Tomorrow, GE chairman and CEO Jeffrey Immelt will announce that his company — the fifth largest in the U.S. — is devoting itself to what it calls "ecomagination": the growth of clean energy, clean water, and related technologies.

This is a very big deal, about which Grist will have more to say. For now, go read Joel Makower, who — as with most big moves in the sustainable business sphere — has been working on this behind the scenes.

Ecomagination, says Immelt, aims to "focus our unique energy, technology, manufacturing, and infrastructure capabilities to develop tomorrow’s solutions such as solar energy, hybrid locomotives, fuel cells, lower-emission aircraft engines, lighter and stronger materials, efficient lighting, and water purification technology."

By almost any measure, it’s a bold move. For GE, the fifth-largest U.S. company, it represents a strategic shift that could catalyze competition among some of the world’s largest companies to accelerate the emerging clean-tech economy.