What is 7 trillion electron volts in mains voltage?

They're different things. An "electron volt" is not the same as a "volt".

An "electron volt" is an amount of energy. It's the work you have to do in order to

lift one electron to a place that's 1 volt more negative, and also the amount of

energy that one electron loses when it falls to a place that's 1 volt more positive.

"1 joule" of energy is the amount of energy you pay for if you use 1 watt for 1 second,

and that's about 6,250,000,000,000,000,000 electron volts of energy.

If you use 1,000 watts for 1 hour, you pay for 1 kilowatt-hour of energy. That's about

22,500,000,000,000,000,000,000,000 electron volts of energy, or 3.6 million joules.

It costs around 15¢ to 25¢ in most places.

The "7 trillion electron volts" in the question is something like the amount of energy

that you'd have to pay for if you used 1 watt for 0.00000112 second. It's not much.