To comply with state and local building codes, your contractor must have a CCB license. Ask the contractors you are considering for their number, and go to Oregon Construction Contractor's Board of to check them out.
The Energy Trust of Oregon requires systems receiving their incentives be installed by one of their certified Trade Allies. These contractors have been trained to make sure your system is designed to meet all of the qualification requirements including TSRF.
To be eligible for Oregon's Residential Energy Tax Credit, Oregon requires the contractor hold a valid Tax Credit Certification. For a list of contractors with these certifications go to Oregon Department of Energy website.
It is recommended that any homeowner having a solar water heating system installed check to make sure that the contractor has a plumbling license or a Solar Thermal License (STL).