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can i use a solar panel without using battery

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  • #16
    5-13Chart.jpgHere is an attached "bell curve" of a 4.5 Kw west facing array
    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

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    • #17
      Mike you just put your bell curve there because its accurate and neat. mine is.. nevermind.

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      • #18
        Originally posted by Sunking View Post
        I did not say that. That is only true assuming the batteries are fully charged.

        Here is some math fun. Current out from the controller is 60 amps, batteries are charging with 30 amps. What is going on?
        Not sure, besides me losing some more brain cells. And, yes, assuming batteries are full, or damn near. The whole point is to maximize battery life....by not using it, until absolutely necessary.

        Another great scenario which fits me is, I get a 5000 watt PV system. I plan on using 100% of my electrical needs during which time those panels can produce that power here in AZ using a sun tracking rig. And I want a battery to provide emergency power at night in case I wake up in the middle of the night and have to puke my guts out cause I drank too much and ate too much mexican food and I need some light and to charge my phone because I forgot to charge it and need to call and order a late night pizza delivery. Do I need a HUGH battery bank for the power which will be used during the time the panels can fully provide that power or just a small battery for when the panels can't produce any power.

        I think that's pretty clear on do I need batteries.

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        • #19
          Until you define your loads - how many watts for how many hours it is just whistling in the wind.
          [SIGPIC][/SIGPIC]

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          • #20
            Hi guys,

            I'm totally new to this although might be researching a similar situation which may answer the ops question.

            Isn't this what a 'shunt' does?

            Scenario: Your battery is full. The sun is shining brightly on the panels. The power being produced at that point by the panels is being 'shunted?' directly to any load you may be using. Completely avoiding any battery charge or discharge.

            Disclaimer: The load would have to be less that equal to what the panel was generating at that time.

            Disclaimer 2: I'm a total newb and this is my 2nd post after my introduction. Be gentle

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            • #21
              One of the basics of solar PV is to know how many watts you are really consuming or planning to consume. Name plates on equipment don't mean much as they are a maximum number and no one wants to spend (waste) the money to be able to supply the maximum.

              One way is a Kill A Watt or similar - you just plug it into the power supply to the TV, fridge or whatever.

              What I have done is use cheap commercial power meters and wire them into the system at certain points plus I have one with plugs on it so I can place it wherever I want. I try to monitor things for days or a week at a minimum. Cost of the meters - about 20$ US each for monophase.
              [SIGPIC][/SIGPIC]

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              • #22
                OK....you have 5,000w of PV. Let's assume, for the sake of argument, they produce 5kw from 7am to 5pm as you have perfect trackers ( I have 3 arrays on trackers, and can tell you it helps, but they ain't perfect )

                Now, as Russ said: What ARE your electrical needs ? 1000w ? 2000w ? 4000w ?

                Say it's 3657w. When do you turn it on ? 6:59 am ? 7:02 am ? ( remember, the sun is rising later as we go into winter ). How do you deal with a passing cloud.....you gonna keep one eye on your load and the other eye on the sky ?

                And let's say a high, Cirrus type cloud cover moves in during the day....does your production fall below 3657w ( or whatever load you have on it at the time ? ).

                And let's say you actually DO have 5,000w of PV production.....are you gonna try to USE the whole thing right up to the last watt of PV production, risking browning out loads ? Or are you gonna stay conservative, stay back at 3,000 or so watts ? If you stay conservative, aren't you wasting the other 2,000 watts when it actually COULD produce them ? ( because it won't if the load isn't there )

                See, this whole thing is merely an academic exercise.....you can't operate a PV system in a PRACTICAL manner without a decent battery bank, or connected to the grid ( using it as your battery bank ) unless you're willing to WAY oversize the PV amount, to the point of being silly.

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                • #23
                  Originally posted by MooChaqa View Post
                  Hi guys,

                  I'm totally new to this although might be researching a similar situation which may answer the ops question.

                  Isn't this what a 'shunt' does?

                  Scenario: Your battery is full. The sun is shining brightly on the panels. The power being produced at that point by the panels is being 'shunted?' directly to any load you may be using. Completely avoiding any battery charge or discharge.

                  Disclaimer: The load would have to be less that equal to what the panel was generating at that time.

                  Disclaimer 2: I'm a total newb and this is my 2nd post after my introduction. Be gentle
                  Disclaimer: I'm not an electrical engineer, nor do I play one on TV.

                  A shunt can have quite a few purposes, but in a solar system, the most often use is to measure a flow of current you can't easily measure directly due it being a really HIGH current. In this case, the shunt is actually a resistor of a known value, and the meter reading in Amps is actually measuring a small voltage across the shunt, the reading value proportional to the current flowing at the time, and shows on the meter as "Amps".

                  The flow of power in a PV system is to the load...no load, no flow.

                  In a battery PV system, power flows from the panels to the charge controller, then to the batteries IF THEY NEED IT, then on to whatever other loads are connected to the system. The batteries are first in line of the list of needs.....the system is designed to take care of them as it's "primary mission".....as best I understand things.....which, self admitted, may be limited.

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                  • #24
                    Originally posted by MooChaqa View Post
                    I'm totally new to this although might be researching a similar situation which may answer the ops question.

                    Isn't this what a 'shunt' does?
                    In terms that you are using it no a shunt is just a precision high wattage resistor used to measure current.
                    MSEE, PE

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                    • #25
                      I got an idea since no one is answering the question I asked 3 times.

                      I want a 5KW system. I know I won't use all that and only a fraction of that most of the time. And 99% of my electrical needs will be during sunlight hours and will fall way below 5KW and it's sunny every day and no clouds. Can I use say 2 Trojan L16RE-B for safe measure? That's only about $600 for batteries. I can live with that.

                      Simple question.

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                      • #26
                        Originally posted by MooChaqa View Post
                        Isn't this what a 'shunt' does?
                        Scenario: Your battery is full. The sun is shining brightly on the panels. The power being produced at that point by the panels is being 'shunted?' directly to any load you may be using. Completely avoiding any battery charge or discharge....
                        No, a shunt is a calibrated resistance used to measure amps

                        You are almost describing a "diversion load" or "opportunity load".
                        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


                        • #27
                          Originally posted by themaxx69 View Post
                          I got an idea since no one is answering the question I asked 3 times.

                          I want a 5KW system. I know I won't use all that and only a fraction of that most of the time. And 99% of my electrical needs will be during sunlight hours and will fall way below 5KW and it's sunny every day and no clouds. Can I use say 2 Trojan L16RE-B for safe measure? That's only about $600 for batteries. I can live with that.

                          Simple question.
                          Simple answer? No

                          How have you defined and measured your loads? A strange situation and usually the bulk of power is consumed in the evening hours
                          [SIGPIC][/SIGPIC]

                          Comment


                          • #28
                            Originally posted by themaxx69 View Post
                            I got an idea since no one is answering the question I asked 3 times.

                            I want a 5KW system. I know I won't use all that and only a fraction of that most of the time. And 99% of my electrical needs will be during sunlight hours and will fall way below 5KW and it's sunny every day and no clouds. Can I use say 2 Trojan L16RE-B for safe measure? That's only about $600 for batteries. I can live with that.

                            Simple question.
                            I'll have to make assumptions, since you have not given (in one place I can find it) all the info we need for the BEST answer, so here's a half assed answer:

                            L-16's a are about 400AH batteries, 2 in series would give you a 12V 400ah bank.

                            Proper charging would be 30 - 40 amps, to provide enough power to "stir" the electrolyte to pervent it from stratifing in the tall batteries.

                            Your inverter, will be powering unknown loads. While the sun shines ?

                            First problem:
                            5Kw of PV yields 333amps @ 15V
                            That will need 6, 60A charge controllers to manage the power Yilkes !

                            2nd problem:
                            Huge wires to carry the 333 amps You won't even be able to lift the wire.

                            3rd problem:
                            Much more esoteric, and problematic. Your large loads this 5Kw array will be powring , will need a HUGE inverter @ 12V. While you might find something on fleabay that lists 5Kw, it can't really exist, as the weight of the copper traces to carry 333amps, is probhitive. If we ignore that issue, we still have the 120hz ripple current, that the inverter imposes on the puny 400ah bank. It will charge & discharge the batteries at 120 hz, as the inverter draws power. Overall, the PV array will keep the batteries charged, but using the batteries as a capacitor, with 100 amps flowing in & out 120 times a second, they will heat up, shed plate material, and die, in a couple days. If your loads are less than 5KW, your 120hz ripple currents will be less.

                            4th problem:
                            If you run your batteries down 30% some evening (70% charge remaining), the high current the array can provide in the AM, when the sun comes up, will cook the batteries, max charge rate for the batteries should be in the 50-60A ballpark. Your 333 amps is much larger.

                            Scaled differently, a 5KW array in to:

                            24 v system = 180 amps, and just 3, 60 amp controllers (4ea, L-16 batteries, or you could easily use smaller, 200a golf cart batteries, and still have the same KWh storage as the 2 L-16s )

                            48 v system = 90a and only 2, 60a controllers, or one 80A controller may do it. (8, 6v batteries needed)

                            Higher voltage systems, give you lower system amps, lower losses, less parts count, except for batteries.
                            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


                            • #29
                              That answers some of my questions. And gives me more to think about.

                              May be this should have been my first question, can I have an off-grid PV system with no batteries. 100% of electrical needs will be covered by the panels.

                              Comment


                              • #30
                                I didn't mention this before because to me it seemed like common sense, but weather I get a 3, 4, or 5kw system, it will be broken down to 2-3 smaller system. Just seems to be more logical to have say two 2kw arrays instead of one 4kw, or three 1kw arrays instead of one 3kw. Each designed for specific equipment, for the most part.

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