Only the "Put into Service" year counts for claiming a credit, I believe.
But, it is possible, I think, that the expenses can be in 2010 and/or 2011 and claim the 2011 credit on the combined expenses if the Put-in-Service date is in 2011.
At least, the PV tax credit worked that way.
See SOC/GID-Meter and CAN-Do Info
2011 LEAF, sold in 2015
2010 Prius, 2014 silver Tesla S
Nissan EVSE, mod to 240/120v 16A
Solar PV: 33 x 225W -> 7 kW max AC
To Sell: X-treme 5000Li EV motorcycle