Let's see, there are at least two photovoltaic manufacturers in Colorado that promise $1.00/watt thin film PV panels "soon". If you add maybe $4.00/watt for installation, and subtract the rebates, which are at least $4.50/watt, it means your PV investment will be almost free, and it wipes out your electricity bill of $50-$150/month.
By any measure, this is a good investment. Think about it for a minute, and you'll conclude that your new zero energy home should be ALL ELECTRIC. It goes against today's conventional wisdom, but things are changing fast. The reason is simply that there is currently no method for a residential building to make natural gas and put it "back on the grid". In the summer, you'll have excess electricity production, but Xcel pays you retail for it. You can't do that with solar thermal either.
It can also be shown that Zero Energy homes with no solar thermal or natural gas appliances are simpler and cheaper to construct, so it's win-win all around.