Dell's three-tiered plan to neutralize its carbon footprint has reached its goal five months early and has just saved the company $3 million.

Overall, Dell lowered total energy demand by about 5 percent through efficiency projects such as lighting upgrades, HVAC retrofits, tweaking building temperature settings and shutting off computers not being used.

Dell's data centers, accounting for about 20 percent of its global power use, represent another opportunity for energy savings.