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The annual energy potential of a wind site cannot be estimated with the commonly available average wind speed data. It rather involves a detailed knowledge of the probability distribution and a complex computation of its cubic power integral over the year. A site with lower average wind speed can have higher energy potential if the speed distribution is flatter. The wind speed variation with time can be accurately represented by the Weibull probability distribution function, which can be approximated by the Raleigh distribution. Since wind power has the cubic relation with the speed, the concept of the root-mean-cube (RMC) speed is defined and developed in the paper. All sites having the same RMC speed would have the same annual energy potential. An analytical expression has been derived that relates the RMC speed with the average speed. It allows a quick and easy determination of the annual energy potential by using the commonly available average wind speed data.

Using the presently available technologies in the fiber composite rotors and in magnetic bearings, it is feasible to design the flywheel energy storage to replace the battery in the spacecraft power system. The potential benefits are reductions in weight, size and cost. The fundamental design considerations in designing the photovoltaic/flywheel power system are investigated in this paper. Since low earth orbit satellites, being battery-heavy, would show greater benefits using the flywheel, the NASA Goddard Space Flight Center’s EOS-AM1 is taken as a case study example. It is seen that the power system using flywheel in this satellite has a potential of saving approximately 35 percent mass, 55 percent volume and 6.6 percent solar array area.