Opinions differ on the potential and timing for increased reliance on alternatives to fossil fuels. Alternatives to fossil fuels include: hydropower, nuclear power, biomass-based fuels, geothermal power, wind power, solar power and wave power. Hydropower has been an inexpensive and reliable source of energy worldwide for quite some time, but nearly all available, cost-effective U.S. dam sites and most international sites have been developed, and concerns over the ecological, recreational and aesthetic impacts of dams have become increasingly important. Nuclear power is also inexpensive and recent technological developments have allowed for significant reductions in nuclear waste generation. However, concerns over security issues, safety, and disposal of generated waste have limited our reliance on nuclear energy. Biomass-based fuels create fuels sources out of corn and other carbon-rich crops. They are currently used for the production of both ethanol - a gasoline additive - and biodiesel - an increasingly feasible alternative to gasoline used in diesel engines. To address future energy needs, some experts have advocated the development of large acreages of corn or other crops to generate bio fuels. Geothermal power relies on the production of heat in geologically active regions such as Iceland. The scope of this power source is geographically limited as few locations exhibit necessary geological qualities for this power source to be widely useful. Lastly, wind and solar power are seen as having less significant environmental impacts, but they also currently generate a small amount of global energy due to their cost (for additional information on wind capacity in the U.S.). Wave and tidal power harness energy from rising and falling ocean waves, which has been researched at the Oregon State Wave Research Laboratory. This form of energy may have great potential, but currently is used in only a few regions. Researchers are continually working to improve the efficiencies of these technologies.