Green Mountain Energy — which is racking up both customers and financial losses as it markets no-coal, no-nuclear power — is planning to make a public stock offering. The company has attracted 36,000 customers in Pennsylvania and 21,000 in California, states which have deregulated their electricity markets. In California, virtually all customers who have opted to switch their power supplier have chosen Green Mountain or two other “green” products from traditional utilities. Some environmentalists have criticized Green Mountain because much of the energy it sells in Pennsylvania comes from large-scale hydropower facilities.