Renewable energy debate

Policy makers often debate the constraints and opportunities of renewable energy. Renewable electricity production, from sources such as wind power and solar power, is sometimes criticized for being variable or intermittent. The International Energy Agency has stated that its significance depends on a range of factors, such as the penetration of the renewables concerned. There have been concerns relating to the visual and other impacts of some wind farms, with local residents sometimes fighting or blocking construction. In the US, the Massachusetts Cape Wind project was delayed for years partly because of such concerns. Residents in other areas have been more positive, and there are community wind farm developments. According to a town councillor, the overwhelming majority of locals believe the Ardrossan Wind Farm in Scotland has enhanced the area. The market for renewable energy technologies has continued to grow. Climate change concerns, coupled with high oil prices, peak oil, and increasing government support, are driving increasing renewable energy legislation, incentives and commercialization. New government spending, regulation and policies helped the industry weather the 2009 economic crisis better than many other sectors. The concerns about environmental impacts of renewable energy are presented by the proponents of theories like degrowth and steady-state economy as one of the proofs that for achieving sustainability technological methods are not enough and there is a need to limit consumption.

Definition of renewable energy The International Energy Agency defines renewable energy saying

Renewable energy is derived from natural processes that are replenished constantly. In its various forms, it derives directly from the sun, or from heat generated deep within the earth. Included in the definition is electricity and heat generated from solar, wind, ocean, hydropower, biomass, geothermal resources, and biofuels and hydrogen derived from renewable resources. Renewable energy resources exist over wide geographical areas, in contrast to other energy sources, which are concentrated in a limited number of countries.

Variable renewable energy

Variability inherently affects solar energy, as the production of electricity from solar sources depends on the amount of light energy in a given location. Solar output varies throughout the day, the seasons, with cloud cover and by latitude on the globe. Windblown sand erodes glass in dry climates, protective layers add expenses. These factors are fairly predictable, and some solar thermal systems make use of molten salt heat storage to produce power when the sun is not shining. Wind-generated power is a variable resource, and the amount of electricity produced at any given point in time by a given plant will depend on wind speeds, air density, and turbine characteristics (among other factors). If wind speed is too low (less than about 2.5 m/s) then the wind turbines will not be able to make electricity, and if it is too high (more than about 25 m/s) the turbines will have to be shut down to avoid damage. While the output from a single turbine can vary greatly and rapidly as local wind speeds vary, as more turbines are connected over larger and larger areas the average power output becomes less variable. Capacity factors for PV solar are rather poor varying between 10 and 20% of the rated nameplate capacity. Onshore wind is better at 20-35% and offshore wind is best at 45%. This means that more total capacity needs to be installed in order to achieve an average output for the year. The capacity factor relates to statements about capacity increases, generation may have increased by a much smaller figure. The International Energy Agency says that there has been too much attention on issue of the variability of renewable electricity production. This issue only applies to certain renewable technologies, mainly wind power and solar photovoltaics, and to a lesser extent run-of-the-river hydroelectricity. The significance of this "predictable variability depends on a range of factors which include the market penetration of the renewables concerned, the nature of the energy sources used to balance the intermittentcy, 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, and additional costs may be required for dispatchable back-up or system modification. Renewable electricity supply in the 20-50+% penetration range has already been implemented in several European systems, albeit in the context of an integrated European grid system: In 2011, the Intergovernmental Panel on Climate Change, the world's leading climate researchers selected by the United Nations, said "as infrastructure and energy systems develop, in spite of the complexities, there are few, if any, fundamental technological limits to integrating a portfolio of renewable energy technologies to meet a majority share of total energy demand in locations where suitable renewable resources exist or can be supplied". IPCC scenarios "generally indicate that growth in renewable energy will be widespread around the world". The IPCC said that if governments were supportive, and the full complement of renewable energy technologies were deployed, renewable energy supply could account for almost 80% of the world's energy use within forty years. Rajendra Pachauri, chairman of the IPCC, said the necessary investment in renewables would cost only about 1% of global GDP annually. This approach could contain greenhouse gas levels to less than 450 parts per million, the safe level beyond which climate change becomes catastrophic and irreversible. Mark Z. Jacobson says that there is no shortage of renewable energy and a "smart mix" of renewable energy sources can be used to reliably meet electricity demand:

Because the wind blows during stormy conditions when the sun does not shine and the sun often shines on calm days with little wind, combining wind and solar can go a long way toward meeting demand, especially when geothermal provides a steady base and hydroelectric can be called on to fill in the gaps.

As physicist Amory Lovins has said:

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