Solar furnace mirror - photo

[Altair]

Construction of the 35 ft (10.7m) mirror at the Mont-Louis Solar Furnace in France. The mirror concentrates solar rays to produce temperatures between 2000°C and 3500°C.




Previously:

Helios solar plane - photo
Solar panel washing tool - GIF

[Philip Davies]

Now here’s a challenge: who can come up with a design for a solar forge, for the back yard? How big would it have to be?

[DIYSwede]

-Not jumping on your challenge bandwagon, Philip, I'm merely doing this as an armchair design exercise:

Seems like some guys in Missoula, MT (47 deg latitude) made a "forge" which just about fixed to melt lead:

GreenPowerScience made a biggie (44 x 34"?) fresnel lens (with a clever and simple tracker) foundry achieving 2100 deg C
(albeit with only a narrow focal point good enuff to melt small drill rods):

To grow your own casting foundry, I guess you'll have to:
1) Get a good and big enough black clay crucible.
2) Devise some insulating firebrick foundry to keep the heat within, and an opening towards the lens.
3) Check for available sun power at your area (Pics below), and get the appropriate lens area from your desired total power input.
4) Smack a simple suntracker together, and perhaps a slow-rev turntable under the crucible?
5) Wait for a cloud- and windfree day, fire up and iron out the shortcomings from the contraption.



A personal guesstimate would be some 4 kW input (>4 sq m lens where I live, at 60 deg latitude,
so I'd need 4 of the GPS's lenses above and 1356 bucks for them to even get started),
and putting the crucible off-focus a bit, run and track for at least 1 hour for an app 2-3 kg Al melt.

Guess I'll continue with charcoal bricks till my 4 kW electrical oven is finished...


Just my 2 cents
Johan

[Philip Davies]

Johan!
Delighted with your response to the challenge, glad that you were intrigued!
Archimedes is alleged to have defended Syracuse by solar power, setting ships ablaze, with solar reflectors, I read once.
Hats off to the GreenPower scientists: it’s a greater challenge than I thought.

[DIYSwede]

Way back, when I was still "young and promising" in the theatre & movie lighting business,
we cobbled together a round 2 m diameter parabolic reflector with app 450 mm focal length:
Styro convex plug, GF & polyester resin, clad with oven foil. 5 kW filament supported by 3x 10 mm all-thread.
A butchered stainless steel soup ladle sorta worked as a front reflector, minimizing stray light.
That ladle eventually got blue from the heat/ radiation.

Still remember using it in a cathedral from the organ loft, 40 m throw length up the aisle,
2 m dia for the beam at target. The 5 kW dimmer weighed 30 kg, hauled up a spiral staircase...
Put it for a 120 sec fade-up "when God's finger would point out the main character".
After a minute most of the audience had turned their heads towards the source in wonder, totally breaking the intended illusion.
Ah well, sometimes all your ambitions and talents makes you overshoot, don't they?

Found it in storage a few years back, pulled it out in the yard on a cloudy March day ,
propped it up somewhat in the general direction and tried to find the focal point with a 2 x 4 pine offcut.
Instant smoke, and full flame after 3 secs when I found it... (in spite of the low angle sun and cloudy sky)

A buddy of mine later took it to his summer cottage, tore the foil out and buried it as a king size bird pool...

-Guess that didn't answer anybody's question - just a bit of freewheeling memories!

[Philip Davies]

Well, of course the pious congregation would seek the source! They’re not there for illusions!

[hemmjo]

When I was teaching we made a 48” diameter parabolic dish using fiberglass and epoxy resin. Covered it with strips of chrome Mylar. As Swede mentioned, it would ignite a 2x4 in mere seconds. I very seldom used it as the light at the focal point was was bright as welding.

It sure did impress the kids who made it!!