Revolutionary power: Direct current in buildings

Jul 20, 2012
Siemens, working together with European partners, is studying if and how direct current (DC) could be used inside buildings in addition to the usual alternating current (AC). This addition could save energy when used in certain applications, such as in office buildings. It could also be advantageous for the integration of renewable energy sources and for grid stability. The project, known as DC Components and Grid (DCC+G), is funded by a number of European research ministries and will run until spring 2015. The picture shows an office where many laptops are at work. Their DC power supply could in the future be replaced by a large rectifier.

Siemens, working together with European partners, is studying if and how direct current (DC) could be used inside buildings in addition to the usual alternating current (AC). This addition could save energy when used in certain applications, such as in office buildings. It could also be advantageous for the integration of renewable energy sources and for grid stability. The project, known as DC Components and Grid (DCC+G), is funded by a number of European research ministries and will run until spring 2015.

According to a directive, buildings constructed after 2020 will have to be nearly -neutral. The main por-tion of their power requirement must be generated on site using . In comparison, buildings are currently among the world’s biggest energy consumers, being responsible for around 40 percent of the total consumption.

Almost every one of today’s consumption points in buildings utilizes DC. Every system or device has its own power supply that takes 230-volt AC from the low-voltage grid and converts it into an appropriate DC voltage. A DC power network within a building would enable the innumerable decentralized power supplies to be replaced by several large rectifiers. Such centralization would boost efficiency for the IT sector, for example, because the power supply units of laptops and computer clusters suffer relatively high losses. The situation is similar in the case of lighting systems that contain light-emitting diodes. LEDs are becoming a mass market item, and could receive another boost if DC networks were used.

The DCC+G consortium, which is led by Corporate Technology (CT), Siemens’ global research department, wants to set up an optimized 380-volt DC network, taking an office building and a superstore as examples. The researchers expect to achieve energy savings of five percent in each case. The partners in the project, which include Philips, Infineon Technologies, and the Fraunhofer Institute for Integrated Systems and Device Technology (IISB) in Erlangen, are working on new semiconductor technologies for high-efficiency control components, switching systems for net-work protection, and rectifiers that serve as network-stabilizing interfaces to the conventional secondary distribution network. They are also studying network architectures and energy man-agement systems for optimal energy distribution in the DC net-work. is focusing here on sensor systems. Among other things, researchers at CT want to develop and integrate new kinds of electrically isolated current and voltage sensors for direct volt-age systems with large bandwidths. They also intend to push forward innovation in sensor systems for monitoring electrical energy flows.

DCC+G is linked to ENIAC (European Nanoelectronics Initiative Advisory Council) and is supported from EU and several european research ministries. In Germany the Federal Research Ministry supports DCC+G with four million Euro using the research pro-gram IKT 2020. The support of highly efficient and economic energy systems reflects the focus of the national research in the ICT sector.​

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Eikka
not rated yet Jul 20, 2012
Real world appliances use a wild variety of different voltages, and transmitting power efficiently requires high voltage anyways unless you want to install wires as thick as concrete rebar, so there's actually a very small niche of applications that would benefit from DC power. For all the rest, you still need the wall-warts and power supplies that contain pretty much the same components they do now whether they're AC or DC. Using DC just brings more complexity to the system and makes it more expensive because you can't use simple components like transformers directly.

Even for solar/wind/etc system, the allure of a full DC system is misleading because the power output must be regulated anyways through a device that is pretty much a DC-to-AC inverter with an extra step that turns it back to DC at the end.

It seems they want to make 5% savings and pay 150% the price for it.
AnalogICman
not rated yet Aug 01, 2012
I agree that high-power applications should not consider dc. There is relatively high cost associated with >50V dc safety. Ground fault isolators are less effective and more complex. The human body is more susceptible to dc than ac. For this reason, dc building wiring may only make sense at 50V.

For lighting, and building automation, and perhaps some low power USB type convenience outlets, 50V could be OK from a copper wiring cost standpoint. Not sure about Europe, but in US, most residential wiring already uses 14 gauge copper for house wiring. For LED lighting applications, this is overkill today, and a new building code would likely be able to get by with significantly less copper.

From an IC cost standpoint, integrating 50V operating with single-chip processing offers a low-cost, low vampire current integration path for any equipment tied to a 50V bus. There is IC industry infrastructure already in place from automotive and communications for 50V (80V to 120V breakdowns).
Eikka
not rated yet Aug 03, 2012
The human body is more susceptible to dc than ac. For this reason, dc building wiring may only make sense at 50V.


That's false. The main mode of injury from DC power is burning, because you don't feel DC going across your body until you do, since it doesn't jolt and cramp your muscles like AC does. As such, it takes many times more current (and indirectly voltage) to make DC as dangerous.

The reason for the 50 VDC limit is that a battery system that is nominally 50 volts will actually reach over 60 volts when full. Compare e.g. a 12 Volt car battery is actually 13.8 to 14.7 Volts at full charge.

60 volts is a completely arbitrary number, it's simply a definition to make a difference between what is meant with low and high voltage, with the assumption that high voltage presents a potential shock hazard. Incidentally, AC power is considered hazardous at 30 volts and above.
Eikka
not rated yet Aug 03, 2012
Not sure about Europe, but in US, most residential wiring already uses 14 gauge copper for house wiring.


In Europe, wiring is graded by the cross-section area in square millimeters, and there exists a rule of thumb for low voltage systems that demands 3 sq-mm for each Ampere to prevent excessive voltage/energy loss in the wire.

Suppose you have a 6 Amp 50 V circuit for lighting a maximum of 300 W worth of CFL/LEDs. That would be 18 sq-mm which corresponds to AWG 5, which has pretty much exactly 1 mOhm/m of resistance, which means a 100 meter run will lose half a volt at full current.