家電產品朝直流電發展 狄高
2009年1月6日 信報財經新聞
目前大部分家庭電器都使用 220V 交流電（AC），如電燈、冷氣機或雪櫃等。但我們日常使用的中、小型電器卻大多數使用直流電；例如電腦、LCD 電視、電話或影音器材等，都是使用火牛（即變壓器）把交流電轉換成直流電（DC）運作。有沒有想過既然很多電器都使用直流電，我們可以把全屋電制變成直流電接口，所有電器便毋須再用火牛，直接插到電制上使用便可以了。
效果更加環保
事實上，日本已有電器生產商朝這個方向發展，研製直流供電系統，直接向全家電器提供直流電。使用了直流供電系統後，電器便毋須再使用火牛，這既可簡化電器的設計，也可以提高電力轉換效率，更加省電環保。
我們使用直流電的電器規格並不統一，因此每件電器都要使用自己的火牛，才可變壓。例如室內無線電話多使用 3.6v 電壓、電腦使用 12v 及 5v，有些家電為配合筆芯電的 1.5v 電壓，因而使用 3v 或 9v，沒有統一標準。直流供電系統出現後，小電器的電壓多會跟隨電腦常用 12v 和 5v，跟電腦規格看齊。
適用於數據中心
當所有電器都使用 12v 和 5v 後，加上全屋使用直流供電，電器便毋須再使用內置變壓器或外置火牛了，可以直接接駁到直流電源上使用。直流供電系統將最先應用在數據中心，這可以令每台伺服器簡化，毋須再使用火牛，令每個機櫃可以安裝更多的伺服器，也減少了火牛發熱的問題。
此外，在目前數據中心的設備中，為確保電力不會中斷，數據中心必須使用 UPS 後備電源。UPS 可以在斷電時繼續提供 220V 交流電，令伺服器繼續運作。若整個數據中心改用直流供電，UPS 便只須提供 12v 直流電便可，設計上可簡單得多。
多年來，我們一直使用高電壓的交流電，是因為在輸電網上，高電壓可以減少電力損耗，但當電力進入家中後，由於現在大部分電子器材都使用低電壓直流電，如果能夠在室內預先把交流電轉成低電壓直流電，避免每件電器自行轉壓，轉換效率可以更高，因此直流供電系統將是一套極具潛力的環保電力系統。
AC/DC: Not just a rock band anymore . Junko Yoshida
02.10.2008 EETimes.com
http://www.eetimes.com/showArticle.jhtml?articleID=210605193
MAKUHARI, Japan — Sharp Corp. and TDK Corp. have revived the apparently never-ending DC vs. AC debate.
You'll recall that it started back when Thomas Edison promoted direct current power generation while Nikola Tesla invented a relatively simple AC induction motor and advocated a alternating current distribution system.
At the Ceatec Japan show here, Sharp showed what the company calls its "DC Eco House," a concept illustrating carbon-neutral living.
Sharp created a miniature house equipped with crystalline solar modules on its roof, generating power in DC, which can be directly distributed throughout the house to power up "the next-generation" refrigerator, air conditioner, LCD TVs and power LED lights, all featuring a DC input.
Similarly, TDK promoted a partly DC-powered "eco home," anticipating a combination of clean energies, such as solar and wind power, and conventional commercial electricity.
The TDK mock-up showed a flow of energy from multiple energy sources not only to the home but throughout the home, with Home Energy Management System installed inside the home.
Both companies are advocating foregoing multiple conversions of DC-to-AC and AC-to-DC. They believe such a step will prevent energy losses by up to "several percent."
They are asking: Isn't it about time for DC power delivery systems to replace, or at least augment, the current AC distribution system " at home?
Some active discussions are already taking place in the United States to promote the use of DC power in facilities such as datacenters.
What's new at Ceatec, a Japanese consumer electronics show, is that the similar debate now includes power to the home.
DC power delivery systems for home?
A Sharp spokeswoman stressed that the company is not being naive. "We understand that proposing a DC infrastructure is a bold move. It affects power companies' business, it asks for alterations in power transmission cables, and it demands big changes in every home appliance now equipped with an AC input," she said.
But Sharp thinks it's time to start exploring enabling technologies capable of supplying constant and stable DC electricity power.
She said, "Today, the power generated by solar cells needs to be converted into AC, before it's sent to the grid. The power, transmitted from the grid back to home, needs to be converted to DC again, at every home appliance. We're introducing a lot of inefficiencies in our energy use."
Historical fact
It is a historical fact that Tesla won the argument as seen in today's utilities, which are designed to generate, transmit, and deliver electricity in the form of alternating current.
But the Japanese companies believe that fundamental premises for the original debate have become obsolete.
For its part, Edison, unable to improve his DC system, lost the battle, because in the 19th century, DC power generation was limited to a relatively low voltage potential and DC power could not be transmitted beyond a mile. Today, high-voltage direct current is a viable method of transmitting power over long distances.
But more importantly, they say, what if future homes do come with solar panels and they start generating their own power?
Further, they pointed out that many consumer electronics devices and appliances today already operate " internally " on DC power.
An official at TDK's booth noted, "Unlike old picture-tube TVs or washing machines of 20 years ago, a growing number of consumer devices today use DC, including PCs, LCD TV and portable devices like cell phones." This is because DC can be precisely regulated for sensitive components.
Neither Sharp nor TDK gave out exact figures -- how much power is actually being wasted in the process of AC-DC conversions, except for saying "several percent." They said that each device and appliance is different.
While the proposal for DC power delivery systems may sound like pie-in-the-sky, both Sharp and TDK believe they can influence the debate, because they have technologies relevant to an eventual transition.
Sharp, armed with crystalline solar cells and LCD technologies, demonstrated a prototype of solar-powered LCD TV.
Calling it "off-the-grid TV," the Japanese company illustrated in its prototype how it's possible for a 52-inch LCD TV, consuming 220 kWh (kilowatt hour) per year (assuming a consumer watches TV 4.5 hours a day), can be powered by crystalline solar modules " measuring roughly 1 meter x 1.6 meters -- capable of generating 220 Wh.
Similarly, TDK displayed the company's dye-sensitized solar cell technology, which can now be applied to flexible cells. TDK also showed: DC-to-DC power modules, essential for stable power supply; a two-way AC-to-DC converter, capable of converting surplus power back into AC, which is in development; and a Lithium ion battery for storing energy, also still in development.
*****
Further reading -
Bringing Back DC Electricity from ecogeek
A Current in Every Ceiling from greentech media
