Energy forms in several ways. But some sources of energy form in similar ways. For example, biofuels and fossil fuels both are formed when the sunlight hits plants and causes photosynthesis. The difference is that for biofuels, we harvest them and burn them for energy. But for fossil fuels, the plants decay and over many years, they will start to turn into fossil fuels without help from humans. Another example is hydroelectric power and tidal power. Both of them involve water moving a turbine. But with hydroelectric power, the water goes down "penstocks" (ramps) built by people, and spins a turbine. But with tidal power, the water spins a turbine because of neutral tides. One more similarity is that fossil fuels, geothermal, and nuclear energy all are found inside the Earth. They form by heat and pressure in the Earth.