Prices are dropping, panel sizes increasing; What do I consider with new panels?

foolios
foolios Solar Expert Posts: 53 ✭✭
edited October 2016 in Solar Beginners Corner #1
It's been 2 years since I bought my panels.
Now panels are cheaper and supply more wattage.
I want to add more panels and see some really good deals for panels that produce more.
I have 12v panels in series for a 24v system. Which makes this confusing for me to match up the specs.
This is the 12v spec:
Specifications for Renogy 12v 100 Watt Panel 
Maximum Power: 100W 
Maximum System Voltage: 600V DC (UL) 
Optimum Operating Voltage (Vmp): 18.9V 
Optimum Operating Voltage (Vmp): 18.9V 
Open-Circuit Voltage (Voc): 22.5V 
Short-Circuit Current (Isc): 5.75A 
Dimensions: 47 X 21.3 X 1.4 In 
Weight: 16.5lbs 
https://www.amazon.com/RENOGY%C2%AE-Monocrystalline-Photovoltaic-Battery-Charging/dp/B009Z6CW7O/ref=cm_cd_al_qh_dp_t?th=1

But I don't know how to relate this to the 24v spec since I have these strung together.

Here is a new Renogy 260 Watt Panel that is already 24v:
Voc 37.6v
Vmp 30.4v
https://www.renogy.com/renogy-260-watt-24-volt-monocrystalline-solar-panel/

I was gonna assume I could just use a 24v panel in my 24v system, but looking at the specs between various watt sizes of panels shows me that the Voc and the Vmp differs between them. So I am rethinking there's more to matching the panels than I guessed.

Will these work together nicely?

Here are some Polycrystalline's that I want to consider:
Can Mono and Poly be mixed? Just gotta make sure Cell size is the same?
https://www.renogy.com/renogy-270-watt-24-volt-polycrystalline-solar-panel/

https://www.renogy.com/renogy-310-watt-24-volt-polycrystalline-solar-panel/

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Comments

  • BB.
    BB. Super Moderators, Administrators Posts: 33,642 admin
    #2
    Yea--You see the issue... You really need Vmp~36 volts (72 cell panel) for a PWM charge controller on a 24 volt lead acid battery bank.

    A Vmp~30 volt panel (60 cell) just is not going to cut it.

    Your standard choice is to pay more for Vmp~18 volt panels (typically around 140 Watts or smaller) and add them to your existing array (and PWM charge controller).

    Or, buy the Vmp~30 volt panels, and put 3 in series with a MPPT charge controller (cheaper panels, more expensive MPPT charge controller). Also the larger format solar panels may cost more to ship and can limit you to truck (vs UPS, bus, etc.).

    Nominally, 60 Cell mono and poly panels can fit together--Match panels in series (Imp ~ 10% or better match). And match parallel panel strings to Vmp-array within 10%.

    You can parallel the two solar charge controllers to one battery bank (controllers should be set to about the same voltage set point, but they will not be in "sync" i.e, from bulk to absorb to float--But that does not really matter--they do not have to be in sync. The one with the highest voltage set point will "win").

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • Raj174
    Raj174 Solar Expert Posts: 795 ✭✭✭✭
    #3
    The Renogy 300 watt panel would be the best match for your setup, with a VMP of 37.46. The only problem is that a minimum purchase of 2 is required because they have to be shipped by freight truck, and that is about 200 dollars extra. I know because I bought 12 of them. The more you buy, the less you pay for shipping per panel.


    4480W PV, MNE175DR-TR, MN Classic 150, Outback Radian GS4048A, Mate3, 51.2V 360AH nominal LiFePO4, Kohler Pro 5.2E genset.
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