Turbines are designed to run for decades with very little maintenance of the main elements; overhaul intervals are on the order of several years. Maintenance of the runners and parts exposed to water include removal, inspection, and repair of worn parts.
Normal wear and tear is pitting from cavitation, fatigue cracking, and abrasion from suspended solids in the water. Steel elements are repaired by welding, usually with stainless steel rod. Damage areas are cut or ground out, then welding back up to their original or an improved profile. Old turbine runners may have a significant amount of stainless steel added this way by the end of their lifetime. Elaborate welding procedures may be used to achieve the highest quality repairs.
Other elements requiring inspection and repair during overhauls include bearings, packing box and shaft sleeves, servomotors, cooling systems for the bearings and generator coils, seal rings, wicket gate linkage elements and all surfaces.
Water turbines have had both positive and negative impacts on the environment.
They are one of the cleanest producers of power, replacing the burning of fossil fuels and eliminating nuclear waste. Burning fossil fuels produces smoke and ash, and toxic gases such as carbon monoxide. Nuclear waste emits dangerous radiation and is difficult to dispose of. They use a renewable energy source and are designed to operate for decades. They produce significant amounts of the world's electrical supply.
Historically there have also been negative consequences. The rotating blades or gated runners of water turbines can interrupt the natural ecology of rivers, killing fish, stopping migrations, and disrupting peoples' livelihoods. For example, American Indian tribes in the Pacific Northwest had livelihoods built around salmon fishing, but aggressive dam-building destroyed their way of life. Since the late 20th century, it has been possible to construct hydropower systems that divert fish and other organisms away from turbine intakes without significant damage or loss of power; such systems require less cleaning but are substantially more expensive to construct. In the United States, it is now illegal to block the migration of fish so fish ladders must be provided by dam builders.
AWD-Arena
The HDI-Arena is a football stadium in Hanover, a city in north Germany. It is the home stadium of the football club Hannover 96. The HDI-Arena was built from 1952 to 1954 and called "Niedersachsenstadion" (stadium of lower Saxony) and later "AWD-Arena". Lower Saxony is a German federal state and Hanover is its capital.
Originally the Niedersachsenstadium was large enough to hold about 80.000 people. It was changed for international football championships in 1974 and 1988, especially changing standing room into seats. In 2003, it became changed to be used only for football and the name was sold to the German company of AWD. Today it can hold 49.000 people.
In 2006, the Football World Championships were played there.
Renewable energy
Renewable energy comes from renewable resources. It is different from fossil fuels as it does not produce as many greenhouse gases and other pollutants as fossil fuel combustion.
People have used traditional wind power, hydropower, biofuel, and solar energy for many centuries, all around the world. The mass production of electricity using renewable energy sources is now becoming more common.
From the end of 2004, worldwide renewable energy capacity grew at rates of 10–60% annually for many technologies. For wind power and many other renewable technologies, growth sped up in 2009 relative to the previous four years. More wind power was added during 2009 than any other renewable technology. However, grid-connected PV increased the fastest of all renewables technologies, with a 60% annual average growth rate.
Projections vary, but scientists have advanced a plan to power 100% of the world's energy with wind, hydroelectric, and solar power by the year 2030.
Wind power capacity has expanded quickly to 336 GW in June 2014, and wind energy production was about 4% of total worldwide electricity usage, and growing fast. Wind power is widely used in European countries, and more recently in the United States and Asia. Wind power accounts for approximately 19% of electricity generation in Denmark, 11% in Spain and Portugal, and 9% in the Republic of Ireland. These are some of the largest wind farms in the world, as of January 2010:
A wind farm is a group of wind turbines in the same location used for production of electricity. A large wind farm may consist of several hundred individual wind turbines distributed over an extended area, but the land between the turbines may be used for agricultural or other purposes. A wind farm may also be located offshore.
Solar photovoltaic cells convert sunlight into electricity and many solar photovoltaic power stations have been built, mainly in Europe. As of December 2010, the largest photovoltaic (PV) power plants in the world are the Sarnia Photovoltaic Power Plant (Canada, 97 MW), Montalto di Castro Photovoltaic Power Station (Italy, 84.2 MW), Finsterwalde Solar Park (Germany, 80.7 MW), Rovigo Photovoltaic Power Plant (Italy, 70 MW), Olmedilla Photovoltaic Park (Spain, 60 MW), the Strasskirchen Solar Park (Germany, 54 MW), and the Lieberose Photovoltaic Park (Germany, 53 MW). Larger power stations are under construction, some proposed will have a capacity of 150 MW or more.
Many of these plants are integrated with agriculture and some use innovative tracking systems that follow the sun's daily path across the sky to generate more electricity than conventional fixed-mounted systems. There are no fuel costs or emissions during operation of the power stations.
Large solar thermal power stations include the 354 megawatt (MW) Solar Energy Generating Systems power installation in the USA, Solnova Solar Power Station (Spain, 150 MW), Andasol solar power station (Spain, 100 MW), Nevada Solar One (USA, 64 MW), PS20 solar power tower (Spain, 20 MW), and the PS10 solar power tower (Spain, 11 MW). The 370 MW Ivanpah Solar Power Facility, located in California's Mojave Desert, is the world’s largest solar thermal power plant project currently under construction.
The solar thermal power industry is growing fast with 1.2 GW under construction as of April 2009 and another 13.9 GW announced globally through 2014. Spain is the epicenter of solar thermal power development with 22 projects for 1,037 MW under construction, all of which are projected to come online by the end of 2010. In the United States, 5,600 MW of solar thermal power projects have been announced. In developing countries, three World Bank projects for integrated solar thermal/combined-cycle gas-turbine power plants in Egypt, Mexico, and Morocco have been approved.
Variable renewable energy is a renewable energy source that is non-dispatchable due to its fluctuating nature, like wind power and solar power, as opposed to a controllable renewable energy source such as hydroelectricity, or biomass, or a relatively constant source such as geothermal power or run-of-the-river hydroelectricity. Critics of wind and solar power warn of their variable output, but many studies have shown that the grid can cope, and it is doing so in Denmark and Spain.
The International Energy Agency says that there has been too much focus on issue of the variability. Its significance depends on a range of factors which include the market penetration of the renewables concerned, the balance of plant, and the wider connectivity of the system, as well as demand side flexibility. Variability will rarely be a barrier to increased renewable energy deployment. But at high levels of market penetration it requires careful analysis and management.