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  • FM60 Array Sizing/Layout & Inverter Sizing

    Hello Gurus - I have put in a couple small 2-panel arrays and used inexpensive MPPT chargers, so while I'm not a total newb, i definitely don't know everything. My next challenge is to setup an off grid system that will be capable of running a fridge as well as a few lights and LCD tv. I am currently working on convincing the in-laws (their cabin) to purchase a DC fridge, instead of a standard AC unit.

    We have been using an ancient propane fridge that is barely working (plus chewing through gas), and the cost of a new propane unit, plus the inconvenience of having to continuously refill 20lb bottles (in-laws don't want to try to deal with bigger bottles, and a permanent tank/delivery service is a non-starter given the access to the property) In the spring/summer/fall months when there is decent insolation, I think this can work. We have a small Honda generator that they are currently using to run led lights/charge phones in the evening so it won't be too much extra load to run a small inverter instead, and the generator can be just for tools and backup battery charging.

    My questions start with the maximum Wattage and arrangement I can connect to the FM60. I am thinking I would like to install a 2P3S configuration, using 2 strings of 300Watt 60cell Panels. Unfortunately the roof is shaded at various times of the day in the shoulder seasons so to maximize potential production I would like to put 3 panels on the Eastern facing part of the roof, and 3 more panels on the western facing part of the roof. I am up around the 51degN so none of this is ideal but I'm just aiming to make it work the best I can. FM60 manual lists 1500W as the Max Recommended Array Size for 24V Battery Bank, but My array will technically total 1800W. It will, however, likely never ever make that kind of power given the arrangement/orientation. Anyone think this is a bad plan? I could bump up to the FM80, but we've settled on 430Ah (20Hr) 24V battery bank and so the 80A charge rate seems overkill. Due to some last-minute decisions on adding the fridge (was originally going to be a 2-4 panel array on a Chinese MPPT) I am going to have to work with this bank as it's already been purchased. (4x Crown CR430)

    If I can convince them to buy a DC Fridge, I will pickup a <1000W inverter to power up the inside, if not, I guess I'll need to get a >1500W unit to handle the fridge inrush....


    Related Thoughts:
    Battery Bank 24V @ 430Ah (20hr) /8 = ~53A Max charge rate
    430 * 24 = 10.3Kwh * 0.5 = 5160Wh @ 50% DOD

    TV is ~ 30W * 2h = 60Wh/day
    Lights ~5W * 4 * 4h = 80Wh/day
    Cell Chargers ~8W * 2 * 2H = 32Wh/day
    Tablets ~15W * 2 * 2H = 60Wh/day
    Inverter Parasitic Losses ~16W * 8hr = 128Wh/day

    General Loads = 360Wh/day (incl inverter losses)
    DC Fridge = 600Wh/day (estimated for 13cu/ft Unique Off-Grid DC Fridge)

    Total Loads = 960Wh/day but let's round that up to 1kWh/day for fun * 1.2 buffer = 1.2kWh/day (50Ah)
    1.2kWh means just over 4 days runtime @ 50% DOD with no solar input.


    With an AC fridge, the inverter sizing losses jump to ~400Wh/day, and the same size fridge is estimate about 1.1Kwh/day so my daily is now 1.732kWh * 1.2 buffer = ~2.1 KWh/day (87.5Ah) so I'm down to only about 2.5 days autonomy...


  • #2
    I think the change over point for break even expenses converting from propane to electric, was about 2 years, the extra PV costs vs all that propane going up the flue.

    AC vs DC how far from the batterry, is the fridge going to be ? That run will need to be heavy cable to allow enough power to start the compressor motor without stalling it. With 120VAC, the weak point is often the inverter not being able to supply the surge, 24VDC the cable becomes the limiting factor.

    Adding panels at different orientations (virtual tracking) is a legit way to spread the harvest over the day. But the panels on each facet, really need to be well matched because the lowest voltage string, will not allow any higher voltage, so those free panels may reduce your total harvest if they are not well matched.
    The spec you watch for and match is the Vmp (Voltage Max Power)
    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


    • #3
      Hi Mike, thanks for the response.

      Batteries will be stored about 10 feet from the fridge, just through the exterior wall in a new enclosure I'm building. From what I can see the DC compressor only needs about 2.5A running, so surge should be around 8 or 9A, but only for a half second? I've never seen the numbers on a DC system. Regardless, it seems like #14 or #12 wire would be sufficient. Anything I'm missing there?

      The panels are going to be purchased new, as a set (I already had 2 panels for their original needs, but I'll get a matched set for the new plan). Looking at probably some Longi 300W 60 cell.

      ​​​​​ Anything else you can think of?

      Comment


      • #4
        Lifetime of the Fridge. Commercial energy star fridges, are good for say, 10 years No idea of the life or repair-ability of the DC fridges

        If you go DC, use at least 10ga wire, it's cheap insurance. And use the right fusing. You may need a 40A fuse, which will drive you to 8ga wire. Repeated starting surges may weaken a small fuse. What does the compressor mfg say about the DC starting surge ?
        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


        • #5
          I will look into it for the starting current on the fridges. A quick bit of googling leads me to believe the DC fridges are actually fairly reliable. Apparently quite a lot more efficient than AC.

          ​For the fuse I'm actually leaning towards using a small SqD breaker panel for the DC Distribution. Keeps the wiring a bit neater and means it's easy to reset instead of unbolting fuses. I don't like the little automotive style fuses so I won't use those.

          Comment


          • #6
            Ok unique doesn't seem to list the surge current specifically, but they do suggest a 30A fuse. So thanks for the heads up on that, I would not have expected that much.

            Comment


            • #7
              Originally posted by Xplode View Post
              Ok unique doesn't seem to list the surge current specifically, but they do suggest a 30A fuse. So thanks for the heads up on that, I would not have expected that much.
              Clever them: low energy, green, and BTW, 30A HA !!
              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


              • #8
                Some questions I would look into:
                Will the shading have a major effect on the panel output since they are being run in series?
                If not aware already, both FM60 and FM80 have a current limiter feature (page 26), you can properly charge batteries.
                http://www.outbackpower.com/download...ner_manual.pdf
                If your array is technically 1800W and it's winter with bare trees, cold temps, and full sun you may be outputting more than Max Recommended Array Size for FM60?
                What will happen to controller if panel array exceeds max size? I'd contact manufacturer to ensure it won't damage controller.
                When you calculate inverter parasitic loads, are you including inverter efficiency? or only power required to have inverter on?
                Then also be sure to account for power factor for sizing inverter to loads if you haven't already.
                https://www.solarpaneltalk.com/forum...-volt-amps-huh
                Another more in depth one Mike has recommended
                http://www.screenlightandgrip.com/ht...rator%20basics

                After 4 days no solar, your inverter parasitic loads have taken out about 10% of your usable power (5160wh).
                128wh X 4 days = 512 wh

                May consider some alternatives to using an inverter.

                Electronics
                Your cell phone chargers and tablets are likely compatible with some USB or other low voltage port.
                You can save power by having them charge on ports from another electronic device (Ex: Tv, gaming console, laptop) that is charging direct from battery.
                It will function like a hub for your smaller electronics.
                1) Get a 24v TV with compatible ports for your devices.
                2) Get a laptop with compatible ports for your devices and add on a TV tuner.
                Then use the correct converter or adapter to power laptop.
                3) Get a converter or adapter that functions as a hub direct-from-battery for charging your cell phone, tablets, and whichever substitute you use for your current TV .

                TV
                Pico projectors may be of interest to you.
                http://aaxatech.com/products/hd_pico_projector.html
                If you check the specifications, this one and several others use about 10W.
                They work best in dark or really low light, not much brighter than that.
                I'd watch some videos of them and see if that might for you for having a display that will save you power.
                May be able to get a TV tuner to work with one as well.

                Lighting
                USB lighting could also work with ports in your 24v TV or laptop or converter/adapter.
                Though may not be up to the task of sufficient lighting.
                If not, then there are also 24v lightbulbs you could use.

                Refrigeration
                I'm am looking into a DC fridge compressor, currently have my eye on the smaller model here.
                https://assets.danfoss.com/documents...3886433214.pdf
                Here's a review and info that
                http://www.truckcamperadventure.com/...nd-a-few-tips/
                For DC fridge, I'd figure up how much panel output I'd be getting on cloudy days and try to get a fridge that can run during that time without draining batteries.
                For AC fridge, being overpaneled on sunny days and using an inverter could work if your batteries can finish charging also.
                If you go this way, you may consider getting a freezer instead to make ice, then store in cooler.
                Will be less stress on the batteries if you make the cold you need when the sun is out.
                Lastly, surge loads on fridges can be rated 5x - 10x times continuous.
                For AC fridge, how will fridge surge loads stack up with power factor?
                I'd keep that in mind if purchasing an AC fridge and contact manufacturer make sure you don't get a "womp womp".

                Comment


                • #9
                  Ok to address the things you have brought to my attention (hopefully i don't miss anything)

                  1) 1800W is the labelled max of the output of the panels, since they're facing opposite directions in the sky by about 30-40 degrees AND not facing south at an optimal angle, they will never product 1800W of actual output power. Honestly I'd be happy if they put out 1000W-1200W in the summer peak times. My goal is to have more harvesting hours in the day by angling half the panels towards sunrise, and the other half sunset. So the FM60 should never see peak power. I may buy the FM80 anyway since it doesn't look much more expensive and then it's a moot point anyway.

                  2) Inverter parasitic losses are posted by the manufacturer - I am just using their numbers. I do not believe the unit's efficiency needs to be applied against this since it's already an efficiency loss. Maybe I'm wrong? that would add another 10-20% to the parasitic loss numbers if it does.

                  3) Options instead of inverter? I am not willing to go down that path since it will drastically increase the amount of installation effort, as well as the complexity of the in-laws using the system. My goal is to keep it as simple as possible. Things like the TV will be on when the lights and chargers are plugged in so the inverter will already be on and the TV/DVD player only draw about 30W total together so I don't think it[s worth the extra cost to convert these items. Using a laptop to feed the TV is probably actually less efficient than their current DVD player setup; I doubt the laptops they have use less than the current TV/DVD setup does. We have family and friends come visit sometimes as well, so I don't want to have to rely on them bringing a compatible USB cord when they'll likely pack an AC charger.

                  4) Pico projector - Again, while this is a neat idea, we're only saving 40Wh/day of usage... sort of... since i'd have to power another device to feed the projector a signal. The LCD TV they use now is quite low draw and is visible in normal lighting so I think they'll be happier with that.

                  5) DC Fridge - the "Unique Off Grid" brand fridges we're looking at are DC and use a DanFoss compressor so I think we're both on the right track here. The 13cu/ft fridge runs at <60W for an estimated 600Wh/day usage. I should be able to pull 56W from the panels pretty much anytime the sun is up with the 6 panel configuration. Even on a cloudy day I think I'll be alright there. It's just the overnight time, keeping the fridge cool, that it will pull from the batteries - the rest of the time the panels will cover the draw.


                  I think my biggest challenge with the in-laws is going to be habit awareness. right now they leave a snake pit of chargers all plugged into a couple of power bars. they're just plugged in 24/7 since they're only powered when the generator is on. lol I have already started warning them that they'll need to unplug and get in the habit of just plugging in what they need WHEN they need it.

                  Greta - are you planning to convert an AC powered fridge to a DC compressor? I haven't looked into that, assuming that the costs would be pretty high to have a HVAC person do the actual work and recharge the refrigerant. have you looked into that? what kind of cost is it?

                  Comment


                  • #10
                    Are you using Square D QO, or QOU breakers for your DC distribution? There's a good amount of info on the Schneider Square D website describing The QO and QOU breakers and their ability to handle DC voltage. If anything over 12 DC system it is best to use the QOU line of breakers.
                    2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                    Comment


                    • #11
                      Yes, looking at the QO series. I've noticed as long time ago that the Schneider SqD stuff is marked 48VDC. And apparently they're actually rated up to 125vdc in some cases

                      Comment


                      • #12
                        Originally posted by Xplode View Post
                        Greta - are you planning to convert an AC powered fridge to a DC compressor? I haven't looked into that, assuming that the costs would be pretty high to have a HVAC person do the actual work and recharge the refrigerant. have you looked into that? what kind of cost is it?
                        I looked into it sometime a year or two ago, I think the recommendation was that it's better to purchase the DC compressor outright.
                        Either way, it'll be more than I want to spend.
                        I pulled apart a cheap AC mini-fridge and put the evaporator in a cooler. It uses about 200wh daily, though that's still too much for my battery.
                        May try to put some heavy insulation on the outside of the cooler since the gutted fridge allows me to keep the condenser separate from the container.

                        About leaving things plugged in, some of your electronics may use a negligible amount of power whereas others may use generously.
                        I tested a netbook (fully charged) and it showed 0.0 watts on kill-a-watt, though it may still be using a tiny amount of wattage.
                        Tested an iPhone (fully charged) too, turned it on and then to screen lock.
                        At first it was using about a steady 0.5 watts plugged in then after about an hour it was jumping back and forth between 0.0 watts and 0.3 watts.
                        If your battery powered devices are fully charged, they may not use as much just being left plugged in whereas a TV might have a steady higher power drain.
                        I'd check your the portable devices once fully charged and see what they draw, TV, and maybe even light bulbs too.

                        If it is a problem, may want to have some kind of low voltage disconnect you can adjust.
                        Here's the inverter I have, I use it for temporary loads.
                        http://www.samlexamerica.com/documen...-0618_Lrez.pdf
                        Thought this was funny (pg 23 & 24), basically it says that for my inverter the low voltage alarm and shut off are useless.
                        Then they recommend an external programmable low voltage disconnect.

                        The fridge you said was 600 wh daily.
                        If your panels produce enough power for fridge 12 hours of day, then maybe estimate 300wh needed nighttime.
                        Having cold water stored in fridge and containers of ice in freezer may lessen the power demands.
                        Also if it is night, the fridge may not get opened as much or at all, so that could be a plus for maintaining cold temps in fridge.
                        For making fridges more efficent, I found a lot of good answers from searching:
                        "Do refrigerators run better full or empty?"
                        I read a good discussion awhile back, they gave actual numbers like the difference in water and air heat capacity, fridge volume and air displacement with contents and the like.
                        Couldn't find it though...
                        Last edited by Greta Gremlin; 03-18-2019, 02:12 AM.

                        Comment


                        • #13
                          Ok I'm still pondering around on options, but I've now read some things taking about optimizers and how they "tune up" a string for effects like mismatched panels and shading. Seems like snake oil, and I don't see much online that clearly describes how the Voodoo works. Are they actually effective? Would using one in my partially shady situation be helpful?

                          Comment


                          • #14
                            The way I understand it, Optimizers will take the shaded panel's output and drop the voltage until the current matches the current of the rest of the unshaded panels in the string so while you will lose some of the total string voltage the current will remain constant. There's probably more going on than that but that's the basic idea.
                            2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                            Comment


                            • #15
                              So it's just mppt for an individual panel in essence... What about string optimizers?

                              Comment

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