Slam Valve Motor, supplying efficient steam engines for homeowners and professional solar installers
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              Commercially available solar collectors for steam, for those who do not want to build their own
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image of vaillant evacuated tube collector Vaillant evacuated tube hot water heater.  Mass produced, commercially available.  The 12 tube unit costs about $1200, can be picked up in San Diego, and according to the spreadsheet tool that the applications engineer gave us, its good for 700 watts of heat at 175 degrees C at 800 watts/square meter solar flux.  This is enough to produce 1 horsepower of mechanical energy at 20% duty cycle for most of the day from a 266 cc steam motor.  The collector consists of 12 evacuated tubes with stainless steel plumbing to receive the heat.  Behind the tubes, there is a low gain fixed curved reflector which increases the stagnation temperature by increasing the solar flux on the tubes.  No moving parts.  No heat pipes are used, water feeds directly through the evacuated tubes.  One disadvantage, the tubes are connected with 6 pairs in parallel.  This means one needs to circulate several times more water through the system than can be converted to steam.  This implies a water pump, but we at slamvalvemotor.com are working on lower cost a pump-less solution to turn the water heater into a steam generator.  This design will likely produce only saturated steam, oil separation and drying will need to be a separate system.

chromasun collectorhttp://www.chromasun.com   This company is developing a high gain tilt able Fresnel reflector. The unit is a flat glass enclosed box containing two black chrome plated stainless steel tubes and an array of tilting mirrors.  The company is targeting $3000 per unit, availability some time in 2010 according to their rep.  The unit puts out up to 220 deg C, up to 1.9 kwatts per unit at 850 watts/square meter insolation according to their data sheet.  The series tube mechanism means it can be configured as a flash boiler.  The flash boiler configuration is most useful for a continuous running operation, like a pump or generator that would feed on fuel when sunlight is not available.  The flash boiler (the mechanism used in refrigeration systems) will automatically dry the oil out by slightly super heating the steam, so the oil system consists of just feeding emulsion into the water pump.  The higher operating temperature yields higher power density and higher efficiency.

patriot reflectorPatroit solar group is a branch of an antenna manufacturer, producing products to break into the solar thermal market.  The products are converted satellite dish technology in various sizes, sold with and without actuators and frames.  At the low end, the offer a dish for $1000 with a free standing frame.  The challenge is to make a collector to go with this without breaking the bank.  The system would need a controller computer to actuate the dish, the collector itself, and flexible tubing system to bring heat back to the steam system.  Flexible high pressure tubing that can flex thousands of times appears to be a difficult technology.

sopogys solar collectorSopogy is a Hawaiian company which makes solar thermal systems.  The company targets medium sized jobs, they want to see upwards of a million dollars per job.  Generally they do large array jobs based on steam turbines.  However each solar collector is properly sized for a residential collector.  The reflectors themselves move, the plumbing is rigid.  Sopogy does do smaller jobs if they can be linked together, for example they do cooling systems for bank branches.  The individual banks are small jobs, but the contract for doing dozens of banks is the right size for them.  Sopogy does not sell an individual collector, and the systems use circulating thermal fluid meaning that the collector itself does not take pressure.