Plant energy is produced by crops specifically grown for use as fuel that offer high biomass output per hectare with low input energy. Some examples of these plants are wheat, which typically yield 7.5–8 tonnes of grain per hectare, and straw, which typically yield 3.5–5 tonnes per hectare in the UK.[68] The grain can be used for liquid transportation fuels while the straw can be burned to produce heat or electricity. Plant biomass can also be degraded from cellulose to glucose through a series of chemical treatments, and the resulting sugar can then be used as a first generation biofuel.
UN Conference on the Human Environment (Stockholm 1972) Brundtlandt Commission Report (1983) Our Common Future (1987) Earth Summit (1992) Rio Declaration on Environment and Development Agenda 21 (1992) Convention on Biological Diversity (1992) ICPD Programme of Action (1994) Earth Charter Lisbon Principles UN Millennium Declaration (2000) Earth Summit 2002 (Rio+10, Johannesburg) United Nations Conference on Sustainable Development (Rio+20, 2012) Sustainable Development Goals
Artificial photosynthesis uses techniques including nanotechnology to store solar electromagnetic energy in chemical bonds by splitting water to produce hydrogen and then using carbon dioxide to make methanol.[182] Researchers in this field are striving to design molecular mimics of photosynthesis that utilize a wider region of the solar spectrum, employ catalytic systems made from abundant, inexpensive materials that are robust, readily repaired, non-toxic, stable in a variety of environmental conditions and perform more efficiently allowing a greater proportion of photon energy to end up in the storage compounds, i.e., carbohydrates (rather than building and sustaining living cells).[183] However, prominent research faces hurdles, Sun Catalytix a MIT spin-off stopped scaling up their prototype fuel-cell in 2012, because it offers few savings over other ways to make hydrogen from sunlight.[184]

In the mid-1990s, development of both, residential and commercial rooftop solar as well as utility-scale photovoltaic power stations, began to accelerate again due to supply issues with oil and natural gas, global warming concerns, and the improving economic position of PV relative to other energy technologies.[34] In the early 2000s, the adoption of feed-in tariffs—a policy mechanism, that gives renewables priority on the grid and defines a fixed price for the generated electricity—led to a high level of investment security and to a soaring number of PV deployments in Europe.
The market for renewable energy technologies has continued to grow. Climate change concerns and increasing in green jobs, coupled with high oil prices, peak oil, oil wars, oil spills, promotion of electric vehicles and renewable electricity, nuclear disasters and increasing government support, are driving increasing renewable energy legislation, incentives and commercialization.[10] New government spending, regulation and policies helped the industry weather the 2009 economic crisis better than many other sectors.[24][197]
Materials for wind turbine parts other than the rotor blades (including the rotor hub, gearbox, frame, and tower) are largely composed of steel. Modern turbines use a couple of tons of copper for generators, cables, and such.[52] Smaller wind turbines have begun incorporating more aluminum based alloys into these components in an effort to make the turbines lighter and more efficient, and may continue to be used increasingly if fatigue and strength properties can be improved. Prestressed concrete has been increasingly used for the material of the tower, but still requires much reinforcing steel to meet the strength requirement of the turbine. Additionally, step-up gearboxes are being increasingly replaced with variable speed generators, increasing the demand for magnetic materials in wind turbines.[46] In particular, this would require an increased supply of the rare earth metal neodymium.
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.
Projections vary. The EIA has predicted that almost two thirds of net additions to power capacity will come from renewables by 2020 due to the combined policy benefits of local pollution, decarbonisation and energy diversification. Some studies have set out roadmaps to power 100% of the world’s energy with wind, hydroelectric and solar by the year 2030.
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.”
Since having the Peimar Solar Panels installed and listening to the advice of the owner I have saved a lot of money on my electric bill. Texas Solar Integrated did the work as quickly and efficiently as promised. If the panels look dirty, since I live around cement plants, I just get my high pressure water hose and spray them off. Thank you to this company and the installers. The owner or another contractor in the office is always ready to answer your questions before and after installation.... read more
Some renewable power sources now cost somewhat more than conventional power, because the market for renewable energy is not fully developed and renewables have received fewer subsidies than fossil and nuclear fuels. Also, the damage to the environment and human health—otherwise known as externalities—caused by fossil fuels and nuclear power is not included in electricity prices. Renewable energy needs your support to overcome these barriers and become less expensive in the future. Look into becoming a green power consumer today!
There is no energy in the wind at those wind speeds, nothing to harvest for the turbine. While it may make you feel good to see your expensive yard toy spin, it is not doing anything meaningful in a breeze like that: To give you some idea, a wind turbine with a diameter of 6 meters (pretty large as small wind turbines go) can realistically produce just 120 Watt at 3.5 m/s wind speed. That same turbine would be rated at 6 kW (or more, see the next section), so energy production at cut-in really is just a drop in the bucket. What is more, due to the way grid-tie inverters work, you are about as likely to be loosing energy around cut-in wind speed to keep the inverter powered, as you are in making any energy, resulting in a net-loss of electricity production.
Enhanced geothermal systems (EGS) are a new type of geothermal power technologies that do not require natural convective hydrothermal resources. The vast majority of geothermal energy within drilling reach is in dry and non-porous rock.[161] EGS technologies "enhance" and/or create geothermal resources in this "hot dry rock (HDR)" through hydraulic stimulation. EGS and HDR technologies, such as hydrothermal geothermal, are expected to be baseload resources which produce power 24 hours a day like a fossil plant. Distinct from hydrothermal, HDR and EGS may be feasible anywhere in the world, depending on the economic limits of drill depth. Good locations are over deep granite covered by a thick (3–5 km) layer of insulating sediments which slow heat loss.[162] There are HDR and EGS systems currently being developed and tested in France, Australia, Japan, Germany, the U.S. and Switzerland. The largest EGS project in the world is a 25 megawatt demonstration plant currently being developed in the Cooper Basin, Australia. The Cooper Basin has the potential to generate 5,000–10,000 MW.
In net metering the price of the electricity produced is the same as the price supplied to the consumer, and the consumer is billed on the difference between production and consumption. Net metering can usually be done with no changes to standard electricity meters, which accurately measure power in both directions and automatically report the difference, and because it allows homeowners and businesses to generate electricity at a different time from consumption, effectively using the grid as a giant storage battery. With net metering, deficits are billed each month while surpluses are rolled over to the following month. Best practices call for perpetual roll over of kWh credits.[97] Excess credits upon termination of service are either lost, or paid for at a rate ranging from wholesale to retail rate or above, as can be excess annual credits. In New Jersey, annual excess credits are paid at the wholesale rate, as are left over credits when a customer terminates service.[98]
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.
A high-capacity light-weight portable power source for juicing A high-capacity light-weight portable power source for juicing up your personal and household electronic devices power tools appliances and more. Whether you're you an outdoor enthusiast/field professional operating in off-the-grid locations or a home-owner worried about power outages the Bayoutech Mobile Power is your perfect solution that charges up on-the-go ...  More + Product Details Close
My system has been installed for about a year now. When I first contracted with Envismart, the sales rep was very available and eager to help with my questions but after the installation, he was very hard to make contact with, seldom returned my calls, and when he did seemed to tell me what he thought I wanted hear and very seldom followed through. The system had a shaky start, it died after one day and after two new inverters and several optimizers over several months of on again, off again operation it seems to be running smoothly, at least for the last few months. Customer support was not very good, to be kind, but the service personnel that came out were prompt and there when they said they would be and very open about what the problems were and quickly fixed them. I was told my recurring system problems were a little unusual and I have to take their word on that but they gave me their personnel cell numbers and told me to call them when I couldn't get Customer Support to call - and when I called them, they came through and got me serviced a lot more quickly. They are the main reason I rated the company a 3.I have to say, the last month or so, it seems like the company is starting to work on changing its image. I have been called on several occasions by the "Quality Assurance" group at their initiation and asked if everything was OK with my system and I usually had an issue about something (admittedly, sometimes very minor). They always followed through with answers and corrected my concerns which was a big change from my previous experiences. I want to encourage them to continue improving their Customer Support after the sale in this manner as that is the real reputation for their company. I am still reserving my opinion but I am very much encouraged by their recent efforts - Keep it up!... read more

There is more trouble with rated power: It only happens at a “rated wind speed”. And the trouble with that is there is no standard for rated wind speed. Since the energy in the wind increases with the cube of the wind speed, it makes a very large difference if rated power is measured at 10 m/s (22 mph), or 12 m/s (27 mph). For example, that 6 meter wind turbine from the previous section could reasonably be expected to produce 5.2 kW at 10 m/s, while it will do 9 kW at 12 m/s!
†Offer is available to Texas residential customers who enroll using the Promotion Code “NIGHTSFREE”. Plan bills a monthly Base Charge, an Energy Charge, and passes through Utility Transmission and Distribution delivery charges. Energy Charges for usage consumed between 9pm and 7am each day is credited back on your bill. The utility charges, including delivery charges for night time hours, are passed through at cost and aggregated on your bill. See Electricity Facts Label for details.
High Temperature Geothermal energy is from thermal energy generated and stored in the Earth. Thermal energy is the energy that determines the temperature of matter. Earth's geothermal energy originates from the original formation of the planet and from radioactive decay of minerals (in currently uncertain[56] but possibly roughly equal[57] proportions). The geothermal gradient, which is the difference in temperature between the core of the planet and its surface, drives a continuous conduction of thermal energy in the form of heat from the core to the surface. The adjective geothermal originates from the Greek roots geo, meaning earth, and thermos, meaning heat.
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]

Many companies are taking the push for 100 percent renewables seriously because they see it as good business — not just today, but for the long term. At the time of publication, 152 companies of various sizes have made a commitment to go 100 percent renewable through RE100. Big names like Apple and Google have already met their targets, while other companies are looking out further into the future, some as far as 2040. That timeline indicates companies are looking beyond today’s prices and present-day marketing benefits.
The first electricity-generating wind turbine was a battery charging machine installed in July 1887 by Scottish academic James Blyth to light his holiday home in Marykirk, Scotland.[7] Some months later American inventor Charles F. Brush was able to build the first automatically operated wind turbine after consulting local University professors and colleagues Jacob S. Gibbs and Brinsley Coleberd and successfully getting the blueprints peer-reviewed for electricity production in Cleveland, Ohio.[7] Although Blyth's turbine was considered uneconomical in the United Kingdom,[7] electricity generation by wind turbines was more cost effective in countries with widely scattered populations.[6]
There are more specific questions you’ll have to ask yourself about your location and home—e.g., is my next-door neighbor’s oak tree going to block all my sunlight? You’ll also have to take local weather conditions into consideration. Luckily, there are plenty of other resources to help you find your solar potential. See our Tools section for more info.
“As Trump’s Tariffs Raise the Cost of Solar Installations, Elon Musk and Tesla Cut Their Prices” • Tesla, unmoved by tariffs, is reducing prices on its solar systems 10–20% in recognition of the progress it has made streamlining its solar sales process by integrating Tesla Energy products into its existing high-traffic storefronts. [Red, Green, and Blue]

Plant energy is produced by crops specifically grown for use as fuel that offer high biomass output per hectare with low input energy. Some examples of these plants are wheat, which typically yield 7.5–8 tonnes of grain per hectare, and straw, which typically yield 3.5–5 tonnes per hectare in the UK.[68] The grain can be used for liquid transportation fuels while the straw can be burned to produce heat or electricity. Plant biomass can also be degraded from cellulose to glucose through a series of chemical treatments, and the resulting sugar can then be used as a first generation biofuel.
Where the reputable, and more expensive manufacturers are good in honouring their warranties, you are likely on your own with the cheap stuff. Even with a good warranty, take our word for it that you would much rather not make use of it. Even if the manufacturer supplies replacement parts, it is still expensive to install them. Not to mention that your turbine will not be making energy meanwhile.

Index of solar energy articles List of concentrating solar thermal power companies List of photovoltaics companies List of photovoltaic power stations List of pioneering solar buildings List of rooftop photovoltaic installations List of solar car teams List of solar powered products List of solar thermal power stations People associated with solar power

Wind energy research dates back several decades to the 1970s when NASA developed an analytical model to predict wind turbine power generation during high winds.[136] Today, both Sandia National Laboratories and National Renewable Energy Laboratory have programs dedicated to wind research. Sandia’s laboratory focuses on the advancement of materials, aerodynamics, and sensors.[137] The NREL wind projects are centered on improving wind plant power production, reducing their capital costs, and making wind energy more cost effective overall.[138] The Field Laboratory for Optimized Wind Energy (FLOWE) at Caltech was established to research renewable approaches to wind energy farming technology practices that have the potential to reduce the cost, size, and environmental impact of wind energy production.[139] The president of Sky WindPower Corporation thinks that wind turbines will be able to produce electricity at a cent/kWh at an average which in comparison to coal-generated electricity is a fractional of the cost.[140]
Since the 1970s, Brazil has had an ethanol fuel program which has allowed the country to become the world's second largest producer of ethanol (after the United States) and the world's largest exporter.[125] Brazil's ethanol fuel program uses modern equipment and cheap sugarcane as feedstock, and the residual cane-waste (bagasse) is used to produce heat and power.[126] There are no longer light vehicles in Brazil running on pure gasoline. By the end of 2008 there were 35,000 filling stations throughout Brazil with at least one ethanol pump.[127] Unfortunately, Operation Car Wash has seriously eroded public trust in oil companies and has implicated several high ranking Brazilian officials.
You should know that we at Solacity love wind turbines! Can’t get enough of ’em. Where the neighbours see life-threatening, blade-shedding, bat-and-bird killing, noise-making contraptions, we see poetry in motion. Kinetic art at its finest; combining form, movement, and function all in one. We could stare at them for hours, while contemplating the meaning of life, the universe, and everything… and have… until the beer ran out. Despite all the information presented here, we are big fans of small wind turbines. This page is about informing you, so you can make a decision based on fact and not marketing hype.
Most small wind turbines do not perform quite as well as their manufacturers want you to believe. That should come as no surprise at this point. What may be surprising is that even the turbines of the more honourable manufacturers that are honest about performance fall short, more often than not. The likely cause is turbulence and improper site selection.

A more recent concept for improving our electrical grid is to beam microwaves from Earth-orbiting satellites or the moon to directly when and where there is demand. The power would be generated from solar energy captured on the lunar surface In this system, the receivers would be "broad, translucent tent-like structures that would receive microwaves and convert them to electricity". NASA said in 2000 that the technology was worth pursuing but it is still too soon to say if the technology will be cost-effective.[77]
Al Gore says the reason is innovation. “The cost-reduction curve that came to technologies like computers, smartphones and flat-panel televisions has come to solar energy, wind energy and battery storage,” he says. “I remember being startled decades ago when people first started to explain to me that the cost of computing was being cut in half every 18 to 24 months. And now this dramatic economic change has begun to utterly transform the electricity markets.”
Al Gore says the reason is innovation. “The cost-reduction curve that came to technologies like computers, smartphones and flat-panel televisions has come to solar energy, wind energy and battery storage,” he says. “I remember being startled decades ago when people first started to explain to me that the cost of computing was being cut in half every 18 to 24 months. And now this dramatic economic change has begun to utterly transform the electricity markets.”
Modern turbines usually have a small onboard crane for hoisting maintenance tools and minor components. However, large heavy components like generator, gearbox, blades and so on are rarely replaced and a heavy lift external crane is needed in those cases. If the turbine has a difficult access road, a containerized crane can be lifted up by the internal crane to provide heavier lifting.[68]
Most horizontal axis turbines have their rotors upwind of its supporting tower. Downwind machines have been built, because they don't need an additional mechanism for keeping them in line with the wind. In high winds, the blades can also be allowed to bend which reduces their swept area and thus their wind resistance. Despite these advantages, upwind designs are preferred, because the change in loading from the wind as each blade passes behind the supporting tower can cause damage to the turbine.
A subtype of Darrieus turbine with straight, as opposed to curved, blades. The cycloturbine variety has variable pitch to reduce the torque pulsation and is self-starting.[33] The advantages of variable pitch are: high starting torque; a wide, relatively flat torque curve; a higher coefficient of performance; more efficient operation in turbulent winds; and a lower blade speed ratio which lowers blade bending stresses. Straight, V, or curved blades may be used.[34]
Our home wind turbene systems are Wind/Solar Hybrid, and are qualified for government tax crdedits of 30%. So, for your investment made in these systems the IRS credits you back 30% within one year of purchase. You get 30% back from the IRS. So, basically the government will pay for almost 1/3 of your investment made in your new home wind Generator energy system. This includes all installation costs and expenses and is a real nice start on your investment payback.
Through collaboration, smaller buyers can benefit from economies of scale, while larger buyers can continue to see cost benefits while achieving their renewable energy goals. Aggregation allows companies to procure in a mutually beneficial way with relatively little give and take. For that reason, RMI believes this marks “the beginning of a trend,” Haley said.  
At Bodine-Scott, our renewable energy options have helped dozens of local homes and businesses reduce their utility bills and any negative environmental impact from the use of traditional energy sources. Our technicians are NABCEP-certified experts, and we keep all of our staff informed and up to date on the latest developments in the solar industries. Our average customer sees a 50 percent reduction in utility costs, to say nothing of the invaluable reduction in environmental impact that comes from using clean energy. If you are serious about making an investment in the future of your home and the Earth, contact us today to speak with one of our renewable energy experts.

Renewable energy technologies are getting cheaper, through technological change and through the benefits of mass production and market competition. A 2011 IEA report said: "A portfolio of renewable energy technologies is becoming cost-competitive in an increasingly broad range of circumstances, in some cases providing investment opportunities without the need for specific economic support," and added that "cost reductions in critical technologies, such as wind and solar, are set to continue."[99]


A Darrieus type vertical axis wind turbine (the egg-beater type) can in theory work almost as good as a horizontal axis turbine. Actual measurement of one of the better designs out there, the UGE VisionAir5, does not bear that out though: It measures in at a pitiful 11% efficiency at 11 m/s wind speed, while a Bergey Excel-6 HAWT clocks in at 22% efficiency for that same wind speed, twice as much. You can read about it in Paul Gipe’s article.  Besides efficiency issues, a Darrieus VAWT unfortunately has a number of inherent issues that put them at a disadvantage: Since they are usually tall and relatively narrow structures the bending forces on their main bearing (at the bottom) are very large. There are similar issues with the forces on the blades. This means that to make a reliable vertical axis turbine takes more material, and more expensive materials, in comparison to a horizontal type turbine. For comparison, that same UGE VisionAir5 weighs 756 kg vs. the Bergey Excel-6 at 350 kg. Keep in mind that the UGE turbine only sweeps about half the area of the Bergey, the latter is a much larger turbine! This makes VAWTs inherently more expensive, or less reliable, or both.

At Bodine-Scott, our renewable energy options have helped dozens of local homes and businesses reduce their utility bills and any negative environmental impact from the use of traditional energy sources. Our technicians are NABCEP-certified experts, and we keep all of our staff informed and up to date on the latest developments in the solar industries. Our average customer sees a 50 percent reduction in utility costs, to say nothing of the invaluable reduction in environmental impact that comes from using clean energy. If you are serious about making an investment in the future of your home and the Earth, contact us today to speak with one of our renewable energy experts.
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]
In 2010, the United States led the world in geothermal electricity production with 3,086 MW of installed capacity from 77 power plants;[132] the largest group of geothermal power plants in the world is located at The Geysers, a geothermal field in California.[133] The Philippines follows the US as the second highest producer of geothermal power in the world, with 1,904 MW of capacity online; geothermal power makes up approximately 18% of the country's electricity generation.[132]
Permanent magnets for wind turbine generators contain rare earth metals such as Nd, Pr, Tb, and Dy. Systems that use magnetic direct drive turbines require higher amounts of rare metals. Therefore, an increase in wind production would increase the demand for these resources. It is estimated that the additional demand for Nd in 2035 may be 4,000 to 18,000 tons and Dy could see an increase of 200 to 1200 tons. These values represent a quarter to half of current production levels. However, since technologies are developing rapidly, driven by supply and price of materials these estimated levels are extremely uncertain.[55]
Most installers overrate the available wind resource. The majority of small wind turbine installations underperforms their predictions, often by a wide margin. Since wind speed is the most important parameter for turbine energy production, getting that wrong has large consequences (the power in the wind goes with the cube of the wind speed, so double the wind speed and the power in it is 2 * 2 * 2 = 8x as much). You have to be realistic about your annual average wind speed.
So how do wind turbines make electricity? Simply stated, a wind turbine works the opposite of a fan. Instead of using electricity to make wind, like a fan, wind turbines use wind to make electricity. The wind turns the blades, which spin a shaft, which connects to a generator and makes electricity. View the wind turbine animation to see how a wind turbine works or take a look inside.
Photovoltaics (PV) uses solar cells assembled into solar panels to convert sunlight into electricity. It's a fast-growing technology doubling its worldwide installed capacity every couple of years. PV systems range from small, residential and commercial rooftop or building integrated installations, to large utility-scale photovoltaic power station. The predominant PV technology is crystalline silicon, while thin-film solar cell technology accounts for about 10 percent of global photovoltaic deployment. In recent years, PV technology has improved its electricity generating efficiency, reduced the installation cost per watt as well as its energy payback time, and has reached grid parity in at least 30 different markets by 2014.[115] Financial institutions are predicting a second solar "gold rush" in the near future.[116][117][118]

A solar cell, or photovoltaic cell (PV), is a device that converts light into electric current using the photovoltaic effect. The first solar cell was constructed by Charles Fritts in the 1880s.[5] The German industrialist Ernst Werner von Siemens was among those who recognized the importance of this discovery.[6] In 1931, the German engineer Bruno Lange developed a photo cell using silver selenide in place of copper oxide,[7] although the prototype selenium cells converted less than 1% of incident light into electricity. Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the silicon solar cell in 1954.[8] These early solar cells cost 286 USD/watt and reached efficiencies of 4.5–6%.[9]

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