Similarly, in the United States, the independent National Research Council has noted that "sufficient domestic renewable resources exist to allow renewable electricity to play a significant role in future electricity generation and thus help confront issues related to climate change, energy security, and the escalation of energy costs … Renewable energy is an attractive option because renewable resources available in the United States, taken collectively, can supply significantly greater amounts of electricity than the total current or projected domestic demand."[154]
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.[99] 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;[100] 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,[101] and a variety of tree species, ranging from eucalyptus to oil palm (palm oil).
In its 2014 edition of the Technology Roadmap: Solar Photovoltaic Energy report, the International Energy Agency (IEA) published prices for residential, commercial and utility-scale PV systems for eight major markets as of 2013 (see table below).[2] However, DOE's SunShot Initiative has reported much lower U.S. installation prices. In 2014, prices continued to decline. The SunShot Initiative modeled U.S. system prices to be in the range of $1.80 to $3.29 per watt.[76] Other sources identify similar price ranges of $1.70 to $3.50 for the different market segments in the U.S.,[77] and in the highly penetrated German market, prices for residential and small commercial rooftop systems of up to 100 kW declined to $1.36 per watt (€1.24/W) by the end of 2014.[78] In 2015, Deutsche Bank estimated costs for small residential rooftop systems in the U.S. around $2.90 per watt. Costs for utility-scale systems in China and India were estimated as low as $1.00 per watt.[79]
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).
A: Modern solar panels typically last twenty to thirty years before there’s a noticeable increase in output loss. Most residential solar providers offer a 20- to 25-year warranty, but many such warranties only guarantee a certain power output (e.g., a guarantee of 80% output for twenty years). Carefully read through the fine print to make sure you understand the warranty and what it covers.

The key disadvantages include the relatively low rotational speed with the consequential higher torque and hence higher cost of the drive train, the inherently lower power coefficient, the 360-degree rotation of the aerofoil within the wind flow during each cycle and hence the highly dynamic loading on the blade, the pulsating torque generated by some rotor designs on the drive train, and the difficulty of modelling the wind flow accurately and hence the challenges of analysing and designing the rotor prior to fabricating a prototype.[28]
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.
A report by the United States Geological Survey estimated the projected materials requirement in order to fulfill the US commitment to supplying 20% of its electricity from wind power by 2030. They did not address requirements for small turbines or offshore turbines since those were not widely deployed in 2008, when the study was created. They found that there are increases in common materials such as cast iron, steel and concrete that represent 2–3% of the material consumption in 2008. Between 110,000 and 115,000 metric tons of fiber glass would be required annually, equivalent to 14% of consumption in 2008. They did not see a high increase in demand for rare metals compared to available supply, however rare metals that are also being used for other technologies such as batteries which are increasing its global demand need to be taken into account. Land, whbich might not be considered a material, is an important resource in deploying wind technologies. Reaching the 2030 goal would require 50,000 square kilometers of onshore land area and 11,000 square kilometers of offshore. This is not considered a problem in the US due to its vast area and the ability to use land for farming and grazing. A greater limitation for the technology would be the variability and transmission infrastructure to areas of higher demand.[54]

Eight solar panels and one measly little wind generator supplied all the power we used. We bolted the pole that supported the wind generator to a wall of our house, which, sound-wise, turned the roof of the house into one big drumhead.  Oops! Live and learn. And when the wind REALLY blew—which was often—the thing broke. The manufacturer replaced the main unit several times before we gave up on wind power.


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).
Jump up ^ James, Paul; Magee, Liam; Scerri, Andy; Steger, Manfred B. (2015). Urban Sustainability in Theory and Practice:. London: Routledge.; Liam Magee; Andy Scerri; Paul James; Jaes A. Thom; Lin Padgham; Sarah Hickmott; Hepu Deng; Felicity Cahill (2013). "Reframing social sustainability reporting: Towards an engaged approach". Environment, Development and Sustainability. Springer.
The heat that is used for geothermal energy can be from deep within the Earth, all the way down to Earth's core – 4,000 miles (6,400 km) down. At the core, temperatures may reach over 9,000 °F (5,000 °C). Heat conducts from the core to surrounding rock. Extremely high temperature and pressure cause some rock to melt, which is commonly known as magma. Magma convects upward since it is lighter than the solid rock. This magma then heats rock and water in the crust, sometimes up to 700 °F (371 °C).[58]
^ Jump up to: a b Werner, Jürgen H. (2 November 2011). "Toxic Substances In Photovoltaic Modules" (PDF). postfreemarket.net. Institute of Photovoltaics, University of Stuttgart, Germany - The 21st International Photovoltaic Science and Engineering Conference 2011 Fukuoka, Japan. p. 2. Archived from the original (PDF) on 23 September 2014. Retrieved 23 September 2014.
"Eggbeater" turbines, or Darrieus turbines, were named after the French inventor, Georges Darrieus.[31] They have good efficiency, but produce large torque ripple and cyclical stress on the tower, which contributes to poor reliability. They also generally require some external power source, or an additional Savonius rotor to start turning, because the starting torque is very low. The torque ripple is reduced by using three or more blades which results in greater solidity of the rotor. Solidity is measured by blade area divided by the rotor area. Newer Darrieus type turbines are not held up by guy-wires but have an external superstructure connected to the top bearing.[32]
The use of a gearbox allows for better matching of the generator speed to that of the turbine but the disadvantage of using a gearbox is that as a mechanical component it is subjected to wear and tear reducing the efficiency of the system. Direct drive however may be more simple and efficient, but the generators rotor shaft and bearings are subjected to the full weight and rotational force of the rotor blades.

By Ellen Coleman—As an American of non-specific cultural identity, I look with envy at families with strong cultural tradition. I wonder who "my people” are. What family traditions will my children (now grown) want to pass on to their own children?  Their exposure has been such a mixed bag of “ritual”—making tamales for Thanksgiving, potstickers for family reunions, fried eggplant for Fourth of July.  What will be their choice of comfort music?  What kinds of homes will they make, what spiritual paths will they take?
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As suppliers of inverters for turbines good, bad, and just plain ugly, we have pretty well seen it all when it comes to turbine failure. We can tell you unequivocally that you get what you pay for. Depending on your sense of adventure that can be good or bad; if you plan to go cheap, plan on (you) being the manufacturer’s R&D department and test center. Being a really good do-it-yourselfer with an understanding of wind turbines, alternators, and all things electric will come in very handy too. Just in case you do not believe us, you can read about it in this Green Power Talk thread. There are more threads with similar content on the forum, just browse around a little.
Concentrated solar power plants may use thermal storage to store solar energy, such as in high-temperature molten salts. These salts are an effective storage medium because they are low-cost, have a high specific heat capacity, and can deliver heat at temperatures compatible with conventional power systems. This method of energy storage is used, for example, by the Solar Two power station, allowing it to store 1.44 TJ in its 68 m³ storage tank, enough to provide full output for close to 39 hours, with an efficiency of about 99%.[110]
Green energy is commonly thought of in the context of electricity, mechanical power, heating and cogeneration. Consumers, businesses, and organizations may purchase green energy in order to support further development, help reduce the environmental impacts of conventional electricity generation, and increase their nation’s energy independence. Renewable energy certificates (green certificates or green tags) have been one way for consumers and businesses to support green energy.
Most PV cells are used by homes and small businesses. PV cells are expensive, they require a lot of room and the electricity produced is reliant on lots of sunshine, so they are not practical to use for large industry at this stage. Until technology improves, users must weigh up the benefits of an environmentally friendly power source over the cost.

Meanwhile, we enjoy life grid intertied here in northern California. Our daughters and their families are nearby using their independent living skills to make their own homes.  One daughter has designed and sold 300 off-grid or gridtie solar electric systems since the first of the year.  The other is baking bread today and figuring out what to do with the multitude of tomatillos, squash and eggplant that are spilling out of our garden.  I’m so proud of my tribe!


Most PV cells are used by homes and small businesses. PV cells are expensive, they require a lot of room and the electricity produced is reliant on lots of sunshine, so they are not practical to use for large industry at this stage. Until technology improves, users must weigh up the benefits of an environmentally friendly power source over the cost.
In the 1980s and early 1990s, most photovoltaic modules provided remote-area power supply, but from around 1995, industry efforts have focused increasingly on developing building integrated photovoltaics and power plants for grid connected applications (see photovoltaic power stations article for details). Currently the largest photovoltaic power plant in North America is the Nellis Solar Power Plant (15 MW).[24][25] There is a proposal to build a Solar power station in Victoria, Australia, which would be the world's largest PV power station, at 154 MW.[26][27] Other large photovoltaic power stations include the Girassol solar power plant (62 MW),[28] and the Waldpolenz Solar Park (40 MW).[29]

Third-generation technologies are not yet widely demonstrated or commercialised. They are on the horizon and may have potential comparable to other renewable energy technologies, but still depend on attracting sufficient attention and RD&D funding. These newest technologies include advanced biomass gasification, biorefinery technologies, solar thermal power stations, hot dry rock geothermal energy and ocean energy.
Other cities won’t have it so easy. Take Atlanta. Residents buy energy from Georgia Power, which is owned by investors. As things stand, Atlantans have no control over how their power is generated, though that may change. In 2019, Georgia Power, by state law, has to update its energy plan. Ted Terry, director of the Georgia chapter of the Sierra Club, says the nonprofit is working with Atlanta officials to incorporate renewables, primarily solar, into the state’s plan. Developing such energy sources on a scale that can power a metro area with 5.8 million people, as in Atlanta, or 7.68 million in the San Francisco Bay Area, or 3.3 million in San Diego, will prove challenging. But it doesn’t seem impossible. In 2015, California set a goal of deriving 50 percent of its energy from renewable sources by 2030. Its three investor-owned utilities—Pacific Gas & Electric, Southern California Edison and San Diego Gas & Electric—are poised to achieve that goal just two years from now, or ten years early.
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Geothermal power is cost effective, reliable, sustainable, and environmentally friendly,[130] but has historically been limited to areas near tectonic plate boundaries. Recent technological advances have expanded the range and size of viable resources, especially for applications such as home heating, opening a potential for widespread exploitation. Geothermal wells release greenhouse gases trapped deep within the earth, but these emissions are much lower per energy unit than those of fossil fuels. As a result, geothermal power has the potential to help mitigate global warming if widely deployed in place of fossil fuels.

Wind turbines are used to generate electricity from the kinetic power of the wind. Historical they were more frequently used as a mechanical device to turn machinery. There are two main kinds of wind generators, those with a vertical axis, and those with a horizontal axis. Wind turbines can be used to generate large amounts of electricity in wind farms both onshore and offshore. The articles on this page are about wind turbines.


Electricity produced by wind generators can be used directly, as in water pumping applications, or it can be stored in batteries for later use. Wind generators can be used alone, or they may be used as part of a hybrid system, in which their output is combined with that of solar panels, and /or a fossil fuel generator. Hybrid systems are especially useful for winter backup of home systems where cloudy weather and windy conditions occur simultaneously.
The overwhelming majority of electricity produced worldwide is used immediately, since storage is usually more expensive and because traditional generators can adapt to demand. However both solar power and wind power are variable renewable energy, meaning that all available output must be taken whenever it is available by moving through transmission lines to where it can be used now. Since solar energy is not available at night, storing its energy is potentially an important issue particularly in off-grid and for future 100% renewable energy scenarios to have continuous electricity availability.[106]

^ Jump up to: a b c d Alsema, E.A.; Wild – Scholten, M.J. de; Fthenakis, V.M. Environmental impacts of PV electricity generation – a critical comparison of energy supply options Archived 6 March 2012 at the Wayback Machine. ECN, September 2006; 7p. Presented at the 21st European Photovoltaic Solar Energy Conference and Exhibition, Dresden, Germany, 4–8 September 2006.


Concentrating solar power plants with wet-cooling systems, on the other hand, have the highest water-consumption intensities of any conventional type of electric power plant; only fossil-fuel plants with carbon-capture and storage may have higher water intensities.[135] A 2013 study comparing various sources of electricity found that the median water consumption during operations of concentrating solar power plants with wet cooling was 810 ga/MWhr for power tower plants and 890 gal/MWhr for trough plants. This was higher than the operational water consumption (with cooling towers) for nuclear (720 gal/MWhr), coal (530 gal/MWhr), or natural gas (210).[134] A 2011 study by the National Renewable Energy Laboratory came to similar conclusions: for power plants with cooling towers, water consumption during operations was 865 gal/MWhr for CSP trough, 786 gal/MWhr for CSP tower, 687 gal/MWhr for coal, 672 gal/MWhr for nuclear, and 198 gal/MWhr for natural gas.[136] The Solar Energy Industries Association noted that the Nevada Solar One trough CSP plant consumes 850 gal/MWhr.[137] The issue of water consumption is heightened because CSP plants are often located in arid environments where water is scarce.
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Concentrating solar power plants with wet-cooling systems, on the other hand, have the highest water-consumption intensities of any conventional type of electric power plant; only fossil-fuel plants with carbon-capture and storage may have higher water intensities.[135] A 2013 study comparing various sources of electricity found that the median water consumption during operations of concentrating solar power plants with wet cooling was 810 ga/MWhr for power tower plants and 890 gal/MWhr for trough plants. This was higher than the operational water consumption (with cooling towers) for nuclear (720 gal/MWhr), coal (530 gal/MWhr), or natural gas (210).[134] A 2011 study by the National Renewable Energy Laboratory came to similar conclusions: for power plants with cooling towers, water consumption during operations was 865 gal/MWhr for CSP trough, 786 gal/MWhr for CSP tower, 687 gal/MWhr for coal, 672 gal/MWhr for nuclear, and 198 gal/MWhr for natural gas.[136] The Solar Energy Industries Association noted that the Nevada Solar One trough CSP plant consumes 850 gal/MWhr.[137] The issue of water consumption is heightened because CSP plants are often located in arid environments where water is scarce.

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.
"Eggbeater" turbines, or Darrieus turbines, were named after the French inventor, Georges Darrieus.[31] They have good efficiency, but produce large torque ripple and cyclical stress on the tower, which contributes to poor reliability. They also generally require some external power source, or an additional Savonius rotor to start turning, because the starting torque is very low. The torque ripple is reduced by using three or more blades which results in greater solidity of the rotor. Solidity is measured by blade area divided by the rotor area. Newer Darrieus type turbines are not held up by guy-wires but have an external superstructure connected to the top bearing.[32]
Nearly all the gasoline sold in the United States today is mixed with 10% ethanol,[128] and motor vehicle manufacturers already produce vehicles designed to run on much higher ethanol blends. Ford, Daimler AG, and GM are among the automobile companies that sell "flexible-fuel" cars, trucks, and minivans that can use gasoline and ethanol blends ranging from pure gasoline up to 85% ethanol. By mid-2006, there were approximately 6 million ethanol compatible vehicles on U.S. roads.[129]
The Vestas V164 has a rated capacity of 8 MW,[79] later upgraded to 9.5 MW.[80][81] The wind turbine has an overall height of 220 m (722 ft), a diameter of 164 m (538 ft), is for offshore use, and is the world's largest-capacity wind turbine since its introduction in 2014. The conventional drive train consist of a main gearbox and a medium speed PM generator. Prototype installed in 2014 at the National Test Center Denmark nearby Østerild. Series production began end of 2015.
As suppliers of inverters for turbines good, bad, and just plain ugly, we have pretty well seen it all when it comes to turbine failure. We can tell you unequivocally that you get what you pay for. Depending on your sense of adventure that can be good or bad; if you plan to go cheap, plan on (you) being the manufacturer’s R&D department and test center. Being a really good do-it-yourselfer with an understanding of wind turbines, alternators, and all things electric will come in very handy too. Just in case you do not believe us, you can read about it in this Green Power Talk thread. There are more threads with similar content on the forum, just browse around a little.
Wind turbines are manufactured in a wide range of vertical and horizontal axis. The smallest turbines are used for applications such as battery charging for auxiliary power for boats or caravans or to power traffic warning signs. Slightly larger turbines can be used for making contributions to a domestic power supply while selling unused power back to the utility supplier via the electrical grid. Arrays of large turbines, known as wind farms, are becoming an increasingly important source of intermittent renewable energy and are used by many countries as part of a strategy to reduce their reliance on fossil fuels. One assessment claimed that, as of 2009, wind had the "lowest relative greenhouse gas emissions, the least water consumption demands and... the most favourable social impacts" compared to photovoltaic, hydro, geothermal, coal and gas.[1]

Green energy is commonly thought of in the context of electricity, mechanical power, heating and cogeneration. Consumers, businesses, and organizations may purchase green energy in order to support further development, help reduce the environmental impacts of conventional electricity generation, and increase their nation’s energy independence. Renewable energy certificates (green certificates or green tags) have been one way for consumers and businesses to support green energy.

Although not permitted under the US National Electric Code, it is technically possible to have a “plug and play” PV microinverter. A recent review article found that careful system design would enable such systems to meet all technical, though not all safety requirements.[112] There are several companies selling plug and play solar systems available on the web, but there is a concern that if people install their own it will reduce the enormous employment advantage solar has over fossil fuels.[113]

The terms wind energy or wind power describe the process by which the wind is used to generate mechanical power or electricity. Wind turbines convert the kinetic energy in the wind into mechanical power. This mechanical power can be used for specific tasks (such as grinding grain or pumping water) or a generator can convert this mechanical power into electricity.


Going forward, there is hope for the small wind future! Certification programs are under way in various places to provide real turbine performance data. In North America this is being spearheaded by the Small Wind Certification Council, which requires third-party certification of turbine performance in a standardized fashion. Manufacturers will no longer be able to fudge power curves, or specify ‘rated power’ at hurricane-force wind speeds. This will allow you, the consumer, to compare turbines on a much more even footing.
Another situation where a small wind turbine can make good sense is in case your province, state, or country has rebates or other incentives that make it cheap to install one (just keep ongoing maintenance and repair cost in mind as well). While we would like to advocate responsible spending of government money, the small wind industry needs many more customers to mature. It takes time and installation numbers for manufacturers to work out the bugs, make better turbines, and make them cheaper.

“Five New State Governors Aim for 100% Renewables” • Five governors-elect in Colorado, Illinois, Nevada, Connecticut, and Maine, states with a combined population of 26 million, put forth campaign goals of 100% renewable electricity. Currently, only California and Hawaii have a deadline to move to 100% zero-carbon electricity. [pv magazine International]


Today that initiative, the Green Climate Fund, is an “empty shell,” Mr. Ban said in a recent phone interview. The lifelong diplomat — who recently assumed the presidency of the Global Green Growth Institute, an international organization based in Seoul, South Korea, that focuses on clean energy development — said he hoped to use the next chapter of his career to help poor countries meet their goals under the Paris agreement on climate change.
A regular alternator out of a car needs to be modified to produce anything meaningful above a few volts if any at low RPM. If this guy is not totally bullshit lieing, he is using a modified PMA alternator (permanent magnet alternator) and if not the voltage he is so proudly showing is actually a voltage drop caused by the alternator using power to power it's field coil. This is very misleading to newcomers to the field of renewable energy and makes a mockery of it. And if he really wanted to help people build this he would have should people how to wire the alternator up . Including explaining things like the wires on the regulator the ignition switch , the stator and the field wires. This is why rednecks laugh at liberals because they see shit like this. .

What is a small wind turbine? Anything under, say, 10 meters rotor diameter (30 feet) is well within the “small wind” category. That works out to wind turbines with a rated power up to around 20 kW (at 11 m/s, or 25 mph). For larger wind turbines the manufacturers are usually a little more honest, and more money is available to do a good site analysis. The information in this article is generic: The same applies to all the other brands and models, be they of the HAWT (Horizontal Axis Wind Turbine) or VAWT (Vertical Axis Wind Turbine) persuasion.
“California Wildfires: Trump Visits State’s Deadliest Blaze” • President Donald Trump went to California to survey the most destructive and deadliest wildfire in the its history. He said it had not changed his point of view on climate change, adding, “I want great climate and we’re going to have that and we’re going to have forests that are very safe.” [BBC]
Responsible development of all of America’s rich energy resources -- including solar, wind, water, geothermal, bioenergy & nuclear -- will help ensure America’s continued leadership in clean energy. Moving forward, the Energy Department will continue to drive strategic investments in the transition to a cleaner, domestic and more secure energy future.
The journal also welcomes papers on other related topics provided that such topics are within the context of the broader multi-disciplinary scope of Renewable Energy. It should be noted, however, that papers are within scope only if they are concerned with power generation and that the power is generated in a renewable or sustainable way. For instance, a paper concerning development and characterisation of a material for use in a renewable energy system, without any measure of the energy that this new material will convert, would be out of scope.
The early development of solar technologies starting in the 1860s was driven by an expectation that coal would soon become scarce. Charles Fritts installed the world's first rooftop photovoltaic solar array, using 1%-efficient selenium cells, on a New York City roof in 1884.[28] However, development of solar technologies stagnated in the early 20th century in the face of the increasing availability, economy, and utility of coal and petroleum.[29] In 1974 it was estimated that only six private homes in all of North America were entirely heated or cooled by functional solar power systems.[30] The 1973 oil embargo and 1979 energy crisis caused a reorganization of energy policies around the world and brought renewed attention to developing solar technologies.[31][32] Deployment strategies focused on incentive programs such as the Federal Photovoltaic Utilization Program in the US and the Sunshine Program in Japan. Other efforts included the formation of research facilities in the United States (SERI, now NREL), Japan (NEDO), and Germany (Fraunhofer–ISE).[33] Between 1970 and 1983 installations of photovoltaic systems grew rapidly, but falling oil prices in the early 1980s moderated the growth of photovoltaics from 1984 to 1996.
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