Will DC Power Distribution Make a Comeback?

The rise of direct current using devices and direct current generation have some rethinking the use of alternating current in the grid. Let’s start from history of electric power transmission:

In the late 19th century both alternating current (AC) and direct current (DC) were both used to power devices like motors and light bulbs. Over 100 years ago, Edison and Westinghouse were on each side of the DC versus AC debate. Those systems were not interchangeable and they competed for dominance. Thomas Edison developed the first power transmission systems using DC. Meanwhile, AC was pushed by George Westinghouse and several European companies that used Nikola Tesla’s inventions. Finally AC won the game because it made easier to transmit power over long distances using thinner and cheaper wires (voltage could be changed with a simple transformer). Besides problems on going long distance DC had also issues like arcing and connector corrosion.

Has Thomas Edison ultimately won the DC vs AC power transmission controversy against Tesla? Nowadays there are several application fields where DC is making comeback:

These homes that live off the grid (more than 25 percent of the world) easily could accept and benefit from a DC power source, such as solar panels. There might not be any need for DC to AC conversion that wastes some power. How do we get to a DC-powered home? article speculates that the DC-powered future home most likely will need two DC buses. The “other,” electronics, and lighting categories could use a low-power DC bus, for example 12V to 48V. However, the heating, cooling, and appliances categories would benefit from a much higher voltage, for example 380V to 400V. DC will likely be used for new communities that rely on renewable power sources. There are also visions that Wind, solar could provide 99.9% of ALL POWER by 2030.

I would say that design of the DC outlets would need special care (especially at higher voltages): if you unplug a DC device while it’s running, the electricity could arc through the air. This can also cause corrosion and pitting in the metal components. Besides the connectors, there are needs for some redesign on power switching components (light switches, relays etc.) and protection components (fuses, breakers, fault detectors etc..). Edison’s Revenge: Will Direct Current Make a Comeback in the U.S.? article says that DC power system will become cheaper over time, and there are envisions of buildings with both AC and DC power outlets. The biggest issue is going to be the transition.

How do we get to a DC-powered home? article tells that combined, the electronics and “other” categories account for 15-20 percent of the average home total energy use. It is predicted that by 2020 the number can reach 50 percent. More and more of those devices in modern home are DC-powered inside. DC devices such as cell phones, LED lights, and computers typically contain their own rectifier either as separate “wall charger” or built inside device. Most of those devices could be designed in such way that they could accept AC or DC power (very many switched mode AC power supplies can run on DC but not all).

Many small electronics gadgets nowadays can be charged from USB connector (5V power source). There is USB charging specification and EU standards for common mobile phone charger. USB power seems to be becoming more and more commonly available DC power source. There are nowadays mains power extension cords with both normal AC and USB power outputs. And there are even wall Outlet with USB.

AC vs DC power in data center is talked about lately. The preferred DC system is based on a conceptual 380 V DC distribution system (consensus in the literature as a preferred standard) supplying IT equipment that has been modified to accept DC power. Going to DC can help the efficiency compared to USA standard 120/208 system (typically DC systems are 5 to 8 percent more efficient than AC), but best AC power distribution systems today already achieve essentially the same efficiency as hypothetical future DC systems at least then powered from AC source. If the power comes from DC source in the beginning, the situation can be different.

High-voltage direct current transmission (HVDC) is a solution to make more efficient long distance power transmission than what is possible with AC systems. Especially on systems that use cables, the cable capacitance on the high voltage cables causes considerable losses. Transmission losses are lower for DC than for AC voltage, especially in transmission systems that run on several hundred thousand volts. HVDC transmission has typically 30-50% less transmission loss than comparable alternating current overhead lines. High voltage cable links longer than approximately 80 km are only possible with HVDC transmission because the cable capacities absorb the usable electricity at longer runs. The conversion equipment on the both ends of the cable are expensive, which means that HVDC is usually economically feasible on longer than 50 km cable runs and 600 km overhead lines.

DC distribution power systems and energy storages in urban areas is starting to gain interest. DC network built using modern components can be more energy efficient than traditional power distribution (10/20 kV medium voltage and 230/400V low voltage). DC distribution power systems are capable to provide an uninterruptible delivery of current. Feeding house with DC to feed more power for longer distance using existing low voltage cables. There are systems where the power goes to house through existing cables as DC (there are no standards and systems like 900V DC and +-750V DC have been proposed) and is converted to conventional mains AC (230V in Europe) at the house with power electronics. DC in Urban Areas Distribution Power Systems and Microgrids paper says that if the investment costs of the DC power systems can be reduced it could be a strong competitor to conventional AC power systems. Here are some links to papers on this topic (those are in Finnish):

Tekniikka ja Talous magazine article “Tasasähkö tulee takaisin” says that in USA and Asia there are plans to use DC power distribution inside very high buildings which would normally need very expensive medium voltage distribution inside the building. 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. 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.

It is expected that 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.

44 Comments

  1. There Will Be Blood says:

    thank you

    Reply
  2. Tomi Engdahl says:

    Teardown: Cell-phone charger: nice idea done right
    http://www.edn.com/design/power-management/4408109/Cell-phone-charger–nice-idea-done-right

    In terms of actual current (milliamps, or mA), there are three kinds of USB ports dictated by the current specs: a standard downstream port, a charging downstream port, and a dedicated charging port.

    The first two can be found on your computer (and should be labeled as such); the third kind applies to “dumb” wall chargers.

    In the USB 1.0 and 2.0 specs, a standard downstream port is capable of delivering up to 500 mA (0.5A); in USB 3.0, it moves up to 900 mA (0.9A).

    The charging downstream and dedicated charging ports provide up to 1500 mA (1.5A).

    Reply
  3. Friday Fun: AC vs DC human pain test « Tomi Engdahl’s ePanorama blog says:

    [...] Fun: AC vs DC human pain test I just wrote Will DC Power Distribution Make a Comeback? posting and this Friday Fun video AC vs DC human pain test is somewhat related to [...]

    Reply
  4. Tomi Engdahl says:

    Can DC power an entire home?
    http://chrisgammell.com/can-dc-power-an-entire-home/

    AC power vs. DC power: Both are necessary in our everyday lives and switching between the two causes a great deal of strife in electronics. Why do we need both?

    AC of course won out over DC as the power distribution of choice

    Hang on a second though…a DC generator on every home…sounds familiar…where have I heard about something like this before? Oh right, solar power. However, even more interesting than the fact that solar power produces DC power output is that any kind of storage will have to be in DC.

    Concerns about DC wall power: Many devices have different voltages
    Conversions would be required from DC->DC instead of AC->DC.

    Economies of Scale : This is possibly one of the biggest problems that an all DC power system would face: No one does it yet!

    Conversion to AC for certain devices: Motors are the first kind that come to mind. This is basically how Nikola Tesla got started onto AC, proving that it is much more efficient when using AC than DC

    Step up/down transforming: these are VERY high efficiency devices. For power in general, you really can’t beat AC-AC conversion

    Leakage currents and phantom power consumption

    Benfits of using DC instead of AC:

    Higher efficiencies off of battery power
    LED Lighting
    No 60 Hz hum
    Shrinking power supplies

    So the final question comes back to that posed by the giants of the 19th century: AC or DC power? Well, really the answer will be both, as history has shown.

    Reply
  5. Tomi Engdahl says:

    Big Steps In Building: Change Our Wiring to 12 Volt DC
    http://www.treehugger.com/sustainable-product-design/big-steps-in-building-change-our-wiring-to-12-volt-dc.html

    It is time for our codes and our wiring to reflect this, shall we say, transformation. It is time for big steps:
    1) Develop a universal standard around 12 volt dc for all electronics. Enough of this silliness that makes every wall wart a different voltage.
    2) Develop a standard wall plug or distribution system for 12 volt DC. It is ridiculous that the only standard plug for this voltage is the automotive cigarette lighter.
    3) Provide a secondary wiring system in all new houses at 12V DC based on the new plug.
    4) Revise our current wiring codes to reduce the number of 110V outlets and circuits required.

    12VDC power needs no childproofing, no wall warts, creates no EMF and makes adding incremental sources like solar and wind much easier.

    Reply
  6. Tomi Engdahl says:

    DC House
    http://ecmweb.com/contractor/dc-house

    Realizing a cost-effective zero net energy building through direct current (DC) residential distribution

    One ZNE-enabling technology is direct current (DC) residential distribution. Through the use of high-efficiency electronics and bus architecture, a DC distribution system reduces the amount of consumed energy and, subsequently, the amount of on-site renewable generation required, improving the cost-effectiveness of a ZNE residence.

    appliances are fed from multistage power-conversion equipment that first rectifies the incoming AC into DC. Usually, this is followed by a second DC-to-DC converter stage

    The efficiency of the majority of these power supplies usually varies between 70% and 75%.

    If many of the electric loads are native DC, then why not feed them directly from a DC source, making them more efficient due to the reduced number of power-conversion stages?

    Some of these DC-to-DC converters have peak efficiencies as high as 98%.

    A typical DC house could feature two DC voltage buses, a 380VDC for high-power appliances, such as HVAC, washers, and dryers, and a lower 24VDC bus for smaller appliances and lighting. The 24VDC is stepped down from 380VDC and could be distributed throughout the house as a separate power bus (in addition to the 380VDC), or it could be in the form of dedicated power supplies that step down 380VDC to 24VDC for individual applications.

    The DC house would feature one or more renewable sources, such as solar, that would tie directly into the 380VDC bus, as would an energy-storage system, such as a portable battery.

    The DC house today will be powered by a conventional distribution transformer, which will transform the electric utility medium voltage of 13.8kVAC to 240/480VAC, followed by a rectifier that converts the 240/480VAC to 380VDC.

    Because it is designed to be powered in full by local distributed generation sources while disconnected from the grid (island mode), a DC house is inherently a ZNE structure.

    For example, data centers and telecom networks are already converting to DC.

    The first standard to be released by E-Merge is “24VDC for Commercial Spaces.” Used safely in the telecom industry for a long time, safe practices for 48VDC systems have been developed for these systems and can be adopted in DC houses.

    In DC data centers, the industry has agreed upon 380VDC as a standard voltage, organized as a split ±190VDC system, to ensure safety. A similar configuration could be adopted in residences.

    In addition, OEMs are developing connectors that would allow safe disconnection and connection to DC receptacles.

    Reply
  7. Teemu Hakala says:

    Personally I think that 12V is somewhat a low voltage, but that DC has serious advantages over AC in home appliance use.

    I would like to point out a new but established technology, Power Over Ethernet, that has been growing under the radar. It uses cheap standardised cable, the connectors are smallish and numerous and uses a bit higher voltage for efficiency, but still low enough to be very safe. Like all twisted pair Ethernet, galvanic isolation is maintained.

    Messaging goes through the same cable. Very elegant and interesting.

    Most existing applications are along the lines of wifi hotspots powered from their own data cable, but there are some very interesting implementations too, such as Gibson Magic, a multichannel high performance audio transmission network.

    Oh yes, you can power an Arduino via PoE.

    Reply
    • tomi says:

      I also think that 12V is somewhat a low voltage for many things.
      You easily end up needing quite thick wires to get useful power levels and voltage drop.

      I think something higher voltage might be good.. maybe 24V or 48V would be on some sweeter spot.
      Both of them are also widely used voltage levels. 24V is common in trucks and industrial automation systems.
      48V is widely used in telephone systems and also on some automation systems.

      The point on Power Over Ethernet is a good point. I forgot to mention that on my original article for some.
      I have played with it and written on PoE at
      http://www.epanorama.net/blog/2012/05/02/high-power-poe-and-hdbaset/

      Reply
  8. Tomi says:

    In the effort to foster better energy efficiency practices, PMA strives to be part of an industry-wide shift towards DC current.

    There are three contributing factors to this turnaround: Wireless transmission of power is accomplished exclusively in Direct Current formats; battery powered devices – a major beneficiary of the emerging wireless charging spot paradigm – consume power in DC only; and perhaps most significantly, renewable energy sources, such as wind and solar, natively produce energy in DC current.

    Source: http://www.powermatters.org/index.php/power-20/environmental-power

    Reply
  9. Teemu Hakala says:

    I would like to point out that most forms of generating electricity from motion do in fact provide natively AC power. However the frequency might vary wildly so it pays off to have an intermediary state of DC right next to the generator.

    After that, continuing to use DC, even with voltage level shifts, makes much sense. DC networks are in general easier to balance, buffer and synchronise. Building fault-tolerant power delivery does not require very accurate phase matching like that of AC networks.

    The big question seems to be switching off current from network side, when the load is still switched on.

    For small scale, such as for individual small-power devices, PoE seems to be very good.

    Reply
  10. Tomi Engdahl says:

    A follow-up on the DC-powered home
    http://www.edn.com/electronics-blogs/dave-s-power-trips/4406076/A-follow-up-on-the-DC-powered-home

    There certainly are challenges or problems to be addressed on the road to a DC-powered home. Table 1 lists some of the ones discussed in the responses to my original question. The one most often mentioned problem goes all the way back to Edison’s time, DC disconnects. How do you disconnect without drawing an arc? How do you deal with a partial disconnect when an arc is being sustained.

    Probably, the main problem for the low-voltage DC is a lose connection that could have a very small gap where the gap resistance could maintain the current, and the load voltage high enough to keep the appliance working. Eventually, this may cause a thermal problem. At a much higher voltage like 400V DC, a traditional arc problem will occur.

    Distributing low-voltage DC is a problem due to the line loss, particularly at the higher current level. Having to increase the gauge of the wire is not attractive due to the cost. Having a combination, AC and DC, as mentioned above may be a solution. Perhaps choosing a higher DC voltage, 24V+, to help reduce the DC line current, would be beneficial.

    Retrofitting older homes would be a challenge.

    Reply
  11. Tomi Engdahl says:

    IEEE forms 4-pair Power over Ethernet Study Group
    http://www.cablinginstall.com/articles/2013/04/ieee-4pair-poe.html

    The Institute of Electrical and Electronics Engineers (IEEE) announced it has formed a new study group to consider initiating a formal project to standardize four-pair Power over Ethernet (PoE). The 4-pair Power over Ethernet Study Group will consider a four-pair solution’s capability to enhance energy efficiency and provide greater than 25.5 Watts of power in improving PoE.

    “The formation of this study group will allow collaboration on a proposal for the development of a four-pair PoE standard, which would allow support of new PoE applications in the areas of IPTV, industrial Ethernet and more. A four-pair approach would result in increased efficiency, since the use of additional pairs results in lower channel resistance.”

    “PoE has become the dominant powering method in many Ethernet-based products—access points and IP phones, for example—demonstrating that customers will migrate toward convenience. Enabling applications beyond 25.5 Watts will extend this convenience to other products”

    Reply
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    Reply
  14. Tomi Engdahl says:

    Power electronics in renewable energy
    Key power components in solar inverter systems
    http://www.electronicproducts.com/Power_Products/Invertors/Power_electronics_in_renewable_energy.aspx

    Renewable energy, primarily solar and wind, has gained a lot of attention and has proliferated across several countries. Increased efficiency, reduced cost, and reliability are three areas where renewable-energy systems can achieve grid parity. These systems are rapidly advancing on these fronts as they become more intelligent, more loss-less, and smaller in size through increased content in digital and analog power electronics — semiconductor switches, drivers, controllers, and sense elements.

    This article discusses advances in power components, particularly ICs in solar (also called photovoltaic or PV) inverter systems. The goal is to maximize system efficiency through power management control and maximum power point tracking (MPPT). Therefore, particular focus is made on digital controllers that have gained a lot of traction in recent years.

    PV inverters generate a sinusoidal ac waveform at a fixed level from a dc source — PV panels with varying voltages. The output voltage and frequency need to be at a certain level and, if the inverter is connected to the power grid, need to be synchronized with the power-line. Single-, two-, and three-phase types are available for different applications.

    In general, there are three inverter configurations
    Each depends on the power levels.

    A a micro-inverter is a low-power configuration. A medium power configuration between 1 kW to 20 kW is called a string inverter, and a high-power configuration greater than 20 kW is called a central inverter.

    PV inverters are built much like switch-mode power supplies

    In the inverter system, to operate an dc-to-ac converter, the input voltage usually needs to be above the output voltage. To generate a sinusoidal waveform of 230 Vac, an input voltage higher than 400 Vdc is necessary.

    there are three fundamental topologies for inverters:

    Low-frequency transformers (50-60 Hz) (LF)
    High-frequency transformer (HF) and
    Transformer-less inverters (TL)

    The majority of U.S. market uses LF and HF (transformer-based) inverters, as mandated by standards, whereas the majority of the European market uses TL inverters. In the Japan there is an fairly equal split.

    In LF inverters, the transformers are bulky and large, and lower inverter efficiency by 2% to 3%. HF inverters operate greater than 60 Hz, and weigh and cost less. TL inverters weigh less as they have no transformers. They also have increased efficiency due to the absence of the transformer in the system.

    Reply
  15. Tomi Engdahl says:

    Distribution shelf reduces footprint of DAS power cables
    http://www.cablinginstall.com/articles/2013/05/das-power-shelf.html

    At the DAS Congress in Las Vegas (Apr. 30- May 1), GE unveiled its Power Express Class 2 distribution shelf, designed to equip wireless network providers with a solution to reduce the footprint of distributed antenna systems’ (DAS) power cables. The distribution shelf eliminates the need for installing expensive conduit to run the cables, says the company.

    According to GE, the Power Express Class 2 distribution shelves enable power-feed cables to be harnessed in existing infrastructure throughout a commercial building’s data cable raceway. To do this, the distribution modules located on the shelf limit individual circuit outputs to an inherently safe level by taking an input of -48 volt DC power from a battery plant and outputting it in 32 discrete 100-watt circuit cables (levels comparable to a LAN or USB data cable).

    The shelf incorporates internal circuit fusing to the distribution modules, which prevents technicians from installing a higher rated fuse and violating National Electric Code (NEC) Class 2 circuit requirements.

    Class 2 compliance requires that a maximum power output be equal to or less than 100 watts per component. Class 2 circuits are considered to be safer than many others.

    “By delivering an inherently safe power cable complying with the National Electrical Code, the Power Express enables the wireless service provider to run through power cables in existing data cable raceways,” concludes GE’s Schnitzer.

    Reply
  16. Tomi Engdahl says:

    ABB Advance Makes Renewable-Energy Supergrids Practical
    http://www.technologyreview.com/news/507331/abb-advance-makes-renewable-energy-supergrids-practical/

    A high-power circuit breaker makes it possible to create highly efficient DC power grids.

    ABB, the large power and automation company, has developed technology that could provide an efficient way to transmit power from widely distributed solar panels, wind turbines, and other sources of renewable energy. The new technology is a fast and efficient circuit breaker for high-voltage direct-current (DC) power lines, a device that has eluded technologists for 100 years. The breaker makes it possible to join high-voltage DC transmission lines to form a resilient power grid.

    If renewable energy is ever to account for a large part of the total energy supply, countries will need to install new, large-scale transmission grids, both to get power to cities from remote areas such as deserts that often have the best renewable resources, and to combine power from widely distributed wind turbines and solar panels, which can help average out fluctuations in their output. In Europe, there’s been talk for years of a supergrid that would pull together power from hydroelectric dams in Scandinavia with wind farms in Germany and large solar farms in Spain and even North Africa

    But such a supergrid has faced serious technical hurdles.

    The transmission lines that make up conventional power grids use alternating current (AC), which loses large amounts of power over long distances unless complicated and expensive measures are taken. DC is more efficient over long distances, and it offers the additional benefit of working well underground and underwater, reducing or eliminating the need for the unsightly transmission towers that can make it difficult to site new transmission lines.

    ABB’s circuit breaker changes that. Within five milliseconds it can stop the flow of a huge amount of power—equal to the entire output of a nuclear power plant, ABB says.

    Researchers have been trying to develop high-voltage DC circuit breakers for a century (see “Edison’s Revenge: The Rise of DC Power”). Mechanical switches alone didn’t work—they shut off power too slowly. Power electronics made of transistors that can switch on and off large amounts of power offered a possible solution, but they proved far too inefficient. ABB’s solution combines power electronics with a mechanical switch to create a hybrid system that’s both fast and efficient.

    “The hybrid breaker should be less costly.”

    Reply
  17. Tomi Engdahl says:

    Article from 2006:

    A Supergrid for Europe
    http://www.technologyreview.com/news/405558/a-supergrid-for-europe/

    A radical proposal for a high-tech power grid could make possible the continent’s vast expansion of renewable energy sources.

    Europe has big plans for greatly expanding its renewable energy sources, but there’s a problem: weak connections between a patchwork of national power grids. The situation is particularly problematic for wind power, because smaller, isolated grids have more difficulty absorbing the variable power generated by wind farms.

    Last month a Dublin-based wind-farm developer, Airtricity, and Swiss engineering giant ABB began promoting a bold solution to the continent’s power grid bottlenecks: a European subsea supergrid running from Spain to the Baltic Sea, in which high-voltage DC power lines link national grids and deliver power from offshore wind farms. When the wind is blowing over a wind farm on the supergrid, the neighboring cables would carry its power where most needed. When the farms are still, the cables will serve a second role: opening up Europe’s power markets to efficient energy trading.

    The result would be a more integrated and thus more competitive European market, delivering power at lower prices.

    European Union has set a target of 21 percent of electricity from renewable sources by 2010, and much of this will come from wind farms

    A 5,000 megawatt DC power line would carry power west to the U.K., and a second 5,000 megawatt line would run east to continental Europe, perhaps to the Netherlands.

    This flexible DC network would be made possible by digitally controlled, high-voltage DC power converters, a technology that has been entering the market over the past five years. The key, says ABB project manager Lars Stendius, is the newer technology’s ability to reverse a line’s current without changing the “polarity” of its voltage.

    benefits of a European supergrid linking Mediterranean and North Sea wind farms with Norway’s immense hydropower reservoirs would be “considerable.” Those reservoirs could be tapped during periods of low wind, providing a renewable backup to the wind power.

    The challenge is to get the supergrid onto the policy agenda. Because it’s a big-energy concept, Czisch says, it runs counter to the thinking of many renewable energy advocates, who he believes prefer to see renewable energy as local energy sources, such as solar panels on rooftops. “You would have to build huge high-voltage DC lines, huge wind-power plants in Morocco, and so on. This is something that could easily be done by the big utilities – but the utilities are the enemy of the renewables people,” he says.

    Reply
  18. Tomi Engdahl says:

    Time to Rethink the Use of DC Power for the Energy-Smart Home?
    http://www.greentechmedia.com/articles/read/Time-to-Rethink-the-Use-of-DC-Power-for-the-Energy-Smart-Home

    Household batteries and solar, plus LEDs and digital devices

    It’s been more than a century since alternating current (AC) won the battle against direct current (DC) as the technology of choice for distributing electricity across the grid and in buildings. But maybe it’s time to rethink that choice, and convert homes and businesses to DC power for more efficient use of the increasing portion of electricity consumption and generation that runs on direct current.

    That’s the idea behind a U.K. Department of Energy and Climate Change project announced last month, aiming to integrate solar power, batteries and LED lighting and home electronics into a single DC-powered system. The goal is to reduce inefficiencies related to converting DC to AC and back again, and bring the control capabilities that come from a core DC power technology — the USB cable — to better manage household power loads for grid needs.

    That’s how Simon Daniel, founder of U.K. startup Moixa Technology, describes the project’s goals. Moixa has developed DC-powered systems ranging from USB adapters to home energy control systems, and is leading a consortium including KiWi Power, Good Energy, AVC NextGen and Northern Power Grid on the DECC project, one of two awarded £5 million ($8.2 million) in grants last month.

    About 300 homes will be equipped with Moixa’s Maslow home energy management system, coupled with batteries that store power from the grid, as well as from small-scale solar PV systems at a subset of homes

    That DC power, in turn, will supply LED lights in the buildings, as well as use USB to power an array of consumer electronics, he said.

    Daniel described these as the “above the waist” loads in the home, to contrast them with the “below the waist” appliances, pumps and other systems that will continue to run on grid-supplied, AC power. But while household power demand for these below-the-waist devices isn’t growing that fast, “the stuff above the waist keeps going up exponentially, and nobody knows what it’s going to be like in 2020,” he said.

    That’s a problem for utilities struggling to provide peak power to homes and businesses where digital devices make up the fastest-growing share of electricity usage. The U.S. Energy Information Administration (EIA) has projected that household energy use attributable to miscellaneous devices, much of it consumer electronics, is set to nearly double between 2005 and 2015, while most other classes of loads show little projected growth

    using DC power from the battery to power LEDs and digital devices could improve the efficiency of those systems by roughly one-third, compared to the losses that come from converting that power from AC to DC

    Allowing solar PV’s DC output to go directly to batteries or the home’s DC loads could also improve efficiencies on that side

    Changing a century’s worth of technology development and regulations built around AC systems so that they can carry DC power within buildings won’t be easy, of course. But efforts are underway to create the standards to bring DC power into the mainstream.

    In the United States, for instance, the EMerge Alliance, a U.S.-based consortium of lighting and electronics controls manufacturers and construction firms, has been pushing DC power for commercial lighting since 2008. It’s also been promoting standards for DC power in data centers, where technology providers like Validus (now owned by ABB) and data center owners like Facebook have been making some strides.

    Last month, EMerge launched a new initiative to develop DC power standards for homes and small businesses, largely aimed at enabling “hybrid” systems that can simultaneously run DC and AC over typical household wiring.

    “You’re going to be in a hybrid mode most of the time — some AC and some DC,”

    Reply
  19. Tomi Engdahl says:

    Moixa wins share of DECC £5m contracts for energy storage
    http://www.moixatechnology.com/press-release/moixa-wins-share-of-decc-5m-contracts-for-energy-storage.php

    Led by Moixa Technology, a consortium including KiWi Power, Good Energy, AVC NextGen and Northern Power Grid, will deploy innovative smart battery and efficiency systems in houses to reduce peak energy demand, lower electricity bills and help balance electricity networks.

    “Storage provides many opportunities to reduce costs and improve resilience”, says Simon Daniel, CEO of Moixa Technology, “It helps customers save money and reduce peak energy demand, by using low carbon, night, wind and solar resources. This contract and funding will ensure we can continue storage innovation and demonstrate cost-effective wide spread deployment of our MASLOW system”. He comments, “We aim to use smart storage to deliver a price freeze without the politics.”

    The Moixa consortium will deliver a 0.525Mh+ grid scale Distributed Energy Storage (DES) system, by deploying MASLOW smart batteries across 300 homes/sites in 2013/14. The system works locally to store renewable or night energy and power growing peak demand, from electronics, lighting and Internet of Things (a proposed development of the Internet in which every day objects have network connectivity.) This also improves energy efficiency by coupling storage with DC LED lighting, and innovative DC-DC power sockets , and provides resilience.

    Reply
  20. Tomi Engdahl says:

    Did you know that your mobile is one reason it’s time to rethink the grid?
    http://www.abb-conversations.com/2013/06/did-you-know-that-your-mobile-is-one-reason-its-time-to-rethink-the-grid/

    ‘We are seeing a shift towards DC power and will need a lot more DC in the home.’

    Basically all electronic devices in our homes have a rectifier, either an external one as described above or in-built into the device itself. This includes mobile and tablet devices, TVs, radios, PCs, Macs and many more, as well as energy-conserving LEDs (light-emitting diodes).

    The modern world increasingly runs on DC

    AC vs. DC: Both are necessary in our everyday lives. But why? In the 1880s, in the early days of electricity, AC won out over DC for the reason that it was more practical to set up at the time.

    But AC no longer fulfills all our energy needs. Global consumption of energy is constantly growing, especially in emerging economies. More and more electricity is being generated from renewable energy sources such as wind, solar and water. DC is the best technology to transmit power from remote renewable sources over long distances, and the solar panels on the roof produce DC power.

    So we are seeing a shift towards DC power and will need a lot more DC in the home. The most efficient way to deliver DC power would be to convert the power in a larger rectifier before it even enters the building, rather than at each individual device. DC may increasingly become the way in new areas or cities, where new communities are powered for the first time.

    The AC vs. DC battle will go on for a while, but it will hopefully help renewable energy find its place as we move towards a smarter grid for a more sustainable world.

    Reply
  21. Tomi Engdahl says:

    Submarine power cable
    http://en.wikipedia.org/wiki/Submarine_power_cable

    DC switch gear is also more expensive to produce, since arc suppression is more difficult.

    Since DC is constant and doesn’t cycle to zero, a DC switch will draw a much longer arc, and suppressing this arc requires more expensive switching equipment.

    DC power transmission does have some advantages over AC power transmission.
    AC transmission lines need to be designed to handle the peak voltage of the AC sine wave.
    This means that for the same size wire and same insulation on standoffs and other equipment, a DC line can carry 1.4 times as much power as an AC line.

    AC power transmission also suffers from reactive losses, due to the natural capacitance and inductive properties of wire. DC transmission lines do not suffer reactive losses. The only losses in a DC transmission line are the resistive losses, which are present in AC lines as well.

    Reply
  22. Tomi Engdahl says:

    High-voltage DC distribution is key to increased system efficiency and renewable-energy opportunities
    http://www.techonline.com/electrical-engineers/education-training/tech-papers/4427839/High-voltage-DC-distribution-is-key-to-increased-system-efficiency-and-renewable-energy-opportunities

    The pressure throughout the energy supply chain to deliver electrical power more efficiently is intense and growing, particularly in high load applications such as datacenters. This white paper highlights how a transition to 400 VDC for power transmission and conversion offers tangible and significant benefits for both sourcing options and system performance.

    Reply
  23. Tomi Engdahl says:

    Exploring dc power distribution alternatives
    http://www.csemag.com/single-article/exploring-dc-power-distribution-alternatives/b73227a91fc4f74fc233cff10875ddd5.html

    Engineers should know when and where the use of dc power distribution is appropriate, and when it is not. In applications where redundancy, immediate transfer capability, high availability, and energy storage are design criteria, direct current power solutions are beneficial.

    Applications in which dc power is generated or directly used include:

    VFDs

    UPSs

    Battery technology

    Server technology

    Mobile phones and tablets

    Electric vehicles

    LED lighting.

    Switching devices are at the heart of dc power distribution systems.

    Higher voltage, higher power, and higher temperature semiconductor switching devices continue to be developed and are used commercially at significant production levels.

    nherent to the use of power electronics-based dc distribution systems is the ability to reconfigure the system with power management software. Software can control the dc bus output voltage to initiate load transfer from one dc bus to another dc bus through auctioneering diodes. Similarly, power management can be used to change the dc bus voltage of VFDs for optimal motor efficiency. Power converters also lend themselves to diagnostics, metering, and fault-current limiting.

    The switching devices—including thyristors, SCRs, insulated-gate bipolar transistors (IGBTs), and material developments in silicon carbide—enable higher efficiency power converters, motor drives, and UPSs.

    n the data center industry, dc battery UPS systems are used extensively to power critical servers during ac power disturbances and source transfers

    At the core of data centers are servers and telecommunications equipment that often convert ac power to dc for loads that use 12 V dc. Installations exist that use significant battery rooms and immediately invert through a UPS up to 120/208 V ac, 240/415 V ac, or 277/480 V ac; distributing power; and then converting it back to 12 V dc through multiple converters

    Progress has been made in the development of 125, 250, and 380 to 400 V dc system standards.

    Standards for 125 and 250 V dc, which are widely used in powering relaying equipment, include:
    IEEE 399: dc load flow and short circuit analysis recommended practices
    IEEE 485: battery sizing recommended practices
    IEEE 946: dc system analysis methods.

    The 380 to 400 V dc standards are progressing with UL listed equipment. European Telecommunications Standards Institute and International Telecommunications Union standards have been released including 240 V dc power supply systems for telecommunications.

    Data centers also use a significant number of variable speed driven motors for cooling pumps and fans where a redundant dc bus may be beneficial to power multiple drives.

    The automotive industry has produced a reliable battery technology, which has driven down the cost of lead acid batteries. The advent of hybrid and full electric vehicles has driven the industry to pursue other higher power density battery technology.

    Reply
  24. photovoltaic solar panels says:

    Foreman ‘ A foreman is usually promoted from the solar installer position. For business owners,
    you can look for suppliers that have promotions, giving
    away solar panels at lower price, like whole sale or
    timely sale promos. Some of us are still tight on finances no matter how much we
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    For example, some attendees opt to focus on NEC
    requirements, while others turn their attention to battery systems.

    Reply
  25. Tomi Engdahl says:

    Ask Hackaday: Who Wants An All DC House?
    http://hackaday.com/2014/09/04/ask-hackaday-who-wants-an-all-dc-house/

    it all started one hundred and thirty five years ago, when [Thomas Edison] changed the world forever with the first practical electric light bulb.

    That bulb was lit by a Direct Current – the same thing that runs the computer you’re reading this article on.

    Why is it that we transport electricity as AC only to convert it to DC in our homes? You might answer:

    “This argument was played out in the War of Currents back in the 1880’s.”

    Indeed, it was. But that was a long time ago. Technology has changed. Changed so much to the point that the arguments in the War of Currents might no longer be valid. Join us after the break, where we rehash these arguments, and explore the feasibility of an all DC environment.

    Is there any reason we can’t have DC outlets? We’ve seen USB ports built into outlets while strolling the isles of our favorite hardware stores

    You would still need AC for kitchen appliances and such. But consider changing these over to DC. Imagine a house where everything ran on DC!

    Lots of questions still remain

    Reply
  26. Tomi Engdahl says:

    DC distribution in your house and 42-V cars
    http://www.edn.com/electronics-blogs/the-workbench/4423875/DC-distribution-in-your-house-and-42V-cars

    So Edison thought ac was more dangerous for electrocution, but that is not true. In fact the danger with electricity is in starting fires. That is why dc distribution is so tricky. When you get an arc in ac, it is self-quenching; 100 or 120 times a second, 50 and 60 Hz power goes to zero. That really helps extinguish the arc.

    48V is a nice arc-welding voltage. Once you start an arc it just burns and burns.

    trucks and buses with 24V dc power. All the relays and switches would fail much quicker. We could not use the dirt-cheap relays and switches used on 12V cars, they would fail within a year

    The real reason 42-V cars are not here gets back to that arcing in relays and switches. With 42-V cars, every single load has to be switched with transistors, you just can’t use relays or contacts. That might still pay out, many loads these days are handled with FETs anyway. But the deal is, you can use 30V FETs with a 12V car, but you need 200V FETs to handle 36V cars. (The charging voltage is 42, the system just uses three 12-V batteries, so the uncharged voltage is 36.) But the die size of FETs goes up as the square of the voltage. So tripling the voltage makes the FET die nine times bigger

    So now think about distributing dc in your house. If you use 12V you need copper 10 times thicker and more expensive than the wires that carry 120V. If you up the voltage, even a little, you can’t use any mechanical switches or relays anywhere. On top of that, you still have this incredibly lethal wiring that can kill you in a flash, or will arc like crazy if it gets shorted. Heck even with ac distribution, the NSA data center keeps exploding since they can’t quench the arcs.

    It has taken a while to kill Edison’s dc distribution. The last bit of it was only decommissioned in 2007. The 120-V ac power in your house is darn-near perfect. Our good-ol-American power is much safer than 240V European power. I have read that 60Hz has less chance to screw up your heart when you get shocked than 50Hz.

    If you want to improve power in the home lets go to 400Hz like the airplane people.

    Now don’t think that dc is all bad. It makes sense to distribute dc if you have to send power to an island or through a single cable.

    Reply
  27. Tomi Engdahl says:

    NSA’s Data Center Electrical Problems Aren’t That Shocking
    Posted 16 Oct 2013
    http://spectrum.ieee.org/tech-talk/computing/it/nsa-data-center-electrical-problems-arent-that-shocking

    Last week, the Wall Street Journal reported that arc-fault failures—electrical problems that exceed the protective capabilities of circuit breakers and cause metal to melt and go flying—are delaying completion of the NSA’s controversial new Utah data-storage center. The article reported that 10 such meltdowns over the past 13 months had led to disputes about the adequacy of the electric control systems, and suggested that designers and builders of the new data center may have cut corners.

    So we’ll have to wait a bit for more details. But the NSA’s problems raise questions that extend beyond the Utah center or the NSA itself. We’re putting more and more of our data in the cloud daily, driving the construction of bigger and bigger data centers. Should we expect more data center fires in the future, or is the NSA situation unique?

    “You’ve got normal utility power coming into the back of the building, say, at whatever the distribution voltage is—it could be 23 kV, it could be 12 kV. That power hopefully is coming from two independent substations”

    “That power goes into a transformer that steps the power down to 3-phase 480 volts.”

    “an uninterruptible power supply that converts the AC to DC and stores reserve power in batteries and then converts it back to AC again. The AC power is stepped down, typically to 208 volts in the U.S., then it goes into the power supplies in back of servers and storage arrays. These power supplies convert it to 380 volt DC. From there, it is converted within the server or storage array to all the different voltages you need, like 12 volts DC for fan, 5 volts for disk drives, 3.3 volts for memory.”

    An arc fault typically occurs inside the metal clad switch gear, where the power levels are the highest. But, Symanski says, it can happen downstream

    But companies like Google, Amazon, and, lately, the NSA, are entering uncharted waters in terms of data center design. Symanski explains:

    “These new data centers are trying to push the envelope as far as efficiency and space. The electrical load of the computers is going up; some of these have hundreds of thousands of servers, some of these servers have six power cords going into them or some have massive supercomputers drawing 10 megawatts each. They are using huge amounts of power.”

    “With a 380-volt DC setup you have less equipment, you don’t need some of the conversion steps that require additional electronic devices that do fail, and you’ll have less losses, so you are running a more efficient and reliable system.”

    Reply
  28. Tomi Engdahl says:

    DC distribution in your house and 42-V cars
    http://www.edn.com/electronics-blogs/the-workbench/4423875/DC-distribution-in-your-house-and-42V-cars

    I spotted an article in Electronic Products about ac-to-dc converters that fit inside a wall plug. At least that was the intent of the article. Unfortunately it started with a comment about how so much of the stuff in houses run off dc, yet according the author, we waste energy by distributing ac and then having every gizmo make dc inside of it. He noted, “A far more efficient solution would be a central dc-grid supply that would power all of your home electronics appliances, as one large PSU wastes less energy than many separate ac/dc converters.”

    Reply
  29. Tomi Engdahl says:

    Solar Rising in Village Microgrids
    http://www.eetimes.com/document.asp?doc_id=1324266&

    Solar panels are on the rise for microgrids that bring electricity to small villages in the developing world, spawning work on low-power, direct-current homes, according to presentations at a conference here.

    “In India, there’s been a big mindset shift among regulators and utilities in favor of photovoltaics and microgrids,” said Vineeth Vijayaraghavan, director of research and outreach for the non-profit Solarillion Foundation.

    “So far, there’s been little research in networking microgrids, but the government is interested” in ways to connect DC rural grids to each other and to the AC urban grid, he said in a talk at the IEEE Global Humanitarian Technology Conference.

    Five research institutions each in the US and India will collaborate on the design of a 30 to 40 W home that can include at least one LED light, a brushless DC fan, a 12 W cellphone charger, a 23-inch TV, and a 10 W kitchen device with a motor, said Vijayaraghavan.

    The market for solar water pumps is also surging, he added, with as many as 40,000 now installed in India.

    Several speakers at the event said solar is on the rise in Africa and elsewhere, in part due to the falling costs of panels. As much as 20 percent of the world’s population — about 1.5 billion people — have no access to electricity.

    “The reality is 400 million people have no access to electricity in India, and the figure jumps to as much as 600 to 700 million if you add those with only intermittent access,” Vijayaraghavan told the audience.

    The so-called DC House initially targets a 450-600 W home, with plans for a 150W version later.

    The junction box, initially just supporting 80 W, was the most challenging part of the design. The team plans to work on a 450 W version with a single converter.

    The team also created a smart wall plug. It can sense whatever output a device needs and step down from its native 48 V to 5 V or less. Researchers also created a portable dimmable bulb with an embedded battery.

    A shed on the Cal Poly campus served as the first prototype DC house in June

    Several experts said the biggest issues they face are not about the technology

    For instance, the wide variation in subsidy and donor levels creates very different business models. “The diversity is mind boggling… There are so many players it can be confusing,

    If people in one village being charged for electricity hear of people elsewhere for whom it is free, they resist

    “Rural India does not want something urban India does not use — it’s a problem of aspirations,” he said.

    The DC House Project
    Providing access to electricity for the less fortunates
    http://www.calpoly.edu/~taufik/dchouse/

    Reply
  30. maigrir a tout prix says:

    It’s going to be ending of mne day, however before end I am reading this enormous piece of writing to improve my know-how.

    Reply
  31. Tomi Engdahl says:

    Integrate Protection with Isolation
    http://www.eeweb.com/company-blog/avago_technologies/integrate-protection-with-isolation/

    Renewable energy solutions are now common in household settings and are gaining increasing support from governmental bodies. This article discusses how integrating two capabilities (Protection and Isolation) can help simplify system design as well as lower cost.

    The typical renewable energy system has multiple parts operating in different voltage domains.

    The best way to provide isolation for the high-voltage control connections is with gate-drive optocoupler. Simply using high-voltage driver ICs or magnetic coupling can only provide basic insulation separation between voltage domains, and they depend on the integrity of the insulating materials in the packages and windings. Failure of this insulation would result in a direct high-voltage connection to the logic, with immediate destructive results.

    Precision switching in power applications is essential for maximizing power conversion efficiency without com- promising system safety. In order to produce an AC power signal, inverters operate IGBT switches in pairs

    Reply
  32. Tomi Engdahl says:

    The world’ first: UL certification for socket-outlet and plug for 10A 400V class DC distribution system
    http://www.fujitsu.com/emea/news/pr/fceu_20141208-01.html

    NTT FACILITIES, INC. (Minato-ku, Tokyo, President: Kiyoshi Tsutsui) and Fujitsu Component Limited (Shinagawa-ku, Tokyo, President: Koichi Ishizaka) obtained UL(1) certification for its first of a kind socket-outlet and plug for 10A 400V class DC distribution system.

    The DC distribution system (voltage level around 400 V d.c. in ICT or similar application) eliminates energy loss by DC-AC conversion and realizes highly efficient electricity distribution.

    The DC distribution system has been required to ensure safe operation such as the prevention of arc discharge which occurs by current interruption and electric shock. To meet these requirements, NTT FACILITIES and Fujitsu Component jointly developed a socket-outlet and plug for 400V class DC distribution system. It has been mainly adopted in datacenters in Japan since NTT FACILITIES’ promotion starting in November 2010.

    The socket-outlet and plug features following multi-tier safety constructions:

    Embedded arc extinguishing magnet assisted module breaks arc discharge in a short time
    Control make/break by mechanical slide switch which also prevents withdrawal of plug by mistake
    Using flame-retardant safety agency materials

    With these safety functions recognized, the socket-outlet and plug for 400V class DC distribution system obtained certification of the safety standard UL 2695(2) for the first time in the world.

    Reply
  33. Tomi Engdahl says:

    What kind of connectors to use for 400V DC power?

    Saf-D-Grid® 400 – up to 30 Amps
    http://www.andersonpower.com/us/en/products/saf-d-grid/400-vdc.aspx

    First Mate, Last Break Ground Contact
    Integral Latch
    Hot Plug Rated
    Touch Safe / Shock Protection
    Arcing Protection

    Voltage (AC/DC)
    • UL 1977 / CSA 22.2 600
    • IEC 400
    Current Rating (Amperes) 40

    Hot Plug Rated
    • 250 cycles 400V @ 440A in-rush
    • 250 cycles (UL) 400V @ 20A load

    Fault Current Withstand
    UL 467 14 AWG, 300A, 4 Sec.

    Touch Safety with Connector Housing
    IEC 60529 IP20

    Reply
  34. Tomi Engdahl says:

    Anderson Powerpole
    https://en.wikipedia.org/wiki/Anderson_Powerpole

    The Anderson Powerpole is a family of electrical connectors by Anderson Power Products (APP),[1] although plug compatible connectors are now available from alternate sources. Specific variants of this series of connectors have become de facto standards for conveying “higher power” direct current (DC) electrical power, although these standards are inconsistent and sometimes ignored.

    Powerpole connectors are physically and electrically hermaphroditic, thus avoiding the need to worry about which end is the plug and which the socket, or which end has the correct polarity.

    Powerpole connectors are available with current ratings up to 180 Amp. The size most commonly used is the 15 / 30 / 45 ampere variety. These sizes all use the same plastic housing in multiple colors, differing only in the metal contact inserted into the housing

    Larger Powerpole connectors (the SB/Multipole series) with 2 or 3 contacts in one molded housing are commonly used in various industrial settings, including as a battery connection for some UPS devices, removable vehicle winches, many electric forklifts, and other electric powered vehicles.

    Some of Andersons earlier patents have expired, thus other manufacturers have released plug-compatible connectors, such as ” AMP Power Series” by Tyco / TE Connectivity, Sermos, Lightspeed.

    The Powerpole connector has been adopted by some segments of the Amateur Radio (Ham Radio) community as their standard 12-volt DC power connector for everything from radios to accessories.Two notable groups are Amateur Radio Emergency Service (ARES) and Radio Amateur Civil Emergency Service (RACES)

    For use in amateur radio, the community has adopted a standard polarity for assembling pairs of Powerpole connectors. The standard is red positive and black negative.

    Reply
  35. Tomi Engdahl says:

    DC connector
    http://self.gutenberg.org/articles/dc_connector

    A DC connector (or DC plug, for one common type of connector) is an electrical connector for supplying direct current (DC) power.

    Compared to domestic AC power plugs and sockets, DC connectors have many more standard types that are not interchangeable. The dimensions and arrangement of DC connectors can be chosen to prevent accidental interconnection of incompatible sources and loads. Types vary from small coaxial connectors used to power portable electronic devices from AC adapters, to connectors used for automotive accessories and for battery packs in portable equipment.

    Small cylindrical connectors come in a variety of sizes. They may be known as “coaxial power connectors”, “barrel connectors”, “concentric barrel connectors” or “tip connectors”.

    The intended use of these plugs is on the cable connected to a power supply.

    IEC 60906-3:1994

    The International Electrotechnical Commission (IEC) has produced a standard for a system of plugs and socket-outlets for household and similar purposes in fixed and portable applications. Safety extra-low voltage (SELV) plugs and socket-outlets for 16 amps and 6, 12, 24, or 48 volts AC and DC. For use either indoors or outdoors

    In the broadcast, film and television industries, the 4-pin XLR connector is the standard for 12 V power. The connectors are wired pin 1 negative, pin 4 positive. Often pins 1 and 2 will be negative, 3 and 4 positive for a higher current rating. Female connectors are used as supply and male connectors are used on loads.

    In Australia, a T-configuration Clipsal socket is used for extra-low voltage DC power outlets, such as in stand-alone power systems (SAPS) or on boats, in order to prevent accidental connections of 12 V appliances into 240 V socket-outlets.

    Due to the popularity of USB for mobile phones and tablets, USB sockets and plugs have become a common choice for other small devices that require five volts or less, even those that require no data connection.

    DC connector
    From Wikipedia, the free encyclopedia
    https://en.wikipedia.org/wiki/DC_connector

    Reply
  36. Tomi Engdahl says:

    DC connector – IEC 60906-3:1994
    http://helpdesksurvival.com/dc-connector-iec-60906-31994.html

    The International Electrotechnical Commission (IEC) has created a normal for a configuration of plugs and socket-outlets for family and alike motives in secured and mobile applications. Extra-low voltage|Safety extra-low voltage (SELV) plugs and socket-outlets for 16 amps and 6, 12, 24, either 48 volts Alternating Current|AC and Direct Current|DC. For employ whichever inside either out-of-doors.

    IEC 60906-3:1994
    https://webstore.iec.ch/publication/3884

    IEC System of plugs and socket-outlets for household and similar purposes – Part 3: SELV plugs and socket-outlets, 16 A 6V, 12 V, 24 V, 48 V, a.c. and d.c.

    Reply
  37. Tomi Engdahl says:

    Master of Science Jenni Rekola her doctoral dissertation examined the possibility of replacing part of the current low-voltage electricity distribution with DC power distribution.

    He focused in particular on the necessary DC power distribution, power electronics efficiency calculation. The results will benefit future smart grid planning.

    Over a hundred years ago, instead of Edison developed DC power supply stabilized for use in AC power distribution. The reason was that the produced electricity is inherently synchronous generators for electricity exchange and the exchange of alternating current voltage level of the transformer is simple.

    The smart grid of the future management of the exchange will, however, be even more challenging. Rekola that decentralized electricity production increased, the distribution of the uncertainty increases.

    - The use of DC electricity would facilitate the future of the so-called smart grid management, improve customer power quality and reduce customer has experienced electricity outages, says Rekola.

    DC Power Distribution was found technically functional Lappeenranta University of Technology, as well as the Suur-Savo electricity together through pilot equipment. However, the introduction of the Equal Distribution of large-scale conditional on the acquisition and evaluation of operating costs. As a result, Rekola focused her doctoral dissertation balanced distribution of electricity needed for the analysis of power electronic commercial relations. The result was simulation models for DC and inverters, as well as the filters needed to calculate the loss of their context.

    Power electronics is a very high efficiency at rated output, but decreases at low power. The challenge gender distribution of electricity is that consumers’ energy consumption fluctuates over a wide power range and has most of the time very small compared to the instantaneous maximum load. In addition, the integration of power electronics and the current power grid security benefit point of view is challenging.

    Dissertation in the field of Rekola Electrical Energy ”Pienjännitetasasähkönjakelun hyötysuhteeseen vaikuttavat tekijät tehoelektroniikan näkökulmasta” (“Factors affecting the efficiency of the low-voltage DC electricity distribution power electronics perspective”), checked the information and the Faculty of Electrical Engineering Tampere University of Technology next Friday.

    Source: http://etn.fi/index.php?option=com_content&view=article&id=3617:osa-sahkosta-voitaisiin-jakaa-tasasahkona&catid=13&Itemid=101

    Reply
  38. Tomi Engdahl says:

    What Voltage for the All-DC House?
    http://hackaday.com/2017/03/06/what-voltage-for-the-all-dc-house/

    The war of the currents was fairly decisively won by AC. After all, whether you’ve got 110 V or 230 V coming out of your wall sockets, 50 Hz or 60 Hz, the whole world agrees that the frequency of oscillation should be strictly greater than zero. Technically, AC won out because of three intertwined facts. It was more economical to have a few big power plants rather than hundreds of thousands of tiny ones. This meant that power had to be transmitted over relatively long distances, which calls for higher voltages. And at the time, the AC transformer was the only way viable to step up and down voltages.

    But that was then. We’re right now on the cusp of a power-generation revolution, at least if you believe the solar energy aficionados. And this means two things: local power that’s originally generated as DC. And that completely undoes two of the three factors in AC’s favor. (And efficient DC-DC converters kill the transformer.)

    most devices these days use low-voltage DC, with the notable exception of some big appliances. Batteries store DC.

    Resistive Heating

    The problem with lower-voltage wiring is simple physics. For a given power demand, P=I*V, so a lower voltage means pushing more current.

    That’s the reason that, for instance, power over Ethernet (PoE) schemes use around 48 V to transmit something like 30 W of power — those thin Ethernet cables can only carry so much current without wasting most of it away as heat. Even around 50 V, PoE schemes count on a loss of three to five watts in the cabling.

    Safety

    Electricity starts getting dangerous to humans somewhere around 30-50 V.
    you’ve got 110 or 230 V AC in your walls right now

    Which is to say that although sub-30 V DC would be safer, we suspect that the safety will be designed into the connectors, or into circuit breakers.

    Switches and Relays

    Which brings us to the last concern. Have you ever arc welded? How much DC voltage does it take to strike up an arc? Something in the neighborhood of 24 V is a pretty common value for a professional unit, but people have been able to weld with 20 V tool battery packs or even 12 V car batteries.

    Switches and Relays

    Which brings us to the last concern. Have you ever arc welded? How much DC voltage does it take to strike up an arc? Something in the neighborhood of 24 V is a pretty common value for a professional unit, but people have been able to weld with 20 V tool battery packs or even 12 V car batteries.

    Making mechanical switches that work for your DC home electric system is going to be a problem

    The X factor here is progress in MOSFET or IGBT manufacture. Solid state DC circuit breakers aren’t as cheap as mechanical (AC) breakers yet, but at voltages like we’re considering inside the home, they’re getting there.

    Whether this goes from the panel to the battery to the plug at 48 V or 12 V is going to depend on the relative prices of copper and hefty FETs, but we’re betting that FETs get cheaper and copper more expensive. We’d personally like to see this relatively high voltage stepped down at the plug for safety, say to 12 V, but we won’t quibble. It would make the perfect complement to our existing AC infrastructure.

    Reply
  39. Tomi Engdahl says:

    Technology Award for Better Electricity Delivery’

    The innovation developed by the Lappeenranta University of Technology “Low Voltage Equal Distribution System for Public Power Distribution” was awarded the Technology Prize by the Finnish Messrs Foundation. The prize for the first time is € 10,000. The award was announced today at the Technology 17 event opened at the Helsinki Fair Center.

    Since 2005, Lappeenranta University of Technology has been researching a power distribution system based on low-voltage electricity (LVDC) in cooperation with industry. The aim has been to develop a more cost-effective way of replacing existing electricity distribution systems with renewable electricity distribution networks to meet future demands.

    - As a result of the research, there is an innovation from active LVDC distribution, where the familiar energy of the history is connected to modern power electronics, network technology and information systems. LVDC’s business potential in Finland is € 40-60 million a year and its estimated global annual market potential is billions in billions, says Professor Jarmo Partanen.

    - Innovation makes it possible to build electricity distribution networks at a lower cost, to improve the reliability of electricity distribution and the lack of security. In addition, similar technologies have many other applications, ships, real estate, electric car charging systems, said sales manager Marcus Bergström from the Exhibition Center as secretary of the prize drawer.

    Source: http://www.etn.fi/index.php/13-news/6977-teknologia-palkinto-edullisemmalle-saehkoenjakelulle#ETNartikel

    Reply

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