SSD's are great for building your new eco friendly computer. They are much more efficient than the older hard disk drives because they consume a lot less power. In an SSD, there are no moving parts, so noise and heat is reduced greatly. With the reduced heat, you won't need as many fans either, thus reducing noise and power once again.
SSD's last a much longer time now due the quickly improved technology and thus they are definitely a win-win product for building your new green computer.