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mid size system in Belize...need suggestions

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  • mid size system in Belize...need suggestions

    I've been commissioned to build an off-grid system for a client building a home in Belize.

    We ran calculations today and found he should rarely need more than 10KWh/day, most days he will probably use closer to 5KWh, and a maximum of 3500W instantaneous.
    The catch is that he wants a good reserve capacity to avoid running the generator to the greatest extent possible. I am planning the system around a 5 day reserve capacity (at 6KWh/day).

    5kWH x /.93 inverter efficiency x 5 days autonomy / 50% DoD / 48V = 1120Ah 48V battery bank
    I have selected the Trojan L-16-RE-2V 1110AH as the most sensible cells for this application.

    To achieve at least a C8 charge rate on sunny days, I need to provide at least 1110Ah / C8 * 48V = 6660W PV array. I am looking at this as a bare minimum as I'd like to achieve C12 (4440W) on all but the worst cloudy days. He can always shut off a couple strings in the dry season, and limit use of his maximum capacity to the rainy season. I am thinking of running 32 250W 60 cell poly panels, I can get them at a good price and if we hook it up with 4 strings per charge controller, it would be simple to shut off two strings in the dry season (6000W total), and crank them back up in the wet season (8000W total capacity).

    Since his power requirements are pretty modest, I believe that he doesn't need to go crazy with his inverter selection. I use the Outback FP1 FX3048T and I am suggesting the same system for his needs, with the addition of a 2nd Flexmax 80 for obvious reasons.

    The one I'm really struggling with is the backup generator selection. I do not know what ~6000W generator would be a good choice which is propane/butane compatible (fuel choice by necessity in Belize ) Please help me with suggestions on a good generator. Looking at this Generac right now - http://www.electricgeneratorsdirect....or/i10669.html

    Any other comments/criticisms or suggestions are welcome and coveted, I want to make sure I get his system build to support him for many years, TIA

    The worst solar insolation month here in Belize is 4.0 - http://www.gaisma.com/en/location/belize.html
    3680W - FLEXmax 80 - FX3048T - 8x L16P-AC 435Ah

  • #2
    I just discovered one big issue with the FX3048T that comes with the FP1 system I was looking at....the battery charging is limited to only 35A...only about 1/3 of the current needed to achieve a C12 rate
    So then there is the FP2 FX3048T which doubles everything and would provide up to 70A of charge current for the battery bank, which gets me a lot closer.
    But, if I really want to get up to a proper charge rate for the battery bank I think I might need to go to the Radian FPR-8048A which can output 115A for battery charging, or about C10.

    Any other ideas or thoughts about this system?
    3680W - FLEXmax 80 - FX3048T - 8x L16P-AC 435Ah

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    • #3
      I guess that means I nailed it? Everything is about perfect and nothing needs any changes? Wow, I'm getting good at this LOL
      3680W - FLEXmax 80 - FX3048T - 8x L16P-AC 435Ah

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      • #4
        Originally posted by miahallen View Post
        I guess that means I nailed it? Everything is about perfect and nothing needs any changes? Wow, I'm getting good at this LOL
        Either that or maybe most people do not want to spend time designing a system that will be used in a foreign country where they know little to nothing about the rules and codes.

        I will tell you that if you plan on using a daily 50% DOD it will reduce the life span of the battery so IMO I would go with a larger Ah system which then increases your CC and pv array size.

        At least you are thinking about having a bottle gas fuel generator. Although I have heard Generac are ok for short runs (i have a 3250watt rated one myself) they do not last as long as some of the other big name generators.

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        • #5
          Originally posted by SunEagle View Post
          Either that or maybe most people do not want to spend time designing a system that will be used in a foreign country where they know little to nothing about the rules and codes.

          I will tell you that if you plan on using a daily 50% DOD it will reduce the life span of the battery so IMO I would go with a larger Ah system which then increases your CC and pv array size.

          At least you are thinking about having a bottle gas fuel generator. Although I have heard Generac are ok for short runs (i have a 3250watt rated one myself) they do not last as long as some of the other big name generators.
          I thought the way I wrote it indicated that 50% DoD would be a worst case scenario if solar was poor for 5 days straight. This would NOT be a daily target. I think the system is planned pretty well to rarely drop below 80% SoC.
          Belize is a 3rd world country and rules/regulations here are mostly non-existent (and off-grid is completely unregulated).

          We've also switched our focus to the Generac "EcoGen" series which runs a lower RPM and seems to be a much more reliable choice. I doubt if the generator will get more use than about 100 hours per year.
          3680W - FLEXmax 80 - FX3048T - 8x L16P-AC 435Ah

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          • #6
            Originally posted by miahallen View Post
            I thought the way I wrote it indicated that 50% DoD would be a worst case scenario if solar was poor for 5 days straight. This would NOT be a daily target. I think the system is planned pretty well to rarely drop below 80% SoC.
            Belize is a 3rd world country and rules/regulations here are mostly non-existent (and off-grid is completely unregulated).

            We've also switched our focus to the Generac "EcoGen" series which runs a lower RPM and seems to be a much more reliable choice. I doubt if the generator will get more use than about 100 hours per year.
            Ok. I misunderstood what your daily usage would be on the batteries. I would say you have done your homework designing the off grid system.

            I am unfamiliar with the Radian CC so can't help you determine if it will be a good piece of equipment. At least you are looking into finding a CC that will get you a charge rate between C/8 and C/12.

            Just another path to research. I believe that there are charge controllers that you can stack so if you can't find one that gets you 115amp maybe getting 2 that each get you 60amp would solve your requirement.

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            • #7
              All those good expensive 6000 watts /48 volts DC Inverter are capable charging the battery bank. Like Xantrex XW6848 Inverters.

              It is crazy to use so many panels and battery storage just to power 5 to 10 kwh daily because you don't want to run the generator during rainy season and bad weather.

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