Oregonian: Gone are the days when you could pay $650 for a $13,000 solar system installed on your roof. Oregon solar installers say a rule quietly enacted by a state agency July 1 — and announced late Wednesday — cuts a crucial tax credit, boosting costs of rooftop residential energy production. A 2,000-watt solar system that once cost a homeowner about $650, after credits and a rebate, will now cost about $3,325, Oregon Energy Department officials confirm. That could still …