The 70% is not for conversion into electricity but for total useable energy if the waste heat is used in district heating networks. It can reach up to 80% of th

The 70% is not for conversion into electricity but for total useable energy if the waste heat is used in district heating networks. It can reach up to 80% of the primary fuel used. While that seems worse then simply burning it at the end user you have to keep in mind that you also gain electricity which can be used to drive a heat pump. This is by far the best way to burn gas if heat is needed as a result. https://en.wikipedia.org/wiki/Cogeneration https://en.wikipedia.org/wiki/Cogeneration