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  • "partial" off-grid system

    Its always been my understanding, that if you want to have solar panels on your roof, but not enough to supply 100% of the power you consume, you need to stay connected to the grid and rely on "energy credits" to save money on your power bills.
    Im wondering if its possible, instead, to use the solar panels on your roof to charge a battery bank, and use that stored power, directly, when its available. Meanwhile, staying connected to the grid and using that power to pick up the slack when your batteries are dead.

    Is this something that's done?

    I'm pretty new to this subject, so, apologies if this is one of those questions that gets asked all the time.

  • #2
    Originally posted by jwelsh View Post
    Its always been my understanding, that if you want to have solar panels on your roof, but not enough to supply 100% of the power you consume, you need to stay connected to the grid and rely on "energy credits" to save money on your power bills.
    Im wondering if its possible, instead, to use the solar panels on your roof to charge a battery bank, and use that stored power, directly, when its available. Meanwhile, staying connected to the grid and using that power to pick up the slack when your batteries are dead.

    Is this something that's done?

    I'm pretty new to this subject, so, apologies if this is one of those questions that gets asked all the time.
    Hi Jwelsh,

    This can be done with a grid hybrid inverter system such as the Outback Radian series inverter charger running the Grid Zero application. There is a 4000 and an 8000 watt version. Here are a couple of links for information.

    http://www.altenergymag.com/news/201...ommunity/33810

    http://www.google.com/url?sa=t&rct=j...,d.aWw&cad=rja

    Google "outback power" for their website.

    I believe Xantrex makes one also but I'm not very familiar with that one. Others here have them though, and I'm sure they will discuss those.

    Good luck,
    Raj
    3.6 kw PV, Classic 150, Radian GS4048A, LFP 195A

    Comment


    • #3
      Originally posted by jwelsh View Post
      Im wondering if its possible, instead, to use the solar panels on your roof to charge a battery bank, and use that stored power, directly, when its available. Meanwhile, staying connected to the grid and using that power to pick up the slack when your batteries are dead.

      Is this something that's done?
      Doable yes.
      Something I'd do? No.
      Batteries and fancy charging systems for them cost $.
      I have got reliable grid power already and can use the grid as a "battery" (sending power to the grid when I don't need it, getting power from it when I do) So at least in my case there's no reason for me to spend $ on a battery bank.
      Even if I had a number of blackouts each year, I'd probably still be better off getting a small generator rather than buying batteries and such.

      Comment


      • #4
        In Jamaica we have frequent power cut and the rate is high @45 to 55 US cents per KWH, and we don't have net-metering, What we do is installed a minimum off grid system with an automatic transfer switch, we program the inverter when the battery bank reach to a set voltage, the inverter turn off itself and the transfer switch connect to the power company and use the grid until the battery get charged by either the solar or generator if the system has one.

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        • #5
          It can be done, but if you have grid power most likely economically foolish. In the lower 48 USA a Kwh cost anywhere from 6 to 15 cents. Take that Kwh off grid and the battery cost alone is 50 to 70 cents per Kwh or 5 to 10 times more than you can buy it for.
          MSEE, PE

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          • #6
            Dereck,
            In the USA it is foolish to go off grid, In Jamaica it maybe make sense depend on how you look at it.

            Because I have grid access so I don't have to size the battery bank to the 5 days things, I only size the battery bank to the day to about 25 to 35% DOD. Any rainy day I will use the grid power.

            I used to use around 800 to 1200KWH per month. Since I go semi off grid I manage to consume around 20 to 24 KWH per day that is about 600 to 650 KWH per month. I used to pay about US$350 to 500 per month for my electricity bill. Now I pay US$30 to $80 per month depend on the days if it is over cast most of the time of sunny. Where I live we have a lot of clouds passing by so I have to over size my panels.

            The installation is cheap in Jamaica because the labour is cheap and my flat concrete roof is help a little too. Because it off grid so to speak I don't need any permit and inspections, So I use back the automatic switch that come with the generator from 20 years ago to do the semi off grid. I have to do a minor change in the main panel and install a sub panels to take care of the PV system.

            My system cost me about US$22,000 to date and generate 20 to 30 KWH each day depend on the weather. I try to diversify the consumption in the day and in the night it use minimum current. in the day it use around 30 to 40 amps DC @53 volts and in the evening it use ~25 amps DC and in the night it use ~11 to 18amps DC. I use automatic switch to turn off the freezer and the refrigerator in the night.

            If I am still on the grid full time I will have to pay about ~US$270 to 300 per month as my consumption now. So if my battery bank last me 5 years and I replace the batteries for another 5 years it would cost me around US$6000 for the 16 batteries. the total cost for the 10 years will be US$28,000. which is US$2,800 per year. The grid will cost US$32,400 for these 10 years if I didn't use Solar. So hopefully it will work out for me.

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            • #7
              Originally posted by paulcheung View Post
              Dereck,
              In the USA it is foolish to go off grid
              I thought I said that. Who said anything about Jamaica?
              MSEE, PE

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              • #8
                Im wondering if its possible, instead, to use the solar panels on your roof to charge a battery bank, and use that stored power, directly, when its available. Meanwhile, staying connected to the grid and using that power to pick up the slack when your batteries are dead.
                Price a suitable set of batteries, and then price a genset & several fuel cans. If you only expect to use the batteries less than 30days a year, the genset wins. Once you buy batteries, their "age death clock" starts ticking. Use them or on standby, they will die in 3-7 years, and you get to buy them again.
                Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
                || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
                || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

                solar: http://tinyurl.com/LMR-Solar
                gen: http://tinyurl.com/LMR-Lister

                Comment


                • #9
                  Originally posted by jwelsh View Post
                  Im wondering if its possible, instead, to use the solar panels on your roof to charge a battery bank, and use that stored power, directly, when its available.
                  It's possible, unless you have very abnormal reasons don't do it.

                  Originally posted by jwelsh View Post
                  Its always been my understanding, that if you want to have solar panels on your roof, but not enough to supply 100% of the power you consume, you need to stay connected to the grid and rely on "energy credits" to save money on your power bills.
                  Grid tie is probably what you want to do, you would essentially use your power company as a battery bank. As such you would be buying zero batteries for your system! The advantage of this is that you don't have to keep buying more batteries, you don't have to keep track of the water in your batteries, you don't have to worry whether your batteries are getting enough sun or do you need to charge them some other way, and you wouldn't waste power charging the batteries.

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