Stirlingengineforum.com

So, there are a couple companies that make Stirling-based free-piston type solar generators (the type with a parabolic mirror focusing the solar heat on the Stirling engine parts). What is the benefit of this approach to solar-electric power generation versus just using PV solar panels?

I know one company managed to get this Stirling-based device on a spacecraft, so I'm quite curious. Smaller size for same output? Greater longevity of service life? Lower expense than PV cells?

Dave

Hi,

Commercially available PV cells (silicone based) are around 20% efficient at turning solar energy into electricity (although I think the maximum achieved is about 40-50% at the moment). Also they cost quite a lot.

If you get it right then you can make a solar concentrator & stirling engine up to 30% efficient at the same thing, and possibly for less money, which is what a few companies (like SES & Infinia) are up to at the moment. However there are a few alternative PV cells which are less efficient, but also far less costly which are being developed at the moment (i.e. First Solar).

If you can make a cheap, very efficient stirling engine and a cheap robust concentrator I still think it would be quite a lot cheaper than solar cells on a mass production scale.

I'm waiting for some one to come up with a paint system for roof paint/PV system, paint the whole roof, it would not need to be highly efficient because of the large area---never say never. Ian S C

You've probably seen it before, but this flexible PV sheet sounds like an intermediate step in the right direction. I think it's about the 6% efficiency mark, but costs 2-4 US dollars per watt of capacity and weighs perhaps 100 lbs/kW capacity, so could probably go on your roof without serious reinforcement.

There's an example sales listing here.

PKM, thats the sort of thing, its going to get that solar hot water, and electricity will be required at least on all new houses, and comercial buildings.
Solar stirling engines I imagine being used in large installations, could North Africa supply the power for most of Europe, with stations right across the Sahara from east to west. Ian S C

Theropod2, I think all means of power generation have got to be used, PV, solar Stirling, wind power and tidal generation. I don't think its a good idea to grow crops to make fuel to generate electricity, or make automotive fuel. Maybe a new generation of nuclear generators will help, maybe small ones running stirling engines could supply towns, or parts of cities, eliminating transmission wires to a great extent. Ian S C

"Can any of us claim to be able to produce an engine that will run every day for 25 years?"

Not without maintenance / oil changes / replacing seals...

I think if you were careful though you could get away with only basic maintenance once a year or so, and replacing parts every 10 years or more. Similar to car maintenance really. It will all come down to economics - if it is cheaper (£ or $ per kwh) to produce electricity using more efficient solar concentrating systems which require you spending some of your profit on maintenance, than a larger, less efficient, but cheaper system which requires no maintenance.

On another note though, would having more people employed (i.e. maintaining kit) make a system more attractive (i.e. politicians like more jobs...)?

Also, who got one on a spacecraft?? Stirling engines are usually quite weighty aren't they...?

NASA, the Voyager space craft that left earth about 30 years ago, they have a nuclear heat source, thats still got 100 years or so of life, I heard a n interveiw with a NASA scientist a few months ago, they are still in contact, the time for the radio signals is in hours- or it may be days now. The motor I think is a free piston, pressurised engine, and only a few (can't remember how many) watts. Ian S C

Sorry Theropod, my mistake, there are stirling engines out there some were, must look it up. Thats pretty good out put for a thermocouple power supply. ian S C

One of the major advantages of a Stirling-based solar generator (as opposed to a PV approach) is that it is technologically much more primitive.

In order to replace an aged, dying PV panel one has to either have access to a huge chain of chemical and industrial processes, beginning with silicon/germanium semiconductor wafer synthesis, or access to a developed market.
In order to replace a Stirling, all you need is a lathe, a mill, some steel lying around and a good machinist. You don't even need to replace it completely, it will last forever with proper maintenance (replacing worn-out components, ensuring proper lubrication, ...).

This is an important factor in areas where access to high-tech goods is restricted or economically nonviable (3rd world) or perhaps for those of us who would like to have power available after the civilization crumbles and PV factories shut down.