I have of course been following this thread with great interest, and there has been some good info presented, and some that is not accurate in NH.
The Tesla roof panels, like the solar window films and flow batteries sound intriguing and very promising but in my opinion not yet ready for prime time, and especially in an environment as harsh as northern New England's. Plus as pointed out the installation is incredibly expensive at this point.
The focus of NH Solar at this point is on total off-grids, grid tied with energy backup, and bifacial ground mount arrays. We rarely have time in our schedule anymore to do simple roof installs unless they are a part of one of those systems, but still about half of our installs include roof mounts because they are initially the least expensive.
As a rough estimate of costs you can figure the price of a simple turn key roof mount from us at $2.60-2.70 per watt. Using that a 20 module 6.8 kW array would have a gross cost of ~$18,000. Uncle Sam will kick back 26% as a Renewable Energy Tax Credit and that will drop your net down to ~$13,300. The State of NH PUC also has a rebate program but it being changed this month and traditionally in the past if there was a change the reabte would decrease. The previous program however would have granted you a rebate of $1,000, so the net for the example would now have been ~$12,300.
The amount of
kilo
watt
hours produced annually depends on both the azimuth and pitch of the installation. Perfect solar south in this region for a fixed mount is at around 194 degrees with a pitch of 25 degrees. This would grant you a production factor (kW of array vs projected annual kWh production) of ~1.3, and thus the 6.8 kW array could be expected to produce an annual production of just under 9,000 kWh. At the current average utility rate of 0.16 per kWh it would take 8.54 years for the production from the solar array to offset the net cost of the system ($12,300 net / 9 mWh x 0.16) but this will likely shorten as utility rates on the average slowly climb.
A roof mount however most often has less than a perfect orientation and the production factor will be less than 1.3 depending upon the deviations. I consider an array with anything better than 1.0 as still being worthwhile and in most cases this amounts to about a 30-35 degree deviation from 194' azimuth, and a flatter roof is generally more forgiving of deviation than a steeper roof. Beyond those parameters the return drops off drastically ...unless you install a split East-West array.
An EW array gives a far longer day and spreads the flow of power off the roof nicely and this results in a far greater degree of the solar production being self consumed, thus avoiding the 25% net metering discount granted to the utilities by the PUC. IE, whenever you export excess solar production (usually midday, and especially in early summer) you will receive ~75 cents on the dollar in credit. These credits are banked and will be withdrawn at night and during the short days of winter. As previously pointed out in this thread you are in effect using the grid as a "battery" and this is a good deal both for the consumer and fair for the utilities.
If a shingled roof is over ten years old we generally advise replacing the south plane before installing a solar array. The shingles may look fine but after ten+ years of being baked by the sun they will no doubt have become somewhat brittle. As the array is installed the walking on the shingles will result in microfractures and it is likely that at some time in the future they will begin to leak. Removing and replacing a solar array is not just a simple matter of removing and replacing modules and the cost no doubt would run into many thousands of dollars. Installing a new roof surface will avoid this because the fresh flexible shingles won't be brittle, and because they will going forward be forever shaded from the drying UV rays by the array. Only the shingles outside of the array will age and they can usually easily be sistered into when they become brittle in 20-30 years. Here's the kicker, Uncle Sam has been allowing the 26% ITC to be applied to that portion of re-the roofing cost under the array.
My personal wish for the upcoming PUC rebate change would be that it be eliminated from the array size parameter and applied instead toward home energy storage (battery). A simple solar system actually adds stress to the utility grid through what is known as "the
duck production curve". Home energy storage on the other hand can alleviate the late afternoon surge because some of the excess production from the midday will have been stored in the battery rather than exported. The stored power can then be drawn back form the battery during the late afternoon and early evening, a time when a lot of grids are under their highest demand. As a side benefit for the homeowner this power is self consumed and thus not subject to the 25% net metering discount.
By far and away the most popular storage system we install is the
SolarEdge EnergyHub system. At an add-on cost of $14K it isn't cheap, but as the link shows there are multiple benefits. The key of course is that you will almost never be out of power because if the grid goes down the system instantly islands itself and begins drawing power from just the solar array and/or battery. You may run out of power if the outage occurs late at night and you have already drained the battery. If that happens you have two choices; go to bed and wait for the sun to come up the next day to recharge the battery, or plug in a small portable generator and run that for just long enough to restore the charge. A third alternative that is used by many of our clients is to program the system during the winter months to not draw power for self consumption, that way the battery is always sitting fully charged when the grid goes down.
As far as solar arrays aesthetics that is truly a matter of personal taste. Even still, as I drive around the Lakes Region I see an awful lot of systems that could have been done so much better if the installer had just put a little more thought into the aesthetics of their work. We install only all black modules on roofs. If you look at the
Google website for NH Solar you should be able to open up the more details tabs and see some of our work. I bet that you might even recognise some of them ;-)