Advice greatly appreciated for purchasing solar system&sufficient number of batteries

2»

Comments

  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: Advice greatly appreciated for purchasing solar system&sufficient number of batte

    In the end from Tony's summary--don't shade the panels (winter and summer). Shade, clouds, dead leaves, dust/dirt, snow, etc. all lead to decreased output.

    If you have snow, mount the panels so you can tilt them to near vertical with the bottoms of the array will above the ground (roof edge, etc.) so that they can self clear/easier to clear after a storm.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • hillbillyhillbilly Solar Expert Posts: 334 ✭✭
    Re: Advice greatly appreciated for purchasing solar system&sufficient number of batte

    Crystal, I would (did) agree with Tony's point that if one is looking to use a fair number of low voltage DC loads, then 12V is certainly advantageous there. As for the efficiency factor, for the most part as long as you have a higher PV voltage than battery voltage the differences in terms of converting that power are pretty small. The shading issue is NOT small, so do all you can to maximize your shade free time: if you cannot do this, and have to deal with some shading then you may want to look into more parallel panels vs series panels as Tony suggests.
    My suggestion for 24V was mostly due to being able to add more panels at a later date and still keep the wiring costs and losses down. If the system grows then higher currents mean more potential for "lost" energy. I'm not sure if you've looked into voltage drop yet, but if you have not I would take a look at the charts and play with some numbers (including pricing the wire for heavier gauge wire); this is a fairly important part of designing a PV system, so it's worth considering. Don't scrimp on wire size, especially if you think there is any chance the system will grow later, as having to run extra wire and conduit, or rewire at a heavier gauge later on is both expensive and a hassle.
    Take my suggestion, and any others for that matter with a grain of salt. Do play with the numbers for a while, considering all the "what if's": what if we wish to add 1 more panel later on, what if we wish to add 2 or 3, what if we wish to run a washing machine later, or what if we wish to ____ (fill in the blank).
    Good luck with the design phase (the second most fun part imo)
    HB
  • hillbillyhillbilly Solar Expert Posts: 334 ✭✭
    Re: Advice greatly appreciated for purchasing solar system&sufficient number of batte
    icarus wrote: »
    For a number of reasons, I disagree. I think that a 12vdc is a great starting system.
    Tony

    Actually I agree with a 12V system being a great starting system; mostly I would suggest that if it may grow later on to have the potential to change that to a 24V system. In other words not locking into that system voltage with a battery bank that is only able to be configured as 12V (say 4 6V batteries instead of 3 12V), a 12V only charger...etc.
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Advice greatly appreciated for purchasing solar system&sufficient number of batte

    My point on shaded panels was non to clearly written. Everyone knows intuitively not to shade their panels, but not everyone knows the consequences of partial shading. My situation is fairly unique, but I suspect all too common.

    I have six panels, all currently wired in parallel to 12vdc. 4 of these are on the roof, and two are on the front wall. The two on the front wall serve as the "fail safe" panels that never get snow on them, so that if I leave for a while in the winter, there is always enough PV to keep the batteries in float (around 6 amps). These are wired in parallel and share a home run to the controller. It is important to note that one of these panels comes on way earlier in the morning, while the other stays in the sun much longer in the after noon. There is nothing I can do about this situation due to where they are. Ideally, I would wire these for 24 vdc (series) so I could reduce my line loss and increase my mppt head room, but in doing so, I would effectively loose ~2 hours of sun on both panels. So these panels put out ~3 amps for 5 hours each, each day, for a total of 3x2x5=30ah, minus some line loss. Now if I wired them for 24 vdc, each panel would be in the sun for the same 5 hours, but because panel A is shaded from 10 in the morning, but stays lit until 3 = 5 hours, and panel B is lit at 9 but goes dark at 2= 5 hours, the net result would be, the panels wouldn't come near full production until 10am, and then it would drop off at 2, leaving them to produce for only 4 hours. Leaving an effective 3amps x 2 panels x 4 hours =24 ah,(12vdc) minus line loss that would be less than if they were wired for 12vdc. Clearly I would get more harvest wiring them for 12 vdc.

    Now the 6 on the roof present a similar challenge. The roof starts getting sun from the western edge about 9 am, with the eastern edge in full sun by about 11. The sun begins to go off the western edge by about 1, and is off the eastern edge by about 3.
    So each panel begins to come into full sun, long before the next further east panel. There is only a small window from ~11-1 that all 4 panels get full sun, so wiring them in any incarnation other than parallel 12 vdc makes no sense.

    I realize that my insolation numbers are terrible at first glance, but in fact the harvest is pretty good considering the less than ideal location. The reason it works well is that the winter harvest is augmented by considerable reflection off the snow, and cold PV temps. The summer, is helped by the fact that because the sun is so high, that the sun goes off them quite early, but the sun comes on them very early leaving a pretty long harvest. Additionally, the loading is nearly non existent in the summer, as it isn't dark until ~11pm and is light again by 4 am, so there is virtually no lighting load.
    I could build a ground mount rack, ~200' away, but then I would have to send 24-48 vdc a long way adding a bunch more potential failure points all for a few hours more sun in the summer. Really not worth it. What I do, is I have one more panel that moves with the season that plugs in with Anderson connectors in a couple of different locations to give a bit of a boost here and there. Really not needed, but as every one knows, seeing those ammeter numbers makes ones heart jump!

    So to get back to the point, as you are laying out any potential array, consider the effects of even partial shading carefully, as how you wire your Pv can have a huge effect on harvest, even with identical amounts of sun and identical panels.

    Tony
  • CrystalCrystal Solar Expert Posts: 119 ✭✭✭
    Re: Advice greatly appreciated for purchasing solar system&sufficient number of batte

    Fortunately we were able to design our house so that it faces within a few degrees of due south. We have trees on our east and west sides, but none on the south. The sun hits the western part of the south wall around 10am. The south side has full sun (as long as it is shining) until about 4pm. So I don't see any shading issues with our site. We should have good sun for about 5 hours.
    The two on the front wall serve as the "fail safe" panels that never get snow on them, so that if I leave for a while in the winter.

    We are going to mount our panel(s) on our southfacing wall. However, I have not been able to find a mount that will work.
    Does anyone know of one that will work with the Evergreen?
    Could you possibly build one, if they don't manufacture them?

    I am so glad that you are all so helpful...I would be completely lost in this process, otherwise. ;)
  • icarusicarus Solar Expert Posts: 5,400 ✭✭✭✭
    Re: Advice greatly appreciated for purchasing solar system&sufficient number of batte

    My wall mount panels are mounted on hinges. They are hinged at the top with large strap hinges bolted to the frame, the leg of the hinge mounted on the wall. That way I can adjust the angle while I am home, to the proper angle. A simple adjustable prop mounted on the bottom of the panel with a stepped foot on the wall allows me to micro adjust the panels as often as I like.

    When I leave, I simply hinge the panels flat to the wall, held to the wall with a screen door rolling catch. Pretty simple if not very elegant.

    One thing you have to be careful with is flexing or twisting the panels, over stressing the glass or the Pv modules themselves. I don't know why it shouldn't work with larger panels if you are careful.

    Tony

    Ps You do want to be careful with your selection of metals in your fasteners however. Stainless or aluminum rivets/ bolts prevent electrolysis.
  • CrystalCrystal Solar Expert Posts: 119 ✭✭✭
    Re: Advice greatly appreciated for purchasing solar system&sufficient number of batte
    My wall mount panels are mounted on hinges. They are hinged at the top with large strap hinges bolted to the frame, the leg of the hinge mounted on the wall. That way I can adjust the angle while I am home, to the proper angle. A simple adjustable prop mounted on the bottom of the panel with a stepped foot on the wall allows me to micro adjust the panels as often as I like.

    Thanks a bunch on the advice for wall mounted panels. I don't see any reason why this would not work for us too. We are all about "do it yourself" projects.:-)

    Since finding this forum and hearing all the different input, we are considering getting one more 200 watt Evergreen panel. However, there has been some issues with them being in stock. So we might have to go with something else...what would you all suggest?
    Also 2 more batteries would probably be better and a larger amp charge control (or maybe two Morningstar 15 amp MPPT). We have to look into that part more.

    Another question I have is about wiring. We will be wiring from the south side of our house to the back northwest corner to our battery/equipment room. This is a 20 foot run. So what size wire is recommended?

    You are all great!!!
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Advice greatly appreciated for purchasing solar system&sufficient number of batte

    Just a (probably obvious) note about expanding a system.

    You can usually add panels with no trouble, except for the possible need to increase charge controller capacity.

    But you usually can't increase battery bank size without adding more PV and dealing with the whole "old vs. new batteries" issue.

    I have to admit I'm completely lost as to what your existing set-up is, so won't offer any advice beyond that in respects to additional panels/controller/batteries. :blush:
  • CrystalCrystal Solar Expert Posts: 119 ✭✭✭
    Re: Advice greatly appreciated for purchasing solar system&sufficient number of batte

    As of now we don't have any solar set up...just trying to figure it all out before we purchase.
    Here is a rundown of what we may go with, if it will work together:

    2- 200 watt Evergreen panels
    2- 15 amp Morningstar MPPT charge control??? maybe one with more amps
    Samlex 300 watt inverter
    IOTA battery charger 55 amp
    Trimetric 2020 battery moniter +100 amp shunt
    4- T105 batteries 6 volt
  • BB.BB. Super Moderators, Administrators Posts: 30,520 admin
    Re: Advice greatly appreciated for purchasing solar system&sufficient number of batte

    The MorningStar 15 amp MPPT charge controller is a great unit--however, I would probably look at something bigger rather than getting two of those.

    Look at the 30 Amp Rogue unit or the 60 amp Xantrex XW MPPT controller. Outback has been around for years with their MPPT amp units.

    Or, if you can wait a few months (just guessing), MorningStar is supposed to have a new, very nice, mid-range MPPT controller available (just know what I read here).

    Other people will make their suggestions too.

    If you are 400 watts or above with solar panels--you probably should really see if you can justify the 60+ amp MPPT units. They can operate upwards of 140 VDC on the PV panel input--can be a big help if you have a lot of panels and/or a good size distance away from the charge controller (the charge controller should always be mounted near the batteries).

    I don't remember if you decided on a 12 or 24 volt system... Choosing the charge oontroller and the number/configuration of panels will affect your wiring choices to a degree too (sorry, everything is sort of mixed together).

    If you cannot get the same Evergreen panel, any of the major mono/poly crystalline solar panel vendors out there should be fine (shop on price delivered). You do have to pick the right Vmp/Imp match if it will mix with your existing Evergreen (if you already have one). If the panels are in parallel, then Vmp should match within 10% or better. If the panels will be in series, they should match Imp within 10% or less.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: Advice greatly appreciated for purchasing solar system&sufficient number of batte

    The MorningStar TriStar MPPT chargers should be available now, they come in both 45 and 60 amp models
  • hillbillyhillbilly Solar Expert Posts: 334 ✭✭
    Re: Advice greatly appreciated for purchasing solar system&sufficient number of batte

    Crystal on wire sizing, it basically comes down to the amount of amps you have from your solar panels, the distance those amps must travel through the wire run and the the voltage. The higher the voltage the lower the amps get, and thus the lessen the need for larger wire sizing.
    There are two issues that you'd need to address, one is the basic code/safety issue meeting the minimum size so as not to risk overheating the wire and melting the insulation (then you could get a short, and start a fire). I don't have my books right here at the moment, so I can't look that up right now. The second is the voltage drop, keeping the resistance low enough so that you'll not be loosing too much power to friction within the wires (a 2%voltage drop or less is a typical design). Usually sizing your wires to provide for a low voltage drop should meet the minimum code size as well.
    Here are a couple of quick examples on wire size, you can ponder over:
    400w PV array in a parallel configuration (12V array)= I think your panels are roughly 11amps each so thats 22 amps which puts you right around #4 for slightly more than a 2% drop or go with #2 for less than 2%.
    400w array in series (24V)= 11amps would allow for wire sized as small as #10

    (Note these numbers are just rough illustrations on voltage drop, and may or may not pass code)

    Then you might consider sizing the wires for future expansion, as it's much easier to just run larger wires up front. Otherwise you may end up wanting to run a second wire run later on, if it were me I'd stick with one wire run to one controller.

    so lets say you wanted to run an array of 800watts later on down the road:

    800w in parallel 12V configuration= ~44amps thus needing wire size of 1/0

    800w in 24 series/parallel configuration= 22 amps or #6

    800w in 48V series configuration = 11amps or #12

    just to give you some ideas...
    HB
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Advice greatly appreciated for purchasing solar system&sufficient number of batte

    hillbilly,
    anyone who has played around with the voltage drop calculator has probably seen what you described and we here have been generalizing how higher voltages will lessen losses and the wire size needed, but............... your example for a fixed array wattage of 800w does show quite dramatically the impact of what going to a higher voltage can mean on wire sizing. i did not recheck your calculations for accuracy although the general trend is shown quite well and is what i am keying on. those are large differences and many may think that just doubling the voltage will only reap a 2x benefit, but you benefit from the raised voltage (factor of 2) and the halving of the current (another factor of 2) for a 4x benefit overall just through doubling the voltage.
  • hillbillyhillbilly Solar Expert Posts: 334 ✭✭
    Re: Advice greatly appreciated for purchasing solar system&sufficient number of batte

    Thanks Niel,
    I wanted to illustrate that since I know that I personally didn't really grasp the drastic difference in Voltage drop until I went to add a couple more panels to a 12V array. Once I calculated the cost of the new wire that I would have to buy, I considered upping the voltage and thats when the number crunching really opened my own eyes.

    Regarding the accuracy of those calculations; I should just reiterate that those were kind of quick rough math calculations just to point out the effects of voltage drop, and to encourage the idea of going with a bit larger sized wire if there is any desire to possibly add more PV later.

    Crystal,
    If you wish for a more exact answer on wire size, give us all the details once you have made some decisions and I (as well as others I'm sure) would be happy to do a more complete calculation.
  • CrystalCrystal Solar Expert Posts: 119 ✭✭✭
    Re: Advice greatly appreciated for purchasing solar system&sufficient number of batte

    Ok, so here is what we have decided on for a 12 volt system:

    2- Evergreen 200 watt panels
    4- T105 Trojan batteries
    Rouge 30 amp MPPT charge control
    IOTA battery charger 55 amp 12 volt
    Samlex inverter 300 watt
    TriMetric 2020 battery moniter w/ 100 amp shunt
    Hydrometer Brady 10"

    I believe that these components will work out for a small system, however, if anyone see's a problem, please let me know.


    Also, if there is any advice on specific wiring from the proper calculations, that would be very helpful!
    There will be a 20-25 foot run from the panels to the battery room.

    Thanks Again!:D
Sign In or Register to comment.