Wall Street Journal: The solar industry has been struggling this year against weak demand, ample supply and sliding prices. Which means that for anyone thinking about putting solar panels on their roof, there probably hasn’t been a better time. All along the supply chain, prices have been falling, and could fall further still. Silicon, a main ingredient in most panels, has been selling for as little as half what it went for a year ago, while some panels and installed systems can be had for 25% less, …