Fossil fuels are based on the carbon cycle and allow to use stored (solar) energy of past times today. In the process, the carbon dioxide (CO2) stored in natural gas, oil or coal is released again.
Energy alternatives are alternative and renewable energy sources. Alternative energy sources do not release CO2. Renewable energy sources first extract the CO2 from the air, which they release again when energy is released, are only climate neutral.
Alternative energy sources include the use of wind energy, solar radiation (solar cells and solar panels) and water currents, biomass energy recovery, and tidal and geothermal energy. What all these forms of energy have in common is that they are obtained without CO2 emissions. But solar cells, wind turbines, etc. are not yet produced and recycled without CO2.
Renewable energy sources are, for example, aethanol or biodiesel from vegetable oils (rapeseed, sunflower, etc.), as already added to super gasoline E5 and E10. Unfortunately, this clearly differentiated definition has not yet become established, alternative, renewable and regenerative forms of energy are mixed without regard to CO2 emissions, cf. https://de.wikipedia.org/wiki/Erneuerbare_Energien
