The promise is unfulfilled.

In college in the late 1970s I was taken with the science of alternative energy and considered a career in the field. A growth industry and the opportunity to do well by doing good it seemed. But by the time I graduated in 1982, I took a different path. Researching the history of alternative energy, there seemed an always receding horizon of optimism, whether biomass, solar, hydro, wind, etc. Just one more breakthrough would seal the deal. Just a little more subsidy would get the industry to a critical mass and escape velocity.

And each step forward in turn proved insufficient.

Technological progress was made but it never closed the gap with the cheap flexible carbon based alternatives, and each of the alternative energy sources had their own environmental drawbacks to be considered as well.

I can't claim great wisdom or insight but it was sufficient to put me on a better track than I would have experienced had I remained in alternative energy.

The receding horizon for breakthrough that I saw then is still with us today as described in Solar's Bright Future Is Further Away Than It Seems by Tyler Cowen.

There is now a doctrine of what I call “solar triumphalism”: the price of panels has been falling exponentially, the technology makes good practical sense, and only a few further nudges are needed for solar to become a major energy source. Unfortunately, this view seems to be wrong. Solar energy could be a boon to mankind and the environment, but it’s going to need a lot more support and entrepreneurial and policy dynamism.

Varun Sivaram, in his forthcoming “Taming the Sun: Innovations to Harness Solar Energy and Power the Planet” lays out this case in what may be the first important policy book of 2018. To be clear, Sivaram, who holds a doctorate in physics, is a solar expert and an energy adviser -- he’s no enemy of alternative energy sources. He thinks government should increase its support for energy research and development, aiming at diverse pathways, applied at various stages of technology development, and targeting game-changing breakthroughs. In other words, we need to recognize the limitations of today’s solar power if we are going to make it really work.

Read the whole thing for the complete bleakness of today's prospects.

The technology is still simply insufficient and there are no likely prospects to change that analysis.

The promise is still there and discovery is often a random walk, there is no telling when a pivotal discovery might change the equation.

But for the time being, the promise is unfulfilled.