When will residential customers be able to buy solar for money reasons? The cost now is dear and ROI on a typical install could easily be a couple of decades. I am wondering if the cash for caulkers, with its 50% government match, may be reason for some people to at least consider things like solar water heaters.
Depends on the state. In La ROI's can be as low as 5-7 years using current electric costs and electricity is pretty darn cheap here right now.
One of the biggest hurdles in getting prices to continue to drop is streamlining the paperwork for incentives, rebates, utility interconnection etc... Once that happens you can realistically start talking about plug and play DIY solar kits that would cut the labor costs out.
Panel prices will continue to drop but labor and paperwork/inspections will still remain relatively constant. New racking systems that integrate other balance of system components, such as conduits, will help drive labor costs down even more but we are coming close to hitting a plateau on the labor side.
New MPPT (Maximum Power Point Trackers) are starting to gain traction as well. They help maximize the output of your solar system and are especially helpful in systems that for whatever reasons the panels are not installed uniformly (a few panels are on a different roof slope for example). Again, this is a great solution for a DIY installers were the home owner doesn't have the knowledge to properly layout the system to maximize production.
Big picture wise, none of this really matters unless we have a grid that can properly rely on the power being generated. As it is today we could put solar on half the homes in the country and we would still have to keep the same amount of conventional power generation online.