  We study sensor networks with energy harvesting nodes. The generated energy
at a node can be stored in a buffer. A sensor node periodically senses a random
field and generates a packet. These packets are stored in a queue and
transmitted using the energy available at that time at the node. For such
networks we develop efficient energy management policies. First, for a single
node, we obtain policies that are throughput optimal, i.e., the data queue
stays stable for the largest possible data rate. Next we obtain energy
management policies which minimize the mean delay in the queue. We also compare
performance of several easily implementable suboptimal policies. A greedy
policy is identified which, in low SNR regime, is throughput optimal and also
minimizes mean delay. Next using the results for a single node, we develop
efficient MAC policies.
