The most recent of these, the European Union's ExternE study, examined the external costs of wind under nine headings: noise, visual intrusion, accidents during manufacture and operation to plant personnel, accidents to public, acid rain damage (from energy used in construction), global warming effects, effect on birds of wind turbines, impacts on local ecosystems, and electro-magnetic interference. A value for costs under the last three headings was deemed unquantifiable, mainly because they were "likely to be very small at all locations outside recreationally important areas designated for scenic reasons."
The range of cost estimates -- for two specific British sites -- lay in the range $0.0025-0.0050/kWh. This is consistent with other studies, which generally show lower external costs for wind than either PV or biomass, although all are small.
It is clear from the list that the analysis was very thorough and included estimates of external costs incurred during the manufacturing processes, as well as operation of the plant. Nevertheless, the overall conclusion from the EU study was that the highest estimate of external costs for wind was below the minimum estimate of the external costs for coal. Excluding global warming, the costs for coal were $0.007-$0.018/kWh.