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Hot Water by Solar Electric direct via MPPT ?

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  • #76
    That appears to be a better deal than the techluk and not an unreasonable price. The fotobooster appears to be a capacitor bank. I've built my own system that works this way and it works great. At least when the sun shines. Love to hear your results after it is installed. The manual is crap and it is hard to figure out what they are doing. Besides MPPT, t appears you might be able to set a fixed power point voltage so it could operate in parallel with an existing controller.

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    • #77
      An important thing to recognize is that for this application a unique operating mode is required for the output stage of the inverter:

      Instead of delivering as much current as is available at voltage of the current grid connection (grid tie) or delivering as much current as is available at the relatively constant, known battery bank voltage (Charge controller) or as much current as demanded up to the limit of the input power, at a fixed voltage (stand alone inverter), this unit must recognize that the load is a fixed resistance, and to get it to absorb the available PV power it must regulate the output voltage such that the resistive load consumes exactly the available power. This is totally independent of the MPPT operation on the input side.
      SunnyBoy 3000 US, 18 BP Solar 175B panels.

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      • #78
        The those who want to avoid a lot of home made hassle.

        Missouri wind & solar has DC water heater elements
        https://mwands.com/store/index.php?r...ater%20element

        This one is 200watt DC and has a thermostat built in to it and it $72 shipped on ebay
        http://mwands.com/store/adjustable-w...ater%20element

        https://www.ebay.com/itm/12-Volt-200...edirect=mobile

        Since this element is DC it could be ran off the batteries, off the PV direct, or off the dump load depending on your CC programming.

        This would work good if you have 2 thermostats and can replace the lower one or if you're willing to swap out your single AC thermostat with this one.

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        • #79
          Definitely change the heating element. A potential problem with any direct input DC system is the ability of the resistance element to generate heat. A 4500-watt element designed to run on 240 volts is only going to put out 280 watts with 60 volts and significantly less with 48 volts. This would waste a large amount of the solar power if you had 750 watts of possible power. The Missouri wind & solar element above looks like a good bet. If you have 1000 watts of power you need to be able to put that somewhere. The heating element doesn't care whether it is AC or DC, but the voltage does matter. If cut the voltage in half then your heat output will be one quarter of what it was.
          Last edited by cretch; 02-10-2019, 08:37 PM.

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          • #80
            Does anyone know of a high resistance baseboard heater? The best I could find is a 120v 1000 watt strip. ( https://www.homedepot.com/p/KING-KP-...1210/307675585 ) which would only put out 250 watts at 60V DC. At that rate it would cost almost $500 to absorb 1 KW.

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            • #81
              Do you actually have 1KW panel overage to put into a heater. 250W seems like a good match for two panels. I have one of those oil filled heaters. It has two elements and is capable of 1,500W. I can dump 300 some watts into it at 60V and you can't put your hand on it. This is just used to take the chill off at a comfortable ambient. If below freezing it could take the full watts.

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              • #82
                Yes, because I'm not allowed to export to the grid. The power company will not accept any. I been trying to figure out what to do without going to a large battery packs. I've looked into the Outback Radian but on Gridzero that constantly cycles the batteries, does not a good solution to me. Any suggestion?

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                • #83
                  Originally posted by cretch View Post
                  Definitely change the heating element. A potential problem with any direct input DC system is the ability of the resistance element to generate heat. A 4500-watt element designed to run on 240 volts is only going to put out 280 watts with 60 volts and significantly less with 48 volts. This would waste a large amount of the solar power if you had 750 watts of possible power. The Missouri wind & solar element above looks like a good bet. If you have 1000 watts of power you need to be able to put that somewhere. The heating element doesn't care whether it is AC or DC, but the voltage does matter. If cut the voltage in half then your heat output will be one quarter of what it was.
                  This is why the guy at TechLuck recommends higher voltage and the standard AC element. You said it yourself, power is proportional to voltage squared;
                  I'd love to hear feedback about that German controller since the online doc's are sorely lacking; it's unclear to me what DC voltage is going to the heating element.

                  As for TechLuck:
                  If you have 1000W of PV (say 4-250W panels at ~28VDC each) on a 4500W AC element (~12.8 ohm), that's: (28x4)^2 / 12.8 = 980W, full use of your PV!
                  Problem is switching 120VDC without arcing, supposedly TechLuck solved this but I haven't tried one yet.

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                  • #84
                    Originally posted by PNPmacnab View Post
                    Do you actually have 1KW panel overage to put into a heater. 250W seems like a good match for two panels. I have one of those oil filled heaters. It has two elements and is capable of 1,500W. I can dump 300 some watts into it at 60V and you can't put your hand on it. This is just used to take the chill off at a comfortable ambient. If below freezing it could take the full watts.
                    I am planning to do the same thing with 2-300W PV panels at 32.6Vmpp each but I am concerned about the internal AC switches of the oil filled radiator handling 65.2VDC.
                    Sounds like you've had no issues with arcing?

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                    • #85
                      Originally posted by psablo View Post

                      This is why the guy at TechLuck recommends higher voltage and the standard AC element. You said it yourself, power is proportional to voltage squared;
                      I'd love to hear feedback about that German controller since the online doc's are sorely lacking; it's unclear to me what DC voltage is going to the heating element.

                      As for TechLuck:
                      If you have 1000W of PV (say 4-250W panels at ~28VDC each) on a 4500W AC element (~12.8 ohm), that's: (28x4)^2 / 12.8 = 980W, full use of your PV!
                      Problem is switching 120VDC without arcing, supposedly TechLuck solved this but I haven't tried one yet.
                      Thanks, I didn't realize Techluck controller could put through 100 volts, this solves a lot of problems. Most Mppt controller out put at 60 volts max.

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                      • #86
                        Just from what little I've read, the German unit is better and cheaper. However it uses a thermal sensor to switch off. The techluck uses a fixed dead time and don't think the capacitor bank is sufficient to store all that energy during it. Real efficiency is not power in vs power out. It is using all the power that is available. A MPPT charge controller can not be connected stand alone to a heater.

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                        • #87
                          The heating element will not care whether the applied voltage is AC or DC, but the thermostat, if one is used, certainly will. Any thermostat, switch, or relay will generally have a lower interrupting voltage and/or current compared to its AC rating.
                          SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                          • #88
                            Originally posted by PNPmacnab View Post
                            Just from what little I've read, the German unit is better and cheaper. However it uses a thermal sensor to switch off. The techluck uses a fixed dead time and don't think the capacitor bank is sufficient to store all that energy during it. Real efficiency is not power in vs power out. It is using all the power that is available. A MPPT charge controller can not be connected stand alone to a heater.
                            Measuring efficiency involves power out/power in. That's a quotient and different than finding the most efficient use of the input for a desired output. That involves minimizing that quotient for the process.

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                            • #89
                              Don't know what your point is. I've seen MPPT controllers not operating at the real power point voltage, but lower. A MPPT water heater controller may operate at MPPT during on cycle, but not have enough capacitance to store all the energy of the off cycle. Hunting and algorithms can also reduce real output over a time interval.

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