Just over a century ago oil pooled on the surface a worthless byproduct of the earth. The cost of obtaining oil was the effort it took to dip a bucket, basically zero. The discovery that oil provided a source of illumination changed perceptions and extraction began. Depletion of the free oil necessitated drilling in search of energy resources below the surface.
The early 20th century marked a paradigm shift in transportation and accelerated the need for energy. Greater demand led to higher prices which made a business case for increased investment. As the easy oil was siphoned off, supply of accessible resources decreased, leading to increased prices, and further investment in deeper wells.
Over the past century the oil and gas industry has realized gains through innovation and economies of scale; however, depletion of accessible resources has offset incremental gains in productivity. Spikes in output may lower prices temporarily, but the long-term trend is a global increase in demand for energy and a decrease in availability of hydrocarbon fuel sources.
Sunlight hits the earth like a bottomless pool of oil free for the taking. The availability of solar will be constant in the future, regardless of present consumption. The barrier to adoption of renewables has been the cost of harnessing the energy, essentially the cost of the bucket. But renewables also benefit from innovation and economies of scale and, since supply is infinite, the cost of converting renewable resources to energy will always trend downward.
A tipping point is approaching. A rising middle class in emerging markets is increasing global energy demand, while at the same time the cost of renewables is nearing parity with traditional fuel sources. It is inevitable that the rising marginal cost of hydrocarbon fuels will intersect with the decreasing marginal cost of renewables; at that point we will see an exponential shift in the energy landscape.