Author Topic: DC "micro-grids"?  (Read 438 times)

Perd Hapley

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DC "micro-grids"?
« on: June 25, 2018, 09:07:54 AM »
https://energywatchnews.com/10-reasons-the-future-of-lighting-is-dc-grids/

Quote
There are a host of factors driving local – and regional – electricity distribution towards direct current, and with lighting installations going all LED, it’s time the lighting industry began supporting it. Here’s 10 reasons why it makes sense:

1) Lighting has effectively gone DC thanks to LEDs. Why have the expense of local drivers for each luminaire when they can all be run off the same local DC network?

2) The power industry is moving to distributed power generation, thanks to a switch to renewables such as solar panels and the advent of energy storage.

3) It’s much easier to integrate battery packs such as those produced by Siemens and Tesla into DC systems and grids. DC to DC converters are up to 20 times smaller that AC/DC equivalents.

4) There’s a significant energy loss every time power is converted from AC to DC at each device. Removing a stage can improve system efficiency by 5 to 10 per cent.

5) System reliability will be improved. By removing AC/DC converters, especially those with electrolytic capacitors, we can dramatically improve the mean time between failures.

6) By using a relatively higher voltage such 380V DC rather than 48V DC, we can solve the challenges of direct current such as voltage drop and increased cabling sizes, while maintaining safety.

7) There’s less local heat at the luminaires when there is no power conversion electronics built into the housing, leading to cooler-running, more efficient and longer life LEDs and cooler ceiling voids and interiors.

8) A local DC grid opens up opportunities to connect other DC devices, such as sensors and cameras, to the lighting to create an network which can use data to deliver new services.

9) The technology is field proven and is used by blue-chip clients such as Carrefour and MaxMara.

10) Louis Vuitton, for instance, is using DC microgrids for its lighting at 40 of its newer stores in both Europe and China.

Does anybody see this going mainstream? What would it take to convert a residence to this kind of system?
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dogmush

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Re: DC "micro-grids"?
« Reply #1 on: June 25, 2018, 09:55:33 AM »
Yes, eventually. 

I've already seen some folks that are using solar panels and power storage here in FL doing it on a small scale.

I'm not sure exactly on codes, but basically what I've seen is the lighting circuits pulled from the AC Breaker panel and moved to a DC Sub Panel.  Existing wiring was then used to run a separate, DC grid in the house.  Specialty LEDs were installed.  The Solar generation/storage setup was wired to the main AC panel as normal, and a separate feed came from the batteries to feed the DC side of the house.  I couldn't tell you what voltages were run.

I suspect you will see stuff like that built in to new construction pretty frequently in the next 10 -15 years, sooner in the areas where people like to be early adopters.

Perd Hapley

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Re: DC "micro-grids"?
« Reply #2 on: June 25, 2018, 09:58:13 AM »
The Solar generation/storage setup was wired to the main AC panel as normal, and a separate feed came from the batteries to feed the DC side of the house.  I couldn't tell you what voltages were run.


Do you know what kind of batteries? Wet or dry?
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K Frame

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Re: DC "micro-grids"?
« Reply #3 on: June 25, 2018, 10:17:45 AM »
Hey, what do you know, Thomas Edison may be vindicated, 125 years after he and Tesla duked it out.
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dogmush

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Re: DC "micro-grids"?
« Reply #4 on: June 25, 2018, 10:22:27 AM »

Do you know what kind of batteries? Wet or dry?

The one system I got to look at in a friends house was using fancy LiIon cells.  According to his brochure the same cells Tesla uses in their PowerWall without the "fund Elon Musk" upcharge.

Brad Johnson

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Re: DC "micro-grids"?
« Reply #5 on: June 25, 2018, 10:50:03 AM »
It's a cherry-picked argument that ignores basic infrastructure requirements. Just because one end product has transitioned to a DC-based technology doesn't change general distribution needs. That's the the stake in the heart of their argument.  Unless 100% of the power is generating within a few square miles of the end user, there still has to be an interlinked master distribution grid. There's simply no getting around it, or getting around the fact that AC is much more efficient in that respect.  

DC as a primary power grid methodology failed because of its inherent shortcomings v. AC-based distribution systems. Lighting systems switching to a DC-based technology doesn't change the infrastructure requirements, nor does it alter the laws of physics with respect to power distribution efficiencies.

Finally, there's the small fact that incandescent lamps work just fine on DC, too. In truth, they were originally developed for it. Basing an argument on LEDs suddenly being a DC-based tech versus older illumination systems, well, it doesn't instill much confidence in their ability to argue technical merits.  

Brad
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Hawkmoon

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Re: DC "micro-grids"?
« Reply #6 on: June 25, 2018, 10:51:51 AM »
The town I live in recently installed a microgrid, with the source being located on the high school property. If the primary power grid goes out (which generally happens around here at least once a year), the micro grid can power the high school, the town hall, the fire house, and the police station. (I don't remember if it also picks up the library, which is in the same cluster of buildings in the center of town.) But I don't think it's direct current. It must "generate" through an inverter.
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Firethorn

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Re: DC "micro-grids"?
« Reply #7 on: June 25, 2018, 11:10:58 AM »
I can see it going mainstream for stores and businesses long before homes.  For homes, "tradition" is where it is at.  For one, stores and businesses have room and space to run new wiring.  

However, for something like a new build home?  It would be dead easy, I think.  380V DC?  You can push a lot of power over that with relatively thin wiring.  LEDs are already long lasting enough(theoretically) to make "Replace the fixture" the solution when one fails over "just" replacing the bulb.  Of course, you can still make things modular if you want, so you can do things like swap out a daylight LED for a warm LED if you darn well want to, or vice versa.

Consider a home that is being built with solar panels and a battery system from the start.  The batteries put out something in the range mentioned - 380V.  Maybe the solar panels add up to 400V, and the battery puts out something around 360V.  This way you don't need any power converters at all.  Much like the lights in a car - many can take anything from about 16V down to like 10.  Car power is "noisy" by default.

As long as the DC devices are designed to operate within the expected range, the only difference is that the lights would be very slightly dimmer when on battery.  Not necessarily a bad thing if they're only dimmer when they aren't fighting the sun's light and human eyes can adjust a bit.

Anyways, given LED efficiency you could light up most homes with a single 15 amp circuit run using 14 gauge wire.  15A@380VDC = 5k watts, at 50 watts per room that's 114 rooms you could cover.  And I'm being miserly.

You'd have 2 breaker panels - one DC, which includes the lighting, and one AC, for traditional appliances.  If it becomes common, I'd imagine that you'd start seeing more DC appliances.  For example, there's no reason why you can't make a fridge that expects ~380VDC if you want, and as they mention, it'd probably actually be a touch more efficient.  Electric motors tend to be more efficient at higher voltages anyways, and the first thing most induction motor controllers do is rectify the incoming AC to DC anyways, so as they say, eliminating the steps from the battery to the motor of DC -> AC -> DC -> AC(frequency controlled) down to DC -> AC saves you some power.  For something like an oven or electric range*, well, heating elements don't care whether it's AC or DC.  They just need to have the proper resistance for the wattage wanted.  You could even get rid of the huge capacitors in things like microwaves and air conditioners.

*I remember when the idea of using battery power for this was insane, but it really isn't anymore.




RoadKingLarry

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Re: DC "micro-grids"?
« Reply #8 on: June 25, 2018, 12:23:32 PM »
Sailboats have been doing this for a long time.
Everything is 12VDC run off of batteries. Either 12V or series/parallel 6V.  Tons of solar and wind options for charging as well as onboard gensets and of course the engine.
When I rework the electrical on my 32' ketch I'll be going back all LED for lighting. Current set up is a pair of wet cell group 29 Deep cycle batteries and a conventional start battery for the diesel engine.
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