Is it possible to use energy from renewable energy sources to break down CO2 and when needed, turn that back into another molecule? Or am I dumb?
And is it efficient?
In: 1
CO2 is already one of the lowest energy carbon molecule, if not the lowest energy. So making it into another molecule would not make sense as you can not get all the energy back. However there is actually a process which almost fit your description. It is called the Sabatier process and works by turning hydrogen and CO2 into oxygen and methane. This process can be easily reversed either by burning the methane or by using a fuel cell to get electricity from it slowly. This process is mainly used in spaceflight.
Currently ISS use this process to conserve most of their oxygen, the methane is vented. This means that supply ships do not have to bring any oxygen, and only some water. The carbon and hydrogen atoms all come from the food that is brought up. This cuts the amount of consumables required for each astronaut by about half. There are also plans to use this process on Mars to create fuel using the CO2 in the atmosphere. The energy can come from solar panels or nuclear power. A rocket only have to bring about 20% of the fuel weight in hydrogen which can then be turned into liquid oxygen and liquid methane to fuel the rockets for the return trip. If possible we could find enough water on Mars to make rocket fuel from this instead of bringing inn hydrogen.
As for efficiency though, no it is not. The Sabatier process use a lot of energy and you will not get much back from the methane. This is why it is only used in very specific situations.
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