Should my 24v panels be wired in series or parallel (only 30v vmp)

Hi guys, I have 2 24v panels 230w each with a vmp of 30v

I have a PWM controller and 4 12v batteries set up as 2 24v.

I know the PWM is not ideal with these panels (with the low vmp) but it just for a cottage and we do not have a large demand for the power.

I have the 2 panels currently wired in series currently. What type of difference will I experience if I wire them in Parallel?

Whats best?

Thanks everyone

Comments

  • VicVic Solar Expert Posts: 2,970 ✭✭✭✭
    Re: Should my 24v panels be wired in series or parallel (only 30v vmp)

    Hi Darryl,

    As you alluded to, these 60 cell PVs are not 24 V PV. A real 24 V module would have a Vmp of 35.5-ish volts or a bit more. So, you have no real choice but to wire the PVs in series.

    Ye, the PWM CC will not make maximum use of the total power available as would an MPPT CC. Your maximum charge current into the battery will be limited to about 75% if the rated Imp of these PVs (under the best possible solar conditions). AND your existing PWM CC will need to be able to withstand the lowest recorded temperature-compensated Voc, and also be able to dissipate the wasted energy -- the difference between the PV output voltage vs battery voltage for the current that is produced by the modules for the given illumination/temperature of the PVs at that particular time.

    All of this may well be perfectly fine with the CC, but some might not like the Voc and the power dissipated, and so on, Vic
    Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH [email protected], 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  25 KVA Polyphase Kubota diesel,  Honda Eu6500isa,  Eu3000is-es, Eu2000,  Eu1000 gensets.  Thanks Wind-Sun for this great Forum.
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: Should my 24v panels be wired in series or parallel (only 30v vmp)

    If wired in parallel the Vmp for the array will be the same as the panel: 30.
    Heat and wiring loss may cause the actual Voltage output to be too low to properly charge the 24 Volt batteries (normally around 28.8 Volts for Absorb). Thus the batteries may never get completely charged.

    Putting two in series solves this problem by raising the array Voltage to 60 (2X 30 Vmp) but at the expense of most of the second panel's power.

    The Imp of these panels is approximately 7.6, so by putting two in series you will get them to work about the same as a panel with specs of 7.6 Imp & 35 Vmp or 266 Watts, rather than the combined power of (2 * 230) 460 Watts. It's like wasting 194 Watts.

    Hence the value of MPPT type charge controllers.
  • darrylgooddarrylgood Solar Expert Posts: 25
    Re: Should my 24v panels be wired in series or parallel (only 30v vmp)

    Thanks so much guys, very clear now.
  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Should my 24v panels be wired in series or parallel (only 30v vmp)

    For 24 volt PWM, You can always use 72 or 80 cell panels. They will usually be 280+ watt panels (80-cell 300+ watt). 72 cell runs 35-36 Vmp, 80 cell runs 39-40 Vmp. If in hot AZ weather you should use 80-cell. 72-cell will work in cooler weather.
  • YehoshuaAgapaoYehoshuaAgapao Solar Expert Posts: 280 ✭✭
    Re: Should my 24v panels be wired in series or parallel (only 30v vmp)

    If you got the $$$, I would go for 150V MPPT, 48 volt battery bank, and strings of 3 60-cell (very common). 60 amp MPPT will take 4 strings (maybe 5 strings at sub-optimal mounting or with 225W panels) at 48 V or 2 strings at 24V or just 1 string at 12V. 80-amp MPPT will take up to 5 strings up to 260W panels (about the max for 60-cell panels). Xantrex 600-80 MPPT will take up to 14 60-cell panels in a single series string (A grid-tie string). THe 600V charge controllers have 2.5x the cost of a 150V charge controller and only have 33% more capacity.
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