input voltage

[mmidnnite]

This might be obvious but I'm learning that nothing really is when you start looking into the details.

For a system with 2700W of panels and a 24V battery bank, what is the maximum array open circuit voltage for the Midnite 150? I want to be sure I'm not making a mistake by adding up all the panel's Voc's and comparing them to a 150V input limit which may be an absolute rating or possibly gets derated due to other factors.

Thanks,

~Dan

[Westbranch]

go here for the array sizing tool, you will need much more info than the array size and 24 volt system...

http://www.midnitesolar.com/classic/classicCP.php

EJ

[mmidnnite]

That is a very cool tool; thanks EJ. It let me do everything I thought I could do.

I'm still interested to know how to manually design my system. Just relating to the control's input voltage, I've read that you want to add up the Voc's on one string and make sure the controller can handle that.

Is that right and is the input voltage of the 150 actually 150V?

[Vic]

Hi m...,

This if from the FAQs on this site:
http://midnitesolar.com/smf_forum/index.php?topic=109.0

The Classic 150 has a Maximum Operating input voltage of 150 volts,  but will simply suspend opertion above that voltage.  BUT the input voltage should not exceed,  in your case 150 volts plus the nominal battery bank voltage.

To dertrmine tha Max VOC of the strings of your exact panels,  use the Voc compensation value from the panel data sheet,  applying this to the Lowest Recorded Temperature for your location.

Breifly,  that is it.  Vic

[mmidnnite]

Thanks Vic. That is helpful. However, I am unable to find the temperature correction factor on the panel I'm looking at: http://www.sunelec.com/sv-solar-panel-205-watts-1840-vmp-p-1649.html

Do you know if these coefficients vary greatly or is there a ballpark figure that can be used as a general guide? I'm guessing this determination does not take into account wire loss.

~Dan

[Vic]

Well, Dan, I do not see it listed.  This info is important,  and the manufacturer needs to spec it.
The Simulator that you ran is good enugh,  if you have reasonably correct lowest temperature data for the site where the panels will be installed.

For kicks,  you could use data from a mainstream name brand panel (is this too harsh?),  and compare your results from an manual calc,  vs  what you ger from the MN simulator.

And,  yes,  this data is under Open Circuit conditions (no current flowing),  so voltage drop in the wire is not a factor.

More later,  Good Luck,  Vic

[mmidnnite]

LOL, Vic. What do you think of such a cheap guy buying discount panels but shoeing out the moola for a high quality controller? So far this project's price tag is more than I can swallow right now but I'm counting the cost before I get into it and doing what I consider the hard part now, that is figuring it all out. The installation ought to be the fun part. I'm almost finished with a project report on this and if you're interested in looking at it (it's only 6 or 7 pages), PM me with your e-addy and I'll send you my analysis. I'd love to have someone with experience poke holes in it and challenge my thinking. The only folks I know who use solar could only tell me that the numbers won't add up and it seemed like I'd be getting into a never-ending project. That was unacceptable to me, to start the job without knowing where the ceiling was and potentially find out that I might not be able to finish it, so I've spent the week researching, testing and evaluating. Having no prior experience with solar, I've done my best to corral available data to spit out a bottom line, about $7k for my requirement. Anyway, thanks for your input. I continue to be impressed with Midnite, this site, the available tools here as well as the support.

~Dan

[Westbranch]

this site appears to have the details you need, assuming that they are the same panel sold in England under a different name.

http://www.gil-lec.co.uk/products/Solar+Photovoltaic+Systems/Solar+PV+Modules/Sovello+205Wp+Polycrystalline+Module/3116530807

ej

[mmidnnite]

Thanks, EJ. That is awesome; I am very happy to have those specs.

I tried to come up with the maximum Voc using several formulas found online and either I was not using them correctly or they are just the wrong formulas. The closest I could get using one of the formulas was an increase of 2V from the rated 23Voc; does that sound feasible?

~Dan

[Westbranch]

what temp. were you using to get that change?

ej

[Vic]

Hi Dan,

2 V per panel may not be far off.

You need to determine your lowest recorded temp,  convert this to degrees C.  The TempCo for this panel from the data sheer is Negetive 0.33 percent per degree C.  So let's say that your lowest temp recorded for your location is negetive 10 C.  This is 35 C lower than the STC Voc -- which it determined at 25 degrees C (77 F).  Multiply 35 times 0.33,  which is 11.55 percent,  or 0.1155.  Multiply the STC Voc, 23.0.  This gives 2.66 Volts,  which needs to be added to the 23.0 Voc,  or 25.66 V.  This is the Voc at minus 10 C.  Multiply this 25.66 times the number of panels per string,  and that would be the Voc Max for your system -- the Max Vin to the CC.

Your Max low is prob different than my example neg 10 C.  You get the idea.

Vic

[mmidnnite]

Yup, no, that's exactly what I did. I think the "research" on a formula just complicated things. My low is 30°F and I finally had done it just as you laid out and that's where I came up with 1.98 Voc increase per panel. So I just wanted to make sure that the answer I chose was the correct one and not just the one I liked the most. Thanks.

[mmidnnite]

Wake up, Dan! I just realized that a winter low temperature really has nothing to do with the panel temperature correction. The low occurs at 4am when the sun is still sleeping. It's the low temperature during daylight that should be used, right? For a stationary (non-tracking) panel, I estimate that it would be like the lowest 9am temperature when the sun is still some angle away from direct incidence to be on the safe side. In that case, I'm looking at probably 50°F for a low in sunny southern California, giving my panel slightly over just one more volt on STC Voc. Thanks for the input helping me to figure that out.

Now I'm just trying to figure out the array arrangement: http://midnitesolar.com/smf_forum/index.php?topic=239.msg1514#msg1514

[Westbranch]

GOOD MORNING Dan,....said like Robin Williams said in the film...

  welcome to the solar learning curve,  it will start to get easier .... soon

ej

[mmidnnite]

Thanks EJ!