They have failed to provide cogent answers to questions about how the intermittency of renewables is to be managed.
They have offered a bifurcated account of the role of fossil fuel generation facilities on the 2050 grid. Claiming both that fossil fuel generator will provide backup for intermittent renewables in 2050, and that the use of fossil fuels will longer be used to generate electricity in 2050.
They have suggested that the problem of intermittency will be solved by "efficiency," "the smart grid," and "diversification" without supplying a detailed analysis of how intermittency will effect the grid, and how "efficiency," "the smart grid," and "diversification" will work separately or collectively to solve the various problems created by intermittency.
Renewables advocates have not recognized the problem of power facility construction inflation on the future costs of renewables, or on the ability of American society to afford proposed renewable power generating systems.
The renewables advocates have failed to notice the decline of the real wealth of American society, and the likely impact of this decline on the ability of American society to finance a high priced predominately renewables generating system.
Renewables advocates have made highly irrational and wildly inaccurate assessments of the costs and limitations of nuclear generating system.
Renewables advocates have failed to offer realistic comparative studies of the cost effectiveness of renewables and nuclear technology.
Renewables advocates have failed to take not of low cost alternative nuclear technologies such as the Liquid Fluoride Thorium Reactor. The LFTR can potentially generate electricity at a cost that is much lower than either renewables or conventional nuclear.
Renewables advocates have failed to assess the likely impact of renewables generated electricity on the economic competitiveness of the United States economy, especially in relationship with India and China. Both countries are currently planning large scale implementation of nuclear generated electrical systems before 2050, and at electrical prices that will be substantially lower than the cost of renewables generated electricity in the United States.