Heat Energy Storage Company Azelio goes bust.
Their molten aluminium & Stirling engine technology has not been a success.
I hope the ones to buy it are able to take it to market, 90% efficiency should have been interesting enough, but its a tough market space.
Azelio were pioneering on too many fronts. Nobody AFAIK has ever built a really big Stirling engine that has operated for any length of time. From memory the EU invested millions into building a 3kW one for Africa over a decade ago, but it never went past the prototype stage. They then went on to fund a more advanced system for long-mission spaceflight but I am not sure if that got off the ground. The EU advanced project was to build a Stirling engine powered by heat from radio-isotopes and there was alo a similar NASA one. Looking at their projects btw, overall efficiency seems to be the usual 30%
http://anstd.ans.org/wp-content/uploads/2015/07/1010.pdf (NASA)
https://cryocooler.org/resources/Documents/C20/387.pdf (EU)
I think both these projects are currently in stasis, but if anyone knows better, please tell.
Nobody AFAIK has ever built a really big Stirling engine that has operated for any length of time.
It depends what you mean by "really big". The 100HP Stirling generators on the Swedish Gotland Class submarines are not exactly small, and have been in service for a long time.
The smaller Microgen 1kw engines also have long service lives - with no maintenance.
The small Strontium-90 powered Harwell Thermo-Mechanical Generator (TMG) ran for something like 20 years.
The problem is that people tend to over-sell Stirling engines, as if they are some kind of magical panacea - and (annoyingly) they often get proposed for use in situations where other technologies would be cheaper.
BTW, the 90% efficiency figure is nothing to do with the engine - it includes the use of stored energy for heating purposes. It is similar to the way efficiency is quoted for IC engine-based CHP units - where the waste heat is used for warming a building.
Personally, I still think the use of molten aluminium as a thermal store is quite a sound one. Melting and freezing pure metals doesn't have the same separation & settling problems that affect the molten salt phase-change thermal stores. One problem though is that the particular Stirling engine design that they chose, in order to also get a large-ish amount of electrical output, is rather expensive to build. It makes the overall system too pricey for their target markets.
Meanwhile...
This company in the US has a contract to develop a radioisotope (Am-241) Stirling cycle generator for lunar use.
Those of you old enough to remember the old SNAP-27 units, used on the Apollo moon landings, will know about thermo-electric generators using heat from Pu decay. This is essentially a development of the same idea - but using a Stirling engine rather than a thermopile.
