About $16K gross will get you a simple 6.4 kW (20 modules) grid tied roof mounted array. If your roof has a good exposure (170-220 azimuth, 8/12 pitch, and solid sun from 9-4) you will get about 8,000 kWh per year of solar harvest. This would equate to an average NHEC monthly bill of just over $100.
You will get a 26% tax credit from Uncle Sam and a $1,000 rebate from the State of NH PUC, so you net cost after incentives would be $10,840.
If you take that net and divide it by 8,000 kWh x .16 (the current Co-op rate) it tells you that the solar system will save $1,280 per year. Divide the net cost of $10,840 by the savings and your ROI is 8.47 years. Ie, that is how long it will take for the savings to justify the net cost of the installation ...if you assume that the electric rate will never go up ...and if you totally dismiss the fact that a monthly electric bill is purely an expense, while the funds spent on a solar array goes toward an asset the adds to both the value and salability of your property.
Oh, and one other little thing, a solar array has a life cycle of 35+ years. If the array has justified its cost in ~8.5 years, that will mean that for the following 26.5+ years your electricity will potentially cost you
nothing. If you take the 26.5 years of free and clear and multiply it by the annual at the current electrical rate the savings is... $33,920. How's that grab you?
To be the devils advocate, what can go wrong during that projected 35+ year life cycle? With the solar modules likely nothing, they almost all carry a 25 year warranty are non-switching and relatively bulletproof. The most likely failure would be an inverter but even those generally have a 12+ year warranty. If you assume realistically that an inverter will fail during the 35+ year life cycle it will cost about $2,500 to have it replaced, but in most cases I tell my clients to consider this pretty much a wash against the slowly creeping electrical rates. Over the past twenty years electrical rates in NH have risen on average about 5% a year.
How long can a solar system potentially last? Most likely much longer than any of us but the modules do degrade in performance at a rate of about 1-2% per year as they age. The 25 year warranty generally actually guarantees the performance of the module and in most cases they are warrantied to produce 80% of the rated power on year 25. Think about that for a minute, 25 years ago we were burning 100 watt light bulbs to get the same illumination that we now get out of an 18 watt bulb, and running electric baseboard heaters that consumed electricity at a rate 2.5 times higher than what it takes now to get the same BTU out of a modern air source heat pump. But don't be too anxious to dump the baseboards and spend a lot of money on a mini-split unless the state of the equipment dictates it. As Thinkxingu has pointed out, baseboards are cheap, reliable, effective for heating, and require little or no maintenance. Yes, just like the hot tub they consume a lot of electricity, but if you have a large enough solar array you won't care and neither will the environment.
If you have yard space, I will almost always recommend a ground mount over a roof mount but not for the common reason. A roof mount properly installed will not cause leakage, but the roof has to be in very good condition before the install is done. The reason I am so enthusiastic about ground mounts lies in
bi-facial modules. Bifacials are clear on the back sheet rather than opaque and will absorb the solar energy reflected of the ground. This is negligible during the summer, but the long days of strong sunlight negate this. Where bifacials really excel is when there is snow on the ground and that is a time when most houses need the extra energy boost the most. A bifacial ground mounted array will outperform a conventional module array by 20-25% all winter long.
This is just a simplified explanation and there are a lot of variables, both good and bad, but solar has really come into its own over the last few years. If you want exact details about your site, contact me and my competitors and get a bunch of bids based on your exact site.