SolarCity PPA vs outright purchase

Hello Friends,
I am located in Maryland, USA and reached out to Solar City a few days ago get a quote.

My current utility charge is $0.129 kWh


Here is their latest quote.

System: 6kW DC (5.27 kW AC)
Annual production: 7052 kWh

PPA: $0.106 per kWh (2.9% annual increase)
PPA: $0.131 per kWh (fixed)
PPA: $0.067 per kWh (based on one-time payment of $9,030)


A friend of mine paid $6,321 for 5.59kW DC system in October, 2011.

I am surprised that the rates have gone up. Is anyone noticing a similar trend?


If do an outright purchase,
System: 6.24 kW DC (5.99 kW AC) [I think it will be 5.48kW AC]
PV Panels: 24 x SolarWorld, Model: SW260 Mono Black
Inverters: 24 x Enphase Energy, Model: M215-60-240-S2x

Contract Amount: $23,450 ($3.76 per watt DC)
Less:
Clean Energy Grant Program - Residential Solar PV
Federal Tax Credit
Net Installed Price per Watt: $2.47 per watt DC ($2.57 per watt AC) [I think it will be $2.81 per watt AC]

Presuming annual production of 7,300 kWh for next 20 years, the price works out to be $0.11 per kWh.

So as per my current calculation, even if I discount SRECs, going with Solar City PPA of one time payment will save me money.


Am I calculating correct?