ice lense experiments?

Another jawdropper from the Designers Manual, make a huge lense out of ice to focus sun's rays onto a point for heating.  Has anyone tried this? can it really extend the growing season? how do you keep it aimed in the right direction? what is this even intended for? if static, it would only get sun through it for a few minutes and maybe heat something up pretty hot.  Maybe that hot thing then stores the heat for a while?  

One of those things Bill Mollison just tossed in there but didn't elaborate on, leaving hundreds of questions for future exploreres.

https://www.youtube.com/watch?v=1K4nbDjduqU

youtuber made a lense (without a mold, so, the hard way, not sure why, they just said they were trying to make a lense).  Proof of concept in general.

and this one started a fire:

https://www.youtube.com/watch?v=Nt3c8hjDnKk

again, why not use a mould??  I think a frisbee would work fine.  A hot water bottle.  Maybe one of those umbrella holder things for patio tables, there's got to be something easily and widely available that could be used.

From the diagram in the Manual it's hard to tell if it's a round lense or a long straight one, maybe, that would sort of catch rays for longer than a round one, but the focal point would then need to be a curved set of points along the ground.

https://www.pbs.org/weta/roughscience/series3/ice/icelens.html

some more tricks for shaping one.

None of these attempts to be as large as what it looks like Mollison is describing here.

Green Power Science made a water lens, using a clear tarp.
This  reminds me of planting a tree in the bottom of a  wide depression, lined with rocks, in order to concentrate the rain and dew in one place.
A big insulated form could be used to make giant ice lenses.
Those lenses could  be set up  to concentrate sunlight onto a cairn next to a tree or in a pond.
As the sun moved, it would focus through each in turn.
There is no net gain in energy, but the energy from a wide area would be focused into a smaller one.

Yes, quite possible. The quality of the lens depends on the quality of the ice (impurities, bubbles, etc.).

But ice changes, morphs and degrades under sunlight, even in extreme cold. The IR will do its work. So, I don't see an ice lens as a tool that can be sustained for long.