construction of voltage transducer to regulate voltage
If maximum is 75V, go lower, to 48V or 60V at maximum. Then the answer is easy- use a DC/DC converter. I would use a buck-boost or SPEPIC probably, since in solar panel you don't always get maximum voltage, so you will have to both step up and down. In any case note, that doing it with descent efficiency is not easy, so you may prefer to find off-the-shelf products that to the job.