1) Yes, you can either run the 12VDC batteries in series to form the 24VDC battery parallel banks or you can purchase 24VDC batteries and combine them in parallel.
2) Budgetary installed pricing with labor and materials is approximately $8 per watt. This cost can vary depending upon your location. In states where PV is common, the $8 per watt is a good number. In states where PV installs are not that common, the cost per watt can go up to $10 or $11 per watt. The cost of the panels have somewhat decreased over the last 5 years since PV is becoming more common as an alternative energy use. Common panel wattages typically range from 150 watts to 300 watts per panel.
3) If you are looking to have a rack mount system installed on a roof, I would add an additional $1 or so per watt due to the additional labor required for roof mounts. The higher the roof and the more slope the roof has, higher labor costs will prevail. A ground mounted system will be more cost effective due to a quicker installation time.
4) Even though your system will be Off-Grid, you still may be eligible for incentives from the United States Department of Energy. Depending upon what state you reside in, they have many rebates, loans and grant programs for various forms of renewable energy.
Check out the link below for your review:
5) I would recommend on having a NABCEP certified technician who is also a licensed electrician install your system. NABCEP is an organization for certifying solar technicians. Many installers out there are NABCEP certified which is good, however, I would also recommend that they be a licensed electrician due to conduit sizing, voltage drops, disconnect switches, proper grounding, etc. Many NABCEP tech's are not licensed electricians and they may not be intimate with the 2011 National Electrical Code. Try to find a tech who is both NABCEP Certified as well as being a licensed electrician.
In addition, I would also recommend that you review your PV installation with your local Authority Having Jurisdiction (AHJ). The AHJ is your local building and/or electrical inspector. Local building codes will always prevail, thus always good to meet with the AHJ in order to keep everyone on a level playing field.
The NABCEP website can also assist you with certified tech's in your area. I would recommend obtaining 3 different proposals. Make sure the installer or company is licensed, bonded and insured. References from previous customers are always a good thing.
See NABCEP link below:
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