Solar Pannel for an rv

2

Comments

  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    Re: Solar Pannel for an rv
    lolcashcow wrote: »
    I see that you recommend the Sears Die-Hard "Advanced" Gold. Not the regular gold agm but "Advanced" gold.....<snip>...It is marked as deep cycle, but I see no Amp hours listed. Do I need to look for a specific group size that I might need?

    You'll get more information about them if you look up East Penn/Deka Intimidator agm. The one you linked to for it's group 94R size is an 80AH at the 20hr rate, but only seen on the actual East-Penn data sheet. The key is not to get one that has been on the shelf too long as BB mentioned. If your counter-guy is honest, he'll know what the date-stickers mean and offer you the freshest one.

    Just realize I commented on these because I have used them myself, (both Sears rebadge and Deka directly) and found them to be very good dual-purpose batteries with an excellent build AND just as importantly, great documentation from East-Penn. They can sometimes be conveniently found locally so you can put a voltmeter to them. But make no mistake, they are NOT true deep cycle, but dual-purpose, but they make a good start for casual solar projects. Note that Deka also makes a true deep cycle solar line. You may also want to look at our own host's battery offerings.

    I'm still not convinced you are actually using 30 watts from a single netbook - unless it is charging the internal battery while running flat out all at the same time!

    As for military use, yes Odysseys are used there, along with Hawker agm's. Unlike most agm's that can only accept up to 0.3C max charge current typically, these babies can handle MAJOR charge current well in excess of 1C - sometimes up to 5C. If you've got the power, they'll get you out of a jam. Again, overkill for a netbook.
  • lolcashcow
    lolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv

    Hi guys,

    SO sorry for getting back to you all so late. The RV needed some work in the engine and that set me back for a while. Things are much stable now and I am looking back into the solar panel addition. The latest thing that happen was that I got in touch with the friend who wants to let me have a solar panel, but he said that I needed to know the specifics of the inverter on the RV. He said that I needed to know what the specs on the inverter was so the solar panel could work. I think he said that the panel and the inverter on the RV have to be the same voltage to work. I think he said 12dc? to 1 kilowatt or something like that. I was really puzzled. The way he laid it out it made me think that he thinks I want to hook up the panels to the rv through the RV's Inverter. So mid way through the conversation I just dropped the line saying that I wanted to connect the panels by themselves to a separate inverter, but he did not agree I did not recall his exact words. He says I need t know the specifics of the inverter on the RV....

    In all honesty I don't want to connect the panels to the RV and use the outlets of the RV because of the old wiring that is inside of it. I'm just afraid that something might get fried. It is an old 1975 RV that was bought last year. I don't use the gas/electric refrigerator, gas thermo and the stove. I have used the electric water pump and that one works fine. I just wanted to buy an agm battery, charge controller, buy an inverter, and ... I guess that is all? I have that cobra inverter that I mentioned before: http://www.amazon.com/Cobra-400-Watt-12-Volt-120-Volt-Inverter/dp/B001RNOHBC

    Since the RV is old I honestly don't know if the inverter in the RV works. Actually I don't think it even has an inverter. The only thing I found that I thought was the inverter was this

    http://imgur.com/c2yaz4A

    It is across from the power outlet that you use at the rv parks it says converter but I don't know if that's the same thing as an inverter. The rv also has a fuse box...

    I need help! If that little box is not the inverter then can I just tell my friend that the rv does not have an inverter and that I will buy one?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar Pannel for an rv

    You're friend's POV is simplistic.

    The inverter runs from a battery. They need to have matched nominal Voltages in order for the system to work.
    Panels recharge the battery through a charge controller. As long as the panels' Vmp is high enough to charge the battery it will work. Usually this is 17-18 on a "12 Volt" system, but with the right controller (MPPT type) higher panel Vmp will work as well.

    Many RV's, especially older ones, don't have inverters at all. They instead have converters which are big DC power supplies to run the DC items and charge batteries while plugged in to shore power. This is what your image shows. Any in-house 120 VAC items would run from that shore power or from a generator when needed; no inverter to supply the AC.
  • lolcashcow
    lolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv

    Hi Cariboo,

    Thanks for your reply. Okay, so the RV does not have an inverter.

    So what happens is that part of the AC shore power is routed as DC through the converter for the batteries of the RV? and the other items like lights/cigar ligther? While another part of the shore power goes directly into the power outlets as AC for use of in-home items through the power outlets across the RV? Or is it that the power outlets in the RV also provide DC only through the converter? But then how do people back then in 1975 run the in-house electrics? Sorry for the question I'm just trying to figure that out.

    Okay so I will just tell my friend the RV doesn't have any inverter and that I bought one and tell him the specs on the box. Hopefully that will be enough and he doesn't ask me anymore questions :). Like charge controllers and batteries specs and all :(.
    You're friend's POV is simplistic.

    The inverter runs from a battery. They need to have matched nominal Voltages in order for the system to work.
    Panels recharge the battery through a charge controller. As long as the panels' Vmp is high enough to charge the battery it will work. Usually this is 17-18 on a "12 Volt" system, but with the right controller (MPPT type) higher panel Vmp will work as well.

    Many RV's, especially older ones, don't have inverters at all. They instead have converters which are big DC power supplies to run the DC items and charge batteries while plugged in to shore power. This is what your image shows. Any in-house 120 VAC items would run from that shore power or from a generator when needed; no inverter to supply the AC.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar Pannel for an rv
    lolcashcow wrote: »
    Hi Cariboo,

    Thanks for your reply. Okay, so the RV does not have an inverter.

    So what happens is that part of the AC shore power is routed as DC through the converter for the batteries of the RV? and the other items like lights/cigar ligther? While another part of the shore power goes directly into the power outlets as AC for use of in-home items through the power outlets across the RV? Or is it that the power outlets in the RV also provide DC only through the converter? But then how do people back then in 1975 run the in-house electrics? Sorry for the question I'm just trying to figure that out.

    Okay so I will just tell my friend the RV doesn't have any inverter and that I bought one and tell him the specs on the box. Hopefully that will be enough and he doesn't ask me anymore questions :). Like charge controllers and batteries specs and all :(.

    It is as you suspect: the converter converts AC supplied from the shore power to DC for the DC devices. Any AC outlets are powered directly from the shore power. If there is no shore power the AC would be supplied by a generator, which may or may not be automatic start (usually not). In 1975 inverter technology was not that good so they didn't even try to use it in RV's.

    If your friend wants to sell you a panel he should just provide the specs and let you worry about how to use it. I think he's gotten confused with grid-tie inverters which do run directly from PV.
  • lolcashcow
    lolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv
    It is as you suspect: the converter converts AC supplied from the shore power to DC for the DC devices. Any AC outlets are powered directly from the shore power. If there is no shore power the AC would be supplied by a generator, which may or may not be automatic start (usually not). In 1975 inverter technology was not that good so they didn't even try to use it in RV's.

    If your friend wants to sell you a panel he should just provide the specs and let you worry about how to use it. I think he's gotten confused with grid-tie inverters which do run directly from PV.

    Okay I called my friend and mentioned that and he said that the panels he has are 30v and not 12v so he said they would not work with my Cobra CPI 480 400-Watt 12-Volt DC to 120-Volt AC Power Inverter; basically he said that it would not work because it is 12v inverter. So... should I give up my idea on a free solar panel from my friend? or is there an option to make his 30v panel work for my set up?

    I did a quick search on amazon and found this one:

    http://www.amazon.com/500W-Inverter-10-8-30V-Turbine-Power/dp/B007WQDKMA

    but it says: Power Factor:0.99;AC Input Voltage Range : 10.8V ~ 30V(AC, not DC),Peak Inverter Efficiency: 92%;Standby Power consumption: <0.5W

    So does this mean it only takes in AC? I believe the panels put out DC right?

    Will I also need to buy a different kind of battery from the one I was interested in originally? http://www.sears.com/diehard-advanced-gold-agm-battery-group-size-94r/p-02850793000P?prdNo=1&blockNo=1&blockType=G1
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar Pannel for an rv
    lolcashcow wrote: »
    Okay I called my friend and mentioned that and he said that the panels he has are 30v and not 12v so he said they would not work with my Cobra CPI 480 400-Watt 12-Volt DC to 120-Volt AC Power Inverter; basically he said that it would not work because it is 12v inverter. So... should I give up my idea on a free solar panel from my friend? or is there an option to make his 30v panel work for my set up?

    Again he is only half-right: a 30 Vmp panel will not work efficiently with a 12 Volt system through a PWM type charge controller. An MPPT type charge controller can take the Voltage difference and turn it into current.

    So what you really want to know is how many Watts this 30 Vmp panel is and then determine if that's enough for your system. An MPPT type controller is going to cost $300 or more but could be worth it if the free panel is sufficient to charge the system. Keep in mind it may not be, and/or it may not fit where you want it, and/or you may not be able to get a match to it so that you can increase the array size. Details, details!
  • lolcashcow
    lolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv
    it may not fit where you want it, and/or you may not be able to get a match to it so that you can increase the array size. Details, details!

    Does this mean that this type of solar panels are much larger than 12v panels?

    So if I want to add another panel later on it will have to be the exact same? It does not work with other 30v panels and/or different wattage?

    Then the inverter I have will work with this 30v panel (if it has the MPPT), but it will be less efficient and some wattage will be lost along the way? Should I not then buy an inverter that will work efficiently with this type of panel? Or do these inverters cost way too much?

    If I were to get the specific inverter for the 30v Will I then not need to buy the mppt charge controller? What would the price difference be like?

    Will I also need to buy a different kind of battery from the one I was interested in originally? http://www.sears.com/diehard-advanced-gold-agm-battery-group-size-94r/p-02850793000P?prdNo=1&blockNo=1&blockType=G1
  • Blackcherry04
    Blackcherry04 Solar Expert Posts: 2,490 ✭✭✭
    Re: Solar Pannel for an rv

    That Is NOT a Inverter it is a Power CONVERTER to step down 120 VAC ( shore Power ) to 12VDC.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar Pannel for an rv

    First, what Blackcherry said: don't touch that Amazon thing with a 40 foot power pole.
    lolcashcow wrote: »
    Does this mean that this type of solar panels are much larger than 12v panels?

    Solar panels are all made of the same stuff, light falls at the same amount, ergo more Watts = bigger panel. The only variation is that monocrystaline are more efficient than polycrystaline (sometimes called "multicrystaline" in what I believe to be a deliberate attempt to mislead the buying public) which are more efficient than amorphous (generally avoided altogether).
    So if I want to add another panel later on it will have to be the exact same? It does not work with other 30v panels and/or different wattage?

    It is very difficult to mix dissimilar panels on the same charge controller. As a rule if the Vmp is within 5-10% you can parallel them. If the Imp is within 5-10% you can put them in series. Matching panels always work best.
    Then the inverter I have will work with this 30v panel (if it has the MPPT), but it will be less efficient and some wattage will be lost along the way? Should I not then buy an inverter that will work efficiently with this type of panel? Or do these inverters cost way too much?

    If I were to get the specific inverter for the 30v Will I then not need to buy the mppt charge controller? What would the price difference be like?

    Okay let's get this cleared up: off-grid inverters do not care what panels you have. They run from the battery, not the panel. The panel recharges the battery through the charge controller.
    If you use an 'incorrect Voltage' panel with a PWM controller all you get is the current. In essence a panel with specs of 240 Watts, 30 Vmp, 8 Imp on a 12 Volt system with a PWM controller becomes the equivalent of a 140 Watt panel due to the power loss caused by the Voltage difference.

    A mobile/RV application is the one instance where a 12 Volt system is viable due to the number of 12 Volt devices available and the ready charge source of a vehicle (which can at least keep the battery from going completely dead).
    Will I also need to buy a different kind of battery from the one I was interested in originally? http://www.sears.com/diehard-advanced-gold-agm-battery-group-size-94r/p-02850793000P?prdNo=1&blockNo=1&blockType=G1

    Because I am in Canada I can not see the link you put up (auto-redirect to Sears.ca). Chances are it is not a true deep cycle battery. I can't imagine Sears sells them, even in the US. Beware of RV/Marine batteries and anything that talks about "reserve capacity" or "cold cranking Amps"; those are not terms used with deep cycle batteries.
  • lolcashcow
    lolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv

    Hi guys,

    Thanks blackcherry for letting me know it was a converter!

    Oh, I'm so sorry you are right. I had forgotten how the devices are set up and what is connected to what. Panel to Charge Controller. Charge Controller to Battery. Battery to Inverter. So sorry about that I was confusing myself. I kept thinking the inverter was connected to the panel... oops.

    Out of curiosity, and i'm so sorry for pushing on the subject but, is there no charge controller that works fully efficient with a 30v panel? 100 watt loss on a 240 panel is almost 50% loss, right? Is it that 30v panels are made to work best for residential/city power grid use?

    I don't see cold cranking amps or reserve capacity listed on the battery description.
    Here are the specs on the battery I linked:

    $151 before a 20% discount deal.

    DieHard Advanced Gold AGM Battery - Group Size 94 (Price with Exchange)
    Specifications & Dimensions
    Dimensions:
    Group Size: 94R
    Design & Construction:
    Battery Design: Absorbed Glass Mat
    Battery Grade: DieHard Gold
    Container Material: Polypropylene (PP)
    Maintenance: Maintenance Free
    Overall Type: Deep-cycle
    Temperate Zone: All climates
    Terminal Post Location: Top
    Warranties & Coverage:
    Free Replacement Warranty Term: 36 months

    DieHard Gold 94 Battery Is Better Than the Rest

    The new DieHard Gold Size 94 Car Batteries are the best DieHard Advanced Gold batteries ever, offering genuine AGM technology for more power and longer life. This maintenance-free, deep-cycle battery is engineered for all climates, and it offers two times the cycle life for long-lasting performance: just what you look for in an auto battery. To boost your confidence, consider that this DieHard battery has passed more than 250 quality control checks for durability and longevity, and it comes with a great warranty.

    This DieHard Gold 94 Battery also passes the test when it comes to protective instincts. Its spill-proof design offers extra protection for sophisticated electrical equipment, while an Enhanced Electronic Suspension System helps protect internal components by absorbing more electrolytes. Finally, it's got 20 times more vibration protection, to help your battery stand the test of time. All of this, and you can be proud that this gold standard of batteries is made right here in the good ole U.S. of A.

    DieHard Gold Size 94 Car Batteries are the best Advanced Gold batteries DieHard has to offer, thanks to the long-lasting power of AGM technology
    Deep-cycle, maintenance-free battery for all climates
    Group Size: 94
    Flat-Plate Absorbent Glass Mat (AGM) design offers more power per pound
    20 times more vibration protection, so your battery performance stays safeguarded over time
    Two times the cycle life, for extended performance and life
    Faster recharging power more electronics longer
    Spill-proof design keeps sophisticated electronic equipment safe
    Enhanced Electronic Suspension System absorbs more electrolytes for internal component protection
    Passes more than 250 quality control checks, so you can be confident in its durability and longevity
    36-month free replacement warranty, for that extra measure of confidence
    Made in the U.S.A.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar Pannel for an rv

    The 30 Vmp panels are designed for use with grid-tie inverters. Usually in strings of twelve (360 Volts) for central inverters or individually for micro-inverters.

    They can be used with battery-based systems but must use MPPT type controllers for maximum efficiency. A 30 Vmp panel is too high a Voltage for direct use on a 12 Volt system (normal Vmp 17-18 ) and too low for direct use on a 24 Volt system (normal Vmp 35-36). An MPPT controller will down-convert any Voltage above the minimum required for the system and turn it into current. Not all of these controllers are the same, and some have strange limitations. Usually it is just a maximum input Voltage, though.

    The battery description does not look like a deep cycle despite its "over-all type". The clues would be the lack of any Amp hour listing and use of the term "Car Batteries". Keep in mind that some new vehicles actually spec AGM batteries. Look at the listing for the Concorde AGM's: http://www.solar-electric.com/concorde-sun-xtender-pvx-solar-deep-cycle-batteries.html
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Solar Pannel for an rv

    Actually (I think) it is battery based 12 VDC to 120 VAC GT inverter designed to use as a "dump load" for a wind or water powered turbine charging a battery bank.
    500W Wind Grid Tie Inverter AC 10.8-30V To AC 110V Turbine Power Dump Load

    In any case, not the unit for use with a typical RV installation.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lolcashcow
    lolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv

    Hi BB :)
    They can be used with battery-based systems but must use MPPT type controllers for maximum efficiency.

    OH I see now. Then with a PWN charge controller there will be a loss of almost 50% wattage while an MPPT charge controller will give you full, if not near full, wattage from the pannel?

    Then with an MPPT charge controller a 30v solar panel that gives you 300 watts will give you 300 watts or close to its maximum out put? That is if lighting conditions are optimal right?


    Option #1
    Free used Solar Panel $0 Unknown Wattage
    MPPT Charge Controller $300????
    AGM Battery $140 /w the discount
    Digital Clamp-On Ammeter $60 If able to afford it http://www.sears.com/shc/s/p_10153_12605_03482369000P
    Total: $500 usd

    Option #2
    new 100w Amazon Panel $150 /w shipping http://www.amazon.com/RENOGY-Monocrystalline-Photovoltaic-Battery-Charging/dp/B009Z6CW7O/ref=sr_1_1?ie=UTF8&qid=1393106529&sr=8-1&keywords=RENOGY+100+Watt+100w+Monocrystalline+Photovoltaic+PV+Solar+Panel+Module+12V+Battery+Charging
    PWN Charge Controller $80 http://www.solar-electric.com/modubachco251.html
    AGM Battery $140 /w the discount
    Digital Clamp-On Ammeter $60 If able to afford it
    Total: $430 usd

    So I guess the deal breaker would depend on the panel my friend can give me? Would have to be over 100 watts and able to operate fully and provide the full wattage to the charge controller/battery. The main risk with the used solar panel is... is it in working condition? Will it die off soon? and other unknowns I guess.

    What are your thoughts on that? Would it have to be a 300 watt or 450 watt panel?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar Pannel for an rv

    It is unlikely to be a 300 Watt or 450 Watt panel is the thing. 30 Vmp GT panels start around 200 Watts and go up to 315, by which time they are quite large. This means the current from a single panel is anywhere from 6 Amps to about 10 Amps. Converted to 12 Volts through MPPT you'd get 12 Amps to 20 Amps, more or less.

    How well that would do for recharging your battery depends on what the Amp hour capacity of the battery is. At this point that is another unknown. The bad part of that is that it should be the first component to be determined.
  • lolcashcow
    lolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv
    It is unlikely to be a 300 Watt or 450 Watt panel is the thing. 30 Vmp GT panels start around 200 Watts and go up to 315, by which time they are quite large. This means the current from a single panel is anywhere from 6 Amps to about 10 Amps. Converted to 12 Volts through MPPT you'd get 12 Amps to 20 Amps, more or less.

    How well that would do for recharging your battery depends on what the Amp hour capacity of the battery is. At this point that is another unknown. The bad part of that is that it should be the first component to be determined.

    Geh :( and since the amp hour capacity is not listed for that one AGM battery I listed... we just hit a dead end unless I look for one that does have the AMP hours. Well! This is quite troublesome lol. OH okay, so the 30v panel starts around 200 and goes up to 315. By quite large what do you mean exactly? Could it possibly be something like 15 feet by 15 feet O_O?
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar Pannel for an rv

    Well PV efficiency isn't that bad, but it isn't good. You're looking 66" x 52" for the big one.
  • lolcashcow
    lolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv
    Well PV efficiency isn't that bad, but it isn't good. You're looking 66" x 52" for the big one.

    Okay, I should be able to fit that panel size on the RV. Looking at the price difference between the two options it seems the better option is to buy a new panel even if it has less wattage. Mainly because of the cost of the MPPT controller. Is there no MPPT controller that can accommodate my needs, but be priced at $200? Is $300 the least an MPPT controller can cost? Sorry for asking I'm just not familiar with the prices. From your experience with controllers would you say a $200 MPPT controller that will work for my set up i possible?

    Though I could still use a PWM controller for this set up couldn't I? The only downside is that the panel's wattage will be cut down by %50? If my friend has a 200 watt or 300 watt panel it should end between 100 to 150 watts with a regular PWM controller? Is this a possible idea? What do you guys think? With a free panel and a PWM controller the price becomes quite affordable... I could use the PWM controller temporarily as I save for a MPPT type. Thoughts?

    Thank you all for the input :)
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar Pannel for an rv
    lolcashcow wrote: »
    Okay, I should be able to fit that panel size on the RV. Looking at the price difference between the two options it seems the better option is to buy a new panel even if it has less wattage. Mainly because of the cost of the MPPT controller. Is there no MPPT controller that can accommodate my needs, but be priced at $200? Is $300 the least an MPPT controller can cost? Sorry for asking I'm just not familiar with the prices. From your experience with controllers would you say a $200 MPPT controller that will work for my set up i possible?

    Though I could still use a PWM controller for this set up couldn't I? The only downside is that the panel's wattage will be cut down by %50? If my friend has a 200 watt or 300 watt panel it should end between 100 to 150 watts with a regular PWM controller? Is this a possible idea? What do you guys think? With a free panel and a PWM controller the price becomes quite affordable... I could use the PWM controller temporarily as I save for a MPPT type. Thoughts?

    Thank you all for the input :)

    Well for one thing if you buy any panel that doesn't have a Vmp suitable to the system Voltage you'll need the MPPT controller anyway or else lose power. That's 17-18 Vmp on a 12 Volt system or 35-16 Vmp on a 24 Volt system (and of course about double that when you go up to 48 Volts). A $200 MPPT controller is most likely a PWM unit made in China with the letters "MPPT" printed on it to make it sell better. There's a lot of components to a real one and that adds to the cost. Even the smallest real MPT controller is over $200: http://www.solar-electric.com/mosumpsochco.html And that only handles 15 Amps. On a 12 Volt system 15 Amps is about 200 Watts maximum input (technically up to about 235).

    Usually the switch to MPPT becomes practical dollar-wise when you get over a 400 Watt array: at about that point you can switch to GT type panels which cost $1 per Watt less and that "$400" in combination with what a conventional PWM controller costs gives you the price of the MPPT controller. (This is if buying all new equipment.)
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Solar Pannel for an rv

    Here are some smaller MPPT controllers (that I am aware of--I am not in the business and have not heard of any Asian low cost imports that stand out yet):

    http://www.roguepowertech.com/products/controllers.htm (Rogue)
    http://www.solar-electric.com/admpchco.html (MorningStar)
    http://www.solar-electric.com/midnite-solar-kid-controller-accessories.html (Midnite Solar)

    Just to give you an idea on the math. A good compromise for the maximum solar array on a controller. With the output rating of the controller and the battery bank charging voltage--The math would look like:

    15 amp output (small MorningStar) * 14.5 volt battery charging * 1/0.77 panel+controller deratings = 282 Watt Array for 15 amp MPPT controller

    Go to a 24 volt battery bank, you can install a 2x larger solar array on the same controller (assuming it is also a 24 volt capable controller).

    MPPT controllers (good ones anyway) will limit their output current to its rated value (safely/reliably). You can place a larger solar array, but you will start "clipping" more and more power. At 0.77 derating, the clipping does not happy that often (typically clear/cool days near noon--for minutes or so per day). And the actual loss of output current is not very large.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • lolcashcow
    lolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv
    Well for one thing if you buy any panel that doesn't have a Vmp suitable to the system Voltage you'll need the MPPT controller anyway or else lose power. That's 17-18 Vmp on a 12 Volt system or 35-16 Vmp on a 24 Volt system (and of course about double that when you go up to 48 Volts).

    Ah, I see. I asked another friend about using a PWM unit with a 30v panel and he said the unit could fry because it is not made to regulate that much volt. Is this true? Would it be safe to use a PWM unit to run for example a 300 watt panel? Would the unit fry? And would the output be only half of what the panel should give?
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Solar Pannel for an rv

    There are pwm units that will work with Voc up to 125 volts. So panel voltage is not a big problem with the controller.

    Power = volts x amps

    with pwm controllers, the output current is the panel current.

    If the battery is charging at 29 volts x 2 amps, that of 58 Watts.

    Same panel and controller charging at 14.5 volts x 2 amps, you only get 29 Watts.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar Pannel for an rv
    lolcashcow wrote: »
    Ah, I see. I asked another friend about using a PWM unit with a 30v panel and he said the unit could fry because it is not made to regulate that much volt. Is this true? Would it be safe to use a PWM unit to run for example a 300 watt panel? Would the unit fry? And would the output be only half of what the panel should give?

    Most PWM controllers are designed to handle 12 or 24 Volt systems (but not 48 ). As such the Voc of a 24 Volt panel will not affect them no matter what the system Voltage. As Bill points out the components are usually good for at least 50 Volts on input. Since panels are current sources, once the controller makes the connection the panel Voltage drops to the level of the battery. Current output is independent of this and with full insolation will remain at Imp if required as circuit Voltage rises up to Vmp. Since the controller regulates output by Voltage, the battery will never actually see > charging Voltage to it as such.

    The difference is one of taking the Imp of the "24 Volt" panel and multiplying it by the typical Vmp of a 12 Volt panel. A 175 Watt 35 Vmp 5Imp panel connected directly to a 12 Volt system performs like an 87.5 Watt 17.5Vmp 5Imp panel would.
  • lolcashcow
    lolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv

    Hi guys,

    Thank you BB for the list of MPPT charge controllers. The MidNite Solar Kid looks to be the cheapest of the list that can go up to 30v. I will definitely keep it in mind :).

    My friend who wants to give me the solar panel for free says the panel is 120 watts 30v. Much less than what I expected it to be :(. He says that he can look for another panel, but will get back to me tomorrow about it. The wattage would be different though. Truly I wished it to be more of a 300 watt panel even if the size was much bigger. The panel will be of different wattage but the same volts.

    Sorry Cariboo if I asked the same question twice I still battling on in taking all the information. I highly appreciate the help though :)
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar Pannel for an rv

    120 Watts 30 Volts? Well that's an oddball for sure. A 120 Watt panel would normally be a "12 Volt" panel with Vmp of 17.5 and Voc of 22 or so. That won't supply much charging current in either case.

    Possibly he doesn't know what he's got.
  • lolcashcow
    lolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv
    120 Watts 30 Volts? Well that's an oddball for sure. A 120 Watt panel would normally be a "12 Volt" panel with Vmp of 17.5 and Voc of 22 or so. That won't supply much charging current in either case.

    Possibly he doesn't know what he's got.

    Let's hope that it is! That way it will save me a ton of headaches :). Either way if all goes well I should have the panel tomorrow. I will take some pictures once I get back home with it if all goes well. I am also hoping my friend has an extra panel. Here is hoping!

    Thank you all for your amazing help :). BB, Cariboo, and everyone else I highly appreciate your patience!
  • lolcashcow
    lolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv

    Hi Guys,

    Okay here are the specs on the panel

    http://i.imgur.com/o2zzrBL.jpg

    Would it still be possible to use the panel with a lower cost PWM controller at its full or near full capacity?

    Out of curiosity why does it say that one should not scratch the back of the panel? When I got it I lightly rested it on its side against a wall. The wind tilted it over and it fell face first on the concrete. The fall was not so bad since it was on its side instead of stading up right. Nothing broke or anything. I hope it still works.

    I think I saw a light scratch on the back but it wasnt from the fall i think it was there since it is a used panel. It fell face first and the framing is made so the back can't touch anything just the front.
  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Solar Pannel for an rv
    lolcashcow wrote: »
    Hi Guys,

    Okay here are the specs on the panel

    http://i.imgur.com/o2zzrBL.jpg

    Would it still be possible to use the panel with a lower cost PWM controller at its full or near full capacity?

    Out of curiosity why does it say that one should not scratch the back of the panel? When I got it I lightly rested it on its side against a wall. The wind tilted it over and it fell face first on the concrete. The fall was not so bad since it was on its side instead of stading up right. Nothing broke or anything. I hope it still works.

    I think I saw a light scratch on the back but it wasnt from the fall i think it was there since it is a used panel. It fell face first and the framing is made so the back can't touch anything just the front.

    Nope.
    That is a "real 24 Volt" panel with a Vmp of 35.4. Used as a "12 Volt" panel it will produce its Imp of 4.8 and thus perform like a (4.8 * 17.5) 84 Watt panel. Less than half its rated power.
  • lolcashcow
    lolcashcow Solar Expert Posts: 118 ✭✭
    Re: Solar Pannel for an rv
    Nope.
    That is a "real 24 Volt" panel with a Vmp of 35.4. Used as a "12 Volt" panel it will produce its Imp of 4.8 and thus perform like a (4.8 * 17.5) 84 Watt panel. Less than half its rated power.

    Hi Cariboo!

    Then if I use a PWM CC it will only perform at 84 watts? I could use it that way as a temporary solution until I can gather up the needed cash for an MPPT? When you say that it is a "Real" 24V panel ... does it mean I can use an MPPT CC that covers up to 24v?

    The cheapest MPPT for a 24v that was listed earlier was the morningstar sun saver

    http://www.solar-electric.com/mosumpsochco.html

    Thank you SO much BB for that amazing list you made for me :) Highly appreciated !
  • bill von novak
    bill von novak Solar Expert Posts: 891 ✭✭✭✭
    Re: Solar Pannel for an rv
    lolcashcow wrote: »
    Would it still be possible to use the panel with a lower cost PWM controller at its full or near full capacity?

    If it's hot out and you have a long wire run then performance on a 24V system might be similar with a PWM and an MPPT controller. It will not work well with a 12V panel without an MPPT.
    Out of curiosity why does it say that one should not scratch the back of the panel?

    Because it is generally plastic (or more accurately Tedlar or a similar material) that is not as damage resistant as the glass on the front.