RE:Einstein….Yep, energy can be generally described as anything that can cause momentum (mass x velocity). The photons in light knock electrons free in voltaic cells. Free electrons are also known as electricity. Sound is pressure waves vibrating your ear drums or the windows of my home when I was younger blasting Frank Zappa. Lol. Heat is energy because it causes atoms and molecules to vibrate faster. There are many other forms. Frank, you described the First Law of Thermodynamics precisely.
The Second Law of Thermodynamics aka The Law of Entropy says that you can transform energy from one form to another but you will end up increasing the amount of disordered forms of energy in the universe by doing so. It also says that it's impossible to reverse the transformation process. Like you can transform an ordered form of energy like a log into disordered forms like heat, light, sound, smoke, soot, ash energies but you can't collect all of that stuff and recreate the log again.
So there is no such thing as renewable energy in the sense that you can return the environment back into its initial state. Again, how flooding millions of hectares of boreal forest is considered renewable is beyond me.