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Potential

While currently renewable energy sources only supply a modest fraction of current energy use (ca. 14% of primary energy use, mostly from traditional biomass), there is a much potential that could be exploited in the future. As the table below shows, the technical potential of renewable energy sources is more than 18 times current global primary energy use and furthermore several times higher than projected energy use in 2100.

The theoretical potential indicates the amount of energy theoretically available for energy purposes, such as, in the case of solar power, the amount of incoming radiation at the earth's surface. The technical potential is a more practical estimate of how much could be put to human use by considering conversion efficiencies of the available technology and available land area. In the latter case, the estimate for solar energy assumes that 1% of the world's unused land surface is used for solar power.

The Renewable Energy Resource Base (Exajoules a year)

	Current use (2001)	Technical potential	Theoretical potential
Hydropower	9	50	147
Biomass energy	50	>276	2.900
Solar energy	0,1	>1.575	3.900.000
Wind energy	0,12	640	6.000
Geothermal energy	0,6	5.000	140.000.000
Ocean energy	not estimated	not estimated	7.400
Total	60	>7.600	>144.000.000
Current use is in primary energy equivalent. For comparison, the current global primary energy use (2001) is 402 Exajoules a year. Source: World Energy Assessment 2001<ref>, World Energy Assessment 2001, Chapter 5: Energy Resources (table 5.26), coordinating lead author Hans-Holger Rogner. Available for download at [UNDP http://www.undp.org/energy/activities/wea/drafts-frame.html]

The technical potentials generally do not include economic or other environmental constraints, and the potentials that could be realised at an economically competitive level under current conditions is much lower.