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  • Starting Small with hopes to expand ... Help Please

    I'm brand new to this but I've been doing a lot of research. I have limited space for panels so I'd like to go with the highest watt possible, maybe a E19 320. I'd also like to keep my options open for expansion later so I thought starting with a 48v system would be best. I'd like to get at least a 45 amp MPPT and at least a 1000w pure sine inverter.

    My question is what battery AH could one 320 watt panel in San Diego Sun for 8 hours a day successfully charge?

  • #2
    I am new to it all as well but that is a good question. I am trying to do some sort of power extending in my home but by means of saving. I know certain ways cost more or less in the long run.
    [URL="http://greentumble.com/"]Greentumble[/URL]

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    • #3
      Originally posted by Dmonicle View Post
      I'm brand new to this but I've been doing a lot of research. I have limited space for panels so I'd like to go with the highest watt possible, maybe a E19 320. I'd also like to keep my options open for expansion later so I thought starting with a 48v system would be best. I'd like to get at least a 45 amp MPPT and at least a 1000w pure sine inverter.

      My question is what battery AH could one 320 watt panel in San Diego Sun for 8 hours a day successfully charge?
      What are you trying to achieve? If the goal is to save money on electricity, forget the batteries and go for a grid-tied system.
      CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

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      • #4
        Originally posted by Dmonicle View Post
        I'm brand new to this but I've been doing a lot of research. I have limited space for panels so I'd like to go with the highest watt possible, maybe a E19 320. I'd also like to keep my options open for expansion later so I thought starting with a 48v system would be best. I'd like to get at least a 45 amp MPPT and at least a 1000w pure sine inverter.

        My question is what battery AH could one 320 watt panel in San Diego Sun for 8 hours a day successfully charge?
        Rule of thumb says that for a 48V battery the panel watts should be 4X the battery AH rating.
        So a 320W panel would be OK for an 80AH 48V battery bank.
        But that is only one rule.
        The other is to take your total load in watt-hours for one day, divide by 48 to get amp hours and put that number aside for later use. Then figure out how many watt hours you get from a 320W panel in 5 solar noon equivalent hours (summer only). I get 1600 watt-hours (wh). Compare that to your load watt-hour number to see if you were able to replace it. Allow at least 20% more panel power to make up for inefficient charging.
        SunnyBoy 3000 US, 18 BP Solar 175B panels.

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        • #5
          Originally posted by Dmonicle View Post
          My question is what battery AH could one 320 watt panel in San Diego Sun for 8 hours a day successfully charge?
          That's going about it backwards, and planning for "expansion" is the most expensive way to do it. It frequently results in a total redesign / change of hardware as things are just thrown against the wall to see if they stick.

          Before you buy *anything*, one wants to start measuring their power needs over time. Find the stuff you want to power, figure out how long you want it to run on battery power each day, and THEN you can start to properly plan your system. A common tool to do this is a P3 International Kill-A-Watt meter.

          Also note that "8 hours of sunlight" typically represents the "sunrise-to-sunset" mindset. Those are not the hours we use to calculate your array's ability to properly recharge your battery as early morning and late afternoon hours are usually pretty weak from a solar panel standpoint. Instead, we use "solar-insolation" hours, which are much smaller, typically centered around noon, and depends on your geographic location. Online charts are available to see these solar-insolation hours. For San Diego, you are a bit luckier than most, having about 6 hours summer, and 4-5 winter. Under *IDEAL* conditions. With solar, one goes conservative, so I'd count on no more than 4 in winter.

          These hours of actual useful sun, are a determining factor when choosing your panel array size to make sure your batteries get a decent charge.

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          • #6
            Originally posted by PNjunction View Post
            ...
            These hours of actual useful sun, are a determining factor when choosing your panel array size to make sure your batteries get a decent charge.
            Note that this measure of available sun does not mean that you have 4 good hours centered on solar noon and you ignore the rest.
            It means that you take all of the energy you get during the sunrise to sunset period and divide it by the theoretical maximum power output of the panels under solar noon sun to get an equivalent number of hours.
            Just like you divide miles traveled by total time to get average miles per hour, but you may never actually have been traveling at that speed.

            As a practical matter, the hours closer to noon contribute more to the total than hours farther away, so those are the hours where shade and other issues are more important, and were you will get your greatest benefit from TOU rates when using grid tied PV.
            SunnyBoy 3000 US, 18 BP Solar 175B panels.

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            • #7
              Originally posted by sensij View Post
              What are you trying to achieve? If the goal is to save money on electricity, forget the batteries and go for a grid-tied system.
              I'd like to take my garage fridge off grid and have back up power for rolling blackouts here in San Diego

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              • #8
                Originally posted by PNjunction View Post
                That's going about it backwards, and planning for "expansion" is the most expensive way to do it. It frequently results in a total redesign / change of hardware as things are just thrown against the wall to see if they stick.

                Before you buy *anything*, one wants to start measuring their power needs over time. Find the stuff you want to power, figure out how long you want it to run on battery power each day, and THEN you can start to properly plan your system. A common tool to do this is a P3 International Kill-A-Watt meter.

                Also note that "8 hours of sunlight" typically represents the "sunrise-to-sunset" mindset. Those are not the hours we use to calculate your array's ability to properly recharge your battery as early morning and late afternoon hours are usually pretty weak from a solar panel standpoint. Instead, we use "solar-insolation" hours, which are much smaller, typically centered around noon, and depends on your geographic location. Online charts are available to see these solar-insolation hours. For San Diego, you are a bit luckier than most, having about 6 hours summer, and 4-5 winter. Under *IDEAL* conditions. With solar, one goes conservative, so I'd count on no more than 4 in winter.

                These hours of actual useful sun, are a determining factor when choosing your panel array size to make sure your batteries get a decent charge.
                Good advice, thank you. I just started my kill a watt crusade. So far my garage fridge is about 2 khw/day at 150 watts/1.5 amps

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                • #9
                  Thank you everyone for your help, another thought is to go 12v with the 320w panel ... can a MPPT bring 55 ish volts down to 12-14 volts while boosting amps correctly? I read somewhere that 12-24v over target is what flexmax recommends.

                  Comment


                  • #10
                    garage fridge

                    Originally posted by Dmonicle View Post
                    I just started my kill a watt crusade. So far my garage fridge is about
                    2 khw/day at 150 watts/1.5 amps
                    Thats about right for older equipment. A decade ago I got rid of my old fridge and bought the best
                    Energy Star fridge/freeze then. It only uses 1 KWH a day. Bruce Roe

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                    • #11
                      Originally posted by inetdog View Post
                      Note that this measure of available sun does not mean that you have 4 good hours centered on solar noon and you ignore the rest.
                      It means that you take all of the energy you get during the sunrise to sunset period and divide it by the theoretical maximum power output of the panels under solar noon sun to get an equivalent number of hours. Just like you divide miles traveled by total time to get average miles per hour, but you may never actually have been traveling at that speed.
                      I would just caution anybody doing off-grid battery storage not to jump for joy and start figuring in sunrise-to-sunset hours. Since the early and late hours are so inefficient when it comes to charging (if you aren't over-paneling) on a properly sized bank, it is best to throw those hours away to be conservative and have a real-world safety net against possible FLA stratification, agm undercharge, etc. Yes, on paper sunrise to sunset works. Real world with a battery is already hard enough to keep things charged properly without a hedge or conservatism.

                      As a practical matter, the hours closer to noon contribute more to the total than hours farther away, so those are the hours where shade and other issues are more important, and were you will get your greatest benefit from TOU rates when using grid tied PV.
                      Definitely for grid-tied where the characteristics of charging a battery efficiently are no longer an issue.

                      Comment

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