At $.06/kwH you are paying way below national average which is about $.11/kwH. So, I am not sure you are getting it that low really? Some of the taxes are fixed. Some will be based on use as a percent, so as you begin to run that meter backwards those taxes shrink with your net usage which would go to close to zero.
My math says that $120 divided by 750 kwH is at $.16 per kwH. You are stating $.06 and that's $.10 from what I see in your numbers. In a zone 3, with that high an energy cost, you are at 7 years or better in my opinion but depends on your site. My costs are $.11 in a zone 2 and I will just beat 7 years here is what I am on track for.
The big part of the payback you are missing is the equity improvement to the property. Which many have told me is as good as 100%. Better than adding a swimming pool etc. this system makes your home more valuable and MUCH more appealing in a real estate market comparing to homes who have no backup emergency power, no green feature, no cost of ownership savings. This home, with this system is simply worth far more than it was. It makes it's own electricity and in a blackout has 3 additional sources of power, wind. solar, and battery. Electronics are safer because if your utility had a sag, spike, or brownout, the automatic tranfer switching would maintain your power to keep your electronics safe. Your alarm clocks don't even reset, that's how fast our automatic transfer switching is.
So, this system is arguably paid back from time of installation. It's money in your property equity. In a way it's paid back from first day, then delivering profit. Say you spent 10,000 on it, used it 5 years and had to sell the home. The home is worth 10,000 more than it was before and you can get that back. Your ROI (return on investment) was already made the day it got operational. In a tough market, this home, has a major drawing feature that is must see. It has a lower cost of ownership forever compared to other homes.
Even if you ignore that equity, it has a 10 year ROI strictly by energy production. THEN, it has a long life beyong that 10 years as these systems are designed for a minimum 30 year life. It's robust heavy duty hardware with stainless steel parts etc. There's only 2 moving parts in the whole system to limit wear and extend life. So, aside from equity which is 100% payback, there's another 300% ROI ove the next 30 years. That's a 300% return making it a very good investment.
You are in the northeast where coal power is HEAVY. If you don't think power costs are going through the roof I got news for you. That slides the curve dramatically. Your cost will be rising very soon and very sharp. My utility passed annonced a hike for 15% per year for next three years.. componded. That's because of coal plants having to be scrapped and replaced or the government taxes that will be put on dirty power in this part of the country.
So, in summary, if you have the money and you like the ideas of reliable green power, energy independance, emergency power, environmental responsibility, energy security, it's the best system to buy and at a great price. Yes, I would do this grid tie and a whole house three turbine system will carry that home in a zone 3. There is no question this is a sound investment for you. As a dealer you can completely recover your cost with 8 systems. An article in the local paper can get you on your way there. Call me.