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Thread: Help with Solar panel Design for 24 volt system

  1. #1

    Default Help with Solar panel Design for 24 volt system

    I have finally figured out how to make a solar panel that will last!!! 
    Now I have a few questions about the wiring, I have currently been building my panels w/38 cells for a 12 volt system putting me around 18 or 19 volts out put and round 3.5 amps. 3x6 cells
    My question is regarding a 24 volts system… I have 2 sets of breakers in my house 1st is a 120 volts, which will be handled by the 12volts system and the 240 volts switches, which is where the 24 volts system comes in. My question is How should I wire the solar panels for the 24 volts system.. Should I ..
    A.) continue to make 18,19 volt panels and wire them together in series or,
    B.) make a complete panel out of 76 cells and come down at 38 volts??

    What I’m thinking is:
    I think that by wiring 2 panels together in series I’ll lose a lot of wattage vs just wiring the whole panel for 32 volts in from the start..
    Example 1: 38 cells @ 1.5 watts =57 watts, @0.5 volts = 19 volts = if I wire 2 of those in series I have 38 volts but I’m still at 57 watts, losing the other 57 watts from the other panel.
    Example 2: 76 cells @1.5 watts= 114 watts @0.5 volts = 38volts, don’t have to wire in series because I already have needed voltage.

    So am I correct in thinking that I need to use example 2 when designing my solar panels for 24 volt system???

    Now to the Good part, HOW TO MAKE A SOLAR PANEL THAT WILL LAST

    1st step, tab the front of all solar cells

    2nd step, go buy your encapsulating product, I found a cheap over the counter product that doesn’t seem to yellow that much, I’ve had my panel out in the elements for a month now and still no yellowing… this is the product I’m using: http://www.biosafe-inc.com/glazecoat.htm (you can get this product from Lowes or Home depot for $22.00, it’s rated for indoor use, I’m in Atlanta GA and it’s been extremely hot and I’ve had no problems out of it, and it doesn’t yellow)

    3rd step-PRIME the front of your solar cell, basically mix a small batch of Epoxy and paint it on the front of the solar cell (make sure paint brush strokes are in the same direction of the tabbing wire, don’t paint the epoxy on the front of it going against the tabbing wire, you might lift it up or break a soldered boned) After putting the epoxy on the front of the solar cell, put it on the glass face down where you want it to go. Do this for all the cells you plan to put in the panel, make sure you put the cells where you want them because once the Epoxy hardens it’s on there for good. (Wait a day for the epoxy to harden then go to step 4)

    4th step- Solder the back of the solar cells together linking them in series. And wire all your bus bars, the cells are not moving while you work

    5th step- Now that all the cells are linked together, out line the entire piece of glass with silicone. (What your trying to do is keep the Epoxy from drain off the glass onto your work area)

    6th step – Mix more Epoxy and pour it all over the cells, don’t worry about bubbles, you fixed that problem when you painted the epoxy on the front of the cells in step 3 , like I said before I use this stuff. http://www.biosafe-inc.com/glazecoat.htm (wait a day for it to harden)

    7th step- After it hardens, you’re pretty much done, get your miter saw and 2 L channels aluminum trim and cut your frame, actually, I do this step first; I mount my L channels to the glass to help keep the epoxy from spilling.

    Now you have a long lasting solar panel.

  2. #2

    Default Re: Help with Solar panel Design for 24 volt system

    It sounds like you are mixing 12 VDC and 24 VDC with 120 VAC and 240 VAC. This is a really bad idea. AC breakers aren't rated for DC Voltages, and you do not want to have AC and DC in the same panel box. One mis-wiring and things go up in flames.

    As for a 24 VDC system, some manufacturers make higher Voltage panels. In terms of charging a 24 Volt system you can either use the higher Voltage panels or put two "12 Volt" panels in series.

    A 185 Watt "24 Volt" panel may have specs like this:
    Vmp 36.4, Voc 45.0, Imp 5.09, Isc 5.43, Length 62.2", Width 31.8"

    A 135 Watt "12 Volt" panel may have specs like this:
    Vmp 17.7, Voc 22.1, Imp 7.63, Isc 8.37, Length 59.1", Width 26.3"

    As you can see the "24 Volt" panel is physically larger and the cells are configured for higher Voltage but lower current.

    It doesn't matter to the batteries which way you do it: higher Voltage panel or two lower Voltage in series.
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  3. #3

    Default Re: Help with Solar panel Design for 24 volt system

    Quote Originally Posted by Cariboocoot View Post
    As you can see the "24 Volt" panel is physically larger and the cells are configured for higher Voltage but lower current.

    It doesn't matter to the batteries which way you do it: higher Voltage panel or two lower Voltage in series.
    how do you config for Higher voltage but low current?

  4. #4
    Join Date
    Sep 2006
    Location
    Willits, CA
    Posts
    5,572

    Default Re: Help with Solar panel Design for 24 volt system

    Such a recipie for disaster
    I'm just not going to say anything more
    http://tinyurl.com/LMR-Solar
    http://tinyurl.com/LMR-BigLug
    http://tinyurl.com/LMR-NiFe

    Grundfos 10 SO5-9 with 3 wire Franklin motor (1/2hp 240V 1ph # 214505 ) on a timer for 3 hr noontime run - Runs off PV
    Powerfab poletop PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe battery | 15, Evergreen 205w "12V" PV | Midnight ePanel || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT

  5. #5

    Default Re: Help with Solar panel Design for 24 volt system

    I think it is great that you are building you own panels. I would like to add a suggestion.
    You have only done a month of testing as far as the yellowing. you should really check the panel output the first day you make them and then in a month. Not yellowing does not mean that some of the suns rays are not being blocked, it just means that you cannot tell a difference by looking at them. Make one today and lay it side by side with the month old one and see if you can tell the difference. Also, a months time, in the effective 20 year lifespan of a panel, is just a drop in the bucket. What if a year from now the panel is so discolored that you cannot see through it any more? I am baseing(sp) this on years of automotive and remodeling work and pretty much everything I have ever used has a tinting problem with age, and alot of it is not in direct sunlight.

    Just food for thought.
    Classic 150 and 3x Kyo 210 and 3 kyo 215s. I have miles to go before I sleep.

  6. #6
    Join Date
    Apr 2010
    Location
    Austin, TX, USA
    Posts
    1,850

    Default Re: Help with Solar panel Design for 24 volt system

    Quote Originally Posted by Urbandialect View Post
    What Iím thinking is:
    I think that by wiring 2 panels together in series Iíll lose a lot of wattage vs just wiring the whole panel for 32 volts in from the start..
    Example 1: 38 cells @ 1.5 watts =57 watts, @0.5 volts = 19 volts = if I wire 2 of those in series I have 38 volts but Iím still at 57 watts, losing the other 57 watts from the other panel.
    No. Whether you wire in series or parallel, the power (Watts) is additive. In series the voltage adds but the current is constant. In parallel the current adds but the voltage is constant. Power is the product of voltage and current, so the power is additive no matter how you connect the cells.

  7. #7

    Default Re: Help with Solar panel Design for 24 volt system

    Quote Originally Posted by ggunn View Post
    No. Whether you wire in series or parallel, the power (Watts) is additive. In series the voltage adds but the current is constant. In parallel the current adds but the voltage is constant. Power is the product of voltage and current, so the power is additive no matter how you connect the cells.
    you have 2 ..6volt, 225amp hour batteries wired in seires... you don't get 12volts at 450amp hours, you get 12 volts at 225amp hours, Solar panels work the same way from what i understand..

    So wiring them together in series will give me 2x the amount of voltage but the wattage doesn't go up...this is what i thought, am i right?

  8. #8

    Default Re: Help with Solar panel Design for 24 volt system

    Quote Originally Posted by Urbandialect View Post
    you have 2 ..6volt, 225amp hour batteries wired in seires... you don't get 12volts at 450amp hours, you get 12 volts at 225amp hours, Solar panels work the same way from what i understand..

    So wiring them together in series will give me 2x the amount of voltage but the wattage doesn't go up...this is what i thought, am i right?
    225 Amp hours @ 6 Volts is 1350 Watt hours. 225 Amp hours @ 12 Volts is 2700 Watt hours.

    Watts, or Watt hours, represent the total power: the Amps * the Volts (not including power factor which is why Watts sometimes doesn't equal Volt Amps - but that doesn't really apply here).

    Wiring two panels in series the Voltage goes up, the Amps stays the same, the Watts go up.
    Wiring two panels in parallel the Voltage stays the same, the Amps go up, the Watts go up.

    Higher power panels typically have parallel strings of cells with by-pass diodes too. Gets complicated fast, doesn't it?
    1220 Watts of PV, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  9. #9

    Default Re: Help with Solar panel Design for 24 volt system

    Quote Originally Posted by Cariboocoot View Post
    Wiring two panels in series the Voltage goes up, the Amps stays the same, the Watts go up.
    Wiring two panels in parallel the Voltage stays the same, the Amps go up, the Watts go up.

    Higher power panels typically have parallel strings of cells with by-pass diodes too. Gets complicated fast, doesn't it?
    Yes it does

    What in the world, how can the wattage go up but not the amps? I thought the amps were dependent on the wattage? So if the wattage goes up then the amps will go up as well, right? OH, i get it.. never mind i figured it out.. Yes the wattage does go up, it has to go up, but so did the voltage, i'm no longer working at 12 volts i'm at 24 volts, in order for the amps to remain the same at 24 volts the wattage needs to double, So yes, the wattage does go up.. I stand corrected

  10. #10
    Join Date
    Jun 2003
    Location
    pittsburgh, pa
    Posts
    10,239

    Default Re: Help with Solar panel Design for 24 volt system

    my comments and questions in bold.

    Quote Originally Posted by Urbandialect View Post
    I have finally figured out how to make a solar panel that will last!!! 
    what is that at the end of those exclamation marks and what does it mean?

    Now I have a few questions about the wiring, I have currently been building my panels w/38 cells for a 12 volt system putting me around 18 or 19 volts out put and round 3.5 amps. 3x6 cells
    there is no need to go with 38 cells as the standard 36 cells would do just fine.

    My question is regarding a 24 volts system… I have 2 sets of breakers in my house 1st is a 120 volts, which will be handled by the 12volts system and the 240 volts switches, which is where the 24 volts system comes in. My question is How should I wire the solar panels for the 24 volts system.. Should I ..
    A.) continue to make 18,19 volt panels and wire them together in series or,
    B.) make a complete panel out of 76 cells and come down at 38 volts??
    you are scaring me. my question to you is, what are you doing as this can be misconstrued to mean something else unsafe here with your comments on mixing voltages at the breakers? btw, do you realize just how big 1 pv would be? i would just put 2 in series.

    What I’m thinking is:
    I think that by wiring 2 panels together in series I’ll lose a lot of wattage vs just wiring the whole panel for 32 volts in from the start..
    Example 1: 38 cells @ 1.5 watts =57 watts, @0.5 volts = 19 volts = if I wire 2 of those in series I have 38 volts but I’m still at 57 watts, losing the other 57 watts from the other panel.
    false for the current is the same and the voltage doubled making the power double.

    Example 2: 76 cells @1.5 watts= 114 watts @0.5 volts = 38volts, don’t have to wire in series because I already have needed voltage.

    So am I correct in thinking that I need to use example 2 when designing my solar panels for 24 volt system???
    no, as you can get it by putting 2 pvs in series. it makes no difference if that same number of cells are in series in 1 pv or split between 2 pvs. only difference would be an external interconnecting wire instead of tabs and it would be easier mounting 2 smaller pvs that 1 extra large pv that may need a crane to get it up there.

    Now to the Good part, HOW TO MAKE A SOLAR PANEL THAT WILL LAST

    1st step, tab the front of all solar cells

    2nd step, go buy your encapsulating product, I found a cheap over the counter product that doesn’t seem to yellow that much, I’ve had my panel out in the elements for a month now and still no yellowing… this is the product I’m using: http://www.biosafe-inc.com/glazecoat.htm (you can get this product from Lowes or Home depot for $22.00, it’s rated for indoor use, I’m in Atlanta GA and it’s been extremely hot and I’ve had no problems out of it, and it doesn’t yellow)

    3rd step-PRIME the front of your solar cell, basically mix a small batch of Epoxy and paint it on the front of the solar cell (make sure paint brush strokes are in the same direction of the tabbing wire, don’t paint the epoxy on the front of it going against the tabbing wire, you might lift it up or break a soldered boned) After putting the epoxy on the front of the solar cell, put it on the glass face down where you want it to go. Do this for all the cells you plan to put in the panel, make sure you put the cells where you want them because once the Epoxy hardens it’s on there for good. (Wait a day for the epoxy to harden then go to step 4)

    4th step- Solder the back of the solar cells together linking them in series. And wire all your bus bars, the cells are not moving while you work

    5th step- Now that all the cells are linked together, out line the entire piece of glass with silicone. (What your trying to do is keep the Epoxy from drain off the glass onto your work area)

    6th step – Mix more Epoxy and pour it all over the cells, don’t worry about bubbles, you fixed that problem when you painted the epoxy on the front of the cells in step 3 , like I said before I use this stuff. http://www.biosafe-inc.com/glazecoat.htm (wait a day for it to harden)

    7th step- After it hardens, you’re pretty much done, get your miter saw and 2 L channels aluminum trim and cut your frame, actually, I do this step first; I mount my L channels to the glass to help keep the epoxy from spilling.

    Now you have a long lasting solar panel.
    i won't comment on your building methods as i don't agree with building them for large home systems and it should be confined to the smaller diy solar projects that aren't critical.
    NIEL

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