Title text:
Oh, and do you have any tips on how to vacuum up copper that's melted into your carpet?
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3211/
It's less based on the capacity, and more on how much time is likely a premium.
E.g. motorway services are more expensive, since people need the power and want to get back on the road. It's exactly the same logic as the price of petrol there.