The 3 year ROI on solar is based on typical US costs for electricity at ~$0.15/kWh. Friedcat gets ~$0.06/kWh. His solar ROI is too far out to make sense, especially since he's going to need to have a bunch of UPS so he can switch back over to the grid at night without everything going down.
(By the way, the 3 year ROI is really good - something I'd consider for my own home. Can you get me a source for that? Last I'd heard was 9-10 years, with subsidy.)
Cost of solar in China is $500/kW.
His cost is $.06/kWh
So, he needs 8,333 hours for ROI. @ 7 hours a day for sunlight, that's 1190 days, or 3.26 years.
If he buys in bulk, he can get it considerably less than $500/kW, cause those are retail prices, and for a data center, he can get wholesale. If he does a wind/solar hybrid in a suitable location, the ROI will be closer to 2 years.
For buying for your home in the US, this site has a decent cost comparison:
http://www.ecobusinesslinks.com/surveys/free-solar-panel-price-survey/