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Minimal battery storage solution for powering freezers (on-demand not required)

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  • Minimal battery storage solution for powering freezers (on-demand not required)

    Here’s my goal:
    To utilise my solar PV array just to power a couple of freezers, and dump any excess on long summer days into the hot water cylinder. i.e. No requirement to store power for on-demand use. Don’t have much in the way of financial resources.

    What I do have is 6x 140-watt PV panels (840 Watts), and a 40-Amp Tracer MPPT charge controller.

    Because I am only powering freezers, the power doesn’t need to be on-demand, it can just come on when there is sufficient output from the panels. Therefore I believe I should be able to minimise battery storage and use the battery sort of like a capacitor (to handle compressor startup loads) rather than a long term storage device.

    My proposed setup (proposed changes welcomed!!): PV panels configured in two series-strings of 3 panels, going through the 40-Amp MPPT charge controller into a 24V battery, then out through a pure sine inverter to the freezer loads (pure sine wave required to run a compressor)

    The freezers each draw about 150 watts while running, with a 1KW surge on startup. I would like to stagger the startup timing so that only one surge load happens at once (bright ideas anyone?)

    But my big challenge is to find a cost-effective battery or battery-substitute solution that will provide a short term boost to handle the startup load, and is able to handle up to 40 amps of charge current without being fried. It can be minimal in capacity, as I am fine with it switching the load on and off as PV output permits.

    Does anyone have any knowledge they could share to get me on the road with this?

  • #2
    Good luck, not going to happen without batteries and a inverter.
    MSEE, PE

    Comment


    • #3
      He is willing to use pure shine inverter and cheap batteries or alternatives. To the OP, all you need to do is buy 4 cheap golf cart 6 volts 225 AH batteries and use them and make sure get one inverter has the low battery cut off at around 24 volts or one with adjustable cut off voltage.

      Cheers

      Comment


      • #4
        Originally posted by NakiKiwi View Post
        Here’s my goal:
        To utilise my solar PV array just to power a couple of freezers, and dump any excess on long summer days into the hot water cylinder. i.e. No requirement to store power for on-demand use. Don’t have much in the way of financial resources.

        What I do have is 6x 140-watt PV panels (840 Watts), and a 40-Amp Tracer MPPT charge controller.

        Because I am only powering freezers, the power doesn’t need to be on-demand, it can just come on when there is sufficient output from the panels. Therefore I believe I should be able to minimise battery storage and use the battery sort of like a capacitor (to handle compressor startup loads) rather than a long term storage device.

        My proposed setup (proposed changes welcomed!!): PV panels configured in two series-strings of 3 panels, going through the 40-Amp MPPT charge controller into a 24V battery, then out through a pure sine inverter to the freezer loads (pure sine wave required to run a compressor)

        The freezers each draw about 150 watts while running, with a 1KW surge on startup. I would like to stagger the startup timing so that only one surge load happens at once (bright ideas anyone?)

        But my big challenge is to find a cost-effective battery or battery-substitute solution that will provide a short term boost to handle the startup load, and is able to handle up to 40 amps of charge current without being fried. It can be minimal in capacity, as I am fine with it switching the load on and off as PV output permits.

        Does anyone have any knowledge they could share to get me on the road with this?
        You have two things going against your plan.

        First you indicated you "don't have much in the way of financial resources". Second you are looking for a battery that can provide just enough for a 1kw surge that doesn't cost much and requires a control circuit that staggers the start of each.

        If you do not have finances then you do not have enough money for a solar battery system. There are less expensive ways to power some freezers and heat water.

        First off use grid power it is the cheapest. Next used a generator and run it just long enough to maintain the freezer temperature. Next get a "grid tie" solar panel system. Last and I mean last is to use a battery to run those loads. That is the most expensive way to go.

        Comment


        • #5
          More thoughts

          Thanks very much for these initial responses. They are quite different from each other!

          Paul you are right, I am definitely assuming I will need some sort of battery storage and an inverter arrangement.

          Because I am happy to store a bare minimum of energy (just enough to achieve startup load of the freezers) I think I should be able to have minimal battery storage, and appreciate the thoughts around that.

          ... and also correct that my next challenge is timing the supply of the power to the loads/freezers so they don't both start up at the same instant. Using more than one inverter with adjustable cut-in and out voltages sounds good but adds cost. If I could get something on the mains power side (a simple delay gadget that sits between the power outlet and the freezer power plug and delays the supply by say 30 seconds) that would help. If I used a single inverter, and put two such devices on the outputs with different delays, that would give the inverter time to power up, then the relay to the first freezer would kick in some seconds later, then the relay to the second freezer would kick in some more seconds later.

          So two handy devices that would really assist my cause are
          1. A voltage-based (24V/40A) relay with adjustable cut-in and cut-out voltages, to sit between the battery bank and inverter; and
          2. One or two timer-based relays (mains voltage/1KW) to control the delay after power-on for starting up each freezer load.

          Does anyone know of such a device by any chance?

          Comment


          • #6
            1) realistic sizing means you 840W of panels, will only yield 420W out of the batteries, x 3 hours winter - that's 1260wh per 3 hour sunny day, OK in Summer, but bad in winter. battery based systems roughly, have 50% system losses.

            2) do you have any power consumption data for your freezers ?

            3) using a timer, a DPDT relay and 2 Well Pump Contactors. Set timer for 2hr on, 2hr off, that should keep the freezers happy, use the timer to control the relay, and the relay controls the heavy duty contactors.
            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


            • #7
              Thanks Mike,

              50% losses for battery systems? Wow if only they told you that up front. I would have guessed at 20 per cent.

              Yes, I have always worked on 3hrs of power generation per day on average.

              per PaulCheung's reply, 4x pre-loved 6volt batteries @ 220AH might do the trick for me.

              My main remaining challenge then is a simple method of staggering the initial startup of the freezers. What I would like is for the inverter to come on at x volts, then 30 seconds later the first freezer load comes on, then a further 30 seconds later the second freezer load comes on. Then when the battery voltage drops below y volts the inverter cuts out.

              I would have thought that for solar PV applications having a staggered startup of multiple loads on a time delay basis from the initial availability of power would be a common requirement?

              An alternative might be simply an adjustable voltage-sensitive relay for each load, with varying cut-in and cut-out voltages to ensure staggered startups. Like this one here:
              http://www.intervolt.com/products/vo...sr-series.aspx

              It would be great if there was a cheap version, or one that had a single voltage input and multiple output relays, where all output relays had adjustable trigger settings (on and of voltages). Has anyone seen anything like this by any chance?

              Comment


              • #8
                Originally posted by NakiKiwi View Post
                Thanks Mike,50% losses for battery systems? Wow if only they told you that up front. I would have guessed at 20 per cent.
                A grid tied system comes in at approximately 15% losses
                [SIGPIC][/SIGPIC]

                Comment


                • #9
                  Originally posted by NakiKiwi View Post
                  Thanks Mike,

                  50% losses for battery systems? Wow if only they told you that up front. I would have guessed at 20 per cent.

                  Yes, I have always worked on 3hrs of power generation per day on average.

                  per PaulCheung's reply, 4x pre-loved 6volt batteries @ 220AH might do the trick for me.

                  My main remaining challenge then is a simple method of staggering the initial startup of the freezers. What I would like is for the inverter to come on at x volts, then 30 seconds later the first freezer load comes on, then a further 30 seconds later the second freezer load comes on. Then when the battery voltage drops below y volts the inverter cuts out.

                  I would have thought that for solar PV applications having a staggered startup of multiple loads on a time delay basis from the initial availability of power would be a common requirement?

                  An alternative might be simply an adjustable voltage-sensitive relay for each load, with varying cut-in and cut-out voltages to ensure staggered startups. Like this one here:
                  http://www.intervolt.com/products/vo...sr-series.aspx

                  It would be great if there was a cheap version, or one that had a single voltage input and multiple output relays, where all output relays had adjustable trigger settings (on and of voltages). Has anyone seen anything like this by any chance?
                  I have not seen a control system as you have described but I am sure you can utilize a PLC with relay outputs to perform the start-up and load shedding based on time and voltage measurements. Depending on which PLC you use the programing for that logic would be pretty basic but can be costly.

                  Comment


                  • #10
                    Originally posted by NakiKiwi View Post
                    ......An alternative might be simply an adjustable voltage-sensitive relay for each load, with varying cut-in and cut-out voltages to ensure staggered startups........
                    That would leave one loaded un powered when batteries are low. There used to be in common usage, Time Delay Relays that would acomplish this function, or you can make up a fairly simple circuit with a small transformer, some series resistors, and some caps. As a resistor / cap pair charges up, it can engage a relay and enable it.

                    you could also use a relay to only allow one device at a time to come on, the alternate one could only come on when the first shuts off.

                    Battery system losses from PV nameplate:
                    20% PV STC to real life conditions in summer
                    5% MPPT charge controller
                    15% internal battery charge losses (lower when batteries are new, less for AGM batteries)
                    10-20% inverter losses, tare & efficiency.
                    2% wiring losses

                    Loads you can use in daylight hours are exempt from the battery recharge loss

                    Grid InterTie only has the GT inverter loss (5%) and STC loss.
                    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

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