The kit is set up for a 6.5ft blade set. 7ft works just fine without changing the turns but the extra turns allows it to cut in a bit earlier. I've run the same alternator with an 8ft blade running at a TSR of 7 with 44 turns and it does very well although you need to set the furling at around 25mph. The alternator will easily do 1kw +, I'm not sure how long it will last at that output. My 6.5ft unit has run 900 watts + for prolonged periods (several hours at a time) without any damage to the stator so far. I rate it at 500 watts because that is the point where its efficiency drops to 50%.
.