Panel choices and Theory

stmar
stmar Solar Expert Posts: 373 ✭✭✭
in General Solar Power Topics #1
What do I need to check/look out for/consider if I want to add panels to my array? I have 12 X 64 watt Solarex panels that are over 15 years old and don't know what the limitations for expanding it would be or if I even need to. Do people actually make their own panels? A guy was telling me he was going to try it but it seems fairly complicated and where would you buy the components at prices that would make the labor worth it?
· Share on Twitter

Comments

  • AuricTech
    AuricTech Solar Expert Posts: 140 ✭✭
    #2
    Re: Panel choices and Theory

    Can your system's charge controller handle more input?
    · Share on Twitter
  • waynefromnscanada
    waynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    #3
    Re: Panel choices and Theory

    What is the Max Power voltage and amperage of your panels? What voltage is your battery bank?
    15 years ago you would have paid dearly for these panels compared to panel prices of today.
    You could well be further ahead to sell the ones you now have and start over with new higher wattage panels and a MPPT controller.
    When I look back at what I paid for my first panels, and compare it with today's prices, I almost cry.
    · Share on Twitter
  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #4
    Re: Panel choices and Theory

    24 volt battery bank, will have to check max of panels.

    I have a Morningstar Prostar 30 controller and it never gets close to 30 amps, the highest I have seen it is 15 amps on a sunny day, usually on a normal day it is about 10 amps or so.
    AuricTech wrote: »
    Can your system's charge controller handle more input?
    · Share on Twitter
  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #5
    Re: Panel choices and Theory
    stmar wrote: »
    Do people actually make their own panels? A guy was telling me he was going to try it but it seems fairly complicated and where would you buy the components at prices that would make the labor worth it?

    The major problem with DIY is that the cells you get on the open market are the ones that don't pass the flash test, or have some other flaw. Online vendors may *claim* they are "grade-A", but there is no law regulating that, so you can call them whatever you want. Cells that pass tests are sold and kept for manufacturers.

    Cells that don't pass these tests, get pawned off on hobbiests. If I were selling flawed cells, I'd call them "Grade-A+++". Just because a cell may put out the required voltage, does not mean it passed all the *other* critical tests.

    The other problem is moisture ingress, which destroys cells. But it doesn't destroy them immediately if reasonable care has been taken with materials, but still, no hobbiest has the machining skills and tools to do it right. (Although some come close). This only delays the inevitable degradation sooner or later after the panel has initially been declared a success, and videos posted. Followup videos 6 months to a year afterwards are rare, and for good reason. :)

    In reality, making your own panel can be a fun science project, but not so much for real-world use. To top it off, if it burns your house down, you have no recourse whatsoever, and they certainly won't pass any inspection.
    · Share on Twitter
  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #6
    Re: Panel choices and Theory

    That is an eye opener, so much for DIY, lol. In that case what are some good brands/values/vendors to look at? I don't even know if I need them but would like to explore the possibility of expanding my array.
    · Share on Twitter
  • PNjunction
    PNjunction Solar Expert Posts: 762 ✭✭✭
    #7
    Re: Panel choices and Theory

    Kyocera and Sharp are two that I like. Our host (NAWS) has a nice selection.

    Without knowing needs beforehand, it makes it hard to recommend between just starting over, or doing a *limited* increase by picking up the same controller, some new panels, and wiring the two controllers to the common battery bank. Using the same controller will minimize the "fighting". Same setup (but not necessarily the same capacity) as the original system of course.

    That would be my KISS / cheap way to go before a total redesign. I wouldn't spend too much on that however, without knowing the actual increase in load requirements.

    Your lifeline agm's won't mind the increase (within reason, and specs for maximum inrush current of course).
    · Share on Twitter
  • Photowhit
    Photowhit Solar Expert Posts: 6,006 ✭✭✭✭✭
    #8
    Re: Panel choices and Theory

    Without direct linking, Solar blvd and Sunelec (easy google searches) tend to deal in close out, manufacturers 2nds(often UL rated) and inexpensive panels for assorted reason, recently had panels from the first large China company that is being allowed to fail...

    These are wholesalers who aren't trying to help you setup a system, but are typically the lowest price per watt. So buyer beware, I've purchased panels 2x from Sunelec and cables from Solar blvd and had reasonable service and product from each. I checked the cables and they were soldered, but I was purchasing for the lease expensive price for 50' cables and put my own ends on(solder alone is not up to NEC code as far as I know) Panels were 'blems' with full warranty, once US made Evergreen, once Evergreen China panels when they were about to be dissolved. They did get purchased by a China Company who appear to be supporting them but the Web site has been static for a while(I didn't check today). ToSUnelec's credit they did replace a panel broken in shipping at their expense, even though they were purchased FOB Miami!
    Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
    - Assorted other systems, pieces and to many panels in the closet to not do more projects.
    · Share on Twitter
  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #9
    Re: Panel choices and Theory

    Thanks for the info. My cabling to the array is substantial, a lot larger than needed, so I assume that the limiting factor is my controller. Can I add panels to my existing array up to my controller's limit? Since my panels are only 64 watts is there an issue with adding higher watt panels? Trying to keep from going down any rabbit holes as I research.
    · Share on Twitter
  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #10
    Re: Panel choices and Theory

    You can add panels to an existing array... But you need to follow a few rules.

    First, you need to decide if you are going to keep your present controller. PWM vs MPPT. As the arrays get larger, there are usually good reasons to go with a larger MPPT controller (very roughly, under a 400 watt array, PWM is usually most cost effective--For an array >~800 watts, MPPT starts to look better).

    When adding panels, you have to mix/match the old panels with the new panels if want to add them to the existing controller. If you just keep your old array+controller, and then add a second parallel charge controller--You simply design the new charging system as works out best for you ("cheap" Vmp>>18 volt panels+expensive MPPT controller; or "expensive" Vmp~175/35 volt panels + cheap PWM controller).

    In general, you need to mix/match panels so that--If panels are added in series, the Imp matches to 10% or better (i.e., one panel at 5.0 amp, the second at 5.5 amps Imp).

    Similar for placing panels in parallel, Vmp should match within 10% or better (i.e., 35 volt Vmp + 38 volt Vmp in parallel).

    If the panels are "too far apart", you will have lower performance and can have damage (depending on what is done/how far apart).

    Your panels?:

    https://www.smud.org/en/about-smud/environment/renewable-energy/documents/solar-regatta-photovoltaic-specs.pdf
    Typical Electrical Characteristics
    MSX-64
    Maximum power (Pmax) 64W
    Voltage @ Pmax (Vmp) 17.5V
    Current @ Pmax (Imp) 3.66A
    Guaranteed minimum Pmax 62W
    Short-circuit current (Isc) 4.0A
    Open-circuit voltage (Voc) 21.3V

    If you are still getting ~15 amps from them and they look in good shape--You do not lose much by keeping them and getting ~140 Watt Vmp~17.5 volt panels (or Vmp~35 volt) panels in series/parallel with them.

    However, if you are going to enlarge your array significantly, then you should, at the very least consider using GT Solar panels (typical Vmp~30 volts) with a MPPT charge controller (run array at ~60 to 90 VDC Vmp)... Panels will be cheaper per Watt, less wiring/panels to mount (250 watt panels vs 140 watt panels), and smaller diameter wire/longer runs possible from array to charge controller+battery shed.

    For your battery bank (24 volt @ 400 AH?), the typical array with 5-13% rate of charge:

    400 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 375 Watt minimum array
    400 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 753 Watt nominal array
    400 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 979 Watt "cost effective" maximum array

    You have 12*64 watt = 768 Watt array -- Already a pretty good sized array for your AGM battery bank... Are you going to install a larger battery bank at some point?

    Your 4,000 Watt AC inverter could work very nicely with an 800 AH @ 24 volt battery bank very nicely (this would be the minimum recommended flooded cell battery bank AH capacity--AGMs support better surge).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
    · Share on Twitter
  • stmar
    stmar Solar Expert Posts: 373 ✭✭✭
    #11
    Re: Panel choices and Theory

    At this point I will probably keep the 400ah bank and not add to it. I was trying to find out if I really needed to expand my array and I think I have the answer. If it was just a matter of buying a couple of panels and wiring them into the existing system I would do it, but it looks like there are more factors to consider. It is good to know that my inverter will take more capacity if I do decide to expand the bank and array. Thanks for the input.
    · Share on Twitter

Categories