The Massachusetts Institute of Technology, MIT no less, actually offers access for free to a number of previously taught courses on various topics including several that related to the solar or clean energy industry. The program is called MIT Open Course Ware (OCW). OCW is open and available to the world and is a permanent MIT activity. T
Advanced Free Solar Energy Training
All of the courses I would say are at the advanced level (maybe even research) and typically requires at least an undergraduate degree in science or engineering.
However if feel you have the background, it is free. Dick K.P. Yue, Professor, MIT School of Engineering
The fundamentals of Solar Photovoltaics
Introduction to Sustainable Energy
Fundamentals of Energy in Buildings
The Physics of Energy
The fundamentals of advanced Energy Conversion
There are lots of other courses available for free from MIT so check it out.