You talk to various groups in the Solar photovoltaic industry and they say that the $1 per Watt barrier is the measure to beat. Sort of like the 4-minute mile. Everyone is shooting for it. Unfortunately, according to a recent post in Greentech Media... this is way wrong. It depends on what the cost per Watt already is in your particular power grid. If you are in an expensive cost-per-Watt area already, you might not have to reach $1/watt to make your investment in solar photovoltaics worth the effort.
What this barrier also doesn't look at is the rate of inflation. If folks were talking about the purchasing power of the dollar about 15 years ago or even 5 years ago... it has no bearing on what that dollar is worth today. There are also more efficiencies involved... and you must also see how many days of insolation you have in your particular location. You'll get far less solar photovoltaic energy from an Alaskan photovoltaic installation in the winter than you would in Arizona or Hawaii. Of course, you'll get a whole lot more photovoltaic energy from a solar installation in Alaska during the northern hemisphere SUMMER.
For more information on this you can go to the Greentech Post About Cost per Watt Barrier for Photovoltaic Power.