Hi there,

just want to summarize the typical efficiency of electrical power sources:

Coal (http://de.wikipedia.org/wiki/Braunkohlekraftwerk) (Germany): 38% (typical) to 43,7% (maximum brown coal), 46% (max. stone coal)

Gas (http://de.wikipedia.org/wiki/Gas-und-Dampf-Kombikraftwerk): up to 60.7%, about 55% typical (http://de.wikipedia.org/wiki/Well-to-Tank)

Nuclear power plants: 33% (although not really applicable due to nuclear reaction)

Water, Wind & PV: 100% (as I regard these sources as endless)

Biomass and auxiliary: 90%

Energymix in 2013 (Germany):

http://www.crp-infotec.de/08spezi/energie/grafs_basics/deutschland_strommix.gif

The overall efficiency of electric power generation in Germany was at 2010: 52,57%, at the wall outlet of the customer is therefore: 49,4% (http://de.wikipedia.org/wiki/Well-to-Tank),  and here

So, for every kWh that comes out of the outlet, 2.02 kWh of primary energy was necessary. This means that 454g of CO2 per kWh electrical power have been issued.