drop to around $400/kw. The engine has multi-fuel capability and full power levels at high altitudes. The 25kw unit is small and compact– roughly 2 feet high and one foot in diameter.

In early 2001, ADI will complete a 25 kW prototype system and begin a performance validation program. Through early 2002, ADI will develop five additional prototypes and begin work to commercialize the product. ADI plans to sell complete power generation systems ranging from 25 to 100 kW beginning in late 2002.

ADI’s advanced Dual Shell system utilizes a host of patent pending and proprietary technologies that will significantly improve the efficiency of a Stirling engine while simplifying construction and reducing manufacturing costs. Principle among these are a dual pressure vessel design which allows the engine to operate at higher temperatures while still using relatively common materials, and a reduced cost heater head design which reduces the number of manufacturing steps by a factor of ten.

The are looking for equity investors and a strategic partner. I can supply additional details and a copy of the business plan.

Wayne Bliesner, President, 425-402-9632,

Additional Background
ADI’s advanced Dual Shell system has the high efficiency and low system cost required for success in the power generation market. Its patented dual shell design enables the engine to operate at temperatures much higher than existing Stirling engines, increasing the relative efficiency by 20%. It also uses a specially designed regenerator that improves the relative efficiency another 5% by recycling the waste heat into the hot cycle of the working gas. On most Stirling engines the heater head component is responsible for 50% of the system cost — primarily due to the complicated series of welds required. On the advanced Dual Shell system a patented design reduces the number of welds from 280 to 30. ADI had also invented a proprietary process that allows all 30 welds to occur simultaneously in a single step. Tests of this process have been conducted with outstanding success. These and several other patented or proprietary design and manufacturing improvements will allow ADI to produce high quality, low cost engines.

ADI has used advanced modeling techniques and testing to reduce the development risk of the Dual Shell system. For instance, software developed by NASA to study Stirling engine performance has been used by both ADI and independently by NASA to validate ADI’s power and efficiency estimates. The results have instilled a high level of credibility in the advanced Dual Shell design. In addition, numerous prototypes of key components have been built to test and simplify manufacturing methods.

Reliability and flexibility have been designed in from the start. ADI projects that these engines can be run continuously for ten years with only four maintenance intervals. The basic system is expandable to allow easy development of higher power systems by simply connecting several units in series. (ADI has conceived of a way to allow each unit to be individually de-clutched from the power train so that, on the rare occasion that maintenance is required, the multi-unit generator set may remain safely and continuously on-line — operating at slightly higher capacity on the remaining units.)

ADI’s prototype engine drives a standard “off-the-shelf” electric generator at 1800 rpm to produce a minimum of 25 kW of continuous power at 480 Volts and 60 Hz.

On Site Hydrogen for Generator Cooling

Proton Energy Systems, as you know, is one of the prominent new companies on the new “energy technology” scene, having done its IPO last Fall. One thing that sets them apart from other fuel cell companies is the fact that they have a successful commercial product line, namely the HOGEN hydrogen generator. While they continue development of an advanced regenerative fuel cell system based on PEM technology, the HOGEN is already entering the market, in many exciting applications. In discussions with David Wolff, VP of Marketing and Sales at Proton, I’ve learned that they are gearing up a significant effort to introduce HOGEN for generator cooling. I asked Dave to outline the main points of their story, so that UFTO companies could check into it sooner. Here is his note.

Thank you, Ed, for your enthusiastic support and knowledgable advice as Proton positions our products within the electric generator cooling market. As you are aware, electric generator cooling is only one of many exciting market segments for HOGEN hydrogen generators, but the electric generator cooling segment has many unique attributes which make this the right time for an onsite hydrogen solution. I will review the important issues in this e-mail.

Onsite hydrogen is not new in electric generator cooling:

– Onsite hydrogen via electrolysis is not a new idea for electrical generator cooling. General Electric sold electric generators equipped for self-generation of hydrogen using old-style KOH (potassium hydroxide – “caustic”) electrolyzers for many years during the mid-20th century. These systems were generally shipped to developing countries where the hydrogen infrastructure was non-existent, and the self-generation of hydrogen made it possible to have the high efficiency of a hydrogen cooled generator in these isolated areas. The downside to these old style electrolyzers was that they were very expensive, very labor intensive to operate (often requiring a dedicated staff of their own), were expensive to purchase, required constant maintenance, involved hazardous KOH electrolyte and asbestos cell separators, and had to be equipped with a compressor because they made hydrogen at a pressure of less than one psig.

How Proton’s HOGEN hydrogen generator has changed the playing field for hydrogen generators:

Proton’s HOGEN hydrogen generator uses innovative Proton Exchange Membrane (PEM) electrolysis technology instead of the customary liquid electrolyte technology to achieve electrolysis. But it is not just the interesting technology, but the total advantages of the system that make the difference:

– Very compact systems – our boxes are 10% of the size and weight of the “traditional” KOH systems, and half the size and 30% of the weight of the “advanced” KOH systems now being introduced by Stuart, Hydrogen Systems and others.
– One box, all-in-one “Plug and Play” design – our systems contain all required components in a single box for ease of installation.
– The average installation time for a HOGEN 40 hydrogen generator is a couple of hours: a 380 installation and startup takes one day start to finish.
– Unmanned operation – Proton’s HOGEN hydrogen generators operate unattended and require routine maintenance only once per year
– Fast delivery from stock – Proton has begun routine production of the HOGEN 40 hydrogen generator and they will be available for rapid delivery
– Process pressure without a compressor – HOGEN hydrogen generators deliver 150 psig or higher (depending on model) UHP grade hydrogen without the need for a mechanical compressor, eliminating the cost, electrical consumption, maintenance and operational complexity associated with the use of a hydrogen compressor.
– Highest purity – our systems deliver 99.999+% pure UHP grade hydrogen without the need for purification and without the risk of KOH carryover
– Aggressive pricing – our systems offer superior performance and are priced at or below the cost of a complete system offered by our competitors.

While Proton has introduced exciting new technology and convenience, some of the excitement is driven by changes in the electrical utility
market and industrial gas market:

– Under regulation, utilities used to have little incentive to reduce costs, since they were guaranteed a cost-plus profit – in essence
– the more they spent, the more they made. All this has changd under deregulation, and utilities are examining every chance to reduce costs.
– The cost reduction efforts have squeezed plant staffing, and the staff that used to be used to monitor the frequent hydrogen
– deliveries (hydrogen is a highly hazardous material and procedure is that the deliveries would be monitored by plant personnel) is no longer available. By eliminating or reducing deliveries, a HOGEN hydrogen generator frees up staff.
– The price of hydrogen has been rising at the rate of 10+% annually for the past several years (propelled by increases in natural
– gas, diesel fuel, regulation and labor) – the “cost to beat” for electrolysis is getting easier.

It is important to note that use of a HOGEN hydrogen generator may not eliminate the need to get delivered backup gas, and to have the ability to get hydrogen gas delivered for a generator refill (approximately once annually). The most cost-effective generator is sized to meet the steady-state needs of a generator, not the refill. For example, we know that a GE Frame 7 gas turbine requires approximately 21 cubic feet of hydrogen per hour for makeup gas, but requires 7500 scf of hydrogen to refill the generator after it has been purged of hydrogen. The refill gas is best supplied though a bulk delivery by an industrial gas supplier or some other supply method.

Also be aware that Proton’s fundamental business philosophy is that we will access our markets through qualified incumbent distribution methods. In the case of hydrogen supply, the incumbent method is through industrial gas companies such as Air Liquide, Praxair, Airgas etc. Since we believe that sites will continue to require backup storage (often rented) and delivered gas for refilling after a purge, we believe that Proton’s business goals and the customers’ total requirements for technology, products and services may be best suited by accessing HOGEN hydrogen generators through industrial gas suppliers.

Beyond products and services, industrial gas suppliers can supply financing services to electric utilities. We are finding that in the new business environment, that generating stations are looking for a maximum two year payback on capital expenditures. We are often right on the edge of a two year payback, and thus it is difficult for the facility to make the right decision. Financing via a full service lease from an industrial gas company makes it an operating expenditure rather than a capital investment and makes the right decision easier to implement.

Current models of HOGEN hydrogen generators deliver 150-200 psig hydrogen without a compressor. We expect to be building systems within the near future that can deliver 1600 psig and up without a compressor. This would eliminated the need for delivered backup hydrogen because the systems would be able to pressurize the existing tube banks present at many electrical generating plants to their working storage pressure – making our own backup gas.

While the opportunities in generator cooling for HOGEN systems are exciting in the U.S. and in Western Europe, there are even more exciting opportunities possible outside of these areas. In many developing countries, regional and national utilities have been so desperate for reliable hydrogen supply that decades ago they purchased a small number of old fashioned KOH electrolyzers with large reciprocating compressor which they set up at centralized sites and they fill their own cylinders which they then truck hundreds of miles to their various electric generation sites. Thus they have the worst of both worlds – high cost hydrogen, and high cost distriibution. Our proposed “White paper” (which may be the presentation that we give at Power-Gen Latin America in Oct ’01) will talk about replacing this far flung network with compact onsite hydrogen generators at each generation station, allowing the old central systems to be retired, decreasing costs and increasing reliability.

Hope this information is helpful. Thank you again for your enthusiasm and assistance.

David E. Wolff
V.P. Marketing and Sales
Proton Energy Systems
50 Inwood Rd.
Rocky Hill, CT. 06067
(860) 571-6533 x254
(860) 571-6505 FAX

AET – Solar Hot Water

American Energy Technologies (AET) of Jacksonville, FL has been a leader in solar hot water heating systems since 1987. They now have two new products that represent a major advance in the state of the art in residential solar hot water. In addition, they are nearing the demonstration phase of a new high temperature solar collector suitable for power generation or process steam applications.

These two programs represent new technology and new business or investment opportunities. (Disclosure- I am a consultant for the company.)

I. Residential Solar Hot Water

“Sav’nSun” system is a pre-assembled system designed for easy retrofit installation. The system is freeze-proof, and features a smaller, more attractive solar collector that resembles a skylight on the roof.

“EagleSun” is designed specifically for new home construction – an attractive, economical, low-maintenance solar water heater that actually becomes part of the roof while the home is being built. Unlike a conventional thermosiphon system with its unsightly tank above the collector, the EagleSun appliance is fully integrated into the roof structure and presents a clean skylight appearance. Each system is factory pre-assembled making installation quick and easy. Unlike other ICS systems, EagleSun works in freezing and non-freezing conditions, and does not require a secondary tank and heating element , making it the first true solar appliance for the building industry in all regions of the country.

Both system use AETs’ proprietary Black Crystal selective coating ? which absorbs more energy in the day and loses less energy at night than conventional collector coatings. The Black Crystal coating, which is also non-toxic and environmentally friendly, was developed in cooperation with Sandia National Labs. See:

These systems are enjoying a very positive response among builders. The company is seeking $1.5-$2.0 million for to ramp up commercialization, and is also interested in finding strategic partners.

II. Solar Thermal Electric

AET is also developing a high temperature solar collector (HTSC), suitable for process steam and electric power production, but without the limited applicability and high cost of concentrators and vacuum collectors. (A new separate company will be formed for this program.)

The HTSC is a flat plate (one-sun) collector. “One-sun” means there is no concentration of the sun’s energy. It can operate with diffuse light and has a wide acceptance angle. Until HTSC, vacuum tubes were the only one-sun technology with the ability to achieve sufficiently high temperatures for STE applications. U.S. Patent No. 5,653,222

The Jacksonville Electric Authority has determined that HTSC, if proven, would provide an attractive return for them, compared to the alternatives of PV, biomass, and fuel cell technologies. JEA is therefore working with AET to develop a combined cycle pilot project in 2001. If this proves successful, JEA is considering 100 MW of HTSC as part of a new 500 MW plant being planned. Such an installation would require HTSC array covering approximately 50 acres.

An initial outside investment $1.0 million is needed for development of a production model of the high temperature collector system and to support the pilot project in 2001.


I can supply copies of brochures, studies and business plans for these two programs.

Richard Squires, CEO
904.781.7000 x102