Resizing my PV system

Vic

Re: Resizing my PV system

gpspowell wrote: »

ARGGGG! Eighteen months of living with this system and I am still WAY behind the learning curve. Vic: The link doesn't work but I found the sizing calculator you recommended and the results are a bit tight. As to the panels: The string amps are nearly the same; The existing panels are ET 250s and the new ones are their replacement models (ET 255s). I'm not sure about your question re: cold temp VOC, the calculator says I will enter "Hyper VOC" at -104.8ºF. The panels will be configured into 4 strings of 4. The calculator concludes that I need 1.1 CCs (their recommendation is that a second CC is required at 1.2). Okay, it looks like I'm pushing it unless I add a second CC. I don't want to be pushing so hard as to burn up components. I guess I dig out the checkbook again.

Hi gpspowell,

Thanks for the added info.

Yea, do not know where I got the bad Voc data for the PVs that had thought you were using ... I had the string Voc at 150 V with STC -- 25 degree C temps. This is way off for the 60-cell PVs that you appear to be using. May have just entered the wrong data into the Sizer. Sorry that that link did not work for you ... it still works for me, when clicking it in that post.

Your CC may not be as taxed as it would be if it were a pure off-grid system, where almost every day, the CC is expected to do 100% of the battery charging, as you do have the grid for a backup. Still, Classics do rely on fans for cooling, and the Cl 200 and 250s operate a bit less efficiently as the Cl 150, when operating at elevated string voltages (for which they were designed). When your system is in the later stages of Absorb, and in Float, the Vin rises. This further reduces the CC efficiency, and the CC might run hotter than when it is delivering its maximum current. And two CCs will dissipate the heat much better than will one, and so on. So, if you can afford it, a second CC will help.

You are on the edge of the capabilities of the Classic. Had a similar decision to make on a system design, and decided to add a second Classic instead of running one near 100% for at least part of the charge cycles.

Most MPPT CCs do limit output current to protect themselves from excessive heating - the Classic certainly does, but this limiting will reduce the power harvest when it is active. With two Classics, they have the Follow Me, which will cause each to be in the same charge stage, which is a nice feature. Paralleled CCs usually do not always contribute fairly equally when they are in a voltage regulating stage, like Absorb and EQ (or even Float for that matter). But one can usually set the voltage for that stage slightly differently in one CC to allow for better sharing of current, or set the offset a bit differently in one vs the other. Perhaps you can try adding the 8 new PVs and see how the single Classic likes it. But perhaps think about how you will add a second CC at this time.

Yes PVs are usually a family of power out ratings for a given number of cells and frame dimensions. Almost all PVs are 100% Flash Tested after manufacture, and they are "Binned" into different power levels. Usually, as production processes improve, the output levels increase, and therefore somewhat higher output PVs are the bulk of the production.

FWIW, Opinions, Good Luck, Vic

BB.

Re: Resizing my PV system

Be conservative when doing your solar design.

Most of our expertise is with appliances that run at low power with the occasional surge current.

Solar panels and wind turbines can run at full power for hours at a time. Much more heat and stress. Better cooling (fans in area, don't put equipment in small closet, etc.) all helps.

-Bill

softdown

Re: Resizing my PV system

I think these panels started at 180 watts. Then became 185 watt. Now called 190 watt. Which perfectly fits what you are saying.

Vic wrote: »

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Yes PVs are usually a family of power out ratings for a given number of cells and frame dimensions. Almost all PVs are 100% Flash Tested after manufacture, and they are "Binned" into different power levels. Usually, as production processes improve, the output levels increase, and therefore somewhat higher output PVs are the bulk of the production.

FWIW, Opinions, Good Luck, Vic

gpspowell

Re: Resizing my PV system

gww1: The voc of my panels (each) is 37.47

It appears I need to read up on the management of parallel charge controllers and bite the bullet. I don't particularly want to overkill this design but I for sure don't want to "over" kill the components either. I "get" that heat & electronics aren't good partners.

gww1

Re: Resizing my PV system

gps
I believe you would probly be ok but I also believe there is a great comfort in over building and the freedom this gives you for adjusting your system further after you have used it for a bit. I doubt you will be sorry and now that the decision is made you are one step closer to being where you want to be. IE: done and using it.
Good luck
gww