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RE: [hreg] Re: grid tied system

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  • Sean Kaylor
    I noticed that the discussion began with dual wiring schemes. My father is a plans examiner in California and he has told me about the new electrical codes
    Message 1 of 19 , Oct 30, 2006
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      I noticed that the discussion began with dual wiring schemes. My father is a plans examiner in California and he has told me about the new electrical codes which address such issues. Apparently the DC system requires a plug arrangement that is not of the typical three prong setup so as to avoid confusion of mistakenly plugging DC equipment into AC equipment or vice versa. There are also several requirements regarding breaker capacity, segregation of systems and wire gauge, in short more work that few electricians know how to do.

      From my own experience with stand alone dual voltage arrangements I can testify that it is a pain and potentially very dangerous. I would much rather be shocked by 120 volts at a fraction of the amperage than low voltage DC operating at very high amperage. With modern efficient grid-intertie inverters and the pains associated with two wiring schemes I would have to say that DC is just not practical from a grid intertie perspective.


      From: "Gary Beck" <eco@...>
      Reply-To: hreg@yahoogroups.com
      To: <hreg@yahoogroups.com>
      Subject: RE: [hreg] Re: grid tied system
      Date: Sun, 29 Oct 2006 19:08:26 -0600

      Interesting - 100 watts when everything is �off�.  Times 100,000,000 households is 3000 Megawatts (or did I miss a zero?). If not, this is about 6 merchant power plants operating 24x7.


      If each house turned on just 3 � 60 Watt incandecent (hot) light bulbs, this jumps above 10,000 MW. So now 20 merchant plants each likely burning some type of fossil fuel and we have just 3 lights on.


      Actually, due to transmission and distribution losses, many more plants burning much more fuel. Solar-DC-Battery auxilary wiring for lighting alone sounds even better.


      From: hreg@yahoogroups. com [mailto:hreg@yahoogroups. com] On Behalf Of Prasad Enjeti
      Sent: Sunday, October 29, 2006 5:44 PM
      To: hreg@yahoogroups. com
      Subject: Re: [hreg] Re: grid tied system


      Here is another link which details the amount of standby power all our home appliances consume. Click on the link on the left - Home Tours.. a typical US home consumes ~ 100 Watts of electricity when everything in the house is turned off..


      ************ ********* ********* ********* ********* ********* ***
      Dr. Prasad Enjeti Power Electronics & Power Quality Laboratory
      Professor, Fellow of IEEE Department of Electrical Engineering
      Texas A&M University
      College Station, TX - 77843-3128
      Tel: 979-845-7466
      Fax: 979-845-6259
      Email: enjeti@.... edu ; http://enjeti. tamu.edu
      ************ ********* ********* ********* ********* ********* ****


      ----- Original Message ----
      From: Jim & Janet <jhd1@earthlink. net>
      To: hreg@yahoogroups. com
      Sent: Sunday, October 29, 2006 5:05:05 PM
      Subject: Re: [hreg] Re: grid tied system

      Here is a link to a voltage drop calculator. The easy way.

      Or if you are a numbers kinda guy, try this.

      But don't think that line losses only affect DC power. Here is something interesting if you are really concerned with your energy costs.

      Jim Duncan


      ----- Original Message -----

      From: Gary Beck

      Sent: Sunday, October 29, 2006 12:31 PM

      Subject: RE: [hreg] Re: grid tied system


      The DC line loss is an interesting aspect versus DC-AC-DC-AC electrical conversion losses and associated waste heat production.  Any idea how DC line loss compares over 10 feet or 50 feet for typical residential gauge copper wire? A few percent? 10%?

      My point is that solar PV is inherently already a �local� or a distributed low voltage DC power system (rather than a remotely produced and transmitted high voltage power system*).  In comparison a DC-AC-DC-AC path provides multiple opportunities for both electrical energy loss and indoor waste heat production.  Anyone know how do the efficiency conversion numbers might compare?

      (1) Solar PV-DC to 110 V AC (Electrically - how efficient? 90%, 75%?, Waste heat production is not a direct issue since transformer is outdoors, in garage or attic, etc.)

      (2) 110V AC to V DC (computer power supply, battery charging etc.  (Same electrically efficiency? 90%, 75%? Plus unfortunately this one causes indoor waste-heat production)

      (3) Added AC power* to remove this waste-heat from the house � motor driven electrical refrigeration �btu removal� has a pretty low efficiency - 50%

      So even with a �does-it-stick- on-the-wall�  guess, when it happens in this way, I think you are looking at somewhere around 50% to 70% energy �loss� for such a DC-AC-DC-AC path Vs maybe 10% for direct DC path.

      Forget about all �DC� appliances since this is not remotely practical. But consider if on a regional �sunny state� scale, what would happen only if 25% of all future residential lighting and 25% of all residential computer operation power were provided by direct solar DC 18-24V power battery sources?

      Gary Beck, P.E.

      Eco-Holdings LLC

      * This arguement does not even consider that an AC high voltage power production distribution system such as a NG fueled merchant power plant with long transmissions lines is below 40% efficiency for converting NG fuel BTUs to electrical kWs before counting any transmission losses.

      From: hreg@yahoogroups. com [mailto: hreg@yahoogroups. com ] On Behalf Of Garth & Kim Travis
      Sent: Friday, October 27, 2006 7:52 AM
      To: hreg@yahoogroups. com
      Subject: RE: [hreg] Re: grid tied system


      The original electric grid, way back was DC not AC, but then Tesla came up the the AC current and that is what we use.  Why?  DC has major line losses.  I do run some of my stuff directly off DC, but I am very careful to have my batteries really close to where I am using it.  Not a concept that is child friendly.  When wiring a home for AC, until you get a run over 40', you generally don't worry about putting in more copper to prevent line losses.  With DC power, the line losses can be measured on a 10' run.  So, unless the power supply is extremely close to where it will be used, the line losses will more than make up for any power savings.  This is especially true for any centralized power system in the home.

      You have part of the equation very correct, we need to deal with all the heat that our modern living generates.  A home that is not designed to get rid of the heat build up will be very expensive to opperate.  Good ventilation is required.

      Bright Blessings,

      At 07:32 AM 10/27/2006, you wrote:

      Some morning thoughts on solar, PVs, energy efficiency, and off grid concepts �
      Zero Energy Homes - There are low and zero power home designer/builders in Texas in business now. Their concepts are always based on an extreme low energy envelope and maximum natural lighting (an oxymoron of sorts). Then a large PV and solar hot water system is financed in the mortgage allowing an effective payout over 30 years (versus trying to justify the cost in your mind which thinks in much shorter time periods).
      Wasted heat counts - Every time you convert DC to AC, or low voltage to high voltage, or then convert (again) high voltage to low voltage,� such as for a desktop computer (happen internally), a laptop, or any other transformer driven device (answering machine, rechargeable tool, Xbox, cordless phone, florescent lighting, etc�) you waste and loose energy in the form of heat, which you then again waste energy again through its removal by running your air conditioning.
      So my big thought of the morning and question to HREG (and to anyone listening from G.E., Siemens, Sony, Panasonic, Samsung) why hasn�t someone come up with a home dual wiring scheme for purchase 110 Volt-AC and for produced let�s say 24 Volt-DC or 19.9 Volt-DC (a number I remember from my laptop converter). Or even simpler just sell a PV-Battery home install kit system to connect only to (a few) of your many home computer devices (HP-Compaq and Reliant - are you listening too?). How much energy would that alone save in Texas ?    
      Gary Beck, P.E.
      Eco-Holdings LLC
      P.O. Box 25248
      Houston , Texas 77265
      Tel: 713-530-1950
      Fax: 832-201-5338



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