First of all you need to define what do you mean by green IoT? When it comes to the WSNs there are a lot of opportunities out there but also many challenges. From the telemedicine perspective, obviously this challenges might be different from those in another discipline. So, when designing the network, first of all you need to state the critical constraints and try to identify the opportunities that the technology brings along.
To summarize, basically there does not exist a universal approach as to how you may be able to build an green IoT solution.