I would hope that you have a commercial operation included in your system sizing bc 27 kW is like 4 households worth of juice.

Look for paybacks in the 5 to 10 year range. More than that and your installer is selling you more than you need! You sill not compete with your utility =)

And for Pete's sake: 1) conservation (it's free!) 2) efficiency (as much as 10:1 payback for demand reductions and energy use optimization) 3) go ahead and get a pv array.