I dont think the tech is their either...yet.

Looking at us.sunpowercorp.com, their 17sq-ft photovoltaic panel makes 320w at maximum efficiency (daytime sunlight, clean etc...),

320w is like 1 desktop PC...without the monitor or printer.

To power a commercial building, we are looking at 10 or 20,000w, (including HVAC - this number may be off as I dont design a lot of commercial buildings) - so you'd need 1062 sq-ft of solar panel.
Okay, I can find a 100x10' stripe on the roof - we got that.
cost is around 1$ per watt for panels and 1$/watt of inverter. Not sure about batteries, but you are already looking at a $40k cost adder to the building (minus .gov incentives?) without a storage battery solution (without batteries- you only get power when the sun is shining. Batteries add complexity, maintenance (battery acid for cheaper batteries), risk (short circuit?) and take up real estate- they require their own battery room)
Also look at longer-term costs- PV panels are less resistant to Hail damage (though they are rated for such...) and batteries must be replaced every 4 to 10 years depending on how efficient you want them to run.

Its not impossible, but the money just isnt there. Even if they 'pay for themselves' in the long run (utilities are required to pay you for power you make, but not at an advantageous rate...) the upfront cost is just too much right now (without serious subsidies)

-John (not an Electrical engineer =) but I did stay at a Holiday Inn express last night =)

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