Without warning, the C: drive of my main computer quit a couple of days ago. I was able to keep working on a backup machine which is physi...

Video from rimstar.org about Fresnel lenses. He discusses the question of which side of the lens should face the sun. From about 2:20 to ...

I have been watching the progress of сергей юрко on YouTube with his very interesting solar trough project. сергей юрко is Sergey Brisk...