I checked out that linky.
They went about it the hardway!
Take a copper sheet, heat the back with a propane torch till the front has the black oxide. I did not heat as much as they say and mine did not flake off easy. I had to use some steel wool or wet dry sand paper to get the black oxides off (been a year or 2, forgot a few details), don't remove the red oxide, that's what you need!
Once you have the black off and only copper back and red oxide front your done. Connect a lead to the back copper and touch the other lead to the front red oxide and in the sun or under a 100watt bulb you have power. No need for the salt water or other sheet of copper.
I don't remember how much power it was, not much, probably as much as they got I would geuss. Now if you add some kind of grid to the front of the cell you just made you will get more power also. Something like maybe aluminum window screen, it spreads out the area your picking up the power from on the front side, not just where the lead touches.
Problem is the grid then covers that area so that it is also shaded. Not sure how well screen worked, I think I lightly sanded it and can't remember how I mounted it now either. I might have laid the copper cell on flat glass, screen on cell, glass over screen, kinda a gentle press fit to hold it together?
I may try this again after reading that link. I decided it was to hard to get the black oxides off and other reasons I didn't mess with it much. I did a couple and they worked
Looking at the pics they had on that link, I did not heat the copper enough to form a thick enough black oxide probably. Mine certainly did not "JUMP OFF" as it cooled, it took a little work to get it off.
I have some copper sheet bands here from an industrial welder I found at a scarp yard once. I should have got the whole welder, but then I only wanted the copper bands.
If only I knew then what I would be doing now and things I would want for various projects! Oh well, at least I have the copper bands
If I can find them I might give this another try, been thinking about it anyway, and now seeing the link saying the black oxide should jump off makes me want to try that again.