Wind and solar power are often touted as the Metamucil of American energy consumption. However complete sustainability derived from wind power and solar power is largely a hoax without an integrated power system. The problem is that wind isn’t always blowing and the sun isn’t always shining. Constant streams of energy are necessary to meat constant demand. The benefit is only marginal because, when the wind blows slightly less, more fossil fuels are burned. Ultimately, the more we rely on uncertain sources of energy the more uncertainty is priced into electricity. Rendering the price of electricity uneconomical from both a price and and an environmental perspective. People often forget the principle that a choice should be better than its alternatives. Suppose we were to use price premiums to plant trees. I can’t say if that would decrease an equal or greater amount of carbon, but it also can’t be said that paying the same premium for sustainable energy has the same effect.
Take for example a system which relies on 30% solar energy. If cloud cover is intense, and very little light penetrates, then 30% has to be made up somewhere. This means that 30% capacity has to be built into less variable sources such as (nox)ious  coal power plants. This increases upfront construction costs. Furthermore, these fossil inputs are purchased on the open market at a premium. In this scenario increased demand would increase the spot price (the current price). The price of natural gas, coal and oil used in electricity production is largely hedged against major price swings through futures contracts. Finally, a fundamental business and supply chain principle is that unpredictable variability is expensive.
There is hope! The sun will shine somewhere and the wind will blow somewhere. Thus integrating grids, domestically and internationally is the viable mechanism to environmental sustainability. This model would certainly cause the need for excess capacity of wind and solar sources; however, excess sustainable capacity is superior to polluting capacity. Furthermore, obviously there are sustainable sources of predictable and steady energy; sugar based ethanol, hydro power (has its own problems though), geothermal power, etc…