Help me finish/plan my system :) Please

MTguy
MTguy Registered Users Posts: 10
Hello from Afghanistan! Right now I am overseas with the military but I would like to order the rest of the components for my system so they are waiting for me when I get home. I will have about 5 days to complete my system before I leave on my well deserved vacation which is why I want everything ready to go when I get there.
My stuff: I currently own 8 old stock but never used Siemens SP75 (75 watts 12v but switchable to 6V), 2 x 200 amp hour Deka Solar gel cel batteries never used but a few years old (may have to buy new but they were free). I also have a Prostar PS-20m PWM charge controller that is brand new. My camper has propane fridge, heat, and cooking. It is outfitted with LED lights. My major consumers of power will be the water-pump (12v surflo @ 7 amps, apprx 3 gallons/minute), a 12V TV (3 amps) and a 12v radio (7 amps max). The water tanks are only 20 gallons so I can’t pump that much. On a worst case scenario I came up with around 208 amp hours of battery use in a day (that lets me watch a movie and use all of my water).
My project: I am putting together a system for my small camper and I need a little help. I do plan (in approximately 3 years) to move this whole system to an entirely off-grid cabin I will be building. I would like to say that money is not an object. I would also like to say that I am tall, good looking and have a full head of hair…. So, I would like to keep the remaining pieces at $1000 or less if I don’t have to buy new batteries. I don’t think that will be a problem. I only have room for 4 panels on the roof of my camper, but I do want to mount them “permanently”. I would like to take the other 4 panels and make a portable “fold out” set that I can setup relatively quickly as needed. The power should feed into my camper using the existing DC panel and the AC Inverter/charger (don’t know the brand or specs at this point unfortunately).
My questions:
1) Are there any obvious problems you’ve seen yet? 
2) Can I hook the 4 roof mounted panels up in parallel and run them into the Prostar PS-20M, which will run directly to the batteries? Then take the other 4 panels wired in parallel and run them into a separate 20 amp PWM charge controller which connects directly to the batteries. Thus giving me 2 600 watts at 12V…. I think (wiring diagram 1)
3) Would I be better off getting a Tristar 45 amp MPPT charge controller and run that instead of the two 20 amp charge controllers? Possibly giving me parallel strings wired in series to put me at 24V, 600 watts. In order to do this, I foresee the need to come up with a quick detach system of some sort. Any ideas? As I understand it the Tristar should be able to auto detect the increased voltage and convert it to 12V. (wiring diagram 2)
4) Am I ok to have this hooked up with shore power on my camper? The way I understand it the automatic transfer switch in the inverter/charger should make this safe.
5) As I’m sure you noticed; I am not sure where to put the fuses and what size to use.
6) Would there be an advantage to switching the panels to 6V and running them in series at 24V/string?
7) Is there a better way I don’t see?

My sources of information:
Solar Panels:
Prostar PS-20m:
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Comments

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Help me finish/plan my system :) Please

    welcome to the forum,
    you aren't exactly specific on everything employed, but in general it sounds viable. rather than use a pwm cc on the remote pvs it may be advantageous to use an mppt cc. remote setups can be long with wire and the longer it is the heavier the gauge that would be needed so this would allow for a higher pv voltage to be employed helping to overcome the losses and still employ wire that is lighter and more flexible. the actual working lengths and gauges of the setup will need to be run through a voltage drop calculator. better to figure it out on paper before doing it.

    now i'm not particularly familiar with the arrangement on the siemens pvs, but if they allow for full wattage output at 6v this may be advantageous to you to do. the reason is because in a 12v system all pvs would be paralleled. this means a fuse or circuit breaker on the output of each pv before being combined being there would be 4. if the pvs are set at 6v thus doubling their current at 6v then this could be wired in series to another of the same pv making the output result at 12v with less wires to be combined at a combiner. this arrangement would result in 2 strings to be combined and would eliminate the need for the fusing/cb and would greatly simplify the combining. 6v pv in series with 6v pv combined with 6v pv in series with 6v pv could work out well for the rv roof.

    similarly to the above with the remotes if you opt for a pwm cc to handle those pvs, but there could be some heavy wire involved to keep v drop losses low. if it's an mppt it could take the pvs as 12v with putting a pv in series with another at 12v which would result in a series string of 24v and being the current is kept the same it lowers the losses through those wires back to the cc. you could do this with the last 2 pvs and just combine the 2 strings of 24v before the cc. remember more than 2 to be combined will result in the requirement of fuses/cb.

    with the remote pvs they could be arranged as all in series at 12v too for a total of 48v, but would necessitate that all 4 of the pvs be near one another to make the series chain. you could also wire this as each pv at 6v with doubled current all in series for a total of 24v into the mppt cc, but again all 4 of the pvs would need to be near one another. it would be easier with mounting 2 pvs on a remote mount together prewired so as to just hook straight to the mppt cc after positioning. it would be heavier than single mounts, but you won't need to struggle to get the 2 to aim exactly the same and that symmetry is important in a string. you should try to aim the 2nd set exactly as the first to keep things fairly equal between both strings too, but this can't be helped as it would be difficult to mount all 4 remote pvs to a single mount and i wouldn't rule this out or to be impossible to do.
  • vtmaps
    vtmaps Solar Expert Posts: 3,741 ✭✭✭✭
    Re: Help me finish/plan my system :) Please

    Welcome to the forum MTguy,
    Niel's advice about array configuration is very good.
    One thing to consider is shading. Any shading (overhead wires, antenna, etc) on a panel will severely reduce the output of not just that one panel, but the entire series string that the panel is part of.

    If there are shading issues on the top of your camper, put those panels in parallel. If you can avoid shading on the portable panels, then put them in series or series/parallel to get a higher voltage. You will need two controllers to do this.

    --vtMaps
    4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
  • MTguy
    MTguy Registered Users Posts: 10
    Re: Help me finish/plan my system :) Please

    Thank you both for the help. I am fortunate that I don’t foresee any shading problems on the roof due to the location of the vents /air conditioning in relationship to the panels. For the roof panels, If I understand you correctly you are recommending that I switch them to 6V (wattage maintained and amps increased if I am reading the spec's correctly) and run 2 strings (parallel) of 2 panels in series. This would give me 12V at 17.4 amps max.
    Here are the Specs for the SP75 at 12V and 6V
    Electrical Parameters1 12V 6V*
    Maximum power rating, Pmax [Watts] 75 75
    Minimum power rating, Pmin [Watts] 70 70
    Rated current, Imp [Amps] 4.4 8.8
    Rated voltage, Vmp [Volts] 17.0 8.5
    Short circuit current, Isc [Amps] 4.8 9.6
    Open circuit voltage, Voc [Volts] 21.7 10.9

    I would then combine the 2 strings in an outdoor electrical box while still on the camper's roof and run 1 set of wires to the charge controller. The max that run would be is 20’, 12V at 17.6 amps max would give me approximately a .14V drop with 6 gauge wire. I’ve got a suspicion I’ve messed up the amps here, but hopefully reading posts on this forum for the past several days has got me close.

    For the portable setup I would like to mount all four panels in a folding accordion style using piano hinges and aluminum hardware. I think this will eliminate the concerns about making sure they are all getting the same sun. This setup would weigh a little over 70lbs, just a bit more than a small Honda generator with a full tank of fuel. Because I am planning on putting the entire system on a roof mount in the future, I am thinking of going with the MPPT 45 for my second charge controller. If I do that, I think I would be well served to set all of the portable panels at 6V and run them in parallel (correction as you will run the pvs in series. niel) for 24V and 8.8 amps. I could just as easily run it at 48V and 4.4 amps I suppose though. I wouldn’t want to have a run of wire longer than 40’. The resistance at 40’ and 8.8 amps causes .14V loss for a 6 gauge wire. That might be a little stiff for wire so I could look at 8 gauge I am looking at .225V loss. The MPPT cc should help with this long run and I can use it and combine all of the panels on the one controller in the future.

    Once again, thank you for all of the advice.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Help me finish/plan my system :) Please

    i think you've got it for the most part. the outdoor box would make it easy to connect things or you can run them inside separately to combine inside too away from any weather. up to you. do realize that you can't combine the different pv setups from the rv roof and the remotes together until after they have gone through their respective controllers. they will be separate systems going to common batteries. this means you will have need of a combiner for the rooftop pvs and a straight through for the remote pvs, but a separate box outside for the remotes allows ease of connecting and disconnecting the remote pvs. these boxes will need to be weather tight. you could also incorporate a disconnect switch for the pvs in the box too and often times we use a circuit breaker for that function keeping in mind you aren't required to have breakers with the limited combinations of 2 or less strings.

    as to the voltage dropped this gets divided into the system voltage be it the vmp of the pv system or divided into the battery voltage (nominal). for instance that .14v dropped divided by the total vmp of the pvs would be .14v dropped/17v vmp=.8%. at .225v dropped/17v vmp=1.3%. this percentage will be added to the percentage of the cc to battery run of wire to get the total v drop loss percentage. btw, the 17.6a is correct. to figure the v drop loss percentage on the cc to battery wires you should reference to the nominal battery voltage which in your case is 12v. battery voltages will go higher when charged, but lower if discharged to any great dod percentages. that means if you drain the battery back to 11.5v that the v drop percentage will actually be worse that what you figured it at for 12v. even though a lighter wire may fit the bill for the v drops if you have the opportunity to use heavier wire then do so.

    i should note we used to try to go with the nominal pv voltages, but seeing as how pv voltage now vary so widely it is more convenient to use the vmp or voltage at the max power point. the voltage of the pvs could be drawn lower than the vmp voltage and would represent a worse v drop percentage.
  • MTguy
    MTguy Registered Users Posts: 10
    Re: Help me finish/plan my system :) Please

    Thanks again for the help. I think the advantage for me to do the combiner box on the roof is that I can take a weatherproof electrical box and put that over the "hole" that I'll make to route the wires into the camper. Right now I'm thinking that putting the charge controller for the portable panels at the panels will be the easiest. Then I can run the wires to the batteries and connect with battery clamps. I'm wondering if I can find a heavy duty extension cord that I can modify the ends on?

    I will need some sort of monitoring for the system so I was thinking about combining the AEE Digital DC Volt Meter and the AAC Digital AMP Meter. I am thinking that these will work for my setup being hooked directly to the batteries rather than using the metering that can be purchased as part of the TriStar charge controller. Thanks again for all of the help... I'll send me wind project to another forum :).
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Help me finish/plan my system :) Please

    "Right now I'm thinking that putting the charge controller for the portable panels at the panels will be the easiest."

    i would not advise putting a controller at the array exposed to the elements. if you need a combiner it's possible to do so at the array, but let the higher voltages travel back to the rv to be converted by the mppt controller inside the shelter of the rv.

    i did not look at the meters you posted, but our host does also carry some that may be more inclusive. also do not 100% go by a monitor as small errors over time can add up to becoming way off down the line.
  • MTguy
    MTguy Registered Users Posts: 10
    Re: Help me finish/plan my system :) Please

    Thanks, that makes sense to put the controller closer to the batteries. Would there be any use to a car audio capacitor/battery in a solar installation? It is a hybrid of sorts between a deep cycle battery and a capacitor. I wondered if it would help with things with a high start up draw i/e AC or microwave? Or possibly for those who have a bit higher end stereo/theatre system in their cabins/RVs. For an example of what I'm talking about see the link below. I actually have one from a project that I ended up not needing it for.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Help me finish/plan my system :) Please
    MTguy wrote: »
    Thanks, that makes sense to put the controller closer to the batteries. Would there be any use to a car audio capacitor/battery in a solar installation? It is a hybrid of sorts between a deep cycle battery and a capacitor. I wondered if it would help with things with a high start up draw i/e AC or microwave? Or possibly for those who have a bit higher end stereo/theatre system in their cabins/RVs. For an example of what I'm talking about see the link below. I actually have one from a project that I ended up not needing it for.

    No--Capacitors do not really help. Capacitors work by having voltage changes (to store energy). Batteries support loads with a (more or less) constant voltage.

    Size the battery bank to your daily loads and, usually, you will be fine.

    That "Cap Cell" or "SCELL" you linked to is only 7AH of storage and 3-6 year cycle life--Not much different than just putting the money into more battery bank.

    When you look into the details of "super caps"--They really are not that super for average off grid power usage... Expensive, not much energy storage for the $$$, and pretty short cycle life (if you use for supporting multiple starting surge current hits per day--and they "age" just because they have voltage applied).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MTguy
    MTguy Registered Users Posts: 10
    Re: Help me finish/plan my system :) Please

    Thanks, I just had one lying around and wondered if it would be useful. Thanks again for all the help everyone.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Help me finish/plan my system :) Please

    It might be marginally useful (extend battery lifetime a bit) and reduce system electrical noise if you are using an AC inverter--Basically inverters produce 120 Hz (for a 60 Hz inverter) current sine wave squared wave form and adding the capacitor could help reduce peak current loads (and lower self heating I2R effects a bit).

    It will not help over the long term (seconds/minutes/etc.) as the capacitor is only storing around 1/120th of a second worth of useful power.

    If you have one--you can try installing it and see if you find any differences (batteries running cooler, use a DC Current Clamp meter to measure AC ripple current in the capacitor power lead, does the capacitor get work under heavy AC loads, etc.).

    I would not suggest buying one--But since you have one, you could figure out if it supplies any advange.

    Be a little careful--Inductance of wiring and large capacitors can create an LC inductor (tank circuit). For example if you had XX feet of DC wiring and attached the capacitor near the AC inverter's DC power input--You could cause the DC harness+capacitor to "ring"--Which could cause all sorts of stability issues (confuse inverter, charge controllers, etc.).

    I would suggest installing the capacitor at the battery bank instead (lots of capacitance from the battery, not much wiring inductance).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MTguy
    MTguy Registered Users Posts: 10
    Re: Help me finish/plan my system :) Please

    Going back and looking at my project, I thought I could get by with 2 Morningstar SunSaver 15 Amp MPPT Solar Charge Controllers. In order to do this I would have to switch the panels to 6v and run them in series. That should give me 2 strings of 300 W, 24V @ 12.5 amps. This would reduce the cost and footprint of the charge controller. It should also help me save a bit of money on the wiring and charge controllers. Now, that being said, I was putting the specs in the morningstar string calculator and it says that it will not work. Can someone explain this to me? I've attached the screenshot of the calculations it came up with. Is it because the Vmp is actually 8.5 volts rather than 6 volts? As always, any help is appreciated.
    Attachment not found.
  • BB.
    BB. Super Moderators, Administrators Posts: 33,433 admin
    Re: Help me finish/plan my system :) Please

    I am not sure why it says it will not work... But there are (I think) a couple errors in the data...

    First, your maximum battery voltage is probably closer to 15.0 volts, not 13.0 volts (does not matter for your needs here).

    Second, the Isc Amp/C was entered as 2.08 ... I would guess that if you enter that data, it should be closer to 0.010 or so (just a guess)...

    If you put your mouse over the red labels, it will tell you why they "fail" the configuration (entering your numbers, it appears fails due to exceeds maximum power rating). This odd because I tested another array configuration and I can get green on higher wattages that 225 watts...

    Playing around, it appears the maximum power rating is based on the maximum battery voltage entered. More or less the website limits are set:

    Vbatt-max*15 amps (max controller current) = Maximum Power Rating
    • 13 volt max battery * 15 amps = 195 watt max power rating
    • 16 volt max battery * 15 amps = 240 watt max power rating

    This is not really a "RED" limit. Because the controller has the ability to control its output current to rated maximum (part of how a MPPT controller functions), you can certainly put an array (or even a 24 volt battery bank) on the input that greatly exceeds Max Power Rating and the controller will always output 15 amps maximum.

    It is just, as the you put a larger array, the controller would will current limit for more hours of the day--Wasting sunlight/power.

    My personal suggestion, the maximum "cost effective array" for a 15 amp MPPT controller would be around:
    • 14.5 volts charging * 15 amps * 1/0.77 panel+controller derating = 282.4 watts maximum "cost effective" array

    You can certainly install an array >282 watts--It will simply limit its output current to 15 amps vs getting the next size larger controller which will pass full available current (for a higher cost).

    So, my personal choice would have been to mark the ~200 watt to 282 watt range in "yellow" (approaching current limit) and "orange" (will be in current limit much of the middle of the day)... And reserve "red" for exceeds input voltage or is too low to charge battery bank.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • MTguy
    MTguy Registered Users Posts: 10
    Re: Help me finish/plan my system :) Please

    I put in the 2.06 as that is the amps but not the ratio. The ratio is .04% or .0004 according to the panels specs. I was thinking the same thing that I might cut my top end off if I have excellent conditions. With these panels being mounted flat on my camper I don't see "perfect" conditions in my future. I've also got more than enough panel to supply what I'll be using, so I am still considering this route.