Possible DIY Sterling dish?

[rcavictim]

This beautiful, fully transportable C-band earth station antenna followed me home last year.  If I cover the petal panels with aluminized mylar reflective surface and put a 15 kW Sterling generator receiver in the prime focus I could have a sweet solar power system with commercial level capabilities.  The 7.6m dish (25 foot diameter) has about 44 square meters of collection area.

[rcavictim]

Yeah, the strangest things can follow you home if you bat your eyelids at them or feed them or pet them

Jens

Well I didn't try to pet the animal that regularly feeds from this dish!  

Now that pictures are working again I have attached two more of the disassembly operation early last November.  This package is one slick piece of engineering.  The 24 dish petals and 24 radial trusses all stow neatly in prepared storage racks.  The insulated, heated and air conditioned equipment room has two 19" rack cabinets for the broadcasting electronics.  This package could be delivered to a remote site for a special communications event and in three days at the hands of a small trained crew be all ready to go.  Precious few transportable satellite antennas of this large size were ever built. 

I obtained it with the intention of using it as a teaching radio telescope but with the way things are going it might become the center of a far less cerebral excersise and one of more urgent practicality.

[mike90045]

Wow - that will beat the pants off the Solar Death Ray 3000, at only 12'
Hot Dogs in 5 seconds.  And because the film is cold, the fat/juices mop right up off the mylar



http://www.hoodville.org/v/sdr2007/DSCF4923.JPG.html

[rcavictim]

Well I'd sure hope so!  BTW, I thought Jimi Hendrix was dead.

Here is a pic of a commercial Sterling dish equivalent to a 30 foot dish.  Makes 25 kW. Sterling Energy Systems out of California. Their 4-cylinder engine is complicated and expensive to build.  Five of these in the photo have been under evaluation at Sandia National Labs in NM.

I believe this form of C.S.P. is in our future in large scale if photovoltaic does not catch up.  Somebody needs to simplify the heat engine/generator module.

[Curbie]

Link to an engineering student's who re-designed 12' satellite dish and a "Reliable Steam
Engines" turbine for low RPM intermittent electricity generation on a very small scale.
http://etd.lib.fsu.edu/theses_1/available/etd-01052007-181917/unrestricted/Newton_Manuscript.pdf

I point this out for several reason, 1) the crux and approach of the idea is pretty similar, 2) the solar math in the manuscript is sound and may be helpful, and 3) he also started with aluminized mylar and in his conclusions recommends finding something else.

MIRROR FILM:
ReflecTech®
http://www.reflectechsolar.com/
It was developed by National Renewable Energy Laboratory (NREL) specifically for this use, it's expensive but if you're even thinking about a Stirling, the cost of mirror film is the least of your worries.

STIRLING ENGINE:
In my view this is your tallest hurdle, the DIY engineering is not that bad, but material selection to withstand the temperatures, pressures, and fiction involve leads to exotic and expensive materials. This is the same reason mass produced commercial offerings are rare, the only one I know of is WhisperGen:
http://www.whispergen.com/

1 kw @ ~$4000, I bring the WhisperGen up to relation to cost of 15 kw commercial, custom, or DIY unit.

STRESS ISSUES:
With a 25' diameter dish you basically have a ~500Ft^2 sail, wind loading can produce some large stresses which cause optical error that reduces performance, also consider that you're not hanging a 1 pound satellite receiver at the focal point, (what the dish was designed for) you're hanging a much heaver spinning engine there.

My advise would be to clear the Stirling engine hurdle to get an estimation of it's weight so you can clear the stress issues hurdle, if it was me, I would do these estimations mathematically to see if you can get this idea to produce a viable return on investment.

Good luck,

Curbie

[rcavictim]

Curbie,

Thank you for your comments and suggestions.

When I said "aluminized mylar" I was not actually specifying that product specifically.  I was aware of the improved surface you mentioned.  The high performance reflective surface you mentioned would be essential IMO.

The dish when used at 7.5cm wavelength has to maintain it's surface in winds to within 7.5mm of a true paraboloid (i.e. + or - 3.25mm).  This very high accuracy spec is inherent in this design.  Specs for solar collectors are very much relaxed from this because, and this is key, coherent light is not required, just concentrated photons, phase be damned. In addition, just like a solar collector, the microwave dish has to maintain precise pointing within a fraction of a degree in high winds or the signal will be lost. The quality of concentrated optical solar spot from one of these telecom dishes is actually of very high quality and quite small.  I have used a simple technique to establish this. I boresight the dish on the sun and have a running garden hose with which to constantly wet the surface of the dish to make it a better optical reflector.  I hold a target card in the focal point and move it in and out of the focal plane.  Wear welding goggles!  The concentrated spot on my Andrew 4.5m (15 foot) dish is about 2-3" in size.

Your point about the extra strength frame to hold the Sterling head in proper position is spot on, no pun intended.  Yes, that would be an issue to work out.

Yes a Sterling generator head of 15 kW size will be expensive.  A transportable solar collector of this size would also be very expensive, possibly $100k.  Half that if not transportable.  A telecom dish like this cost easily $500k in 1980 dollars because it has to be phase additive.  Shame to use such an expensive reflector where the accuracy is not required.  Outfitting this dish as a state of the art radio telescope costs significantly more than the cost of a commercial 15 kW Sterling generator.  The ultra low noise cryogenically cooled HEMT receiver head alone costs $500k, custom built to order in the US.  During my tenure with the National Research Council I manufactured one from 'spare parts' and now have it in my arsenal.  I'm actually all set equipment wise to make a very nice radio telescope because that is one of the things I do. It was the reason I pulled out all the stops to acquire this extremely rare antenna when opportunity knocked. The point of my post was that with this hardware the opportunity exists to do something else which pays better than radio astronomy in hard times.  The payback is immediately useable and recognizable as of value to any neurotypical.

With my wind turbine in operation I may not need to venture into another challenging renewable energy project for self purposes, but I believe that it is interesting to think about such ideas.  This forum is all about ideas.  If some actually make it to fruition that is even better!

[cognos]

It is unlikely that most could afford to purchase a 3 KW setup, even though the manufacturer advertises the pricing as "comparable" to PV setups of similar capacity. I'll believe that when I see it...

In all my "research" into free piston stirling engines that power linear alternators, I find very little information regarding pricing or specs for the smaller FPSE/alternators. They seem to be mostly produced for extremely specialized uses.
Most of the sites have lots of information about what they produce, or plan to produce, but one needs to contact them for more information. Several have more information for potential investors than for someone who actually wants to use one of their products... that makes me suspicious...

I can't see DIY'ing one of the power units if the engine/alternator is already commercially available. What I can see DIY'ing is mating a purchased power unit to a DIY collector/tracker/cooler unit in a home-use cogen sysytem.

The 30% efficiency is nice, the low maintenance on the power unit is great.

I could see one of the 35 watt units mated to a "pizza dish" satellite dish for a proof-of-concept project to charge batteries at the cottage, ferinstance...

[rcavictim]

Cognos said...
"I can't see DIY'ing one of the power units if the engine/alternator is already commercially available. What I can see DIY'ing is mating a purchased power unit to a DIY collector/tracker/cooler unit in a home-use cogen system."

I totally agree with you.  I like to DIY as a method of obtaining stuff I cannot afford to purchase but there are areas where I draw the line.  Making a suitable Sterling generator head is approaching one of those areas.

I recently learned about Infinia Corp and a sweet, very very nicely engineered Sterling dish system they are gearing up to make in mass production.  They claim 3 kW system for $15k.  This is very easily within reach for many.  People spend a lot more than that on their automobiles.

The engine is a single cylinder linear resonant design.  I am totally impressed with what I saw on the website.  Even Paul Allen, co-founder of Microsoft has a big stake in this venture.  I believe they have hit on a winning formula!  Check it out here.

http://www.infiniacorp.com/infinia-solar-system.html

BTW, it is interesting to note that the cryogenic refrigerator in my expensive receiver front end is a small single cylinder Sterling engine using compressed, lab grade pure helium gas.  You cannot use 'balloon grade' helium because the contaminants freeze out as debris near absolute zero and clog up the machine.

[cognos]

Yes. That Infinia 3KW system looks very well designed. If the pricing is competitive, I'd like to see solar fields full of these 30% efficient units, as compared to 14-15% efficient solar PV cells. The waste heat could be used for many things.

I was looking at the Sunpower engine, they have an extensive line, from 35 watts up to 7.5 KW. But they are apparently available only to the aerospace industry, and may be powered by plutonium - or maybe diesel or biomass, they're kinda vague on that...

I let my plutonium license expire, so that's out.

With so few moving parts, I think with modern manufacturing techniques these things should be cheap, cheap, cheap... I mean, you see titanium components in cars these days... that stuff poses some challenges... I don't see too much exotica in a sealed FPSE...

[Curbie]

I'd like to see solar fields full of these 30% efficient units, as compared to 14-15% efficient solar PV cells.

I think the issue is fiction wear on exotic materials and the resulting maintenance, say what you will about corporate America, but they're generally pretty good at bean counting. Maintenance was also the basic problem for steam concentrating dishes in the 80's. I think that's why most current commercial endeavors are solar steam via troughs or heliostat arrays.

Good to see you still lurking around.

Curbie

[Curbie]

I recently learned about Infinia Corp and a sweet, very very nicely engineered Sterling dish system they are gearing up to make in mass production.  They claim 3 kW system for $15k.

It looks like a nice design, NASA used a free piston linear resonant design for one of there projects.

Curbie

[rcavictim]

Just to be clear.  There is NO WAY that I would go to any system using steam.  Much too potentially dangerous IMO.  Pressures can flash beyond material strengths here in mere seconds.  Flying, hot metal parts can kill.

[cognos]

I've no fear of steam systems, but I have a healthy respect...

I've seen a solar concentrator using a big-ass (2 metre square, easy) fresnel lens generate steam that powered a tiny - probably less than 1 HP, was only 12" in diameter or so - steam turbine at 125 psi inlet.

This was a commercial Coppus turbine, which drove a small condensate re-injection pump that put the condensed steam back into the boiler system - for a neat closed system. Closed - except for makeup water due to leaking packings, etc.. and the whole steam system was over-designed with appropriate relief valves on the whole system. Plus, it was fully manual - you had to watch the pressures and water levels, and make the adjustments on the fly... truly not a candidate for even brief periods of unattended running. And there's no way to truly safely automate a system like this in any kind of reasonable budget. And it was filled with treated, de-ionized water.

The "boiler" and associated vessels were made out of welded schedule 80 pipe, and was a professionally designed and certified pressure vessel.

This was built by a millwright hobbyist I knew. Just for fun.

But ya, DIY steam, in the wrong hands, I'm sure can be pretty hazardous. That's why these FPSE systems are so interesting to me - no half-baked user-modifications to the moving parts are possible.

[Ronmar]

Just to be clear.  There is NO WAY that I would go to any system using steam.  Much too potentially dangerous IMO.  Pressures can flash beyond material strengths here in mere seconds.  Flying, hot metal parts can kill.

I think you will find that you can get the same hot flying metal parts with the energy avaialble if applied to a failing/failed stirling engine...  KW from torque/linear force, still requires the same forces, and pressure differentials to develop those forces.  The problem with stirling and DIY is the complexity of the build.  Steam is relatively simple when compared to stirling.

The technology to mitigate steam system overpressure situations is however well proven and reliable...  I have a 3 meter dish I am planning on getting heat from.  I have toyed with the idea of incorporating a steam engine into the mix.  The beauty of steam is that after I have used it to create horsepower, I can still reclaim a lot of heat from it...

Here is an interesting link.  http://www.greensteamengine.com/

Good luck, that is a monster of a dish.  Why don't things like that ever follow me home:)

[mobile_bob]

i too have been following the Green engine for some time, it is a fascinating little machine isn't it?

as for steam power, that is something i would really like to explore at somepoint down the road.

i am wanting to build up a large diameter vein type motor, much like an airmotor but run it on steam
and of course at a more reasonable rpm range.

with access to a laser cutter it would be easy for me to get the rotor, and body cut, along with endplates
and then mill the vein slots and fit them with brass veins or some other material that would hold up to the heat
and high temperature.

i would really like to build up one that is about 6-8" diameter rotor that uses a large frame alternator shaft
as the motor shaft in lieu of the normal pulley. make it direct drive and run it at about 4-5krpm, although i got
to do the math to see if the vein speed in ft/min would be to high for brass.

i just can't imagine a cooler sounding genset

even if it was only a batch fired system, it would be useful as a battery charger.

bob g