maybe i've got it wrong, but part 1 ($500 limit) looks to me to be for energy improvements to the home ie windows, insulation, furnace, etc and is unrelated to part 2, where energy production devices come in.
the part (in part 1) where they ask for previous year claims refers to line 11, which is on part 1 of the previous year, nowhere does it ask how much you have claimed from part 2. from my understanding, the only limit for a single year claim on part 2 is that you can't get back more than you paid in tax. if your total federal tax paid for the year was $5000 and your solar credit was $8000, you can only get $5000 of it back that year and the rest has to carry over.