Query: […]until we develop a practical, cost-competitive alternative to fossil fuels, it is unlikely that renewable energy will ever make up more than 15-20% of global energy requirements.

Relevant passages:
Cellulosic ethanol <=SEP=> Cellulosic ethanol is ethanol ( ethyl alcohol ) produced from cellulose ( the stringy fiber of a plant ) rather than from the plant 's seeds or fruit . It is a biofuel produced from grasses , wood , algae , or other plants . The fibrous parts of the plants are mostly inedible to animals , including humans , except for ruminants ( grazing , cud-chewing animals such as cows or sheep ) .   Considerable interest in cellulosic ethanol exists because it has the potential for strong economic importance . Growth of cellulose by plants is a mechanism that captures and stores solar energy chemically in nontoxic ways with resultant supplies that are easy to transport and store . Additionally , transport may be unneeded anyway , because grasses or trees can grow almost anywhere temperate . This is why commercially practical cellulosic ethanol is widely viewed as a next level of development for the biofuel industry that could reduce demand for oil and gas drilling and even nuclear power in ways that grain-based ethanol fuel alone can not . Potential exists for the many benefits of carbonaceous liquid fuels and petrochemicals ( which today 's standard of living depends on ) but in a carbon cycle -- balanced and renewable way ( recycling surface and atmosphere carbon instead of pumping underground carbon up into it and thus adding to it ) . Commercially practical cellulosic alcohol could also avoid one of the problems with today 's conventional ( grain-based ) biofuels , which is that they set up competition for grain with food purposes , potentially driving up the price of food . To date , what stands in the way of these goals is that production of cellulosic alcohol is not yet sufficiently practical on a commercial scale .

Renewable energy <=SEP=> Renewable energy is energy that is collected from renewable resources , which are naturally replenished on a human timescale , such as sunlight , wind , rain , tides , waves , and geothermal heat . Renewable energy often provides energy in four important areas : electricity generation , air and water heating/cooling , transportation , and rural ( off-grid ) energy services .   Based on REN21 's 2016 report , renewables contributed 19.2 % to humans ' global energy consumption and 23.7 % to their generation of electricity in 2014 and 2015 , respectively . This energy consumption is divided as 8.9 % coming from traditional biomass , 4.2 % as heat energy ( modern biomass , geothermal and solar heat ) , 3.9 % hydro electricity and 2.2 % is electricity from wind , solar , geothermal , and biomass . Worldwide investments in renewable technologies amounted to more than US$ 286 billion in 2015 , with countries like China and the United States heavily investing in wind , hydro , solar and biofuels . Globally , there are an estimated 7.7 million jobs associated with the renewable energy industries , with solar photovoltaics being the largest renewable employer . As of 2015 worldwide , more than half of all new electricity capacity installed was renewable .   Renewable energy resources exist over wide geographical areas , in contrast to other energy sources , which are concentrated in a limited number of countries . Rapid deployment of renewable energy and energy efficiency is resulting in significant energy security , climate change mitigation , and economic benefits . The results of a recent review of the literature concluded that as greenhouse gas ( GHG ) emitters begin to be held liable for damages resulting from GHG emissions resulting in climate change , a high value for liability mitigation would provide powerful incentives for deployment of renewable energy technologies . In international public opinion surveys there is strong support for promoting renewable sources such as solar power and wind power . At the national level , at least 30 nations around the world already have renewable energy contributing more than 20 percent of energy supply . National renewable energy markets are projected to continue to grow strongly in the coming decade and beyond . Some places and at least two countries , Iceland and Norway generate all their electricity using renewable energy already , and many other countries have the set a goal to reach 100 % renewable energy in the future . For example , in Denmark the government decided to switch the total energy supply ( electricity , mobility and heating/cooling ) to 100 % renewable energy by 2050 .   While many renewable energy projects are large-scale , renewable technologies are also suited to rural and remote areas and developing countries , where energy is often crucial in human development . United Nations ' Secretary-General Ban Ki-moon has said that renewable energy has the ability to lift the poorest nations to new levels of prosperity . As most of renewables provide electricity , renewable energy deployment is often applied in conjunction with further electrification , which has several benefits : Electricity can be converted to heat ( where necessary generating higher temperatures than fossil fuels ) , can be converted into mechanical energy with high efficiency and is clean at the point of consumption . In addition to that electrification with renewable energy is much more efficient and therefore leads to a significant reduction in primary energy requirements , because most renewables do n't have a steam cycle with high losses ( fossil power plants usually have losses of 40 to 65 % ) .   Renewable energy systems are rapidly becoming more efficient and cheaper . Their share of total energy consumption is increasing . Growth in consumption of coal and oil could end by 2020 due to increased uptake of renewables and natural gas .

Nuclear power debate <=SEP=> The nuclear power debate is a controversy about the deployment and use of nuclear fission reactors to generate electricity from nuclear fuel for civilian purposes . The debate about nuclear power peaked during the 1970s and 1980s , when it `` reached an intensity unprecedented in the history of technology controversies '' , in some countries . Observers attribute the nuclear controversy to the impossibility of generating a shared perception between social actors over the use of this technology as well as systemic mismatches between expectations and experience .   Proponents of nuclear energy argue that nuclear power is a sustainable energy source which reduces carbon emissions and can increase energy security if its use supplants a dependence on imported fuels . Proponents advance the notion that nuclear power produces virtually no air pollution , in contrast to the chief viable alternative of fossil fuel . Proponents also believe that nuclear power is the only viable course to achieve energy independence for most Western countries . They emphasize that the risks of storing waste are small and can be further reduced by using the latest technology in newer reactors , and the operational safety record in the Western world is excellent when compared to the other major kinds of power plants .   Opponents say that nuclear power poses numerous threats to people and the environment and point to studies in the literature that question if it will ever be a sustainable energy source . These threats include health risks and environmental damage from uranium mining , processing and transport , the risk of nuclear weapons proliferation or sabotage , and the unsolved problem of radioactive nuclear waste . They also contend that reactors themselves are enormously complex machines where many things can and do go wrong , and there have been many serious nuclear accidents . Critics do not believe that these risks can be reduced through new technology . They argue that when all the energy-intensive stages of the nuclear fuel chain are considered , from uranium mining to nuclear decommissioning , nuclear power is not a low-carbon electricity source .   Three of the world 's four largest economies now generate more electricity from non-hydro renewable energy than from nuclear sources . New power generation using solar power was 33 % of the global total added in 2015 , wind power over 17 % , and 1.3 % for nuclear power , mostly due to development in China .