Renewable energy was dominated by hydroelectricity. Most of this was supplied by large dams. However, the benefits of hydroelectricity are offset by some disadvantages. Millions of people have been displaced by large dams that greatly change water flow with detrimental effects on river channels, aquatic biota, and estuarine fisheries.The other renewable energy sources are geothermal, solar, wind, and tidal power, which supplied approximately 0.004% of global energy in 2000. The use of geothermal power can supply only a small percentage of the global energy requirements. Solar power in its various forms has proven effective mainly for household and other small power requirements, although it is dependent on diurnal and seasonal cycles. Wind power is being used increasingly and has been proposed as an alternative energy source, but it is viable only about 30% of the time due to wind variability and it is encountering increasing public resistance on aesthetic and environmental grounds. Tidal power offers a moderate source of energy, but this and the potentially large amount of energy available from wave power are largely untapped. According to a 2004 study of the relative costs of electricity generation in the United Kingdom, the cheapest electricity was produced by combined-cycle gas turbine plants, followed by nuclear plants, a range of coal-fired plants, onshore wind farms, offshore wind farms, and tidal and wave power sources. The noncarbon alternative energy sources have the potential to make increasing contributions to the overall energy supply and will become more price-competitive if fossil fuel prices rise and carbon sequestration becomes mandatory, but at their present stage of development are unlikely to provide a major alternative to fossil fuels for several decades.According to the US Energy Information Administration the Palo Verde Nuclear Generating Station, rated at 3,937 net megawatts, is the largest nuclear power plant and the second largest power plant of any kind in the nation. Arizona ranked second in the nation in utility-scale electricity generation from solar energy in 2014. Arizona, the 15th most populous state, ranked 44th in the nation in per capita energy consumption in 2013, partly because of the states small industrial sector. Arizonas only operating coal mine, Kayenta, on the Navajo and Hopi reservations, supplies the 7-to-8 million short tons burned annually by the Navajo Generating Stations three 750-megawatt units.Arizonas Renewable Environmental Standard requires 15% of the states electricity consumed in 2025 to come from renewable energy resources; in 2014, 8.9% of Arizonas net electricity generation came from renewable resources, primarily from the Glen Canyon and Hoover Dams. Twenty-five percent of the energy consumed in Arizona homes is for air conditioning, which is more than four times the national average of 6 percent, according to EIAs Residential Energy Consumption Survey.