I’m not sure energy costs will go to zero soon. We need to reduce our dependence on fossil fuels, and a major component appears to be that we need to internalize the cost of co2, for example by way of taxing co2. This may result in increased cost for energy until the market with renewables and storage capacity saturates, which may take a while.

Also, computing itself may not get much cheaper, there are concerns that Moores law is slowing down. Perhaps the cost of computing will plateau for a while.