Renewable electricity production, from sources such as wind power and solar power, is sometimes criticized for being variable or intermittent, but is not true for concentrated solar, geothermal and biofuels, that have continuity. In any case, the International Energy Agency has stated that deployment of renewable technologies usually increases the diversity of electricity sources and, through local generation, contributes to the flexibility of the system and its resistance to central shocks.[191]

In 2007, the world's first turbine to create commercial amounts of energy using tidal power was installed in the narrows of Strangford Lough in Ireland. The 1.2 MW underwater tidal electricity generator takes advantage of the fast tidal flow in the lough which can be up to 4m/s. Although the generator is powerful enough to power up to a thousand homes, the turbine has a minimal environmental impact, as it is almost entirely submerged, and the rotors turn slowly enough that they pose no danger to wildlife.[48][49]
Most current solar power plants are made from an array of similar units where each unit is continuously adjusted, e.g., with some step motors, so that the light converter stays in focus of the sun light. The cost of focusing light on converters such as high-power solar panels, Stirling engine, etc. can be dramatically decreased with a simple and efficient rope mechanics.[55] In this technique many units are connected with a network of ropes so that pulling two or three ropes is sufficient to keep all light converters simultaneously in focus as the direction of the sun changes.
“What Changes Will Maine’s New Government Bring to Your Life?” • Swept to sizable majorities in last week’s elections, Maine’s Democrats will be in full control of state government for the first time since 2010. They are likely to look for ways to address a number of pressing issues, one of which is climate change. [Kennebec Journal & Morning Sentinel]
It is unfortunate to see how well marketing for small wind turbines is working: I often see people post questions on forums, where they are looking for a wind turbine “with a low cut-in wind speed”. Depending on whom you ask, the cut-in wind speed is either the wind speed where the turbine starts turning, or the wind speed where it starts to produce some power. For most wind turbines it is around 2.5 – 3.5 m/s (5.5 – 8 mph), and it is an utterly meaningless parameter.
“California Invests in ‘By Location’ Distributed Energy Resources” • California leads the US with several pilot projects to reward rooftop solar energy generators and other distributed energy resources in specific locations as an alternative to having utilities meet needs by investing in upgrading their electricity generation networks. [CleanTechnica]
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There is one more area where buyers may get a false sense of security: Several states in the US have lists of “approved” wind turbines for their rebate programs. An example of this is the California list. The problem is that approval for this list, and the performance data provided (such as rated power and energy production) are essentially self-certified. The less-scrupulous manufacturers can ‘manufacture’ data and submit it under the pretence that it was measured.  The only value of those lists is in telling you what rebates are available, they do not provide reliable turbine information.
Biomass is biological material derived from living, or recently living organisms. It most often refers to plants or plant-derived materials which are specifically called lignocellulosic biomass.[65] As an energy source, biomass can either be used directly via combustion to produce heat, or indirectly after converting it to various forms of biofuel. Conversion of biomass to biofuel can be achieved by different methods which are broadly classified into: thermal, chemical, and biochemical methods. Wood remains the largest biomass energy source today;[66] examples include forest residues – such as dead trees, branches and tree stumps –, yard clippings, wood chips and even municipal solid waste. In the second sense, biomass includes plant or animal matter that can be converted into fibers or other industrial chemicals, including biofuels. Industrial biomass can be grown from numerous types of plants, including miscanthus, switchgrass, hemp, corn, poplar, willow, sorghum, sugarcane, bamboo,[67] and a variety of tree species, ranging from eucalyptus to oil palm (palm oil).

These high strength magnets are usually made from rare earth materials such as neodymium iron (NdFe), or samarium cobalt (SmCo) eliminating the need for the field windings to provide a constant magnetic field, leading to a simpler, more rugged construction. Wound field windings have the advantage of matching their magnetism (and therefore power) with the varying wind speed but require an external energy source to generate the required magnetic field.

“Renewable Energy Market to Garner $2,152 Billion by 2025, Reveals Report” • According to a report published by Allied Market Research, renewables industries will very likely result in an impressive growth for the entire market. It projects the global renewable energy market is to reach in excess of $2,152 billion by 2025. [Interesting Engineering]
In October 2018, the American Council for an Energy-Efficient Economy (ACEEE) released its annual "State Energy Efficiency Scorecard." The scorecard concluded that states and electric utility companies are continuing to expand energy efficiency measures in order to meet clean energy goals. In 2017, the U.S. spent $6.6 billion in electricity efficiency programs. $1.3 billion was spent on natural gas efficiency. These programs resulted in 27.3 million megawatt hours (MWh) of electricity saved.[160]
Airflows can be used to run wind turbines. Modern utility-scale wind turbines range from around 600 kW to 5 MW of rated power, although turbines with rated output of 1.5–3 MW have become the most common for commercial use. The largest generator capacity of a single installed onshore wind turbine reached 7.5 MW in 2015. The power available from the wind is a function of the cube of the wind speed, so as wind speed increases, power output increases up to the maximum output for the particular turbine.[42] Areas where winds are stronger and more constant, such as offshore and high altitude sites, are preferred locations for wind farms. Typically full load hours of wind turbines vary between 16 and 57 percent annually, but might be higher in particularly favorable offshore sites.[43]
The advantage of this approach in the United States is that many states offer incentives to offset the cost of installation of a renewable energy system. In California, Massachusetts and several other U.S. states, a new approach to community energy supply called Community Choice Aggregation has provided communities with the means to solicit a competitive electricity supplier and use municipal revenue bonds to finance development of local green energy resources. Individuals are usually assured that the electricity they are using is actually produced from a green energy source that they control. Once the system is paid for, the owner of a renewable energy system will be producing their own renewable electricity for essentially no cost and can sell the excess to the local utility at a profit.
Common battery technologies used in today's home PV systems include, the valve regulated lead-acid battery– a modified version of the conventional lead–acid battery, nickel–cadmium and lithium-ion batteries. Lead-acid batteries are currently the predominant technology used in small-scale, residential PV systems, due to their high reliability, low self discharge and investment and maintenance costs, despite shorter lifetime and lower energy density. However, lithium-ion batteries have the potential to replace lead-acid batteries in the near future, as they are being intensively developed and lower prices are expected due to economies of scale provided by large production facilities such as the Gigafactory 1. In addition, the Li-ion batteries of plug-in electric cars may serve as a future storage devices in a vehicle-to-grid system. Since most vehicles are parked an average of 95 percent of the time, their batteries could be used to let electricity flow from the car to the power lines and back. Other rechargeable batteries used for distributed PV systems include, sodium–sulfur and vanadium redox batteries, two prominent types of a molten salt and a flow battery, respectively.[114][115][116]
The Solar updraft tower is a renewable-energy power plant for generating electricity from low temperature solar heat. Sunshine heats the air beneath a very wide greenhouse-like roofed collector structure surrounding the central base of a very tall chimney tower. The resulting convection causes a hot air updraft in the tower by the chimney effect. This airflow drives wind turbines placed in the chimney updraft or around the chimney base to produce electricity. Plans for scaled-up versions of demonstration models will allow significant power generation, and may allow development of other applications, such as water extraction or distillation, and agriculture or horticulture. A more advanced version of a similarly themed technology is the Vortex engine which aims to replace large physical chimneys with a vortex of air created by a shorter, less-expensive structure.
Several initiatives are being proposed to mitigate distribution problems. First and foremost, the most effective way to reduce USA’s CO2 emissions and slow global warming is through conservation efforts. Opponents of the current US electrical grid have also advocated for decentralizing the grid. This system would increase efficiency by reducing the amount of energy lost in transmission. It would also be economically viable as it would reduce the amount of power lines that will need to be constructed in the future to keep up with demand. Merging heat and power in this system would create added benefits and help to increase its efficiency by up to 80-90%. This is a significant increase from the current fossil fuel plants which only have an efficiency of 34%.[92]
Despite these diverse developments, developments in fossil fuel systems almost entirely eliminated any wind turbine systems larger than supermicro size. In the early 1970s, however, anti-nuclear protests in Denmark spurred artisan mechanics to develop microturbines of 22 kW. Organizing owners into associations and co-operatives lead to the lobbying of the government and utilities and provided incentives for larger turbines throughout the 1980s and later. Local activists in Germany, nascent turbine manufacturers in Spain, and large investors in the United States in the early 1990s then lobbied for policies that stimulated the industry in those countries.

The trouble with rated power is that it does not tell you anything about energy production. Your utility company charges you for the energy you consume, not power. Likewise, for a small wind  turbine you should be interested in the energy it will produce, for your particular site, with your particular annual average wind speed. Rated power of the turbine does not do that. To find out about energy production take a look at the tables presented earlier.
With Georgetown emerging as a brave new model for a renewable city, it makes sense to ask if others can achieve the same magical balance of more power, less pollution and lower costs. In fact, cities ranging from Orlando to St. Louis to San Francisco to Portland, Oregon, have pledged to run entirely on renewable energy. Those places are much larger than Georgetown, of course, and no one would expect misty Portland to power a light bulb for long with solar energy, which is crucial to Georgetown’s success. But beyond its modest size, abundant sunshine and archetype-busting mayor, Georgetown has another edge, one that’s connected to a cherished Lone Star ideal: freedom.
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With investment subsidies, the financial burden falls upon the taxpayer, while with feed-in tariffs the extra cost is distributed across the utilities' customer bases. While the investment subsidy may be simpler to administer, the main argument in favour of feed-in tariffs is the encouragement of quality. Investment subsidies are paid out as a function of the nameplate capacity of the installed system and are independent of its actual power yield over time, thus rewarding the overstatement of power and tolerating poor durability and maintenance. Some electric companies offer rebates to their customers, such as Austin Energy in Texas, which offers $2.50/watt installed up to $15,000.[96]
Due to data transmission problems, structural health monitoring of wind turbines is usually performed using several accelerometers and strain gages attached to the nacelle to monitor the gearbox and equipments. Currently, digital image correlation and stereophotogrammetry are used to measure dynamics of wind turbine blades. These methods usually measure displacement and strain to identify location of defects. Dynamic characteristics of non-rotating wind turbines have been measured using digital image correlation and photogrammetry.[44] Three dimensional point tracking has also been used to measure rotating dynamics of wind turbines.[45]

As of 2012, the Alta Wind Energy Center (California, 1,020 MW) is the world's largest wind farm.[107] The London Array (630 MW) is the largest offshore wind farm in the world. The United Kingdom is the world's leading generator of offshore wind power, followed by Denmark.[108] There are several large offshore wind farms operational and under construction and these include Anholt (400 MW), BARD (400 MW), Clyde (548 MW), Fântânele-Cogealac (600 MW), Greater Gabbard (500 MW), Lincs (270 MW), London Array (630 MW), Lower Snake River (343 MW), Macarthur (420 MW), Shepherds Flat (845 MW), and the Sheringham Shoal (317 MW).
Wind power is widely used in Europe, China, and the United States. From 2004 to 2014, worldwide installed capacity of wind power has been growing from 47 GW to 369 GW—a more than sevenfold increase within 10 years with 2014 breaking a new record in global installations (51 GW). As of the end of 2014, China, the United States and Germany combined accounted for half of total global capacity.[83] Several other countries have achieved relatively high levels of wind power penetration, such as 21% of stationary electricity production in Denmark, 18% in Portugal, 16% in Spain, and 14% in Ireland in 2010 and have since continued to expand their installed capacity.[105][106] More than 80 countries around the world are using wind power on a commercial basis.[76]
Floatovoltaics are an emerging form of PV systems that float on the surface of irrigation canals, water reservoirs, quarry lakes, and tailing ponds. Several systems exist in France, India, Japan, Korea, the United Kingdom and the United States.[149][150][151][152] These systems reduce the need of valuable land area, save drinking water that would otherwise be lost through evaporation, and show a higher efficiency of solar energy conversion, as the panels are kept at a cooler temperature than they would be on land.[153] Although not floating, other dual-use facilities with solar power include fisheries.[154]

Biomass can be converted to other usable forms of energy such as methane gas or transportation fuels such as ethanol and biodiesel. Rotting garbage, and agricultural and human waste, all release methane gas – also called landfill gas or biogas. Crops, such as corn and sugarcane, can be fermented to produce the transportation fuel, ethanol. Biodiesel, another transportation fuel, can be produced from left-over food products such as vegetable oils and animal fats.[69] Also, biomass to liquids (BTLs) and cellulosic ethanol are still under research.[70][71] There is a great deal of research involving algal fuel or algae-derived biomass due to the fact that it's a non-food resource and can be produced at rates 5 to 10 times those of other types of land-based agriculture, such as corn and soy. Once harvested, it can be fermented to produce biofuels such as ethanol, butanol, and methane, as well as biodiesel and hydrogen. The biomass used for electricity generation varies by region. Forest by-products, such as wood residues, are common in the United States. Agricultural waste is common in Mauritius (sugar cane residue) and Southeast Asia (rice husks). Animal husbandry residues, such as poultry litter, are common in the United Kingdom.[72]
I wouldn’t consider myself a creative type.  Never painted a picture, never felt confident in color or fabric choices.  But I did get a real creativity boost living off-grid in northern New Mexico, raising children on one income in a home with caught water, gardening at 7600 feet in a climate that gets REALLY cold.  We built a house called an earthship from recycled materials and earth. 
Adam Schultz, a senior policy analyst for the Oregon Department of Energy, says he’s more encouraged than ever about the prospects for renewables. Because the Pacific Northwest features large-scale hydropower plants built as part of the New Deal, energy already tends to be less expensive there than the U.S. average. But solar and wind power have “gotten cheaper over the last couple years to the point that I can’t even tell you what the costs are because costs have been dropping so rapidly,” Schultz says. “We have enough sunshine,” he says (presumably referring to the eastern part of the state), “so it’s just a matter of time.”
Manufacturers often claim that their vertical axis turbine is better at extracting power from low speed winds. Unfortunately the laws of physics get in the way here: There is very little power in low speed winds. The blade of a vertical or horizontal type turbine is equally good at extracting that power, though with the vertical type the blades move at an angle to the wind where they do not extract energy for part of every rotation, adding drag and making a vertical type turbine just a little less efficient than a similar sized horizontal one. There is no advantage when it comes to low winds.
In a twist that has some Republicans in this oil- and gas-rich state whistling Dixie, Ross is now friends with Al Gore, who featured Ross in An Inconvenient Sequel, the 2017 follow-up to An Inconvenient Truth, his Oscar-winning documentary about global warming. “We bonded right away,” Ross recalls. “I said, ‘Mr. Vice President, we’ve got a lot in common. You invented the internet. I invented green energy.’” Trained as an accountant, Ross still works as one—being mayor of Georgetown is a part-time job—and there’s no mistaking his zeal for the other kind of green. When conservatives complain about his energy politics, he is quick to remind them that the city has the lowest effective tax rate in Central Texas.
Wind turbines need wind to produce energy. That message seems lost, not only on most small wind turbine owners, but also on many manufacturers and installers of said devices. One of the world’s largest manufacturers of small wind turbines, located in the USA (now bankrupt by the way, though their turbines are still sold), markets their flag-ship machine with a 12 meter (36 feet) tower. Their dealers are trained to tell you it will produce 60% of your electricity bill. If you are one of those that is convinced the earth is flat, this is the turbine for you!
Geothermal energy is produced by tapping into the thermal energy created and stored within the earth. It arises from the radioactive decay of an isotope of potassium and other elements found in the Earth's crust.[144] Geothermal energy can be obtained by drilling into the ground, very similar to oil exploration, and then it is carried by a heat-transfer fluid (e.g. water, brine or steam).[144] Geothermal systems that are mainly dominated by water have the potential to provide greater benefits to the system and will generate more power.[145] Within these liquid-dominated systems, there are possible concerns of subsidence and contamination of ground-water resources. Therefore, protection of ground-water resources is necessary in these systems. This means that careful reservoir production and engineering is necessary in liquid-dominated geothermal reservoir systems.[145] Geothermal energy is considered sustainable because that thermal energy is constantly replenished.[146] However, the science of geothermal energy generation is still young and developing economic viability. Several entities, such as the National Renewable Energy Laboratory[147] and Sandia National Laboratories[148] are conducting research toward the goal of establishing a proven science around geothermal energy. The International Centre for Geothermal Research (IGC), a German geosciences research organization, is largely focused on geothermal energy development research.[149]

In 2014 global wind power capacity expanded 16% to 369,553 MW.[83] Yearly wind energy production is also growing rapidly and has reached around 4% of worldwide electricity usage,[84] 11.4% in the EU,[85] and it is widely used in Asia, and the United States. In 2015, worldwide installed photovoltaics capacity increased to 227 gigawatts (GW), sufficient to supply 1 percent of global electricity demands.[86] Solar thermal energy stations operate in the United States and Spain, and as of 2016, the largest of these is the 392 MW Ivanpah Solar Electric Generating System in California.[87][88] The world's largest geothermal power installation is The Geysers in California, with a rated capacity of 750 MW. Brazil has one of the largest renewable energy programs in the world, involving production of ethanol fuel from sugar cane, and ethanol now provides 18% of the country's automotive fuel. Ethanol fuel is also widely available in the United States.
As of 2014, offshore wind power amounted to 8,771 megawatt of global installed capacity. Although offshore capacity doubled within three years (from 4,117 MW in 2011), it accounted for only 2.3% of the total wind power capacity. The United Kingdom is the undisputed leader of offshore power with half of the world's installed capacity ahead of Denmark, Germany, Belgium and China.
A hybrid system combines (C)PV and CSP with one another or with other forms of generation such as diesel, wind and biogas. The combined form of generation may enable the system to modulate power output as a function of demand or at least reduce the fluctuating nature of solar power and the consumption of non renewable fuel. Hybrid systems are most often found on islands.
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