General Electric may not pay taxes, but it sure does spend big on its Ecomagination line of pro-green business. In fact, GE spent as much as $1.8 billion on research and development into clean energy and green technology last year, according to its latest report on the subject released this week. That puts the conglomerate on track to reach a cumulative $10 billion in green R&D by 2015 — and so far, it’s been a profitable investment, given that Ecomagination lines of business brought GE $18 billion in revenues for 2010 and $85 billion since 2005. Products launched under the brand last year include the Wattstation car charger and the Nucleus home energy manager. GE’s venture-backed investments into greentech startups also played a role in its investment total, with about $55 million given out to the first 12 winners of its “Ecomagination Challenge” so far, mostly in the field of smart grid systems. The next round of GE’s challenge is focused on home energy, and GE is set to announce winners of that round tomorrow — stay tuned for more details.