Complex sentence: Note: one has to be careful to not confuse energy payback with financial payback, which can be quite different, especially if different forms of energy-that is, electricity, coal, food-command different prices for the same kilojoule.
Split into simpler sentences: Note: one has to be careful to not confuse energy gain with financial gain, which can be quite different. Different sources of energy-like coal, oil or food-command different prices for the same kilojoule.