The following checklist can be used to determine if an installer's proposal is complete:
Does the installer hold a valid license?
Is the installer insured for Workman's Compensation?
Has there been any complaints against the installer?
Does the installer have a contractor's bond, to ensure that you receive your money back if something goes wrong?
What is the time length that the state requires the contractors to warranty their work?
Does the service warranty provide any uptime guarantee?
Is the price quoted for the full system, fully installed and hooked to the utility/grid?
Provided only 10-20% retainer which was specifically stated in the contract and rest of balance due after system is up and running
With regards to the modules, inverters, mounting systems, etc, why does the installer prefer a specific make and model?
Did I go over the warrany and manufacturer's spec sheet?
Where did the installer get their assumptions for solar irradiation or wind speed?
What program does the installer use to get the results for assumed system efficiency?
If there is no yield guarantee offered, ask why one isn't offered
If the installer is wrong about the incentive amount, who will be paying the difference?
Does the installer offer recommended efficiency measures? (some states require this)
Does the installer provide a model or drawing of the system? (including the layout of all equipment, its direction, surface area, tilt, etc)
Does the installer offer yield tracking and monitoring with the service?