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  • #61
    Originally posted by LucMan View Post
    Really, and what business are you in may I ask.
    I have been in the HVAC & refrigeration business since 1973 and in the last 4-5 years the equipement being produced has been the worst junk ever, across the board few manufacturers have been immune. The problem in my opinion has been the use of recycled copper used in the refrigeration coils instead of virgin copper. Do some research before you spout off.
    Very interesting, LucMan. Might explain what I have been hearing in my locality and why few suppliers of hot water systems are even interested in selling heat pumps. The same thing applies to solar thermal though it appears to be slightly more fashionable than heat pumps. Several people have said to me, “don’t install solar thermal – it only lasts 6 years”.

    Could it also have something to do with water quality? It’s not good here. The source is ground water with high levels of iron and magnesium.

    Comment


    • #62
      Originally posted by LucMan View Post
      Really, and what business are you in may I ask.
      I have been in the HVAC & refrigeration business since 1973 and in the last 4-5 years the equipement being produced has been the worst junk ever, across the board few manufacturers have been immune. The problem in my opinion has been the use of recycled copper used in the refrigeration coils instead of virgin copper. Do some research before you spout off.
      Home building these days - I buy Schucco for water systems - from Germany - no problems - quit buying junk and you won't have the problems.

      You can the BS before chattering.
      [SIGPIC][/SIGPIC]

      Comment


      • #63
        Originally posted by Bintang View Post
        Sunking, there are some fantastic innovations happening in PV which are going to be ‘game changers’ but they are passing you by.

        Its clear that despite spending 4 years contributing more than 12,000 posts to this forum you have not learnt very much – though if your other posts are of the same quality as your recent ones in this thread I can understand why.

        So I will offer you the same helpful advice that Russ offered me:

        Go figure it out for yourself.
        What innovations? You are spreading BS

        Watch yourself. You are a new member bucking the trend - Sunking is an old hand.
        [SIGPIC][/SIGPIC]

        Comment


        • #64
          Originally posted by Bintang View Post
          Very interesting, LucMan. Might explain what I have been hearing in my locality and why few suppliers of hot water systems are even interested in selling heat pumps. The same thing applies to solar thermal though it appears to be slightly more fashionable than heat pumps. Several people have said to me, “don’t install solar thermal – it only lasts 6 years”.

          Could it also have something to do with water quality? It’s not good here. The source is ground water with high levels of iron and magnesium.
          If you are running the water to be consumed through the panel I guarantee you there will be problems - that is a really poor way.

          There has to be two loops and a heat exchanger - otherwise it is cheap stuff that will not last.
          [SIGPIC][/SIGPIC]

          Comment


          • #65
            Originally posted by Bintang View Post
            Very interesting, LucMan. Might explain what I have been hearing in my locality and why few suppliers of hot water systems are even interested in selling heat pumps. The same thing applies to solar thermal though it appears to be slightly more fashionable than heat pumps. Several people have said to me, “don’t install solar thermal – it only lasts 6 years”.

            Could it also have something to do with water quality? It’s not good here. The source is ground water with high levels of iron and magnesium.
            I agree the life of a solar thermal system is very dependent on the quality of water running through it. We have hard water and unless I flush the system particles will build up and reduce the flow.

            All of the piping is copper so I am not worried about pipes breaking but even copper can leak if the joints were not installed properly.

            Like I said earlier. I had my system installed back in Oct of 2010 and I have not had any issues with it along with getting a lower electric bill by using it instead of a totally electric system.

            Comment


            • #66
              Originally posted by Bintang View Post
              Very interesting, LucMan. Might explain what I have been hearing in my locality and why few suppliers of hot water systems are even interested in selling heat pumps. The same thing applies to solar thermal though it appears to be slightly more fashionable than heat pumps. Several people have said to me, “don’t install solar thermal – it only lasts 6 years”.

              Could it also have something to do with water quality? It’s not good here. The source is ground water with high levels of iron and magnesium.
              Poor quality ground water causes steel tanks,copper HX, and electric elements to fail.
              Should have no bearing on the solar panels since they use water, or glycol and water in a closed loop.
              There have been issues with the evacuated tubes failing but mostly in cold climates. Flat plate panels are highly reliable and should last 30 - 40 years.
              Stainless steel solar tanks with cupro nikle heat exchangers are trouble free with the worst water conditions. The only reguirement may be a semi annual tank flushing from the lower hose bib.
              Research AET drain back solar hot water systems. They have been manufactured since the 70's. Excellent system and warranty.

              Comment


              • #67
                Originally posted by Bintang View Post
                I have already provided the comparison in $/kWh. And here is a little hint for you: 1 kWh = 3412 BTU Now go figure it out for yourself.
                I agree if you use a 1 Kw heater and run it for 1 hour will generate 3412 BTU's. But why on earth would you do that knowing if you take the exact same input of 1000 watts for 1 hour will generate 10,236 BTU's or three times as much heat. What you need to figure out is efficiency. Your way is very inefficient, and my way is 300% more efficient than yours. Now go figure it out.
                MSEE, PE

                Comment


                • #68
                  Originally posted by Bintang View Post
                  Solar thermal is indeed more efficient in terms of the energy it collects per unit area but there are maintenance problems with solar thermal that discourage me from using it.

                  I think electric water heating by solar PV has much promise - especially for off grid.
                  All it requires is an off-grid inverter with MPPT control which does not need to be connected to batteries.
                  I hope to do this. I plan to feed a 24 volt element directly from a 24 volt battery bank via a suitable solid state relay controlled by the PV controller. The element is 1500 watt and the hot water tank 40 gallons. i'll also have a heavy duty thermal cutout as backup. I just need to figure out when the batteries are full charged and the water is hot and the thermostat turns off the SSR that the controller goes back to having a float charge to the batteries.
                  Cheers,

                  Comment


                  • #69
                    Originally posted by LucMan View Post
                    Poor quality ground water causes steel tanks,copper HX, and electric elements to fail.
                    Should have no bearing on the solar panels since they use water, or glycol and water in a closed loop.
                    There have been issues with the evacuated tubes failing but mostly in cold climates. Flat plate panels are highly reliable and should last 30 - 40 years.
                    Stainless steel solar tanks with cupro nikle heat exchangers are trouble free with the worst water conditions. The only reguirement may be a semi annual tank flushing from the lower hose bib.
                    Research AET drain back solar hot water systems. They have been manufactured since the 70's. Excellent system and warranty.
                    FWIW, not all solar H2O heaters use 2 loops and a heat exchanger. Warmer, or only occasional freeze climates will accommodate a direct system if possible freezing is accounted for in the design. I've had a single loop system for 6 + yrs. w/ nothing but a leaky gasket on a flex hose.

                    Comment


                    • #70
                      In response to the equipment linked in the OP, one thing I will say, is that, if you are going to make hot water from a PV panel, this is likely the 'simplest' way to do it. That box is basically a MPPT controller that outputs panel DC to the water heater. No inverting necessary.

                      Now, the reason it ISN'T a good idea for most, is that if you don't have a need for more hot water at a given time, the PV is sitting there doing nothing. If you instead had a grid tie inverter on there, at least when you weren't making hot water, you could be feeding the grid. The 5% losses from the inverter are not enough to worry about.

                      Comment


                      • #71
                        Originally posted by J.P.M. View Post
                        FWIW, not all solar H2O heaters use 2 loops and a heat exchanger. Warmer, or only occasional freeze climates will accommodate a direct system if possible freezing is accounted for in the design. I've had a single loop system for 6 + yrs. w/ nothing but a leaky gasket on a flex hose.
                        Want to REALLY maximize your solar water heating? Use the solar heat to fire an adsorption heat pump to heat the water.

                        Comment


                        • #72
                          Yes it would be a good idea to feed to the grid excess power. In my case that isn't possible with the nearest grid 10 km away. I am hoping the Midnite Classic will give me maximum power from the panels. I have looked into the Teckluck device and emailed back an forth for information but are not 100% convinced how well it would work. Maybe if it had a higher rating it could be more useful for water heating. I'm sure running an element from a battery bank will give me the correct current at the correct voltage.
                          Cheers,

                          Comment


                          • #73
                            Inetdog--or anyone else of course. Can you please break this mppt issue down for me, a total non professional, in a simple manner? Maybe give me a boneheaded math example of what exactly happens if one doesn't use mppt between the panels and element? How to provide mppt or whether is even possible is not the point here at the moment

                            Because I just don't get it. Understand the rational and why mppt helps for charging batteries tho have only used pwm. But a resistive element is simply that, not a battery with it's own innate voltage.

                            So let's imagine I hook six 72 cell,36 mpv, 270 watt panels in series directly to an element of 4500 watts/240 volts so resistance is 12.8 ohms, low enough that panels are maxed out
                            Now sure, only get the max voltage of 216 and 1600 watts for a 1/2 hour but thought i'd get close, rest of solar day but where does mppt come into it? some big loss I'm not aware of? I'm just aware that the max voltage will lower as solar input changes but you're saying that a fixed resistance will lower mpv and watt input into water.

                            Why, mainly, and also how much power loss? Rough guess of course. That's the nut of it. Brutal day. give me a break on incoherence.

                            Many thanks for any attempts

                            Originally posted by inetdog View Post
                            But the problem with driving resistance elements directly from panels is that the resistance has to be varied with time to get the panels to operate at their maximum power point.
                            If the device includes MPPT circuitry, it could at least get the maximum panel power into a fixed resistance heater.
                            There are some similar devices which are UL listed and are being installed in apartments and condos where running water/fluid lines from roof to heater is prohibitively difficult. But the concept has not been proven.

                            Economically, using a grid tie inverter will give you much more money saving than the most efficient use of PV to heat water.
                            The concept has also been used in the EU where backfeeding the utility grid is not allowed, and a local load has to be provided to use up all of the panel power above local electrical loads.

                            The size unit mentioned, especially if not UL listed, does not fall into any of the above categories.

                            Comment


                            • #74
                              Originally posted by lark View Post
                              Inetdog--or anyone else of course. Can you please break this mppt issue down for me, a total non professional, in a simple manner? Maybe give me a boneheaded math example of what exactly happens if one doesn't use mppt between the panels and element? How to provide mppt or whether is even possible is not the point here at the moment

                              Because I just don't get it. Understand the rational and why mppt helps for charging batteries tho have only used pwm. But a resistive element is simply that, not a battery with it's own innate voltage.

                              So let's imagine I hook six 72 cell,36 mpv, 270 watt panels in series directly to an element of 4500 watts/240 volts so resistance is 12.8 ohms, low enough that panels are maxed out
                              Now sure, only get the max voltage of 216 and 1600 watts for a 1/2 hour but thought i'd get close, rest of solar day but where does mppt come into it? some big loss I'm not aware of? I'm just aware that the max voltage will lower as solar input changes but you're saying that a fixed resistance will lower mpv and watt input into water.

                              Why, mainly, and also how much power loss? Rough guess of course. That's the nut of it. Brutal day. give me a break on incoherence.

                              Many thanks for any attempts
                              OK, here is a nice concrete example. For the sake of argument we will assume that you can find any resistance heating element you want in any power rating you want. That is not true in the real world and is another reason for putting active conversion equipment in between source (panels) and load (heating elements.)

                              1. Assume a panel array that will produce 10A at 100V at full noon sun. For any other condition it will produce a lower current, but approximately the same voltage at the maximum power point.
                              2. Assume a matched resistive load (1000W heater element with a resistance of 10 ohms). At full power the 100V from the panel will cause the heater to draw 10A, so a perfect match.

                              Now look what happens when the solar input to the array drops to 50% (a couple of hours either side of solar noon).
                              The voltage, Vmp, will still be 100V but the available current will be only 5A.
                              But a current of 5A into a 10 ohm resistor will correspond to a voltage of only 50V. That means that you will be getting only 50 x 5 = 250 watts out of the array into the heater. If you could cause the resistance of the heater to change to 20 ohm instead of 10 ohm you would get 100V at 5A for a power of 500 watts.
                              Since a fixed resistance is not going to be able to extract full power from the panels at any point other than full design output, you need some active circuitry such as an MPPT input and output stage which will convert the panel output of 100V at 5A to 70.7V at 7.07A. That will be a perfect match to a 10 ohm resistor and will give you the full 500 watts of power.
                              SunnyBoy 3000 US, 18 BP Solar 175B panels.

                              Comment


                              • #75
                                It is really this simple when you look at the math.

                                PWM Output Current = Input Current
                                MPPT Output Current = Panel Wattage / Battery Voltage

                                So now lets use your example of 6 270 watt panels. Such a panel would have a Vmp = 36 volts @ Imp = 7.5 amps. With 6 in series leaves us with 216 volts @ 7.5 amps. On the output we have 1620 watts / 24 volts = 67.5 amps.

                                If we used a PWM controler with 6 panels in series we have 7.5 Amps In = 7.5 Amps Out with 24 volts = 180 watts from your 1620 watt panels. Does that get your attention?

                                In practice if you were to use a PWM controller forces you to wire all the panels in series. With 6 panels you have to use a combiner and fusses on each panel leg and the feeder cable going to the controller. Feeder cable will be very large to handle the 6 x 7.5 amps = 45 amps from the panels. So with PWM 45 amps in and 45 amps out @ 24 volts = 1080 watts from 1620 watts of panels.

                                So in your example if you used a PWM charger you get 45 amps maximum (1080 watts). With MPPT you get 67.5 amps 1600 watts. Understand now?
                                MSEE, PE

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