More solar hot water powered heat engine ideas  I have been working on solar powered hot water engine ideas for some time now.  I keep trying to simplify the designs and I think I have come up with a good one this time.  The operating fluid is a small amount of propane or butane inside a sealed cylinder that the power pistons operate in. This system works a lot like a stirling system would do but uses valves to switch between the hot and cold water for each piston as shown in the pic.       The first two pics show the system using external pumps for water flow and the third shows the pumps built into the motor itself. Click pics for larger versions.   The 3rd system has it’s pumps built right into the design.      The 4th one is the lastest version that can used with any of the output drive systems shown.  This engine is capable of high output pressure from the water pump or air compressor outputs shown.  The rotary drive is easily capable of over 100 lbs torque and approximately 25 rpm or faster.  The 5th picture is just the motor by itself. The center drive section of this one has a different setup from the previous motor so as to allow the gears to be obtained from a standard source without having to modifiy any of them.  The sixth picture is a slightly simplified version of the one above so that off the shelf parts could be used.  It also uses electric solenoid valves instead of a mechanical link. This allows the timing of the engine to be adjusted to best operation. At the bottom of the picture is the math showing what the engine should be capable of with enough flow on the hot and the cold water supply sources. The seventh picture show a standard mechanical link using off the shelf air pistons. This will work fine untill the propane slowly leaks from the pistons. It would have to be recharged on a regular basis. Number eight here is alot like the third and fourth ones above but uses a different plumbing setup to recycle part of the heat from the warm water back into the system to increase efficiency.