What factors should one consider in choosing whether to use one central "string" inverter or micro inverters (Enphase or Eneqsys).
Just looking at inverter material costs  for my likely system of 30 ea 230W panels the costs/ watt of the inverters range from
$0.44 for a Solectria 'string' inverter to $0.77 for the Enphase m215s or $1.10 for the Eneqsys.  While there may be occasional performance benefits of the micro-inverters as clouds pass shading part but not all the array over a long term is there a significant gain?   The installation simplicity, frankly, strongly favors the central inverter!  As solar panel prices have come down the significance of the inverter costs has increased as these costs are relatively unchanged.  At this point the string inverter looks like a clear winner, letting me get below $2/watt for the material.  Again, what am I missing? 

Are you planning on installing the system yourself? It sounds like a grid-tie system(?) Are you in the U.S.? If so, the federal credit of 30% might require that the system be professionally installed, but I am not sure about that. Likewise, some of the rebates from states and/or utilities require professional installation. Installed costs for turn-key grid-tie systems can be on the order of $2/watt, and going that route lets you take advantage of all the learning experience that installers have accumlted before your system install. Just a thought.

Lee,
Yes it will be a grid tied system fully compliant with the U.S. National Electric Code. Please answer my questions. Who does the installation is an entirely different topic, they will install whatever one specify s. Rebates and subsidies are not part of my decision process, I most likely will decline them anyway. From simple material cost the micro-inverter offerings are all over $2/watt while many string inverter systems of this size can be under $2/watt. My question is there a reason to choose the more expensive micro-inverter option.

The advantage to using micro inverters is their ability to convert solar energy without waiting for a string voltage to increase to a high enough voltage to trigger a central inverter.They also work well where partial shading may occur.The net results are a higher overall system effiecency.