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  • No inverter needed

    Q1


    Excluding air conditioning, because dc fans in some areas and some conservative ways could suffice. What necessary home gadgets CURRENTLY don't come in DC versions?

    Q2

    if producing three kilowatts a day, and just using DC gadgets , isn't it hard to compare to inverter and or grid use?

  • #2
    A1. You can get some some DC gadgets, but most are for the RV market which means 12 volts, expensive, and low quality. There are a few exceptions like Danfrost 24 and 48 volt freezers made for off-grid battery systems, but you are talking very expensive small units. There are also some Dc Split Duct HVAC systems made for 24 and 48 volt systems. Again extremely expensive. All are niche products which means very little to no market demand for them. The problem is LOW VOLTAGE. With 120 VAC you can run a 20 amp circuit up to 75 feet one-way, share many circuits using cheap 12 AWG wire with little power loss. That gives you up to 2000 watts on a single circuit. For say a 20 amp DC circuit longer than 5 feet requires up to 1/0 AWG wire, about $1/foot for a single circuit that supplies only 320 watts. You gotta 12 volt 600 wat toy microwave. You had better have the battery sitting right next to it with using a short peice of expensive 6 AWG cable no longer than 5 feet.

    A2. Not at all. All you need to know is not only is using DC battery power extremely expensive to implement initially in equipment as explained above both in gadgets and equipment. Now add in and account for in battery replacement cost alone every few years will cost you 5 to 10 times more than you can buy the power from the POCO the rest of your life. Now ask yourself why would you take anything off-grid if you have grid power available to you?

    One other thing is using solar and battery is extremely inefficient, and you cannot utilize all the potential power. At best for every watt hour you use, requires the panel to generate 1.5 wat hours. Watts means nothing and is just a rate in which power is being used. However in practice you cannot utilize all the power and most is wasted, or not even generated. Good guess is for every potential 3 watt hours, only one watt our is used. This is one reason it is so expensive, and the primary reason battery system are extremely heavy polluters. No money can be saved and you have a huge carbon foot print off-grid. So please do not lie to yourself and say you are doing this to save money or mother earth.

    Look at it this way. You car gas tank is empty and you need to fill up with gasoline. You see 2 gas stations on opposite corners of an intersection. One is called Lefty NoBama Billiary's station selling gasoline for $20/gal, and on the opposite corner you see Righty Chump's station selling gas for $2/Gal. Which one do you believe, err I mean buy?
    Last edited by Sunking; 01-26-2017, 01:22 PM.
    MSEE, PE

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    • #3
      Originally posted by Brian53713 View Post
      Excluding air conditioning, because dc fans in some areas and some conservative ways could suffice. What necessary home gadgets CURRENTLY don't come in DC versions?
      Refrigerators and microwaves come to mind.
      if producing three kilowatts a day, and just using DC gadgets , isn't it hard to compare to inverter and or grid use?
      Is it "hard to compare?" Not really. As SK mentions you're going to spend a lot more on wire. But a kilowatt-hour is a kilowatt-hour, and you still use energy whether it's DC or AC. In some cases getting rid of the inverter helps you a bit (no conversion losses) and sometimes it hurts you (more wiring loss.)

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      • #4
        Originally posted by Brian53713 View Post
        Q1


        Excluding air conditioning, because dc fans in some areas and some conservative ways could suffice. What necessary home gadgets CURRENTLY don't come in DC versions?

        Q2

        if producing three kilowatts a day, and just using DC gadgets , isn't it hard to compare to inverter and or grid use?
        When I calculate the cost of a DC battery system I usually use the max DOD of Ah allowed by the manufacturer for a daily cycle. I multiply that Ah x the battery voltage to get a kWh total.

        I then multiply that kWh usage by the # of listed cycles supplied by the battery. That gets me to the Maximum lifetime kWh generation of that battery system.

        I then take the estimated "installed cost" of the battery system and divide it by the Max kWh generation. That gets me the "best" cost per kWh for that battery.

        I use that number and compare it to what I pay for a kWh from my POCO. That comparison usually shows the battery generated $/kWh as being much more then the POCO purchased $/kWh.

        Now to be more realistic I should take that Maximum kWh generated by the battery and multiply it by some % (say 90%) which gets you closer to a real life power generation number.

        You also have to look at the battery manufacturer warranty period and see if it comes close to the posted # of life cycles divided by 365 days/yr. Most warranties fall far short of the post # of cycles which should tell you that the cycle # is inflated.

        So IMO whatever I calculate for $/kWh using the Max kWh generated by the battery, I would really be paying more due to more realistic and lower kWh generation divided by the installed cost.

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