From: Robert Lynn
> I've also been involved in the development of hydrogen working fluid stirling engines, and while they might look attractive there are big problems: -Very expensive and heavy ($1000/kW, 5-10kg/kW for kinematic engines (ie with crankshaft) That conclusion may be premature and short sighted, given the advantages. The high cost to date for Solar Stirling seems to more of a issue of mass production (lack thereof). Certainly, it can cost 10 to 100 times more to produce engines one-off or low volume now, compared to the typical automotive, robotically enhanced, engine production line. However, I see no ultimate impediment to this for the Stirling concept - once there is demand for millions per year. That kind of demand would be guaranteed if mated to a Ni-H heat source. The Solar 4-95 Stirling engine developed by United Stirling of Sweden, was as an outgrowth of an automotive engine development program - and is expensive due to low volume and the need for exceptional lifetime in operation, far more than any car. But they would not have gotten into it if there was a systemic problem that could not be overcome with higher demand and better engineering. IOW all of the negativity seems to be a short-horizon issue that can be resolved simply by high demand and a few "workarounds." Except for hydrogen seals and the nickel, the cost of a converted ICE should be in the range of standard auto engines (if and when mass production is guaranteed). The easiest solution to the sealing problem (the workaround) is to "live with it" in the sense of providing only the simplest solution - the best O-rings, etc and then to utilize makeup H2 from onboard electrolysis. Only one liter of H2/min (or less) should be adequate for makeup of seal leakage in a 50 kW engine operating as a genset for a Prius style battery pack using standard sealing techniques for hydrogen. That amount of H2 used as a makeup would be parasitic for about 200 watts from the genset and is of no risk as a slow leak, due to the extraordinary mobility of H2. IOW this workaround solution is de minimis in terms of net value of an installed engine which does not demand fossil fuel. Moreover - it sounds like just the kind of objection that the OPEC petro-lobby would dream-up to thwart Stirling development at this critical stage. Jones
