The potential superiority of electricity generated at high altitude is demonstrated in the adjacent table, using the well-known method of levelised cost of energy (LCOE). The computations shown in the table have been applied to three 100 MW electrical power stations powered by different generating methods: coal, ground-based wind and altitude wind. The installation costs for each have been taken from published figures. In these calculations, money is borrowed at rates appropriate to the type of venture involved. Capital is returned over twenty years, while coal is supplied at a subsidised price of $31/tonne. All facilities are depreciated linearly at a rate of 5%/annum.
The costs relate to commercial, electrical generating stations each with nominal outputs of 100 MW. For comparison purposes it was assumed that in both wind systems the 100MW is generated using say 20 individual units, each with a 5.0 MW output at their ground receiving stations. In the case of Altitude Wind, the published charts of the Annual Probability Distribution of Wind Velocity, for typically good Australian sites, show that rated wind speeds of 19.8 m/s will give capacity factors equal to 70% at an altitude of around 4.6km. Importantly, the cost per kg of craft was found following conventional procedures. This procedure is the same as that adopted by aerospace organisations (particularly in US Advanced Project Offices) for estimating the cost competitiveness of aircraft designs. The procedure is essentially costing components on previously known costs of similar components based on a cost per unit of weight method. In the current LCOE estimates, the empty weights of conventional, production-line helicopters were used as the similar components. Thus it has been conservatively assumed that a cost of $850 per kg is appropriate. In addition, this basic cost has been increased to allow for the electromechanical tethers and the ground facilities. In total the installation costs are $1,590,000 per MW. Furthermore, the unit costings are in general agreement with the method given in the US National Renewable Energy Laboratory (NREL) guidelines at a manufacturing rate of 250 units per annum.
The adjacent figure does not include LCOE calculations for solar and other more expensive renewable systems. It can be seen that without any carbon tax, altitude wind is exceedingly cost effective. This is primarily due to the large capacity or availability factor of 70% (see row 4 of the table). This capacity factor, compared to 28% for ground based wind, means that the altitude wind system produces two and a half times more saleable energy per annum. In other words, the airborne system is more expensive to install and operate than ground-based wind turbines, but it gives an outstanding increase in energy output per annum. This produces the vastly superior $-cost per MWh quoted in the table. Fundamentally, this is due to the greater persistence of the winds at altitude.