Q&A:

According to Robert Ayres and Edward Ayres, brothers and co-authors of the recently published book,

Most of the remaining energy is discarded, typically in the form of waste heat that, with the right application of technology, could be used for electricity generation or space and water heating.

(As just one example of the potential, two large American steel companies together generated 190 megawatts of electricity from recycled waste heat in 2005. This was more than the entire United States production of solar-photovoltaic electricity that year.)

NY Times