What do you mean by "backed by"? When we say "paper receipt is backed by gold" it means you can get gold in exchange for receipt at any time. In case of Bitcoin, you are NOT getting back electricity in exchange for your bitcoins, blocks or transactions. Please clarify what you mean by this.
One definition of "backed by" is "guaranteed exchangeable for."
Another is "supported by." As in 'Bitcoin is supported by the scarcity of energy available from natural resources.'
These are totally different definitions and the second one is made up. If you want to point out prerequisites to deal with Bitcoins, you don't need to redefine words. Bitcoins need the same modern capital structure that you also need for having dollars and modern banking. Namely, connectivity, electricity, equipment and many people employed in that area.
Back to the first definition (which is what most people use): what exactly and by whom is guaranteed to be exchanged for irrevocably spent electricity in case of Bitcoin?