system review

MexDog
MexDog Solar Expert Posts: 28
Great Forum. This is my test drive.

I'm setting up a small off grid system at a remote location in Mexico and would love some feedback. My leetle ranchito currently has a very basic 12v system (2 small sunsei panels and two trojan t-105 6v batt's) for the lights which I plan on leaving as is since the wiring is all done already. I'm planning on adding a 24v system to be able to run a small apartment size refrigerator, apartment size washing machine, and 24v ceiling fan.

So far I've managed to acquire (2) sharp 165 panels and (4) more trojan t-105 batteries (225 amp/hrs). I'm planning on taking down an outback MX-60 and Go-Popwer 1000w inverter. I'll run the (4) batt's in series. I'm thinking the Mx-60 and inverter will give me room to grow the system if needed. I can get more batt's and panels there as necessary. The frig is the biggest unknown, bought at Sams club there, it's only 7 cubic feet but I'm not sure of the draw - guessing about 250KW annual given the relatively high ambient temps (average around 80-85 degrees day and 65-70 degrees night inside the house.

I'm anticipating short wire runs - 15- 20 feet from panel to controller then 5 ft to the batt's, 5 ft to the inverter, and another 10-15ft max to the appliances. I plan to use a lightening surge protector between the panels and the controller, a 60A DC fuse between batt's and inverter, and a 6 amp in-line fuse between batt's and the 24vDC fan.

My wife and I are only there for a month at a time max so the batt's have a good chance to catch up in between visits.

My questions are:

1) What guage wire should I be using?
2) Do I need a ground fault if the panels are mounted on the ceramic tile roof?
3)Do I need a separate bus between controller and batt's, or can I go directly to the batt terminals then back off the same terminals to the inverter?
4) Do I need a load center?
5) How does this system look overall, and am I missing anything important?

Thanks so much for any help you can give!

MexDog
«1

Comments

  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: system review

    You really need to find that fridge, with it's energy rating sticker. Often, the mini-fridges consume as much, or even more, than a standard fridge. Cheap guts. Your best bet is an Energy Star fridge, what you will spend in PV panels to keep a small fridge going, will be more than giving the 7CF away, and getting a very efficient fridge.
    maybe I exaggerate a bit, but not much.
    Powerfab top of pole PV mount | 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 ,

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: system review

    mexdog,
    mike is right about the fridge and if you want to be sure about its draw then get yourself a kill-a-watt meter. it is a handy little device that you may have use of for telling you of any draws to the inverter be it the fridge or any devices now or in the future you may put inline. it's one thing that many appliances list their max watt spec, but this isn't typical and the on time is important in knowing what it is drawing altogether in watt/hours or wh. the meter takes the guess work out of both the actual draw and the time considerations.
    now as to each question:
    1> this you can calculate using the voltage drop calculator in the sticky in general solar topics. you don't want to exceed a percentage of 5% from source to load and this would be from the pvs to the batteries and could argueably be to the inverter or the ac loads. a smaller % is better, especially for solar, when the price of pv watts is so high and mppt controllers demand low losses. though the calculator can include more than just the pv run, i suggest you take it in individual steps and then add the steps together. this keeps you aware of each stage's losses and you can use this calculator no matter the power source or load. just remember a run consists of 2 wires so the total wire will be considered and that would be 2x the run length. btw, the calculator uses an excel (xls) program.

    2> ground fault circuit interrupters are not determined by the type of roof used so i'll go with yes.

    3> whatever is easiest for you that still serves its purpose and does not degrade performance or safety. it will all be heavy duty wires and connections to and from the battery.

    4> i would say yes, but it may not have to look like your standard circuit breaker box for your utility type entrance except this is for dc into and out of the batteries. this could go hand-in-hand with the buss question as a load center would make things easier as well as safer.

    5> good thinking on expansion of the system, but don't forget to use a battery temperature sensor.
    you may want to concider wiring the pvs in series to reduce the resistive wire losses going from the pvs to the controller.
    when mounting the pvs be sure there's a minimum of 6 inches clearance to allow for cooling the pvs better.
    don't forget to aim them in a southerly direction with either your latitude angle as the degrees to angle your pvs or your latitude + 15 degrees to aid in winter production. if you can have 2 or more angles on an adjustable mount you can get more yearly production from your pvs. trackers aren't worth it though as you could buy much more in pvs with that dinero and trackers fail often.
    hope i covered everything and i hope this helps you.

    i'm editting to add that for 1 month's use that is a large amount of time and you'll need full capacity in batteries, pvs, etc. and if you only do this a few times a year that could be alot to invest for such small uses. an alternative may be to just supplement the pv system with a good generator. some may suggest to use just that generator, but out in the woods or even if not in the woods one doesn't want to run generators that often as you'd get sick of the noise and running them so often. you won't have a big enough battery bank to supply 1 month's worth of use either so no catchup can occur with a bank that big.
  • MexDog
    MexDog Solar Expert Posts: 28
    Re: system review

    Thank you both for all the terrific advise.

    I think the frig may be energy star. I was just starting to learn about all this when I bought it but didn't understand the significance of that little sticker at that point. If it's not ES I'll heed your advice and replace it.

    I've already ordered kill-a-watt meter. Can't wait to start testing everything in site. Our kids will hate it.

    Think I'll take a pass on the gen set. There is electric to the edge of the property and the cheapest option would be to simply run a line the 1/8 mi. to the house. I'm trying to do right by ma nature this time around, set a good example for the neighbors and other gringos that end up building there, lock in my rates for all eternity (rates are bucking .25/kwh there now!), and hopefully spend entire winters there in future.

    I'm signed up for a PV design/install workshop this fall and may even try to make a business of it in Mexico some day.

    Will follow all other recommendations for fusing, etc.

    Huge Thanks! This will be a big help. The only thing lacking now is confidence!

    MexDog
  • System2
    System2 Posts: 6,290 admin
    Re: system review

    maxdog, thank for starting this tread. i wanted to set up a small solar electric system for small refigerator, computer, tv and some lighting in the house.
    so much info on the net, i am having problem to come up with the basic system for my need.
    i will try to follow this tread may by it will help to get start. my cabin is too far from the utility power.

    MexDog wrote: »
    Great Forum. This is my test drive.

    I'm setting up a small off grid system at a remote location in Mexico and would love some feedback. My leetle ranchito currently has a very basic 12v system (2 small sunsei panels and two trojan t-105 6v batt's) for the lights which I plan on leaving as is since the wiring is all done already. I'm planning on adding a 24v system to be able to run a small apartment size refrigerator, apartment size washing machine, and 24v ceiling fan.

    So far I've managed to acquire (2) sharp 165 panels and (4) more trojan t-105 batteries (225 amp/hrs). I'm planning on taking down an outback MX-60 and Go-Popwer 1000w inverter. I'll run the (4) batt's in series. I'm thinking the Mx-60 and inverter will give me room to grow the system if needed. I can get more batt's and panels there as necessary. The frig is the biggest unknown, bought at Sams club there, it's only 7 cubic feet but I'm not sure of the draw - guessing about 250KW annual given the relatively high ambient temps (average around 80-85 degrees day and 65-70 degrees night inside the house.

    I'm anticipating short wire runs - 15- 20 feet from panel to controller then 5 ft to the batt's, 5 ft to the inverter, and another 10-15ft max to the appliances. I plan to use a lightening surge protector between the panels and the controller, a 60A DC fuse between batt's and inverter, and a 6 amp in-line fuse between batt's and the 24vDC fan.

    My wife and I are only there for a month at a time max so the batt's have a good chance to catch up in between visits.

    My questions are:

    1) What guage wire should I be using?
    2) Do I need a ground fault if the panels are mounted on the ceramic tile roof?
    3)Do I need a separate bus between controller and batt's, or can I go directly to the batt terminals then back off the same terminals to the inverter?
    4) Do I need a load center?
    5) How does this system look overall, and am I missing anything important?

    Thanks so much for any help you can give!

    MexDog
  • MexDog
    MexDog Solar Expert Posts: 28
    Re: system review

    Neil,

    I'll follow your suggestions as to panel set up as well. The roof is perfect South facing but I hadn't considered needing ventilation. The MX-60 has an open voltage rating of 120 and the panels are rated 35v so I believe I can run up to three in series before having to run multiple stings in parallel. Is this correct?

    Do you have any particular load center that you would recommend?

    Thanks again,

    Dan
  • MexDog
    MexDog Solar Expert Posts: 28
    Re: system review

    Boonwsun,

    Thanks for the feedback. i was lost with all this stuff until I picked up two books:

    One is the SEI (Solar Energy International) "Photovoltaics, Design and Installation Manual" and the other is the Giaim Real Goods "Solar Living Source Book" (30th edition).

    Between those two bibles and this excellent website, you'll have everything you need.

    Dan
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: system review
    MexDog wrote: »
    The MX-60 has an open voltage rating of 120 and the panels are rated 35v so I believe I can run up to three in series

    Beware, panels have 2 voltage ratings. The higher one, is Volts Open Circuit, before the charger loads it down as it wakes up in the AM. This is the voltage that will fry the charger, not the lower voltage, listed as Volts Max Power

    Example from data sheet:
    Max Power Voltage - Vmp 35 Vdc [string of 3 = 105v]
    Open Circuit Voltage - Voc 43.8 Vdc [string of 3 = 131.4V ] !!!!

    Additionally, in cold weather (well, some areas get cold) both these voltages can increase several volts, and in a string of 3 panels, an extra 15V [131.4 + 15 = 146.4v ] on a frosty morning , as the sun rises, the charger frys.


    The MX60 has a recording chip that records the max system voltage, and is used to charge you for non-warranty repairs.
    Powerfab top of pole PV mount | 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 ,

  • MexDog
    MexDog Solar Expert Posts: 28
    Re: system review

    Mike,

    From the Sharp 1651U Spec Sheet:

    Open Circuit Voltage (Voc) 43.1V
    Maximum Power Voltage (Vpm) 34.6V

    From the Outback MX-60 Spec Sheet:

    PV Open Circuit Voltage (VOC) 150 VDC absolute maximum coldest conditions / 140 VDC start-up and operating maximum

    Looks to me like up to 3 in series is safe?

    Dan
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: system review
    MexDog wrote: »
    Neil,

    I'll follow your suggestions as to panel set up as well. The roof is perfect South facing but I hadn't considered needing ventilation. The MX-60 has an open voltage rating of 120 and the panels are rated 35v so I believe I can run up to three in series before having to run multiple stings in parallel. Is this correct?

    Do you have any particular load center that you would recommend?

    Thanks again,

    Dan

    i was basing that you noted having 2 of those pvs as 3 in series as was mentioned by you just now would be too much imho. the expansion would have to come with paralleling more of the strings of 2 in series because even if the voltage wouldn't be too high for the controller the higher you go the worse that efficiency from the controller would be.
    as to pv ventilation this would just entail at least 6 inches of space between the pvs and the roof so air can naturally circulate under the pvs. now if you would angle the pvs for say 35 degrees and your roof is a lower angle or flat that you could get the same effect from the pv being raised on one end suffiently. if your roof is about the same angle the pvs will be mounted at then they need raised upward. mounts tend to be like more sophisticated erector sets if you ever had or seen one of those as a child. it can get even more involved with some types of roofs.
    as to a load center you can look over some of them yourself as i have no particular preference. some are available from naws, our forum sponsor.
  • MexDog
    MexDog Solar Expert Posts: 28
    Re: system review

    Another Thank you. I have two panels now but thought I could just add a 3rd in series if needed and then a 4th if more juice is still needed, configured as 2 parallel strings of 2 each. The way I'm understanding you, I would need to grow the system as multiples of 2 rather than 1 at a time. Is this correct?

    As for the mounting, the roof has a moderate southward pitch, probably about 20 degress. For the 2 little sunsei's I have now for the 12v system I just left the lower edge resting on the roof and raised the top edge with a couple of supports. The roof being the 1/4 round spanish ceramic tiles leaves some air space even under that lower edge. Sounds like I am fine doing the same with the new sharps (?), except these will have the supports cemented in place. Can you guess why?

    Hint: it's Mexico and the house is vacant for much of the year.



    niel wrote: »
    i was basing that you noted having 2 of those pvs as 3 in series as was mentioned by you just now would be too much imho. the expansion would have to come with paralleling more of the strings of 2 in series because even if the voltage wouldn't be too high for the controller the higher you go the worse that efficiency from the controller would be.
    as to pv ventilation this would just entail at least 6 inches of space between the pvs and the roof so air can naturally circulate under the pvs. now if you would angle the pvs for say 35 degrees and your roof is a lower angle or flat that you could get the same effect from the pv being raised on one end suffiently. if your roof is about the same angle the pvs will be mounted at then they need raised upward. mounts tend to be like more sophisticated erector sets if you ever had or seen one of those as a child. it can get even more involved with some types of roofs.
    as to a load center you can look over some of them yourself as i have no particular preference. some are available from naws, our forum sponsor.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: system review

    "I would need to grow the system as multiples of 2 rather than 1 at a time. Is this correct?"

    yes, that would be correct. to do this one pv at a time would mean all to be paralleled and you would lose that extra voltage to overcome the resistive losses from the wires. if you run heavier wires you may get away with doing that all in parallel, but the high heat down there may also fold back on the voltage from the pvs to a point making the vpm lower. all paralleled equates to more heavy wiring and possible dropouts of the pvs sooner than would be encountered with raising the voltage by having another pv in series. you can do it either way, but imo the 2 in series and then parallel multiples of 2 in series for any expansions is best overall.
    good deal on the roof and i understand of the need due to possible theft. you may wish to consider buying some nuts and bolts that are geared to be antitheft as our sponsor lists. http://store.solar-electric.com/mohasebo.html
    let us know how things are coming along too.
  • al128
    al128 Solar Expert Posts: 65 ✭✭✭✭
    Re: system review
    MexDog wrote: »
    Mike,

    From the Sharp 1651U Spec Sheet:

    Open Circuit Voltage (Voc) 43.1V
    Maximum Power Voltage (Vpm) 34.6V

    From the Outback MX-60 Spec Sheet:

    PV Open Circuit Voltage (VOC) 150 VDC absolute maximum coldest conditions / 140 VDC start-up and operating maximum

    Looks to me like up to 3 in series is safe?

    Dan

    Estimado,

    DL the MX (or now FM60) owners manual - as a pdf. its an incr. source of information

    IIRC it has very specific sections on how to "correct" the Voc of panels for cold weather ... again, IIRC for temps down to -10 deg. cel. you have to uprate them for like 13% ... which gets you just below the edge of what the 60 will do ... assess for yourself the coldest morning temps (incl. wind-chill) that have been around your location for the last 20+ yrs ... and take your decision

    salu2!
    al
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: system review

    he may still find an mx60 somewhere, but you are correct that the mx60 production is now discontinued. the fm60 has replaced it and if you wish you may go higher with and fm80 if you feel you may need to expand to that point. no matter what get a bts to track battery temperatures with so voltage corrections can be made by the cc.
    confirming again that 3 pvs in series is too much.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: system review
    MexDog wrote: »
    From the Sharp 1651U Spec Sheet: Open Circuit Voltage (Voc) 43.1V

    PV Open Circuit Voltage (VOC) 150 VDC absolute maximum coldest conditions / 140 VDC start-up and operating maximum

    Looks to me like up to 3 in series is safe?

    @ 72F: 43.1 x 3 = 129.3V which is OK at 72F

    At colder temps, the panel voltage will go higher, and at 32F, you may be above the 140VDC
    The MX logs the voltage, so if you over-voltage it, the factory knows.
    Powerfab top of pole PV mount | 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 ,

  • MexDog
    MexDog Solar Expert Posts: 28
    Re: system review
    mike90045 wrote: »
    @ 72F: 43.1 x 3 = 129.3V which is OK at 72F

    At colder temps, the panel voltage will go higher, and at 32F, you may be above the 140VDC
    The MX logs the voltage, so if you over-voltage it, the factory knows.

    My place is pretty far south. I don't think it ever gets below 60 degrees f. there. Given that, would three in series seem like a safe bet? And wouldn't three be more efficient due to the higher voltage? I'm also curious, why don't chg. controllers incorporate a circuit breaker to protect against a voltage spike?

    On another front, I read in the SEI Manual that each piece of equipment in a system should have a disconnect. Does the fusing I described previously count as the required disconnects? And another question: why do DC systems like this generally rely on fuses rather than breakers?
  • rplarry
    rplarry Solar Expert Posts: 203 ✭✭
    Re: system review

    Mexdog
    One thing about your proposed system that I would change would be the inverter. I would use an inverter/charger, maybe I missed it, but I don't see any provision in your system for charging the batteries other than the solar panels. Other than that your system will probably work just fine.
    Larry
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: system review

    as i said before that even if the cc can take the higher voltage of 3 in series, the cc won't operate as efficiently that high up. stay with 2 in series.
  • MexDog
    MexDog Solar Expert Posts: 28
    Re: system review
    niel wrote: »
    as i said before that even if the cc can take the higher voltage of 3 in series, the cc won't operate as efficiently that high up. stay with 2 in series.
    rplarry wrote: »
    Mexdog
    One thing about your proposed system that I would change would be the inverter. I would use an inverter/charger, maybe I missed it, but I don't see any provision in your system for charging the batteries other than the solar panels. Other than that your system will probably work just fine.
    Larry

    Niel & Larry,

    I'll definitely limit it to two panels per series but I'm a confused about the charger. Isn't the MX-60 "smart" enough to provide the best possible charging to the batteries under all conditions? How does an inverter/charger provide additional charging not provided by the cc? And can a stand-alone charger be used instead? (I already went ahead and ordered the Go-Power inverter but can always send it back if necessary).

    Dan
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: system review
    niel wrote: »
    as i said before that even if the cc can take the higher voltage of 3 in series, the cc won't operate as efficiently that high up. stay with 2 in series.

    question-
    How does a 48V array effectively charge a 48V battery bank. I did not think the MX60 or even the FX60 could up-convert array voltage to battery voltage.
    Powerfab top of pole PV mount | 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 ,

  • rplarry
    rplarry Solar Expert Posts: 203 ✭✭
    Re: system review

    Mexdog
    The mx60 is a great charge controller, I like mine alot, but it only controls the charge from the solar panels. When (not "if") you have a few cloudy days, you will be looking for a way to charge those batteries. A stand alone charger will work well, Iota makes some nice ones. Then to power the charger, a Honda EU 1000i or even a 2000i (depending on how large of a charger you get) will be nice and quiet as well as reliable. There are cheaper ways to go, but usually with this type of equipment you get what you pay for. I mentioned an inverter/charger because it is all in one package, so installation is easier, the inverter would have greater capacity, so plenty of room to expand your system later, and not that much more expensive. I think you might be a little surprised by that little refrigerator that you bought down there. I also us an elec refer (18cf energy star 392 kw a year) off grid up here in Bahia, although it is larger than yours. During the cooler winter months it uses about 1kw a day, but in the hotter months it uses 3kw a day. The point is that the power consumption triples with a 20 degree ambient temperature rise. So depending on what time of the year that you are there, your system might do fine, and the next trip the solar panels won't be able to keep up with your elec consumption. You will be looking for another way to charge those batteries other than with the sun. When I started out 10 tears ago, I just had 2 batteries a small inverter, and 80 watts of pv. Since then I have spent thousands of dollars upgrading, and could have saved much of that by buying the better equipment up front rather than using the trial and error method that I used.
    I hope this is helpful to you,
    Larry
  • System2
    System2 Posts: 6,290 admin
    Re: system review
    MexDog wrote: »
    I'm also curious, why don't chg. controllers incorporate a circuit breaker to protect against a voltage spike?

    Circuit breakers protect against too much current, not voltage.

    Cheers,

    Bad Apple
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: system review
    mike90045 wrote: »
    question-
    How does a 48V array effectively charge a 48V battery bank. I did not think the MX60 or even the FX60 could up-convert array voltage to battery voltage.

    mike,
    he stated his current system is 12v, but he wished to go 24v as this was in his 1st post, "I'll run the (4) batt's in series." and note those are 6v batteries. if it goes to a 48v battery system, that can still be charged with the 24v pvs as 2 in series for the vmp, or vpm whichever prefered, is high enough to do so, but may be subjected to high heat and be reduced somewhat at times below what he may want thus making a higher than 48v pv system more a possibility here.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: system review
    niel wrote: »
    mike,
    he stated his current system is 12v, but he wished to go 24v as this was in his 1st post, "I'll run the (4) batt's in series." and note those are 6v batteries. if it goes to a 48v battery system, that can still be charged with the 24v pvs as 2 in series for the vmp, or vpm whichever prefered, is high enough to do so, but may be subjected to high heat and be reduced somewhat at times below what he may want thus making a higher than 48v pv system more a possibility here.

    Duh, some days I'm just a little slow. I guess I invented 48V.

    Sorry about that ya'll.
    Powerfab top of pole PV mount | 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 ,

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: system review

    no problem as i get days like that.:roll:
  • MexDog
    MexDog Solar Expert Posts: 28
    Re: system review

    I'm now working through wiring sizing for this system and would love some input on my calculations:

    If I use (4) PV modules run as (2) parallel sets of (2) panels in series for each set, and I have a 24' one-way run to the CC, then I am estimating I will need #6 wire for this run. My calculations are based on the following:

    sharp 165U1 Panel short circuit rating=5.46A x (2) (# of panels in parallel) = 10.92A rounded up to 15A for the 2% 24v voltage drop chart = #6 gauge wire for a run of between 20.6 & 32.6 feet.

    For the 8' run from the Mx-60 CC to the batteries I am calculating:
    60A rating for the MX-60 x 1.25 (80% of rated capacity) = 75A = #4 wire for a run of between 6.5 & 10.4 feet.

    How does this all look so far?

    Thanks again!

    Dan
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: system review

    mexdog,
    you do not need to go by the isc of the pvs and round up because the low percentage for voltage drops you will shoot for will be more than enough to cover the possibility of short circuits from the pvs or cc. you may of course go with thicker wire if you so chose to, but going by what you wrote this is to be a run of 24ft so that is 48ft of wire right there and you forgot the 5ft or so to interconnect the pvs you have in series, making the wire needed to the cc about 53ft. i am interpreting that you intend each string to run seperately to the cc and at 4.77a that's 53ft of wire at #12 would yield a .97% drop for 48v. if you combine the 2 strings near the pvs and run one set of wires to the cc then a thicker wire will be needed and could be #8 for a drop of .77% at 9.54a.
    the short run to the batteries from the cc you said to be 8ft is now 16ft of wire and using the 9.54a as a reference #10 would drop .74% at 24v. if you use #8 that would see a drop of .46%. the percentage you get from the pvs to the cc must be added to the cc to the batteries percentage. figuring for 1 string of #12, with the other being identical, this is .97% + .74% if using #10 from the cc to the batteries for a total of 1.71% which is very acceptable. if you want room to expand or to drop the percentage, the wire used from the cc to the battery can be made larger in size. each string you would add has its own run of #12 wire and with 3 or more you will need to combine the strings as they get to the cc. if i remember right 2 strings can be accomodated by the mx60, but if i'm remembering wrongly then you will need a combiner. don't forget about fusing at the battery minimumly to be the short circuit value of the cc's output rounded up. if you go with more than 2 strings you will need to fuse each string too.
    hope this didn't confuse you any.
  • MexDog
    MexDog Solar Expert Posts: 28
    Re: system review
    niel wrote: »
    mexdog,
    you do not need to go by the isc of the pvs and round up because the low percentage for voltage drops you will shoot for will be more than enough to cover the possibility of short circuits from the pvs or cc. you may of course go with thicker wire if you so chose to, but going by what you wrote this is to be a run of 24ft so that is 48ft of wire right there and you forgot the 5ft or so to interconnect the pvs you have in series, making the wire needed to the cc about 53ft. i am interpreting that you intend each string to run seperately to the cc and at 4.77a that's 53ft of wire at #12 would yield a .97% drop for 48v. if you combine the 2 strings near the pvs and run one set of wires to the cc then a thicker wire will be needed and could be #8 for a drop of .77% at 9.54a.
    the short run to the batteries from the cc you said to be 8ft is now 16ft of wire and using the 9.54a as a reference #10 would drop .74% at 24v. if you use #8 that would see a drop of .46%. the percentage you get from the pvs to the cc must be added to the cc to the batteries percentage. figuring for 1 string of #12, with the other being identical, this is .97% + .74% if using #10 from the cc to the batteries for a total of 1.71% which is very acceptable. if you want room to expand or to drop the percentage, the wire used from the cc to the battery can be made larger in size. each string you would add has its own run of #12 wire and with 3 or more you will need to combine the strings as they get to the cc. if i remember right 2 strings can be accomodated by the mx60, but if i'm remembering wrongly then you will need a combiner. don't forget about fusing at the battery minimumly to be the short circuit value of the cc's output rounded up. if you go with more than 2 strings you will need to fuse each string too.
    hope this didn't confuse you any.

    I'm confused by this. the SEI manual says to use the distance listed in the 2% voltage drop chart that is equal to or greater than the one way distance to the load in order to determine the correct wire size.

    Also, I was planning on combining the two sets of pvs in parallel near the array and running one thicker wire to the cc. Is there any advantage or disadvantage to making two runs with lighter gauge wire rather than the single run I was planning?
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: system review

    mexdog,
    i have no idea what is contained in that manual to know what it is they are saying. be assured that what i had done is real and with knowledge of the subject as i had inputted the pertinent info for the voltage drop calculator in the solar basics sticky with the actual xls work being done by another solar advocate. from what i was seeing you may have been mixing up the sizing for fuses with that of the requirements for wire. the percentages are real with the info you had provided for use in a 48v pv system to a 24v battery system.

    http://forum.solar-electric.com/showthread.php?t=29

    as to the wiring, you may do it either way and there is not any advantage with 1 set of wires other than it is 1 set of wires. the resistance of the combined 1 set of wires needs to be lower due to the increased current that shall flow through it making the wires larger in diameter. that is why #12 wires cannot be used and in keeping vd losses low if both strings are combined unless you are running seperate wires for each string. i listed example gauges with their percentages for you. if you plan further future expansions then you may wish to do a wiring design for the future goal planned so that new wires won't have to be run because you would need to replace the smaller wires you originally ran with.
    as i said, the percentages i listed are good and will be under 2%. if lower percentages are desired by you then please state your goal vd percentage from pvs to batteries or if you plan for future pv expansions to take place then let me know the total number of strings of those pvs you plan to run as i'd need to figure in the added current to the system wire requirements. you can figure this too if you have an xls (excel) program or its equivalent and use the link to the calculator which is on a site provided to us by brock. if there's any problems to you doing this calculating by yourself, i will gladly lend a hand in doing the calculations for you to the best of my understanding of your proposed system.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: system review

    > Also, I was planning on combining the two sets of pvs in parallel
    > near the array and running one thicker wire to the cc. Is there
    > any advantage or disadvantage to making two runs with lighter
    > gauge wire rather than the single run I was planning?

    Lighter gauge is easier to handle/pull, but if you upgrade later, you have to repeat the job.
    Powerfab top of pole PV mount | 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 ,

  • MexDog
    MexDog Solar Expert Posts: 28
    Re: system review
    niel wrote: »
    mexdog,
    you do not need to go by the isc of the pvs and round up because the low percentage for voltage drops you will shoot for will be more than enough to cover the possibility of short circuits from the pvs or cc. you may of course go with thicker wire if you so chose to, but going by what you wrote this is to be a run of 24ft so that is 48ft of wire right there and you forgot the 5ft or so to interconnect the pvs you have in series, making the wire needed to the cc about 53ft. i am interpreting that you intend each string to run seperately to the cc and at 4.77a that's 53ft of wire at #12 would yield a .97% drop for 48v. if you combine the 2 strings near the pvs and run one set of wires to the cc then a thicker wire will be needed and could be #8 for a drop of .77% at 9.54a.
    the short run to the batteries from the cc you said to be 8ft is now 16ft of wire and using the 9.54a as a reference #10 would drop .74% at 24v. if you use #8 that would see a drop of .46%. the percentage you get from the pvs to the cc must be added to the cc to the batteries percentage. figuring for 1 string of #12, with the other being identical, this is .97% + .74% if using #10 from the cc to the batteries for a total of 1.71% which is very acceptable. if you want room to expand or to drop the percentage, the wire used from the cc to the battery can be made larger in size. each string you would add has its own run of #12 wire and with 3 or more you will need to combine the strings as they get to the cc. if i remember right 2 strings can be accomodated by the mx60, but if i'm remembering wrongly then you will need a combiner. don't forget about fusing at the battery minimumly to be the short circuit value of the cc's output rounded up. if you go with more than 2 strings you will need to fuse each string too.
    hope this didn't confuse you any.

    Niel,

    Some of this makes sense, but it looks like you're using 48v voltage drop calculations for the pv to cc run and 24v calculations for the cc to battery run? Am I missing something here?

    Dan