To overcome the problem of unavailability of grid power in rural India, we explore the possibility of powering WSN Gateways using a bicycle dynamo. The "data mule" bicycle generates its own power to ensure a self sustainable data transfer scheme to benefit small and marginal farmers. In our agricultural scenario, farmers have to generate electricity to get access to the technology. Our power measurements show that it is indeed possible to drive GPRS technologies with this power. We propose Transfer Energy Budget -a two way metric for gateway nodes to announce the available energy for relaying data. To achieve our goal, we exploit the DTN stack in the energy sense and introduce necessary modifications to its configuration. The results indicate that a 50 packet buffer has the least transfer energy budget with a data latency of about 31 seconds.