Cannot erase disc in disc utility before trade in

Looking for some help please.

I am preparing my 2014 MacBook for a trade in. I followed the instructions that Apple sent but failed on the 'turn FileVault off' stage. I did this, but my prediction now is that at some point during the process my battery went flat as everything I'm reading implies that my disc is still encrypted.

I booted up into recovery mode to complete the Erase Hard drive and reinstall MacOS process. Using Disc Utility I then erased the top disc it showed me - 251 GB Apple SSD SM0256F Media.

I then went to erase the 2nd disc it showed Mac OS X Base System (which shows 1.15GB used) However I am unable to erase this in Disc Recovery. In the Erase tab the 'erase free space' / security options / erase buttons are all greyed out.

How can I erase this disc? Presumably this is what I need to reinstall MacOS as currently when I try to run reinstallation from disc recovery no disc shows in the installation dialog

Thanks so much

Solution 1:

The Base System (& the potential 20 or so tiny volumes you may be able to see below that) are part of your current Recovery session. You cannot erase them - nor do you need to. They are ephemeral & will disappear once you again boot to a normal OS.

You install your new OS to the main drive, once it has been erased.