The Electric Side of Hydro Power Conductors, Conduit & Connections Conductor Sizing for 500-Watt TurbineWritten This is actually a reasonable idea.   There was a company working on something like this but I don't remember their name or if they still exist.Things to be solved:Connector/Plus/Receptacle standardization - there isn't a standard for low voltage power plugs12/24/48 VDC?   Which voltages to pick.  48VDC is common for solar panels.  However, 42 VDC and below is a shock hazard threshold, so 24 VDC could be a reasonable choice as well (part of why 24V is so common for things like sprinklers, doorbells, etc.).   12V is a standard battery voltage for lead-acid.Invertor/Converter standards and availability.  A variant of the above: often enough you'll probably need voltage at a different level than you current have.  And 12 volts might not be universal - often appliances take DC voltages from 1.5, 2.0, 2.5, 3.0, 4.5, 5.0, 6.0, 9.0, etc.  The solution is switched mode power supplies but efficiency is best with higher input voltages. 

Again this also relates to connectors, particular on appliances - no standards exists but you'll like a keyed or adaptable solution.It's quite possible to digitally code/communicate load levels (there are de facto standards and products out in the market that do this).  The best way of dealing with many of the above would be to have a bidirectional connection that allows appliances to tell power converters what load they need.  There is a huge legacy issue but an aftermarket "adapter" could be the answer.   The company I can't remember was taking this strategy.Written Until recently, the first question would be "what DC voltage?" 12V would be popular, 24V would have its adherents. Recently however, the world has settled on 5V - for the sole reason that we all have smart phones now. It could just as easily be 12V. Note, that all the examples below have a small DC power supply built in, running off the line voltage. That is the only logical way to do it, since transporting low voltage around a building requires heavy wiring if the voltage drop is not to be a problem.

High voltage DC is not terribly useful. Because DC arcs don't self-quench, it is very hard on switches. home ac unit pricesInduction motors - the kind in fans and air conditioning - can't use it. level ac unitYour vacuum cleaner and blender would still work. what to do with old window ac unitsStrangely enough, all the examples below would be quite happy working on DC, since the first function in any switch mode power supply is to rectify the AC. Anyway, here's your DC distribution system, on an international scale -USAAustraliaBritainFrance and GermanyIndiaItaly(that's enough examples)Written Should the electrical system inside a house provide low-power direct current because most devices need DC?I can think of three reasons why the electrical system in a home should remain AC.

First is the "network effect". There is a huge power system infrastructure in place to supply 60Hz AC. Everything from power generation, distribution, protection, to building regulations, to light bulbs and wall receptacles. To attempt to codify and modify this would require a huge effort.The second problem is the supposed benefit. A typical American home is built for 120 vac at 200 amps. A typical wall receptacle provides 12o vac at 20 amps. If the wall receptacles were changed to provide the same amount of power, say at a safe 12 vdc, then they would need to supply 200 amps to provide the same amount of power. This would take more copper to provide the current safely and in the end, would not be any safer since 200 amps is sufficient to weld.Finally, the supposed benefit is that most devices in home need DC (ignoring the refrigerator, dishwasher, washing machine, and dryer). However, some devices need 3V, or 4.5 volts, or 6 volts, or 9 volts, or 12 volts. There is no standard DC voltage.

If 12 volts were supplied, one would still have to regulate down to the voltage the device needed. If a regulator is involved, why not convert from AC to DC. My iPhone has a wall wart slightly larger than the size of my thumb that takes 120 vac and supplied USB regulated power. A DC to DC converter is likely to be the same size or larger.So, I don't think is necessarily a good idea. Converting from DC to AC and back is not a big deal these days. It can be done with better than 90% efficiency and converting DC to DC would be no more efficient.Ever since George Westinghouse and Nikola Tesla won their "battle of the currents" against Thomas Edison in the late 1800s, electricity generation and distribution systems from the power plant to the end user have been built around alternating current (AC) instead of the kind Edison favored – direct current (DC). Now an alliance that includes lighting and electronic controls manufacturers, construction firms and building materials makers are pushing a renaissance for Edison's current of choice.

"What we're doing is devising a hybrid layer in the building that can use low-voltage direct current," said Brian Patterson, chairman of the EMerge Alliance. The idea is that an electrified ceiling – and maybe walls and floors, or even furniture-powering a shifting array of lighting, audio, and sensor and security equipment without the need for re-wiring, he said. "We're not going to eliminate AC in the building, we're going to complement it with DC –and we can do it very safely and inexpensively by doing it in low voltage," he said. The type of power EMerge is looking at – Class 2 as defined by the National Electric Code, a North American standard – is so low that you couldn't feel it, unless you touched your tongue to the ceiling, he said. While AC has huge advantages over DC for transmitting power, Patterson said, many of the devices in use in buildings today have to convert it into direct current, with resulting efficiency losses, he noted. The common example is a computer, with its AC-to-DC adapter that gets warm as power is converted to heat – lost in the conversion process.

But lots of other gear used in buildings need direct current, including many types of lighting, he said. Electronic ballasts, which control current for some fluorescent and high-intensity lights, use direct current, as do light-emitting diodes, or LEDs, he said. The alliance is working on standards for a low-voltage DC system that could "open up a whole wave of cost savings, improved sustainability and a whole level of flexibility with a plug and play mentality," he said. Patterson is general manager of business development for the building products division of Armstrong World Industries, a major maker of interior ceilings and floors, walls and cabinets with net sales of $3.5 billion last year. Armstrong is also a founding member of the EMerge Alliance. Other EMerge founding members include Johnson Controls, which makes HVAC, security and building management systems; Nextek Power Systems, which makes DC power systems for buildings; Osram Sylvania, which makes lighting systems;

and WAVE, a joint venture of Armstrong and steel products maker Worthington Industries, which makes ceiling suspension systems. Other participants include Webcor, a major California construction company, and the utility Southern California Edison. So is microplasma lighting startup Eden Park Illumination. Eden Park is looking to office ceiling tiles as a first market for its microplasma lights, which can be made of glass or flexible material that sandwiches n aluminum mesh with tiny cavities filled with phosphors, which illuminate when a current is passed through them. Investments into ways to make lighting more efficient and functional has been on the rise, with light-emitting diode, or LED, startups getting a lot of attention from venture capital firms and large lighting companies alike (see Lighting the Way to Efficiency). But that also means that new types of lighting systems are more likely to become more obsolete more quickly, as new technologies supplant the old, Patterson said – yet another reason to seek to make switching them out as cheap and easy as possible.

Of course, any building-wide, low-voltage DC system will also have to deal with the efficiency losses of converting AC grid power, Patterson said. Still, building-scale conversion will be more efficient than converting power on an item-to-item basis, he said. Then there are renewable energy sources to consider, he said. Solar photovoltaic systems and fuel cells, for example, provide DC power that has to be converted to AC via an inverter to be integrated into the electricity grid or building power systems connected to it. Using that power as direct current without conversion, however, means "you can get a pretty big pick-up, sometimes on the order of 30 percent," compared to the efficiency losses involved in converting renewable-generated to AC, and then sometimes back to DC again, he said. EMerge's electrified ceiling concept is being tested in several facilities around the country, Patterson said, though he wouldn't say where. But the concept has the support of Clark Gellings, vice president of technology for the Electric Power Research Institute.

In fact, Gellings said he's been promoting the idea for years. "The majority of appliances and devices around us have, somewhere at the core of their operation, direct current," he said. Efficiency gains, while yet unproven, could be particularly good for devices he calls "PV-DC," or devices made to run on direct current directly from solar photovoltaic systems. Using DC in buildings does present some safety issues that will have to be dealt with through new equipment, Gellings said. Still, "we probably have the technolgoy, the components and the smarts. We just haven't done it yet." EMerge's Patterson says that a key early target market will be buildings that incorporate renewable energy generation, given the efficiency advantages that low-voltage DC systems could provide them. Given that buildings account for about two-fifths of the nation's energy usage, making them "greener" by incorporating energy efficiency or renewable energy technology into them is a field that's seen growing interest from investors (see Green Building: Cheaper Than You Thought).