New Zealand Coal Producer Investigating CO2 Storage Potential for Coal-to-Liquids CCS
Hydrogen Engine Center and ITM Power Exploring Electrolyzer-Engine System

Open Energy and Infinia To Develop a Suncone/Stirling Solar-Electric Power System

A cutaway diagram of Infinia’s 55-W free-piston Stirling generator.

Open Energy Corporation and Infinia Corporation (formerly Stirling Technology Company) plan to integrate Sterling engines and solar concentrators to create a new solar-powered electric generation system.

The engineering teams at Infinia and Open Energy believe that the Suncone CSP solar concentrating power system can be modified to deliver more than 700° C of solar thermal energy to Infinia’s free-piston Sterling engine to generate electricity on a cost-effective basis without burning fossil fuels or emitting greenhouse gases.

A rendering of the Suncone CSP.

Development of the Suncone/Stirling system will begin with a modified version of a 1 kW engine already being produced for residential heating and electricity in Asia and Europe as a proof-of-concept, according to David Saltman, president and CEO of Open Energy.

The free-piston back-and-forth motion in the Infinia Stirling engine drives a patented linear alternator. The SunCone CSP utilizes non-imaging optical cones made of reflective composites to concentrate sunlight on rods at the base of each cone. The cones stay cool, but the fluid flowing through the base is superheated.

We have already achieved solid results with a dish Stirling system at our facility in eastern Washington and have made significant progress on our larger engines. By working with Open Energy, we believe we can accelerate the development and commercial availability of these truly important and unique solar power generation systems. Our companies share a similar goal—to fundamentally change how the world generates and uses energy—and our engineering teams are hard at work to make this happen.

—J.D. Sitton, CEO of Infinia Corporation



Does anyone know what is the thermal efficiency attained by this Stirling engine ?
I suppose it could be something between 37% and 42%


Can't seem to find any more info on the cone itself. Does it track? Does it require pumps for liquids. It sounds like it could work for water heating. Sure sounds promising since it doesn't rely on rare earth metals. I wonder what the price/kwh will be.


Infinia's website cites 24% overall system efficiency for a solar concentrator to electrical power output (3 kW engine).


25% is about right. I could never figure out why you would do this, when you can use triple junction PV cells and get 35%.

kent beuchert

"25% is about right. I could never figure out why you would do this, when you can use triple junction PV cells and get 35%."
Well, you wouldn't if you can assume equal costs. Since they are going ahead and obviously know at least as much as you do, it would seem obvious that they are lower cost and/or looking at higher efficiencies. I'm amazed at how often amateaur observers assume that companies spending millions would (or could) do so without being aware of the odds and prospects. Business doesn't spend developmental money without knowing and understanding its competitors. Sometimes the development
doesn't succeed, but no one would press ahead if success
meant an inferior product on a cost/efficiency basis.


Sometimes companies may do development because they can get a grant. They know that it will advance their technology. That could be enough reason to do this, without any other incentive.


H2 and NA are two leading heat carrier fluid choices for solar concentrator energy systems. Both offer high thermal conductivity, and operating temperatures.


Allen Z.,
I think another advantage of using H2 as the working fluid in Stirling engines is its low viscosity.

Thank you JamesEE, 24% overall efficiency seems very good !!


Patent on a linear alternator? I wonder if the patent office will next hand out a patent for the dynamo. Does no one check prior art?

Stirling generators seem like they would have a place for capturing longer wavelength IR. Dichroic filters would do well to split the spectrum.

Rafael Seidl

Free-piston stirling engines are attractive because they can make do without transfer mechanisms that require lubrication, which fouls the working medium. They can also be hermetically sealed for life, making them cheaper to produce and suitable for unsupervised operation in remote areas.

Unlike the combustion chamber of a reciprocating ICE, the stirling cycle is used for ECEs whose typically dome-shaped hot pole is never exposed to cooling. This limits its temperatures to ~1000 degC at most for affordable metals. Ceramics can go higher but they are lousy at conducting heat, which is an essential function of the dome. Thus, as in many other applications (e.g. steam turbines), thermodynamic efficiency is constrained mostly by the available materials and the ambient temperature.

Note that while hydrogen offers the highest available specific heat of any working medium, many polycrystalline metals are susceptible to interstitial diffusion which leads to embrittling. Helium is a second-best alternative.

Rafael Seidl

Unlike PV panels, stirling engines need a heat sink to operate. In residential, RV and yachting applications, the rejected heat can be accumulated in an insulated water tank. It can also be used to drive a thermal desalination process. Elsewhere, the power take-off is mechanical rather than electromagnetic, with a membrane pump forcing the coolant around the cold pole and also driving a regular fluid turbine.

One possible application for an array of (free-piston) stirling engines would be large-scale structures floating on the surface of bodies of water, e.g. reservoirs behind hydro dams, remote lakes, tide barriers or even certain parts of the open ocean. In principle, the structures could be habitable (cp. houseboats), an expensive but nevertheless interesting concept for places like New Orleans or Bangladesh (which are susceptible to devastating floods) and Israel and Japan (which suffer from a lack of habitable land).

The permanent moorings of such structures would have to adapt to changes in water level. The size of the pontoons would limit their gross motion in the presence of waves, permitting the solar concentrators to track the sun's path more easily and accurately, possibly directly via gross rotation of the whole structure, actuated via the mooring controls.

Joe Greene

This is probably the patent holder on the linear alternator . . .

STARs™ are Qdrive’s patented linear reciprocating motors/alternators. High-Efficiency Affordable STAR™ Reciprocating Motor and Commercial STAR-Powered Acoustic Cryocooler

shaun mann

as for the greater or lesser efficiency, we may also have to consider 24% of what?

24% of all incident light energy or 24% of all incident light energy within a specific frequency range.

this device uses heat to function, solar cells use visible light, so their efficiency ratings may not be comparable.

what we really need to know is the $/kWh ratings given identical light resource and $/kW installed cost.


24% of the heat energy converted to electrical energy. Since no reflector is perfectly efficient, there would be less IR energy reaching the stirling. So yes, the two numbers are comparable. 1000 watts per square meter from the sun converted to electrical energy at 35% for the triple layer PV versus 24% from the stirling. Assuming both have the same reflector/concentrator losses, the PV is more efficient. Cost per watt would probably favor the PV as well.


Cost per watt of PV panels is approx. $5/watt for panels alone with additional cost for the rest of the system. Cost per watt of Stirling Engines systems to convert solar thermal energy into electricity is expected to be just under $1/watt for the entire system when in mass production. Some Stirling systems achieve efficiency of just over 30% of solar insolation striking collector surface into electricity.

Dave Austin

Matthew is right. When comparing apples and oranges the best thing to do is look at $/watt, and Matt's numbers are pretty good. I think PV is better than he suggests though, but still the Stirling design is much cheaper per watt produced. This also means it is much more scalable, which is why Solar thermal produces far more electricity for the world than Solar PV.

Also, since there are no manufacturing bottlenecks that can't be overcome for this design, it is a far more probable solution for the world's energy needs. Albeit PV has it's place, like in sleek, portable, and easily integrated solutions, it will never put a relative dent in the worlds power needs. Currently solar thermal electricity generators hold the most promise when considering $/watt and ease of implementation.

The biggest challenge with PV is producing the purified materials in volumes necessary to positively impact the environment. PV manufacturing processes alone produce tremendous amounts of heat and byproducts that must be dealt with.


Isn't there an issue in comparing overall output of a Stirling AC system to a PV DC system?

If we are charging batteries for hybrid cars the PV would be a good choice.


If a multi-billion dollar comapny like Boeing has just demonstrated the world's most efficient solar collector, why would anyone want to buy a piddly company like open energy?


"If a multi-billion dollar comapny like Boeing has just demonstrated the world's most efficient solar collector, why would anyone want to buy a piddly company like open energy?"

Return on investment. Venture capitalists are always hunting for small companies with terrific products and low capitalization - they pump in some money, hopefully the company starts making money, its net worth increases, thus its capitalization, at which point the VCs can either sell and make a profit or let it ride, depending on business plan and long-term outlook.

Cara cruz

I always think of how the middle age people use renewable energy in their everyday life. I like how you explained it to us.

The comments to this entry are closed.