The Power Conversion Unit (PCU) The Stirling engine’s cylinder block incorporates four sealed cylinder assemblies (pistons, piston rods, and connecting rods domes) along with coolers, regenerators and heater heads. Concentrated solar energy heats up self-contained gas (hydrogen) in the PCU, causing the gas to expand into the cylinders, moving the cylinders and generating electricity. There is a 90-degree timing separation between adjacent cylinders and the working gas is exchanged repeatedly back and forth between the same adjacent cylinders. This cycle is repeated over and over as the engine runs at a steady rate of 1,800 rpm (a low-stress, long duty-life regimen for a conventional gasoline engine). Unlike familiar auto or truck engines, Stirling engines do not rely upon internal combustion to drive the pistons and rotate a crankshaft. In fact, there is no combustion at all. Power is generated by heat transfer from the concentrated solar rays to the working gas in the engine’s heater head, which converts the heat energy into mechanical motion. This power runs the electric generator, which produces electricity with an output of 480 Volts and 60 Hertz, so it is already power-conditioned by the generator’s interface. The generator of each unit in a utility-scale project is connected by underground wire to a small substation where the power can be transformed into a higher voltage for more efficient transmission across the grid.
Proprietary History
In 1996, SES acquired the patent, tooling, and equipment rights to the world's most efficient solar dish concentrator system: the Dish Stirling. Initially developed in the 1980s by McDonnell Douglas (now The Boeing Co.) the Dish Stirling system was field-tested by Southern California Edison and Georgia Power for over 175,000 hours between 1982 and 1988. Edison's test data indicated the Dish Stirling out-performed all other solar-to-electric generating systems by a factor of two, yet had comparable start-up costs. SES optimized the McDonnell Douglas dish to operate with a 25kW Stirling power conversion unit (PCU) developed in Sweden by United Stirling, Kockums and Volvo. The resulting system, the "Dish Stirling", has fewer moving parts than comparable diesel engines and operates relatively quietly. The SES Solar Test Site and related tooling and equipment facilities are located at the Boeing facility in Huntington Beach, California. The 25kW SES Dish Stirling system has an operating track record of more than 17 years. Since 1984, it has held the world record for efficiency in converting solar energy
http://www.stirlingenergy.com/solar_overview.htmExtensively tested (I remember seeing an article in the mid nineties that the DOD was testing a field-portable, 2-man crewed unit which produced 5KW from a 16ft. array in Popular Mechanics.
It's more efficient than PV, with similar capital costs.
Also, for someone with a shop, easy to make your own:
First, you'd need a paraboloidal 'dish.' This can be easily constructed from fiberglass matting in an (actually caternary curvature, but close enough) by suspensing a hoop from your garage ceiling. Drape some light-weight fiberglass matting over the hoop. Apply your choice of thermoset epoxy evenly (you might want to pre-apply it prior to hanging.) Next, by means of a low-speed drill, spin the hoop continuously while it is curing. This will iron out 'kinks' and defects in the shape.
Next, you'd need to apply a reflective coating of chrome paint to the inside surface; you'd probably want to clearcoat this so it stands up to rain, etcetera.
Affix a stirling engine by means of a rod poking out from the dish such that the hot end of it recieves the concentrated sunlight. Place the cool end facing away from your concentrator and toward the sun--you may want to make a tiny 'sun-hat' to keep direct rays off of it. That will increase the temperature differential and total output.
Now, you can buy Stirling cycle engines commercially on the internet. Just google it. Many can be ordered with integrated generators.
Alternate method: make several one-meter dishes such that their focal point (term used loosely since shape not truely parabaloidal--but close enough) points to a common center where a larger engine/generator is affixed. /Fabricate steel or fiberglass frame arms to hold all this together.
Finally you'd need a sun-tracking system.
Options:
1. You are the sun tracker--totally manual, you reposition 5 times a day.
2. You make 8 or 10 azimuth 'rails' which you manually can change the collector's base to with the changing angle of the sun, and you use a small motor and reduction gear to move in response to an solar intensity signal (simple radio-shack photocell placed in bottom of tube) when voltage drops (from improper alignment with sun) it gives a signal to the motor to move until max voltage is achieved again. (you'll have to make a simple TTL logic board for this)
3. Buy a commercial device for doing this.
Efficiencies are roughly double that of the best PV, so that means around 28%. Not bad, eh?