Hello, Imagine that we have a fluid heated up by solar energy (every day during sunlight). Due to higher temperature it would undergo thermal expansion and do some mehanical work while expanding, right? And during night it would cool down and hence compress and do some negative mechanical work. Now, my friend has an idea of constructing a shading system (practically a set of "shading units" that cover people from sun and open at day and close at night). What are the possible complications that might arise?