Evergreen Panels listed as 18V not 24V Why?

May 15, 2008 10:49 pm
Evergreen Panels listed as 18V not 24V Why?

These panels are really 24 Volts.  Why are they listed in the store as 18v?

thanks

578 Posts
May 16, 2008 09:57 am
Re: Evergreen Panels listed as 18V not 24V Why?

because these modules are not really 24 volts nominal

compare the VOC, VMP, and cell count to that of a 24v nominal module, and the difference is apparent.

james
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May 16, 2008 03:12 pm
Re: Evergreen Panels listed as 18V not 24V Why?

Hmm... now I'm confused..  I guess what does "nominal" really mean??  Is that the actual output voltage I'm going to see in real life?

This will really mess up my voltage drop calculations if that's true.  I have a 80ft run between my panel and my MPPT charge controller..  I thought I would get about 24v out of the panel during peak sun.  If I'm only going to get 18v that is a big difference.

Maybe we are just talking semantics/terminology here because the calculations don't make sense with 18v.
Evergreen ES-170:
18v x 6.72a = 120.96 Watts  vs. 25.3v x 6.72 = 170.016 Watts

I guess the "nominal" term makes sense looking at my controller capacity.  If the Evergreen was 24v Nominal, I would never be able to use 2 panels since I would exceed the 36v max input.  If it's 18v I can run 2 in series and not exceed any spec (as long as I have 24v battery).

Morningstar SunSaver MPPT:
Max Voc: 75v
36v PV Nominal Max
Nominal Max Input Power (solar array)
with 12v battery - 200 watts
with 24v battery - 400 watts

52 Posts
May 16, 2008 05:01 pm
Re: Evergreen Panels listed as 18V not 24V Why?

This is from the Learn section of our site:

http://howto.altenergystore.com/Getting-Started-with-Renewable-Energy/Introduction-to-Solar-Electricity/a89/p4/

"PV modules have three different voltage ratings that it’s handy to understand. The Nominal voltage of a panel could also be called the “conversational voltage.” When we talk about the voltage of the panels and the other components of the system, we’ll most often use the nominal voltage. Nominal voltage actually refers to the voltage of the battery that the module is best suited to charge; this is a leftover term from the days when solar panels were used only to charge batteries. The actual voltage output of the panel changes as lighting and temperature conditions change, so there’s never one specific voltage at which the panel operates. Nominal voltage allows us, at a glance, to make sure the panel is compatible with a given system. The second voltage rating is the maximum power voltage (Vmp). This is the highest voltage the panel can produce while connected to a system and operating at peak efficiency. The third voltage is open circuit voltage (Voc). This is the maximum voltage that the panel can produce when not connected to an electrical circuit or system. Voc can be measured with a meter directly contacting the panel’s terminals or the ends of its built-in cables."

The Morningstar SunSaver MPPT specs are saying that the max Voc it can handle as an input is 75v and the max nominal PV input is 36v. So long as your charging a 24v battery bank you can connect two Evergreen ES panels wired in series into the controller.

When I'm doing voltage drop calculations I use Vmp for voltage.

May 16, 2008 05:37 pm
Re: Evergreen Panels listed as 18V not 24V Why?

Thanks!  That does make perfect sense.  I should spend more time in the "learn" section

Seems like "nominal" is pretty obsolete these days.  I tend to always reference Vmp.

Glad to know I was on track using the Vmp for my voltage drop calculations!

578 Posts
May 16, 2008 07:00 pm
Re: Evergreen Panels listed as 18V not 24V Why?

nominal is not obsolete, look at the sizing guidelines for your controller. it says nominal right in there.  nominal is everywhere in off grid systems.  understanding the relationship between nominal voltage, vmp, voc, and number of cells (for crystalline modules) is what is important.  once you understand you can design using whatever components you want as long as they fit the parameters of your situation.

this thread started with the proclamation that those evergreen were really 24v moudles.  hopefully we both understand now that two of those in parallel would likely not work out so well on a 24v nominal system.

james
Alt-E staff

AltE
"Making Renewable Do-able"
http://www.altEstore.com/

Tel: 877.878.4060 x107  or +1.978.562.5858 x107
Fax: 877.242.6718  or +1.978.562.5854

May 16, 2008 11:22 pm
Re: Evergreen Panels listed as 18V not 24V Why?

I do understand now, thank you.

I realize now what was throwing me off. In the SunSaver MPPT manual it says on p.18:
"The SunSaver MPPT can accept 12v, 24v, or 36v nominal off-grid solar module arrays."

I think when I read this, 24v was stuck in my head.  It didn't occur to me that an odd nominal voltage between 12v & 24v existed.

Knowing the Evergreens are 18v nominal, I understand 2 wired in parallel would produce an 18v nominal array.  That won't work for a 24v system.  But 2 wired in series would produce a 36v nominal array, which would be fine for a 24v system.

One Final question on "Nominal" voltages.  How do you determine what a panel's nominal voltage is?  For example, the high wattage Sanyo panels have Vmp in the range of 52-56v.  Nowhere in the spec sheets does it mention its nominal voltage.  If it wasn't listed in the altestore "basic stats" of the panel, I would never know it's a 42v panel.  I might have guessed it to be 48v nominal.

Thanks for the education!

578 Posts
May 19, 2008 11:29 am
Re: Evergreen Panels listed as 18V not 24V Why?

well for the 18v crowd, essentially we know how many volts per cell, which makes for standard cells per module numbers.
12v have 36 cells, 24v have 72 cells, and 18v serves as a catch-all for everything in between although most will have 48-54 cells.  the evergreen i believe has 108, a multiple of 54.

for outliers, like sanyo, it is important to remember that nominal is a distinction based on batteries.  most modules nowadays go to grid tie, so batteries are irrelevant.  the sanyo has no real "nominal" voltage because it was never meant for battery charging, and does not tuck in nicely to a category based on voltages or cells.  that being said you can use them for battery charging, but open format mppt controllers must be used.

if 12v modules run at 17v, then 24v modules run at 34, and 36v nominal (if they existed, or two 18v in series) would run at 51v, then 48v modules (or strings to make 48) would run at 68v.

being that the sanyo runs at 55v at stc, it is above 36v nominal, but below 48.  the 42 number we put on there serves mainly as a warning to those attempting to charge 48v battery banks on a sanyo module that will only get to 55v before temp deration and likely not be successful in charging a battery bank at 48v, especially in warm climates where temps draw voltage down.  the other side is that two of those modules in series in a cold climate will come very close to destroying mppt controllers with max vdc of 150.

good questions, some folks get turned off by this stuff, but i think the more you know, the more fun the system design is, and the more options you have open to you because of that understanding.

cheers,

james
Alt-E staff

AltE
"Making Renewable Do-able"
http://www.altEstore.com/

Tel: 877.878.4060 x107  or +1.978.562.5858 x107
Fax: 877.242.6718  or +1.978.562.5854
« Last Edit: May 28, 2009 02:56 pm by James Cormican »

May 20, 2008 11:49 am
Re: Evergreen Panels listed as 18V not 24V Why?

Thank you for the detailed response!  This all makes much more sense now.  I agree, knowledge can't hurt you    It can only help to make better decisions moving forward!

thanks again!

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