Tuesday, June 24, 2008

Biofuels- Crime against humanity?


Last month Jean Ziegler, the UN special rapporteur on the right to food, called biofuels a "crime against humanity" and asked for a five-year moratorium on the practice of using food crops for fuel.


It was only the latest voice in what seems to be turning into a backlash against biofuels. In September, the Organisation for Economic Co-operation and Development issued a sceptical assessment of biofuels, warning that they could cause more problems than they solve.

For decades, biofuels seemed to promise a clean, sustainable, environmentally friendly way to produce fuel, one that would promote energy independence and at the same time reduce greenhouse gas emissions. But even as governments and corporations are finally throwing their weight behind biofuel production, a small but vocal chorus of critics claims that biofuels are at best a waste of effort and at worst outright damaging. Some critics even question whether biofuels will lower greenhouse gas emissions or actually increase them.


"People are getting smarter. People are beginning to see that the damage ensuing from producing agrofuels by far outweighs any possible benefits," says Tad W. Patzek, a professor of geoengineering at the University of California, Berkeley, and a prominent biofuels sceptic.


Criticism of biofuels comes from several directions. Some critics argue that biofuels will demand more energy than they produce. Others think that biofuels will use up resources that would otherwise go to feeding people. Still others worry about the environmental damage that will be caused by farming of more land — damage that they say could result in higher greenhouse gas emissions. It is even cast as an issue of human rights, as critics worry that more indigenous people will be forced from their land to make way for biofuel plantations.

Although ethanol was used as a transport fuel early in the twentieth century, it was the oil shocks of the 1970s that prompted the US government and others to encourage home-grown bioethanol industries through tax breaks, regulation and research grants. But for much of that time the use of biofuels has struggled against a relatively low petroleum price that has made it hard for them to be cost-competitive.


Now, with oil prices in the US approaching triple digits, worries about potentially dwindling oil supplies and the threat of climate change have combined to give biofuels a boost that supporters think will make them a practical fuel source.


Global ethanol production was 13.4 billion gallons in 2006, according to the Renewable Fuels Association3. The US led production at 4.8 billion gallons, mostly produced from corn, and Brazil was close behind, producing 4.5 billion gallons, mostly from sugar cane. Production increased 20 percent between 2004 and 2006.


New efforts by the US and the EU promise to increase that production further. The US government has announced a goal of doubling ethanol production again by 2012, and the EU has announced a goal of making ten percent of transport fuelled from biofuel by the 2020.

Although technically a biofuel is any fuel that can be derived from biomass, including firewood, the term is usually applied to liquid fuels that can be used for transportation. By that definition, the two most plentiful biofuels produced today are bioethanol and biodiesel.


Bioethanol is made by first fermenting a starchy or sugary feedstock such as corn or sugar cane, then distilling the alcohol in a process not unlike making whiskey or rum. Biodiesel, in contrast, is produced from vegetable oils such as palm or soy oil through a transesterification process that makes the oil suitable for burning in diesel engines.


Net energy
The first question regarding biofuels is whether they can provide enough energy to be worth the effort. Fossil fuels come out of the ground in a form that is relatively energy-dense — their pre-processing has been accomplished by geological forces over millions of years. Corn and sugar cane, on the other hand, are much less energy-efficient. It takes about 2.7 kilograms of corn, or 12 kilograms of sugar cane, to produce a litre of ethanol.


Of course, the energy in biofuels comes free from the sun. But to harvest, transport and process the feedstock requires tractors, trucks and production facilities, all of which need energy for their building and operation. The crops also require nitrogen fertilizer, which is derived from natural gas. Critics say that all the effort isn't worth it, at least in terms of net energy.

Patzek and his colleague David Pimentel, a professor of insect ecology and agricultural sciences at Cornell University, have done a number of analyses on the energy requirements of various biofuels. In a 2005 paper, they attempted to quantify all of the energy inputs required to produce and process a feedstock into ethanol4. When using corn as a feedstock, they concluded, it took 6,597 kilocalories of energy to produce the ethanol, whereas the ethanol would yield only 5,130 kilocalories. In other words, biofuels actually use more energy than they provide. Patzek and Pimentel also calculated that the cost of a litre of ethanol is US$1.24, compared with 33 cents for a litre of gasoline. Their analyses of ethanol from other feedstocks, and of biodiesel, were equally discouraging.


But many other researchers have found net energy gains from biofuels. In a paper presented to the International Symposium on Alcohol Fuels in September 2005, Michael Wang, a fuel systems analyst at Argonne National Laboratory at the University of Chicago, concluded that it takes only 0.74 British thermal units (Btu) of fossil energy to produce one million Btu of ethanol from corn5.


Other researchers have come up with similar numbers. In a paper published in Science in 2006, Alexander E. Farrell, an energy policy analyst at the University of California, Berkeley, and colleagues looked at six studies and concluded that ethanol does have a net energy benefit6.


But Bruce Dale, a chemical engineer at Michigan State University, argues that a net energy analysis is largely irrelevant because it ignores the fact that we value different energy carriers in different ways. For instance, it takes three megajoules of energy from coal to create one megajoule of energy from electricity. But electricity is useful to us in a way that heat from coal is not, so we're willing to pay the price. In the same way, we're willing to pay a price for liquid fuel that we can put in our tanks, Dale says.


Because we're trying to use biofuels to replace liquid fuel for transporation, he says, one of the most important metrics is not the total energy used to create the ethanol, but the amount of petroleum it displaces. He calculates that each megajoule of energy from bioethanol displaces 22 megajoules of energy from petroleum.


Extra emissions
Replacing petroleum with biofuels should, on the face of it, be good for climate change. After all, every tonne of carbon emitted by burning biofuels is just a tonne that was absorbed from the atmosphere by the feedstock crop, resulting in no net change. But it's not that simple. The energy used to create the biofuel also emits greenhouse gases.

If biofuels do provide more energy than the fossil fuels needed to produce them, it makes sense that there would be some reduction in greenhouse gas emissions. But the analysis has to take into account the kind of fuel used to produce the ethanol — ethanol made by using coal to provide heat for distillation, for instance, actually increases carbon emissions compared with gasoline — as well as the greenhouse gasses generated by other aspects of the process, such as increased fertilizer use.


In their Science analysis, Farrell and colleagues noted that there are still unanswered questions about how to calculate greenhouse gas emissions over the life cycle of biofuels6. They calculated that switching to ethanol produced from corn reduces emissions moderately, by about 13 percent, compared with using gasoline.

And a recent paper by P.J. Crutzen of the Max Planck Institute for Chemistry in Mainz, Germany, and colleagues concludes that previous studies underestimated the amount of the greenhouse gas nitrogen oxide produced by agricultural use of nitrogen fertilizer. If their new number is right, they say, ethanol made from corn could actually produce more greenhouse gasses than the use of gasoline7.


An even greater concern is that the increased demand for biofuels will cause farmers to cut down forests in order to plant more corn, sugar cane, oil palm trees or soybeans. According to an analysis by Renton Righelato of the World Land Trust in Suffolk and Dominick V. Spracklen of the University of Leeds, leaving the land forested would sequester two to nine times as much carbon over a 30-year period as would be saved by using biofuels8.

In a study published in September, the World Wildlife Fund warned that biodiesel from palm oil will only have a positive environmental impact if the new plantations are planted on fallow land. If forests are cleared to create new plantations, the resulting biofuel will actually have a negative effect9.

Food or fuel
Another concern is that land that could have been used to grow food will be given over to growing crops for fuel.


"Rushing to turn food crops... into fuel for cars, without first examining the impact on global hunger, is a recipe for disaster," the UN rapporteur on food said in his August report to the UN General Assembly1. The report cited estimates that to fill one car tank with biofuel requires an amount of maize that would feed one person for one year.


The report noted that riots broke out in Mexico in February when the price of corn tortillas rose by over 400 percent, the result of an increase in the price of corn brought on in part by increased demand for corn ethanol.


"Agrofuel production is unacceptable if it brings greater hunger and water scarcity to the poor in developing countries," the report says. It concludes by calling for a five-year moratorium on biofuel production while new biofuel technology is under development.

A new breed of biofuels

The technology many are counting on is called cellulosic ethanol. Unlike conventional bioethanol, which is based on sugars or starches extracted from the feedstock, cellulosic ethanol can be made from a plant structural material called lignocellulose, found in everything from corn husks to grasses.

Part of the promise of cellulosic technology is that for feedstock it could use plants like switchgrass, which can be grown on otherwise marginal lands, without irrigation or fertilizer, leaving prime farmlands for food. Agricultural waste such as corn stalks could also be used.
In 2005, the US Department of Agriculture and Department of Energy concluded that crop residues, forest byproducts and other underutilized resources could produce more than a billion tons a year of biomass for cellulosic conversion in the US alone, enough to replace 30 percent of US petroleum consumption by 2030 (ref. 10).

One of the many attractions of cellulosic ethanol is that producing it is potentially much more energy-efficient than using corn. Corn bioethanol requires an outside energy source to provide the heat needed for processing. But cellulosic processing separates the lignin from the cellulose and then burns the lignin to provide energy for distillation.

Fewer fossil fuels are used, which reduces carbon dioxide emissions. In addition, as long as the feedstock doesn't require nitrogen fertilizer, nitrous oxide emissions are cut. In a 2007 paper, Wang and colleagues concluded that use of cellulosic ethanol would reduce greenhouse gas emissions by 88 percent compared with gasoline11.

One problem: cellulosic ethanol isn't ready for market. There are a number of ways to break down cellulose into component sugars that can be fermented, including applying enzymes and chemicals. But the process is still too expensive to produce ethanol on a large scale at a competitive price.

Zero-sum game
But sceptics aren't so sure. "The fact is that with cellulosic ethanol, we don't have the technology yet. We need major breakthroughs in plant physiology. We might wait for cellulosic for a long time," Holt-Gimenez says.


Patzek and other sceptics worry that biofuels are a distraction from other steps that would make a real difference, including solar and wind power and conservation. They dismiss the biofuels boom as a result of government subsidies.

"This is a completely fictitious market. It's floated by the subsidies, tariffs and targets. If those weren't there, you wouldn't see this boom," Holt-Gimenez says.

He worries that biofuels will simply enrich agrobusinesses while at the same time driving countries in the south to switch cropland and forests over to fuel production.

The Worldwatch Institute also recognizes that danger. But in a 2006 report on biofuels, it concluded that if the biofuel industry is managed effectively, it could actually benefit the environment and third-world farmers, who could profit from growing the crops needed to produce the fuel12.

References:

1. Kurt Kleiner - The backlash against Biofuels
2. Ziegler, J. The Impact of Biofuels on the Right to Food. Report No. A/62/289 (United Nations General Assembly, New York, 2007); http://www.righttofood.org/A62289.pdf
3. Doornbosch, R. & Steenblik, R. Round Table on Sustainable Development. Biofuels: Is the Cure Worse Than the Disease? Report No. SG/SD/RT(2007)3/REV1 (Organisation for Economic Co-operation and Development, Paris, 2007); http://www.oecd.org/dataoecd/9/3/39411732.pdf
4. Renewable Fuels Association; http://www.ethanolrfa.org/industry/statistics/#E
Pimentel, D. & Patzek, T.W. Nature Resour. Res. 14, 65–76 (2005).
5. Wang, M. in 15th International Symoposium on Alcohol Fuels (San Diego, 2005); http://www.transportation.anl.gov/pdfs/TA/354.pdf
6. Farrell, A.E. et al. Science 311, 506–508 (2006). Article PubMed ChemPort
Crutzen, P.J. et al. Atmos. Chem. Phys. Discuss. 7, 11191–11205 (2007).
7. Righelato, R. & Spracklen, D.V. Science 317, 902 (2007). Article PubMed ISI ChemPort
Reinhardt, G., Rettenmaier, N., Gärtner, S. & Pastowski, A. Rainforest for Biodiesel? Ecological Effects of Using Palm Oil as a Source of Energy (World Wildlife Fund Germany, Frankfurt, 2007); http://www.wupperinst.org/uploads/tx_wibeitrag/wwf_palmoil_study_en.pdf
8. Perlack, R.D. et al. Biomass as a Feedstock for a Bioenergy and Bioproducts Industry: the Technical Feasibility of a Billion-Ton Annual Supply. (US Department of Energy and US Department of Agriculture, Washington, DC, 2005); http://www1.eere.energy.gov/biomass/pdfs/final_billionton_vision_report2.pdf
9. Wang, M. et al. Environ. Res. Lett. 2, 024001 (2007).
Biofuels for Transport: Global Potential and Implications for Sustainable Agriculture and Energy in the 21st Century (Worldwatch Institute, Washington, DC, 2006).

India and Iran likely to sign the Gas Pipeline deal


India on Monday said it will sign "very soon" an agreement with Iran and Pakistan in connection with the transnational pipeline project involving the three countries.

Petroleum Minister Murli Deora after a meeting with his Iranian counterpart Gholam Hosein Nozari for talks on the $7.5 billion Iran-Pakistan-India (IPI) pipeline project said there were "some minor problems" which have been sorted out. "There were also some issues with Pakistan that has been taken care of," Deora said. "The Pakistan oil minister has changed and so we have to deal with the new minister who is going to deal with it. Very soon we should be able to sign the agreement with Iran and Pakistan," he said.

The project was first mooted in 1994 but has been stalled by a series of disputes over prices and transit fees. Finance Minister P Chidambaram also accompanied Deora for the talks held on the sidelines of the meeting of world energy ministers in Jeddah to discuss strategies to calm spiralling crude prices. The meeting comes in the backdrop of the UPA government coming under attack from the Left for allegedly "dragging its feet" on the pipeline.

CPM general secretary Prakash Karat said in Chennai that "We want the negotiations to continue so that the deal is completed". Trilateral talks have remained stuck for the past few months. Indian officials at Jeddah said over phone that Deora and Chidambaram also met oil Nigerian oil minister.

Saturday, June 21, 2008

E-Fuel Unveils world's first Home Ethanol system


The world’s first home ethanol system, which allowsconsumers to create their own ethanol and pump it directly into their cars, was unveiled todayby the E-Fuel Corporation (http://www.efuel100.com/). The revolutionary EFuel100 MicroFueler™ isthe first product that allows anyone to reduce their dependency on oil, greatly diminish theircarbon footprint and produce fuel for under $1.00 per gallon.The MicroFueler is a leading edge product that allows consumers to create ethanol, simply andsafely, with the readily available ingredients of sugar, yeast and water, and a standardhousehold 110-220 AC power supply. Cars running on sugar-based ethanol produce 85% fewercarbon emissions than gasoline. Businesses, such as breweries, bars and restaurants can evenuse discarded alcohol beverages to create ethanol, for as little as $0.10 per gallon.“E-Fuel will have a profound impact on the way we obtain and consume fuel, not unlike theparadigm shift that occurred in the 80s from the mainframe computer to the PC,” said TomQuinn, E-Fuel Founder and CEO. “Just as the PC brought desktop computing to the home,E-Fuel will bring the filling station to the home. Making local sugar-based ethanol fuel productionpossible, E-Fuel can solve the commercial ethanol transportation and pump station problemswhile providing consumers lower cost fuel due to micro efficiencies.”The portable MicroFueler unit houses the same consumer-friendly LCD touch screen interfaceand hose pumping system found at the corner gas station, so consumers can produce wherethey consume, eliminating energy waste and saving dollars. The retractable pumping hoseextends up to 50 feet, eliminating the need to situate the unit directly beside the householdvehicle.With its breakthrough membrane technology, E-Fuel has made an industrial process possibleon a much smaller scale, and without dangerous combustion processes. Additionally, theMicroFueler has achieved an 80% power improvement over commercial ethanol manufacturers,thus raising the bar of the renewable fuel standard for carbon reduction.“Henry Ford started the automobile revolution using ethanol, predicting that this renewable andaccessible fuel it would become the ‘fuel of the future,’” said Mr. Quinn. “If not for the Prohibitionlaws in the 1920s and the subsequent rise of the oil industry, ethanol may never have lost itspublic appeal. E-Fuel will deliver on Ford’s prediction, and enable consumers to bypass thecostly oil infrastructure and their reliance on fossil fuels,” said Mr. Quinn.MicroFueler AvailabilityE-Fuel is now accepting orders for the MicroFueler atwww.efuel100.com, and first shipmentswill begin in the fourth quarter of 2008.


The EFuel100 MicroFueler is available in the UnitedStates at $9,995.00, and all initial orders require a deposit. The MicroFueler will also bedistributed to China, Brazil and the UK. For U.S. buyers there are several local and nationalrebates available, and more importantly, E-Fuel will be introducing a Carbon Credit Program tooffset costs and assist in reducing carbon emissions. Consumers and interested resellers canalso attend E-Fuel sponsored workshops to learn more about the MicroFueler operation.Complete details on pricing, availability, the E-Fuel Carbon Credit Program and local workshopscan be found atwww.efuel100.com.About E‐FuelThe E‐Fuel Corporation was founded in March 2007 by Tom Quinn and ethanol scientist FloydButterfield to create efficient micro ethanol refinery products for people who want to break theirdependency on oil. As chairman of E‐Fuel, a privately held company, Quinn has solely funded thecompany and is instrumental in both corporate leadership and product development.


With more than 30 people employed in Los Gatos and Paso Robles, California and China, the employeesof E‐Fuel represent some of the top United States ethanol researchers and proven Silicon Valleyprofessionals who draw upon diverse expertise in the ethanol, electronics, automotive and softwareindustries.E‐Fuel creates ethanol micro refinery products that conform to U.S. safety and durability standards andinclude modern safety features. E‐Fuel products are available for purchase online and through anetwork of worldwide resellers. For more information. Ref: http://www.efuel100.com/

Wednesday, June 18, 2008

Solar Panel Efficiency improves further


Physicist Bram Hoex and colleagues at Eindhoven University of Technology, together with the Fraunhofer Institute in Germany, have developed a process that improves the energy produced by solar panels by six per cent (in relative terms), a new world record in solar cell efficiency.

By using an ultra-thin aluminium oxide layer at the front of the solar cell, Hoex was able to improve the cell’s conversion of sunlight into energy from 21.9 per cent to 23.2 per cent. The record breaking technology was showcased in the USA at a major solar power convention. An improvement of more than 1 per cent (in absolute terms) may at first glance appear modest, but it can enable solar cell manufacturers to greatly increase the performance of their products. The ultra-thin (about 30 nanometers) aluminium oxide film contains unprecedented high levels of built-in negative charges, preventing the significant energy losses that usually escape from the surface of solar cell arrays during the day. It is one of the many innovations developing in the accelerating global solar module industry. A number of major solar cell manufacturers have already shown interest.
The breakthrough takes solar panel technology one step closer in the battle for truly viable and effective sustainable energy. It is hoped that in less than 10 years solar generated power will be as cheap to produce as fossil fuel energy, reducing greenhouse gas emissions and diminishing the effects of global warming. Applying the ultra-thin film is a low-cost process, meaning solar cell manufacturers can adapt their existing production methods to include it. This will be good news for consumers of solar power systems in the future, especially in developing nations as they struggle to meet the energy demands of growing populations.

Friday, June 13, 2008

Inverters attaining new efficiencies


A key technology required for the exploitation of renewable resources is the humble inverter. Widely regarded as a 'black box' component, highly efficient inverters are crucial to enable the widespread introduction of grid-integrated price parity renewables. David Appleyard reports.

Simple enough in conception, inverters, so-named because they perform the opposite function of a rectifier, convert direct current (DC) into alternating current (AC). Used in an endlessly varied range of applications from electronic power supplies to bulk power transmission, in the renewable sector the inverter converts DC from sources such as PV modules to AC either for local use or at voltages more suitable for export to the transmission grid.

In addition, in the case of variable-speed generation devices – such as wind turbines, marine tidal and similar – an inverter is essential for the device to connect to the grid and supply code compliant power. This includes almost all modern wind turbines – which are variable speed – the one exception being turbines that are equipped with a hydrodynamic torque converter that regulates generator speed.

Aside from grid connection, there are numerous advantages associated with the use of an inverter in the wind sector. This includes the ability to help balance the grid, supplying reactive power for instance, and the possibility of reducing the output from a machine during the evening to minimize noise, while still maintaining a grid-code-compliant supply.

There are three main types of inverter system used in the renewables sector, grid-tie (grid-connected), stand-alone and hybrids. In grid-tie systems the solar panels or wind turbines feed the inverter, which in turn supplies the grid. Grid-connected inverters are usually optimized for one type of generator, such as PV, and generally operate at a higher DC voltage than stand-alone inverters. The power output may either be sold to the local utility company or, in the case of commercial and domestic systems, offset a portion of the power used on site.

Stand-alone systems do not have the ability to supply power to the grid and will usually include battery systems that are charged by the renewable technology before the inverter is used to supply mains-quality AC power. Hybrid grid-tie inverters also use batteries, allowing both stand-alone and mains supply operation, although this does result in some efficiency loss when in grid supply mode: with some older inverters, losses can be up to 50% of the available power. To protect utility transmission line workers, inverters are also required to cut grid supply in the event of a grid failure. Switching between mains supply and stand-alone, or island mode, can be achieved by either passive or active islanding detection.

Inverter designs

Simple inverters operate by running a DC input into at least two power switches, rapidly turning these switches off and on, and thus feeding opposite sides of a transformer. The transformer converts this DC input to alternate sides into an AC output, which may be a simple square wave, a modified sine wave, or a true sine wave depending on the complexity of the inverter and its intended application.

In the case of high-voltage transmission used in national transmission grids, a good-quality sine wave voltage supply is required in order to work efficiently. Other applications may be happy with a simple square wave, although simple wave inverters, while cheaper, are less efficient in most applications. However, as costs have fallen the most basic square wave systems, which are only suitable for running some power tools, incandescent lights or heating elements and similar, are becoming increasingly rare.

More complex circuitry allows outputs of a modified sine wave, which is in effect a stepped square wave. Suitable for most domestic appliances, such outputs may not work with micro-electronic systems or more sensitive devices and motors will use about 20% more power when supplied with a modified sine wave, rather than with a true sine wave. Nonetheless, modified square wave inverters are a good choice for many applications since their high surge capacity lets them start motors, while a high efficiency lets them run small appliances economically.

For any grid-connected generation system, one of the most important technical issues is the power quality, with power factor and harmonic consideration significant influences. The most complex inverter systems deliver a true sine wave output that can be of better quality than that supplied from the mains network.

Transistors and various other types of solid state devices have long been incorporated into inverter circuit designs, but since early transistors were not capable of handling the voltages found in most inverter applications it was the development of the thyristor or silicon-controlled rectifier (SCR), in the mid-1950s, that allowed solid state inverter circuits to be developed. Now available in higher voltage and current ratings, semiconductors which can be switched using control signals have become the preferred design for inverter circuits. Today, with the exception of some wind applications, the vast majority of such devices used in the renewable energy sector are microelectronic in design.

A wealth of different inverter design architecture and numerous strategies exist. The waveform can be filtered using capacitors and inductors with low-pass filters allowing the fundamental frequency of the waveform through, while limiting the passage of harmonics. Feedback rectifiers or antiparallel diodes may be used when the switch is off to deal with inductive load currents, since most loads contain inductance.

In renewable applications, inverters are typically designed to provide power at a fixed frequency, in which case a resonant filter can be used to block many of the undesirable harmonics.

The quality of an inverter can be expressed by using Fourier analysis of its output waveform to calculate the total harmonic distortion (THD) of the ideal pure sine wave, though to a large extent the quality of output is characterized by the intended application. The most important inverter parameters are rated DC and AC power, maximum power point (MPP) voltage range, maximum DC/AC current and voltage and rated DC/AC current and voltage. Other parameters are power consumption in standby mode, power in sleeping (night time) mode, power factor, distortion, noise level and such like.

Meanwhile, inverter efficiency is a ratio of AC power out and DC power in as shown:

∏ = AC Power / DC Power

However, inevitably inverters have flaws, modern electronic inverters are very efficient over a wide range of outputs, but some power is required simply to keep the inverter running and they are less efficient when running small loads. Efficiencies are typically rated at 90%–95%, although actual field efficiencies may be less, with some systems consuming power at night for example. Efficiency ratings are usually stated with reference to a resistive load, such as a heating element, but with some applications the efficiency is more accurately broken into two parts – the efficiency of the inverter, and the efficiency of the waveform.

Inverters are also much less efficient when used at the low end of their maximum power, so sizing the inverter for its intended application is a key factor in determining system efficiency. Undersizing the inverter will cause overloading and shutdown or power limitation, while oversizing will see standing losses increase, reducing overall efficiency and increasing the purchase costs. Achieving high efficiency in the face of a varying power output presents design challenges. However, energy management can reduce peak demand, allowing the inverter to be sized at close to the average, rather than theoretical peak, demand. Input voltage to the inverter depends on inverter power – for small domestic systems of say 100 watts an input voltage of 12 volts would be appropriate. For larger systems, inverters can be connected in parallel if higher powers are needed, and for the biggest systems three-phase inverters are available. Along with charge regulating electronics, three-phase inverters are also often used for high power applications, such as utility-scale transmission and HVDC.

Solar PV inverters

One of the world’s fastest growing energy technologies is grid-connected solar photovoltaic, particularly in Japan, southern Europe and the USA. Manufacturers of photovoltaic inverters include SMA Technologie AG, SatCon Technology Corp, Studer Innotec, Xantrex, Fronius, Sputnik and Mitsubishi, among others. Typical grid-connected PV installations feature so-called ‘central inverters’ which are frequently connected as master–slave systems. Under these conditions subsequent inverters are only switched on when solar radiation is above a certain threshold or if the main inverter fails.

String inverters are connected to strings of modules, and are used in applications across a wide range of power outputs. They allow more reliable operation than a single central inverter. Furthermore, maintenance for string inverters may be cheaper – even for large systems – since untrained personnel can exchange them in case of failure, whereas for central inverters considerable, and costly, expertise is required for servicing.

Among the more popular grid-tie inverters in Europe is the SMA ‘Sunny Boy’ system, which is designed to be used with a series wired string of 6–24 modules, depending upon inverter type.
Meanwhile, module inverters are mostly used in small systems; while they may also be suitable for larger systems, cheaper central or string inverters are more frequently used.

Inverters are the most sophisticated electronic devices installed in photovoltaic systems – there are various types in use. In line-commutated inverters, thyristors, are used as switching elements. Line-commutated inverters are not suitable for use in stand-alone systems because AC voltage is required to turn off the thyristors, although self-commutated inverters can operate without AC grid voltage.

In most cases, grid-connected inverters use a current control scheme, which has the advantage of a higher power factor and better transient current suppression. Grid-tie inverters also automatically shut down in the event of a high or low AC grid voltage or frequency, or in the event of grid or inverter failure.

The move to transformerless systems

Transformer-based inverters usually have a much higher maximum surge rating than electronic-based systems. However, transformerless inverters have been increasingly used in PV systems as they are considerably more efficient and can be produced at a much more competitive price.

Developed nearly 30 years ago, the earliest systems used metal oxide semiconductor field effect transistors (MOSFETs) as switching transistors to produce a stepped output voltage. In 1982, the first pulsed transformerless inverter using MOSFETs was developed at the Swiss Federal Institute of Technology in Zurich with an efficiency of 95%.

Pulse-width modulated, self-commutated transformerless inverters remain the most common solution in use today for PV systems, as grid-commutated thyristor devices have increasingly been squeezed out of the market. This is because grid-commutated inverters tend to have a smaller voltage range and need higher reactive power to operate. Indeed, transformerless inverters continue to advance around the world and have achieved a market of about 70%, although the US market is still dominated by transformer-based inverters since standards required DC grounding (earthing), which is not possible with transformerless inverters. The new releases of UL1741 and the NEC2008 no longer require DC grounding so clear the way for transformerless inverters. However, there is still a 600V DC voltage limitation, which particularly constrains three phase transformerless inverters. The devices typically achieve peak efficiencies of up to 98% and European efficiencies of 97.7%.

Development of SiC (silicon carbide) MOSFETs is expected to achieve a significant reduction of switching and conduction losses – of more than 25% – resulting in a peak efficiency of 98.5% and a European efficiency of more than 98% for an entire inverter. Next-generation power switches based on SiC are expected to become commercially available over the next few years. Due to the high switching-speed of SiC semiconductors, in future switching frequencies will be increased further, thus significantly reducing the size and weight of the inductive components of inverters, and consequently costs.

Indeed, in recent weeks the Fraunhofer Institute for Solar Energy Systems (ISE) has set what it says is a new record for inverter efficiency, at 98.5%, using SiC transistors.

In a test using prototype silicon carbide-based MOSFETs, manufactured by CREE, Inc., Fraunhofer researchers report they reduced the power dissipation by 30%–50% when compared with traditional silicon-based transistors. ‘Silicon carbide components switch faster and have a smaller forward bias power loss than traditional silicon-based transistors,’ explains Dr Bruno Burger, head of the Power Electronics Group at Fraunhofer ISE. The Fraunhofer team achieved the result with a single-phase inverter and a nominal power rating of 5 kW.

Certainly, other organizations are also exploring SiC technologies. For instance, SemiSouth Laboratories, Inc. recently announced that, in trials, its enhancement-mode SiC junction field effect transistor (JFET) had significantly improved the efficiency of an off-the-shelf inverter commonly used in residential and commercial solar power energy systems.

Replacing the existing transistors with SemiSouth’s version allowed the inverter to reduce losses by as much as 50% in the grid-connected, low-frequency isolated inverter designed with conventional silicon Insulated Gate Bipolar Transistors (IGBTs).

The new enhancement-mode JFET can be used as a direct replacement for silicon MOSFETs and IGBTs in virtually any off-the-shelf converter or inverter design, the company says. Vess Johnson, SemiSouth’s president and CEO, comments, ‘The fact that the JFETs can be used as a drop-in replacement means that the barrier to entry has been greatly reduced and that designers working with these devices will be able to see immediate performance and efficiency improvements and will be able to drive new and better products to market much faster.’

Remote monitoring

Along with efficiency improvements, cutting the size and weight, and improving the operational flexibility, another development has seen a leap in the availability of inverter communications systems. A number of companies are now offering inverters that can communicate wirelessly with the internet to enable remote monitoring and diagnostics.

Xantrex, for instance, recently launched its Gateway wireless monitoring system for small-scale solar power installations. The communication component keeps the owner or operator, at any location, informed about the system’s operation and energy production by connecting the single-phase grid-tie inverter to the internet. It logs the system’s performance data directly from the inverters and transmits that information to Yahoo™ Widget-based software. The system can monitor a network of up to 20 such inverters. Fronius is among the other companies offering similar wireless transceiver systems.

Looking forward

One issue that remains unresolved to date is that of standards. Differences between, for instance, Europe’s IEC, the c-Tick standard in Australia, GOST in Russia, and the UL and c-UL safety standards in the United States and Canada mean that manufacturers wishing to supply international markets must frequently, in effect, produce two or three designs to achieve an all-but-identical result.

A key objective for the industry is to prepare and publish international standards for all electrical and electronic technologies, including inverters, so that components or systems manufactured in one country can be sold and used in all others.

The renewable energy boom across Europe and elsewhere has opened up an unprecedented market for solar energy-based inverters. Inverters for solar energy systems account for some 99.4% of the renewable energy market, according to recent research from analysis firm Frost & Sullivan, and in Europe at least, revenues are expected to increase at a compound annual growth rate (CAGR) of 24.9% out to 2011.

Chandni Raj, research analyst for the firm, observes: ‘PV inverters offer many advantages; first of all ease in implementation in the urban environment for high consumption generation of electricity even in dim sunlight. They also have limited impact on surroundings. Th ese are two key factors that are encouraging the market. Moreover, they offer better control over power consumption and lower electricity bills.’

Germany takes the lion’s share of sales in Europe, say Frost & Sullivan, maintaining a clear lead as a major producer and consumer of PV inverters. Raj comments: ‘The German trump card is not an excess of sunshine over other regions. It is the far-sighted vision and support of the German government ... feed-in tariffs (FITs) and incentives worked like a magic wand, accelerating renewable energy growth.’

Germany is followed by Spain as another PV inverter hotspot. ‘Spain has made amazing strides in the renewable energy-based inverters industry in a short span of time owing to the generous government subsidies,’ adds Raj, saying that in Europe, Italy, the UK, Austria, Switzerland, Denmark and the Netherlands have growing markets, while Greece and Portugal are evolving to be highly-promising. ‘Some countries are growing fast. Some others are showing interesting signs of expansion. The European market as a whole now sees soaring sales and spiralling growth,’ says Raj.

With significant market growth also seen in the USA and Asia, a large number of players and new entrants are seeing the market for PV inverters become more competitive. As a result, prices are expected to fall and products with innovative features and greater efficiency will flood the marketplace.

This anticipated activity is being reflected in the number of new investments in production capacity which have been announced over the past few months.

For instance, Sputnik Engineering AG is increasing its annual production capacity for string and central inverters with its new facility, which went into initial operation in March in the Biel suburb of Port, Switzerland. The company aims to see its capacity reach 400 MW annually by the end of the year.

The new Sputnik plant will assemble central inverters with outputs from 50 kW upwards. Sputnik managing director Christoph von Bergen identified Germany, Spain and Italy, along with France and Greece as areas showing significant market growth. ‘While the sales to Spain grew by 250%, they increased in Italy by 200% and in France by 180%. At the end of 2007 Sputnik closed a sale on the delivery of 2 MW to Greece,’ he said.

SMA Technologie AG, meanwhile, has begun construction on what it says is the world’s largest solar inverter factory in Kassel, Germany, near its headquarters in Niestetal.

The company is expecting continuous growth in the coming years and to meet this increasing demand is developing a new 15,000 m2 production facility that is designed to be completely CO2-neutral and has a virtually independent power supply with a MW-scale BIPV system. ‘The demand for SMA’s solar inverters is continuously increasing, confirming the growth trend. Expanding our production capacities is an important step to further improve our international competitiveness’, says chief executive Günther Cramer.

It seems that with exciting technological developments set to offer greater efficiencies and higher power ratings, coupled with the industry-wide ramp-up that will inevitably result in cost reductions, the role of the inverter in delivering the price parity goal for the renewables industry is assured.

New and Renewable Energy

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