Renewables have a number of attributes that complement oil and gas within an overall energy portfolio, particularly in terms of sustainability. However, with the exception of biofuels, which face other obstacles, they are not yet effective substitutes for them on the required scale. The output of wind and solar power depends on natural flows that are available much less than half the time, nor can it be stored easily or, in most cases, cost-effectively. The best wind and solar resources are often far from the markets to be supplied, requiring expensive and often controversial transmission lines. Distributed solar power avoids some of these problems but still requires grid-based backup generation, which increasingly relies on fast-reacting natural gas turbines.
Biofuels have been the most effective oil substitutes, so far, but food-crop-based fuels such as grain ethanol and biodiesel produced from oilseeds or animal fat cannot yield sufficient quantities to replace oil at current consumption rates. Such biofuels currently account for just 2% of global liquid fuel supply. Even Brazil produces much more oil than ethanol. Advanced biofuels from non-food sources such as cellulose or algae show great promise but have not yet been produced in truly commercial quantities. Their value chains also pose new challenges, including the handling of enormous quantities of diffuse biomass and their requirement for relatively large land footprints. As a result of all these limitations, the global transportation sector will likely be dominated by petroleum for many years. The International Energy Agency projected last year that fossil fuels will still account for 75% of global energy in 2035.
For at least the next several decades, renewables and oil and gas are likely to coexist in an expanding energy market in which the needs of developed country consumers must continue to be met, albeit more efficiently, at the same time that developing country demand grows and increasing numbers of currently unserved customers gain access to energy. Meeting these diverse needs affordably and in an environmentally acceptable manner will require the contribution of energy sources of all types, including oil and gas from reservoirs that are just now being discovered or accessed using new techniques.