Nobody will ever supply electricity for free that is impossible in this world we live in and even if you can be talking about the power of the sun there will always be generation and operational cost. Now even if the electricity is free, you have a big investment with the equipment and other related expenses. The most important here is that there is always the development of better mining equipment that hopefully will do things faster and most importantly more efficient in the use of power (this is a big concern for many especially environmentalists). I am looking forward to many good innovations and changes soon in the bitcoin mining industry.