Sensing nodes are employed for intelligent ambient monitoring and information dissemination. The primary challenge in making a sensing node autonomous is the ability to power it continuously. The conventional method of powering these nodes through batteries has an associated drawback of periodic maintenance and replacement. Alternate methods of powering sensing nodes are gaining impetus with the advent of low power electronics. The use of piezoelectric harvesters is an alternative approach to power these sensing nodes. These harvesters innately convert the energy from the unused ambient vibration into electrical energy. The energy extractable from vibrations is characterized by the structure of the vibrating surface. We analyze a harvester as a dynamic vibration absorber mounted on a vibrating structure. The influence of mass ratio, damping ratio, and the number of harvesters on the energy transmitted to the harvesters is addressed. We also assess the power levels required by typical sensing nodes. Our analysis addresses the selection of a particular piezoelectric material, categorically, for a given sensing node. We find that the power required by typical sensing nodes can be easily fulfilled by arrays of harvesters. The current work addresses the concept of available energy from vibrations and the selection of appropriate harvesting configuration for a sensing node.