Settle the roof before the array
Panels outlast most roof coverings. If the covering is within a few years of the end of its life, replace it before the array goes on. Removing and reinstalling a system to replace the roof underneath is a cost with no offsetting benefit at all, and it is entirely avoidable at the quoting stage.
Ask for a condition assessment rather than an age estimate, and consider getting it from someone other than the company selling you solar. A roofer has no stake in the array going up this month, and a second opinion on a decision with this much money attached is cheap.
Ask how many layers of covering are on the roof, what the structure underneath is, and whether the framing needs any reinforcement to carry the array. On older housing those are real questions rather than formalities, and an installer who has not been on the roof cannot answer them.
If the roof does need work, having both jobs done in a coordinated sequence is usually cheaper and less disruptive than doing them years apart. Ask the roofer and the installer to speak to each other about timing and about how the mounting will interact with the new covering.
The electrical service is the other prerequisite
A solar system connects into your electrical service, and an older service may not have the capacity or the physical space to accept it without work. That work is a real cost and it belongs in the quote rather than appearing later as a change order.
Ask directly whether your service panel needs upgrading for the proposed system, what that would cost, and whether it is included in the price you have been given. Ask the same question of every installer you speak to, because a quote that has quietly assumed no upgrade will look cheaper than one that has priced the work honestly.
Ask what condition the existing wiring and grounding are in, and whether anything else needs attention to pass inspection. Finding that out at inspection rather than at quoting is how timelines slip and budgets move.
Get the answer in writing. Panel upgrades are one of the most common sources of unexpected cost in residential solar, and the difference between two quotes is often entirely explained by whether one of them included it.
What the system earns once it is running
New Jersey provides full retail net metering, so you receive full retail credit on your utility bill for each kilowatt hour your system produces over the course of a year, either by directly offsetting electricity delivered by the grid or through a credit applied by the electric distribution company after a month of net excess generation.
Separately, the Administratively Determined Incentive pays on generation. One SREC-II is created when a system generates 1,000 kilowatt hours, and the incentive is guaranteed for a term of 15 years, the project's Qualification Life.
Those two streams need two meters. New Jersey's Clean Energy Program states that the metering used for netting and crediting is not capable of measuring gross generation for REC or SREC creation, and that relying on one meter for both would leave the customer-generator short changed. Confirm a separate Solar Production Meter is part of your installation.
Ask for the two streams to be shown separately in any projection. They behave differently and last for different periods, and a single combined savings figure hides which part of the return is doing the work.
Two exemptions, and neither one happens by itself
New Jersey exempts solar energy equipment from state sales tax, but the exemption has a procedure and it happens at purchase. Under N.J.A.C. 18:24-26.4 the purchaser must issue to the seller an Exempt Use Certificate, Form ST-4, or other approved form, indicating on its face that the purchase qualifies for exemption as a solar energy system, with the installation property address inserted.
Ask your installer how that is handled and confirm the certificate was issued rather than assuming the price you were quoted already reflects it. It goes to the seller as part of the transaction, not to the state on a return later.
The property tax exemption is separate. Qualifying renewable energy systems are exempt from real property taxation under N.J.S.A. 54:4-3.113a to g, but Form CRES, the Certification of Renewable Energy System, must be filed with your local municipal tax assessor, and the system must be certified by the local construction code official.
The annual exemption is the difference between the total assessed value of the property before and after the system has been installed. Nobody files Form CRES for you by default, so ask whether your installer assists and put it on your own list either way. Requirements vary between municipalities, so a short call to your own assessor asking what they need is worth more than any general guidance.