2 60W panels in series or parallel?

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arcticcat
arcticcat Registered Users Posts: 2
in Off Grid Solar & Battery Systems #1
I will want to run my panels in paraellel, correct? Which will give me roughly 6.5 charging amps.

What I am using.

2 - 60 watt panels
Nominal Voltage 12V
Operating Voltage(Vmp) 18V
Operating Current(Imp) 3.34A
Open Circuit Voltage(VOC) 21.24V
Short Circuit Current(Isc) 3.66A


Genasun GV-10 MPPT Controller
Maximum Panel Power 140W
Rated Output Current 10.5A
GV-10-Pb Charging Voltages
(For Lead-Acid) Bulk Voltage: 14.4V
Absorption Voltage: 14.2V
Float Voltage: 13.8V
Temperature Compensation: -28 mV/degC
Custom Voltages Available

Samlex PST-150S-12A
Input Volta ge 10.7 to 16.5 VDC 21.4 to 33 V DC
Input Current at No Load < 1 A < 0.8 A
LOW INPUT VOLTAGE WARNING ALARM 10.7 V 21.4 V
LOW INPUT VOLTAGE Shut-down 10 V 20 V
High Input Volta ge Shut-down 16.5 V 33 V
Operat ing Ambient Temperatu re 0 to 40ºC +/- 5ºC 0 to 40ºC +/- 5ºC
Peak Efficiency 85% 85%

130Ah to 150Ah AGM Deep Cycle battery, yet to be named.


Any recommendations on charge controllers, I'd love to hear it. I already have the panels and inverter in hand.

Thanks,
AC
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
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    Re: 2 60W panels in series or parallel?

    Welcome to the forum.

    If it really is an MPPT charge controller you can have the panels either in series or in parallel: the input to the controller is "independent" of the output to the batteries. Given the specs on that controller, however, I doubt it really is MPPT. 10 Amps is not much current and there would be little use in having the complex circuitry if that's all it can manage. Morningstar's 15 Amp unit is about the smallest MPPT of practicality.

    Either way the output current should be about the Imp of the panels X2.

    It would be better to buy an inexpensive PWM type controller and run the panels in parallel if there's not much distance involved. Something like this: http://www.solar-electric.com/ss-6.html Note you will probably never see full current from the panels.

    It's going to be pretty low for charging even a 130 Amp hour battery (should be 6.5 Amps), and definitely too low for 150 Amp hours.

    I'm going to hazard a guess that this is a "learning" system. The battery size will not run anything for very long (maybe 800 Watt hours maximum).
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  • arcticcat
    arcticcat Registered Users Posts: 2
    #3
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    Re: 2 60W panels in series or parallel?

    kind of a back up emergency system. 4-5 hours of "moderate" use. then Im guessing about 10-15 hours for charge time, give or take... full sun, ect.

    Thanks for the info on the charge controller, thats good news! I was cringing at the $100+ cost.

    I may be able to sneak in a 3rd panel to get it up to 9-10 amps. how tempermental are the charge controllers when they get his with to many amps .5 to 1 amps?

    AC
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #4
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    Re: 2 60W panels in series or parallel?

    The higher you go in current, the less you want to leave to chance. For instance when you're in the 60 Amp charge current range you do not want to have the controller "clipping" current all the time because it creates a lot of heat in a very expensive controller. So it's best to size the charge controller larger than the potential current. With smaller units it is not as critical, especially when you consider that the panels usually only produce about 80% of of their nameplate rating (although most of the loss is Voltage not current as PV's are a current source).

    So with three of the panels you'd have a maximum of about 10 Amps. If the battery is deeply discharged and the panels are at the best angle you may see this current. Still a 10 Amp controller would handle it with little fuss (most good controllers can take 10% over their current rating, although they won't pass it).

    Here's a page of Morningstar PWM controller offerings from our host NAWS: http://www.solar-electric.com/stpwmchco.html

    You can see the SunSaver comes in 6, 10, and 20 Amp sizes then there are the ProStar units and the really big TriStar ones. These are in my opinion the best PWM controllers on the market, and the company is great with customer service.

    Ideally you should not have "10-15 hours charge time". That's why you try to keep the discharge rate below 50% and the charge rate above 5%. Rough examples on 130 Amp hours discounting the inefficiencies (Peukart Effect):
    130 * 25% = 32.5 Amp hours used. 10% charge rate = 13 Amps. 32.5 / 13 = 2.5 hours to charge (in reality it will be about 20% longer, depending on the inefficiencies particular to the system).
    130 * 25% = 32.5 Amp hours used. 5% charge rate = 6.5 Amps. 32.5 / 6.5 = 5 hours to charge.
    130 * 50% = 65 Amp hours used. 10% charge rate = 13 Amps. 65 / 13 = 5 hours to charge.

    It is best to get the battery recharged in one day, but longer recharge over two days is acceptable when the depth of discharge is not high and there are no loads drawing at the same time. Batteries really do not like to spend a lot of time in a discharged state. The lower the state of charge and/or longer time spent there the shorter the batter life.

    Always a good read, the battery FAQ'S: http://www.windsun.com/Batteries/Battery_FAQ.htm
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  • Windsun
    Windsun Solar Expert Posts: 1,164 ✭✭
    #5
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    Re: 2 60W panels in series or parallel?

    That Genasun controller is not a true MPPT - it is an analog type, and they tend not to track the max power point very well, so gains are minimal. But, it appears that putting the panels in series with that controller would exceed it's ratings anyway, so you are pretty much stuck with parallel.
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  • genasun
    genasun Registered Users Posts: 4
    #6
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    Re: 2 60W panels in series or parallel?

    Hello Wind-Sun!

    I'm a representative from Genasun. It's already been pointed out that the input voltage limit is 34V, so the panels should be run in parallel not in series. We recommend installing a blocking diode on each panel. We generally recommend against connecting panels in series, because parallel configurations have better shade tolerance and are simply more robust to panel failure/damage.

    I would like to gently assure everyone that our controllers are digitally controlled MPPT. If you open up any of our controllers, you will find a microcontroller and other components necessary for a DC-DC converter (inductor, capacitors, transistors). The controllers do track and adjust to a shifting maximum power point very quickly (20 times/second).

    Windsun and Cariboocoot, if you have time, I'd really appreciate if you could comment on why you think the Genasun controllers are not real MPPT, are analog controlled, and track slowly?

    Best,
    Alexander


    Cariboocoot wrote: »
    Welcome to the forum.

    If it really is an MPPT charge controller you can have the panels either in series or in parallel: the input to the controller is "independent" of the output to the batteries. Given the specs on that controller, however, I doubt it really is MPPT. 10 Amps is not much current and there would be little use in having the complex circuitry if that's all it can manage. Morningstar's 15 Amp unit is about the smallest MPPT of practicality.

    Either way the output current should be about the Imp of the panels X2.

    It would be better to buy an inexpensive PWM type controller and run the panels in parallel if there's not much distance involved. Something like this: http://www.solar-electric.com/ss-6.html Note you will probably never see full current from the panels.

    It's going to be pretty low for charging even a 130 Amp hour battery (should be 6.5 Amps), and definitely too low for 150 Amp hours.

    I'm going to hazard a guess that this is a "learning" system. The battery size will not run anything for very long (maybe 800 Watt hours maximum).
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #7
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    Re: 2 60W panels in series or parallel?

    Welcome to the forum genasun.

    I have no experience with your controllers and could only judge by the specifications provided by the OP. Those specs are eerily similar to a number of "no name" charge controllers we have seen which claim to be "MPPT" but really are not; they just stick the label on because it sells more controllers.

    Your input Voltage limitation will be a problem for many applications, as it is with some other less-expensive MPPT controllers. Standard "24 Volt" panels have a Vmp of 35, which lets them out. Basically it would appear your controller can only be used with "GT panels" or "12 Volt" panels and only on a 12 Volt system. Mind you, we have seen lots of people get in trouble buying GT panels and then finding half the power is lost through PWM controllers. But your product could certainly benefit from a higher max V-in limit. The Voc on a 30 Vmp panel would even represent a danger.

    I'm not so sure there's much need for an MPPT controller of such low Amperage either. I do know of several people who could benefit from one around 30 Amps and we're all waiting for the new Rogue and MidNite to appear.

    Windsun apparently has had some experience with your units so I leave it to him to answer from his POV if and when he has time.
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  • genasun
    genasun Registered Users Posts: 4
    #8
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    Re: 2 60W panels in series or parallel?

    Cariboocoot,

    Thanks for your comments. We are also disturbed by the number of fake "MPPT" controllers out there, and I don't blame your skepticism. Our controllers are designed and assembled in the US, and we set high standards for our products.

    The GV-10 (along with the GV-4 and GV-5) is designed for 12V panel to 12V battery systems. These controllers were designed before GT panels became prevalent, and we don't recommend using GT panels with the GV-10. You're definitely right when you say that a larger MPPT controller that can handle GT panels (like the one you've described) will have much broader applications and will reach much, much larger markets.

    Small MPPT controllers make sense in off-grid applications where size, weight, and performance matter: remote sensing, parking pay stations, street lights/signs, sail boats, RV's, military, golf carts, etc. In many cases, the extra power gained from using an MPPT controller in a 12V panel/12V battery configuration offsets the cost premium over a PWM controller.

    Cheers,
    Alexander

    Cariboocoot wrote: »
    Welcome to the forum genasun.

    I have no experience with your controllers and could only judge by the specifications provided by the OP. Those specs are eerily similar to a number of "no name" charge controllers we have seen which claim to be "MPPT" but really are not; they just stick the label on because it sells more controllers.

    Your input Voltage limitation will be a problem for many applications, as it is with some other less-expensive MPPT controllers. Standard "24 Volt" panels have a Vmp of 35, which lets them out. Basically it would appear your controller can only be used with "GT panels" or "12 Volt" panels and only on a 12 Volt system. Mind you, we have seen lots of people get in trouble buying GT panels and then finding half the power is lost through PWM controllers. But your product could certainly benefit from a higher max V-in limit. The Voc on a 30 Vmp panel would even represent a danger.

    I'm not so sure there's much need for an MPPT controller of such low Amperage either. I do know of several people who could benefit from one around 30 Amps and we're all waiting for the new Rogue and MidNite to appear.

    Windsun apparently has had some experience with your units so I leave it to him to answer from his POV if and when he has time.
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #9
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    Re: 2 60W panels in series or parallel?
    genasun wrote: »
    Small MPPT controllers make sense in off-grid applications where size, weight, and performance matter: remote sensing, parking pay stations, street lights/signs, sail boats, RV's, military, golf carts, etc. In many cases, the extra power gained from using an MPPT controller in a 12V panel/12V battery configuration offsets the cost premium over a PWM controller.

    Cheers,
    Alexander

    That is an interesting POV. We usually find that the claimed power advantage in MPPT vs. PWM is negligible in small systems; that advantage usually doesn't start to show up below 400 Watts, much less be economically sound.

    Far greater advantage can be had from the MPPT's flexibility in array design, which means being able to make use of those GT panels (that we off-gridders call "oddball"). In fact given the difference in price per Watt between "standard" panels and "GT" panels the latter in combination with an MPPT controller often ends up being cheaper for the same amount of power.

    Just how much additional power do you expect to see using your controller with a standard KD140 panel over a PWM type 10 Amp controller? The expected calculation works out to about 1 Amp improvement, which is not much really. How efficient are your controllers?
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  • genasun
    genasun Registered Users Posts: 4
    #10
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    Re: 2 60W panels in series or parallel?

    Most people say that MPPT provides 10% to 30% power gain over PWM depending on conditions. We lean towards the 30% number, because in small autonomous systems that run continuously, the panel is sized based on expected power generation during the winter. In cold temperatures, panel voltages are higher than typical, and battery voltages are lower than typical because they will likely be operating at lower SOC, so the benefit of MPPT is higher than typical.

    Imagine a freezing sunny day with a panel Vmp at around 20V and a discharged battery at 11V. With an MPPT controller, you get at least 80% more power than with a PWM controller, and at a time when the power is needed most.

    Anyway, if you accept the 30% power gain, MPPT has a 42W advantage over PWM. The KD140 street price is ~$2/W, so an MPPT controller is equivalent to a PWM controller that is ~$80 cheaper.

    The GV-10 is 96-98% efficient.
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