Counter-Rotating Vertical-Axis Wind Turbine Arrays: Designing Against the Spacing Tax from the Other Side

A concrete counter-rotating vertical-axis wind turbine array is specified (rotor diameter 1.2 m, height 1.8 m, solidity 0.30, tip-speed ratio 2.0-4.0, counter-rotating pairs at 1.5 rotor diameters, 12.96 m2 of land per rotor, 771.6 rotors per hectare) and computed from stated assumptions. Neighbour interaction is modelled only as assumed factors of 0.85, 1.00, 1.15 and 1.30 multiplying an isolated-rotor power coefficient of 0.25; these factors are assumptions, not established fact. Under a Rayleigh wind with mean 5.5 m/s at rotor height, one rotor produces a mean of 82.31-114.84 W across that assumption range (94.02 W neutral, capacity factor 0.2136, rated 440.2 W). On a single hectare the mean land density is 6.351-8.861 W/m2, above the 0.5-1.0 W/m2 landscape baseline of the horizontal-axis replenishment audit (DOI 10.5281/zenodo.24102414) under every assumption tested, with a break-even interaction factor of 0.1242 against the top of the baseline. Extended over a landscape, however, the density must return to the 0.5-1.0 W/m2 replenishment bound under any assumption. At stated prices of 1350 USD per rotor installed, cost is 3.067 USD per rated watt and 14.36 USD per mean watt, about 1,041,667 USD per hectare, with 385.8 maintenance visits per hectare per year. SIMULATED, NOT MEASURED: nothing was built, field-tested or measured; all numbers come from the deposited compute.py and results.json.