Thanks, Carl, for the details on your actuator, tracker, and system. Exceptionally well done!
I was a fan of air collectors about 27 years ago; the first home I built had both passive and active hot air panel heating; 600 SF of hot air panels in the south (53 degree ) roof face heated air which was recirculated through 2 feet deep, 3 inch rock under the the concrete slab. I did this because it was well known by then that rock storage systems generally became too mold infested to use for direct air heating. They system worked well but took a fair amount of energy to move the around; total of 3/4 HP during the sunny part of the day. A guy named Sanderson used it as a secondary heating system in his amazing 100% solar heated homes in Vermont. The heat output of my roof air collector was comparable to 48,000 watts of electric resistive heating; the lack of insulation under the rock storage was a serious design flaw. The soil and rock did warm up, but the ongoing losses downward to the earth were huge.
I prefer hot water over air panels now that I'm off grid because it takes so little power to move it. My house heat pump is 20 watts, the solar pump about the same. Super insulation keeps the solar hot water heating demand very low and never needs maintenance or replacement.