By about 28 percent in the past decade, and it continues to drop. But installing solar panels on your roof is still prohibitively expensive without big tax breaks by state and federal governments.
Right now, the only cost-effective use of solar on the home (without the tax breaks) is to install a solar water heater. It'll pay for itself within five years, and then you'll be getting your hot water (which is a huge part of your utilities) for free.
