JTR,
Here is a link that I used in my "How to sell solar power/EV" thread.
It seemed to track pretty closely to other sources when I used it last year to look at costs and such.
Clean Power Estimator for California
Googled, and found one for New York (same software?, different cities?):
Clean Power Estimator for New York State
By the way, I had to use IE to make them work (Firefox did not--but I did not take much time for figure out why).
JTR, for NYC, assuming 1,500 kWh/month (18,000 kWh/year) facing south, with a pitched roof, I believe that you will need a 14.5 kWh system to generate 18,111 kWh per year.
The default estimated price is $9,000 per kWh installed (pretty close to the bid I received) would give you a raw cost of $130,500 before rebates, $90,500 after rebates.
I guess, that this is, roughly an (84 to) 87 solar panel system using BP 4175 (currently BP's best performance panel?) at 62.8"x31.1" (14.2 sq ft) and 166 watt minimum power (175 W max power). You will need approximately 1,235 sq ft of roof space for these panels.
Your numbers will vary--but I think that this will give you a good starting point. I think my numbers are within 5%--but they could be out by 10-20%. Also, these numbers were based on a south facing roof at an optimum pitch of 8/12 (colonial style 2 story house). Anything different will reduce your power output.
Please let me know what you numbers you end up with (I don't know your power rates--so I could not really look at payback). If I did the numbers correctly, you are looking at $0.17 per kWh assuming a 30 year life and no maintenance costs (18,000 kWh per year, $90,500 installed system costs after rebates).
-"I am not a solar estimator" Bill
PS: If you are running a business out of your home, you may qualify for a 10-15% Federal tax rebate (based on % of solar power needed to run business???) and a 5 year depreciation schedule.
Also, there are "Green Tag Revenues"—which may include things like Star Bucks paying you $0.20 per installed kW system capacity per year. -BB