Desktop Grids take their place in the e-Science distributed computing infrastructure - scaling into the millions of PCs. Desktop-Grids collect CPU cycles from PCs contributed by donors, by volunteers who are willing to support science and research. The Green key advantage of Desktop-Grids over service Grids and data centers based on clusters of servers is the minimal heat density. Compute Clusters without energy intensive aircondition would run into thermal disaster within minutes. PCs participating in Desktop-Grids usually do not make use of any aircondition. In return and with raising energy prices, data centers have implemented lower costs air-conditioning means like e.g. free cooling, improving their thermodynamic-efficiency and PUE rating. This paper, based on , investigates whether Desktop-Grids still have a Green advantage over Service-Grids and describe several distinct Green Methodologies to optimize compute unit specific energy consumption. Green-IT metrics as âCarbon Footprintâ and PUE are analyzed for their relevance and applied to Desktop-Grids. Pragmatic implementation steps to Green-Desktop-Grids are described.