Choose Central or String inverter for 1MW SPV power plant

I'm designing a 1MW SPV power plant (Utility Scale). I get confused over choosing inverter. I divided 1MW ito 4x250KWp array for which I've selected 4 Central inverters rated @ 250KW nominal power.
Is the selection is correct or should i Consider string inverters for the 1MW SPV plant? For string inverters, I chose 20KWp arrays with 20KW(AC nominal output) Inverters.

By any means, String Inverters are more efficient and down time is minimal due to its distributed generation architecture. Central System over throws String inverter only by economics (of Inverter to Inverters alone). The other costs like Combiners with Communication / Cable (of high size to minimize DC losses from SPV Strings) may be looked into. In the long run, String inverter will be more economical. (see string inverter vs. central inverter)

I have design the system using 4 central inverters having o/p power of 250 kW but in the due course of time as the project got executed it was found out that string inverters are more efficient than central inverters.

String inverters are more recommendable to your project. It is a matter of long term investment versus short term solution... Also I would like to mention, that we have supplied inverters for this kind on installation and we always advice to go string inverter.