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Three measures: Delivering a greener future

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By Steinmetz

With pressures ever increasing to conserve energy and reduce carbon emissions, adoption of cutting-edge power electronics technologies for electrical power, improvement of equipment energy efficiency, and large-scale application of solar power are three key measures that must be undertaken to deliver a greener future.

With the end of fossil fuels on the horizon and the world's energy demands ever rising, energy utilization efficiency must be improved, with new sources utilized. Clean Edge Inc., a global energy market research firm, predicts in its Clean Energy Trends 2011 report that the three major green energy industries (solar, wind & biofuel) will reach a total revenue of USD349.2 billion by 2020.

Carbon emissions have also become a global concern; any company with an image to maintain must make an effort to minimize them. With a goal released by the China State Council in November 2009 to cut overall carbon dioxide emissions against GDP in 2020 by 40 to 45 percent from its 2005 levels, all walks of life have a stake.

Measure 1: Advanced technologies

Three-phrase alternating current (AC) transmitted at 50/60Hz has been the foundation of the modern electrical grid for one hundred years. However, alternative energy sources are bringing changes to the equation. Wind power generates alternating current with varying frequency and voltage, while solar power generates direct current with variable voltage. With electricity consumption, the rotating speed of electric motors, which consume almost half of the overall power generated, needs to be adjustable to meet user needs and save energy; in electricity transmission, the grid needs to be stable, flexible, and maintain a constant frequency to improve the usage rate. All require an efficient power converter to maintain a fixed frequency and voltage, even when the energy source transmits at a changing frequency (or DC) and voltage. Power electronics technologies are suitable under these circumstances.

Power electronics technologies

Power electronics can be defined as the usage of technologies typically employed in the electronics industry for the generation of electrical power. The key technology for the power utilized in electronics is the semiconductor. Power converters are the actual carriers that underpin this technology. Leveraging modern techniques in power control, converters dynamically enable conduction and switch-off of semiconductors during energy conversion from one form to another. These technologies are transforming traditional grid-based power and facilitating energy saving and emission reduction. This transformation spans the entire electrical lifecycle, from generation to consumption.

For generation, it's the energy sources that are transforming. It is estimated that China's wind power capacity will reach 150 million kilowatts in 2020, while its solar power capacity will be around 20 million kilowatts. However, the voltage and frequency for both do not match conventional grid infrastructure. Power converters work as the connectors with the grid to ensure reliable power transmission, At present, power converters can work at the multi-megawatt level for wind and solar generators, so that grid connection is maintained during voltage fluctuations.

During the consumption phase, electronics regulate the power consumption of electric motors, thus saving energy. China's "11th Five-Year Plan" required a two percent reduction in the power consumed by electric motors; this would save 20 billion kWh of power annually, which is equal to twice the annual output of the Three Gorges Hydropower Station. If electronics technologies are fully utilized for electric motors, mainly through fans and water pumps, the power consumed by them can be reduced by 20 percent.

During the transmission phase, electronics technologies, including flexible AC transmission technology, static var compensator technology, SCR-based high-voltage DC transmission technology, and IGBT-based HVDC light technology, are the core technologies that support the development of smart grids.

Electronics technologies have also played major roles in other areas to boost energy saving, including locomotive traction, energy storage, and the automotive industry.

Semiconductors

Semiconductors have been key to the electronic age. Since the first silicon controlled rectifier (SCR) was invented by General Electric in 1958, they have replaced both rotary and static ion converters to convert and control electrical power in electronic circuits.

Semiconductors are vital to electricity generation, transmission, substation operation, distribution, consumption, and storage. Semiconductors accurately and efficiently convert and control the current, voltage, power, and frequency of electricity in a manner similar to the way a faucet controls water.

Semiconductors function as the channels through which energy flows; their efficiency has a direct impact on the efficiency of the entire system. They change the voltage and frequency of the power supply based on the requirements of the device in question, while transmitting power to each component. Therefore, the lower the energy consumption of semiconductors, the higher the power usage rate of the device making them key to energy saving and emission reduction.

The development of semiconductors has gone through three stages; first-generation semiconductors included high-power diodes and SCRs; second-generation offerings emerged in the 1970s and included gate turn-off thyristors (GTO) and high-power bipolar transistors (bipolar junction transistors or giant transistors), while the third generation arrived in the 1980s and includes field-controlled power semiconductors, represented by insulated-gate bipolar transistors (IGBT).

However, new-generation power semiconductors do not necessarily replace or eliminate older ones. Today, SCRs are still irreplaceable components in high-voltage, high-current devices; they account for half of all semiconductors now produced.

In the late 1980s, semiconductor development became integrated and modularized; that is, a variety of semiconductors, similar or diverse, are packaged into one module, based on the topology of the circuit. This helps reduce device size, cuts costs, and improves reliability. IGBTs have gradually taken over the market that once belonged to SCRs and have been developed to operate in high-voltage and high-current scenarios.

During the SCR and GTO stages, China's semiconductor research and production capability was on par with the rest of the world. However, once its competitors reached the IGBT stage, China's semiconductor industry sputtered and remained stagnant for almost 30 years. After appeals from a group of academicians and experts, including Yousheng Wang of the China Academy of Science, the government finally began pushing forward in late 2006. Thanks to the efforts of companies like Huawei, China is finally building its integrated electronic competency in the power generation area.

Measure 2: Improving equipment efficiency

In the future, saving electricity will be more important than generating it. In the ICT industry, energy conservation and emission reduction are still in their infancy. Normally, ITC equipment consumes less than 50 percent of the total energy at an Internet data center (IDC) or base transceiver station (BTS); this represents a power usage effectiveness (PUE: the ratio of total facility power consumption to IT equipment power consumption) of greater than 2. To save energy and cut emissions, the industry needs a comprehensive energy efficiency management system that allows accurate measure and analysis of the power consumed by each electrical device around the clock. To lower the PUE ratio below 1.2, solutions must be highly efficient so that smart and accurate power efficiency management can be enabled; they can include comprehensive IT equipment room management for the IDC and accurate temperature control and power efficiency management for each row or rack of devices in the equipment room.

To reduce the power consumption for telecom equipment, intelligent scheduling, service migration and intelligent dormancy are needed, to be followed by improved power supplies and leveraging power efficiency management to provide precise refrigeration/cooling, direct ventilation, and heat exchange to ensure the safe operation of ICT equipment and strive for the highest overall power efficiency.

Measure 3: Efficiently generated solar power

In recent years, breakthroughs in the solar cell industry have come in the form of third-generation III–V compound multijunction cells. Concentrating photovoltaic (CPV) power generation systems that use third-generation solar cells as their core parts outperform traditional thermal and nuclear power generation in terms of power conversion efficiency and are now used on a large scale.

In June 2011, Siemens acquired a 16 percent stake in Semprius Inc., a U.S. company engaged in the design and production of III–V compound multi-junction solar cells and devices which feature energy conversion efficiencies up to 40 percent.

The Boeing Spectrolab has developed triple-junction solar cells with a conversion efficiency of 41.6 percent at a 364-sun luminosity concentration and an average conversion efficiency of 40.7 percent in mass production. Another U.S. company (Emcore) has achieved an energy conversion efficiency of 39 percent in mass production, while 1cm2 of its triple-junction solar cells, at a 500-sun concentration, generates 8A current, which equals the energy produced by seven 5-inch polycrystalline silicon solar cells; this output also greatly reduces the usage of semiconductors.

Thanks to economies of scale, the end-to-end costs of III–V compound multi-junction solar cell systems are dropping. According to a forecast by the EU Photovoltaic Technology Platform, their output will jump from 20 to 200 Megawatts while their costs will drop from 2.12 to 1.07 Euros per Watt. Given that CPV solar cells occupy less space, their power generation costs will be reduced to USD0.07 per kWh very soon, which promises a bright future for the industry.

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