needs to store energy over a period of time, release the energy only when needed and discharge the energy at a desired power level. A CNT based portable power source should have a basic architecture made of four main components, namely a CNT spring, a supporting structure for the spring, a generator-motor combination, and a coupling mechanism between the spring and the generator. For CNTs arranged in groups/bundles called "forests" as described earlier, efficient packing and good alignment in necessary between the tubes to achieve a high energy density. Good load transfer and effective attachment techniques are required so that the shells can be loaded to near their elastic limit. Choosing the appropriate deformation mode consisting of any amongst axial tension, axial compression, torsion or bending or a combination of any of them. A criterion for choosing a deformation mode is not only the highest energy density, but also the proper integration of the deformed spring with the rest of the power dissipation mechanism. A support structure is required to hold the CNT spring in the fully loaded configuration prior to its release. The design of the support structure will depend on the scale of the spring, the deformation mode the CNT is being subjected to and the architecture of the rest of the system. The material selected for the structure should have high strength, because the added mass and volume of the support contribute to reducing the energy density of the entire system. Energy storage calculations Axial tension Analysis is performed on CNTs subject to tensile loads. A hollow cylindrical structure of CNT of length L, diameter d and mean radius r is considered. The tube has thickness n.h, where n is the number of layers in the CNT and h=0.34 nm is the thickness of one shell. The Young's modulus of the material of the CNT is E. In case of SWCNTs, n=1 and n>1 in case of MWCNTs. The cylinder has inner and outer radii of and . The shell's cross-sectional area is and the total enclosed area is . The strain energy that can be stored in the bar under axial compression to a strain of is ) = The strain energy density is simply the ratio of the strain energy and the enclosed volume. Therefore, in order for the strain energy density to be high the value of should be large. So, a spring in