Peter:
It is incorrect to say that software costs nothing.

1) If software is an organization of 1's and 0's that has any pattern to it other than total randomness then there has been some expendature of energy to bias the bit pattern away from the randomness of the bits.

2) On a more present "everyday" level it takes energy to create the pattern of bits into a useful order.

3) The bit pattern must be captured somehow so that the bits stay in the desired order. The action to implement the capture process takes energy whether it be a single shot action or a repeatitive action.

4) It costs something to provide the storage containment system that keeps the bit pattern at the desired state.

5) If the bit pattern is put to use then it takes energy to interpret the bit order and act on that order.

Michael Karas