Author Topic: Oversizing PV for Classic  (Read 264 times)

bldr

  • Newby
  • *
  • Posts: 6
Oversizing PV for Classic
« on: April 12, 2019, 05:13:10 PM »
How far over the recommended sizing can a Classic be taken?

What I am currently planning is:
4x335w panels 2s2p into a Classic 150 - feeding the side BMS of my 12v200ah lithium setup

While the sizing tools gives this as an "OK 1.0" I am wondering if this will really be enough panel capacity.

This will be on a boat (freshwater) so the array will likely face shading and an almost guaranteed sub-optimal position. Exacerbating this is that I am around 39.5N meaning full sun is certainly not the level of illumination used to arrive at my panel's ratings. I am sure there will be any amount of efficiency lost do to the DIY/newbie-ness of the installation as well.

When trying to assess power demand and charging opportunity/need I looked at the measured solar radiation data from a nearby weather station (couple of years @ 15 minute intervals). Getting above 900 w/m2 is extremely rare and fleeting (peak of summer less than an hour per day at that), much of the shoulder seasons I would be looking at solar radiation peaking in the low 700 w/m2 neighborhood. Is it safe to assume when solar radiation is 700 w/m2 I would really only be looking at 70% of my rated panel output (less additional efficiency losses, etc.).

Would it make sense to consider finding the space to add another string or two?
6x335w panels 2s3p or 8x335w panels 2s4p
The sizing tool gives this an "EXCESSIVE 1.5 / 2.0", but wouldn't that really only be during peak summer days?


Would a setup like that be dangerous during peak summer sun? If that is the case could I just flip breakers to get back to 2s2p and run 6 panels not in summer?

Interested in thoughts.

-Jordan


Vic

  • Hero Member
  • *****
  • Posts: 2105
Re: Oversizing PV for Classic
« Reply #1 on: April 12, 2019, 06:23:15 PM »
Hi bldr,   Welcome to the Forum.

Due to probable Shading of your PVs,  would suggest that you run all PVs in parallel "Strings of one",  if you will.

For a 12 V system,  you do not need to use series PVs,   and the Classic will run a bit cooler at a lower input voltage from parallel connections of the PVs.

Personally,  would use the Sizing Tool as a guide,   and keep below its "Excessive" label on your PV power.

Do not know the exact PVs that you are considering,    but most PVs in the 335 W class are 72 Cells,  with Vmps 36.5-ish to a  bit above 38 V.   This is plenty of headroom for a 12 V system.

FWIW,    Vic
Off Grid - Two systems -- 4 SW+ 5548s, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 3X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes.  Thanks MN for Great Products/Service/Support!

Ron Swanson

  • Jr. Member
  • **
  • Posts: 79
Re: Oversizing PV for Classic
« Reply #2 on: April 12, 2019, 06:45:27 PM »
Agreed, if you have spotty shading you want to run either everything in series or everything in parallel, and agreed about the lesser heating of the Classic.

Do not hesitate to use the 1.2 that Midnite allows you.  Nothing ever works at full specs.  And the controller will just cut itself back if it is really over-paneled.  And I suspect these will not be fully facing the sun either.

Remember on a hot summer day the panels performance really declines.  Cold days are when things get more dicey.

I would go for 6 panels if you can.  You can always drop one panel from the array if it is so far over-paneled by experience, and then it will be there for your use in winter when the sun is low.

bldr

  • Newby
  • *
  • Posts: 6
Re: Oversizing PV for Classic
« Reply #3 on: April 12, 2019, 07:03:33 PM »
Thanks Vic & Ron.

Vic you nailed it on the panels: 72 cell panels w/ VMP 37.26 (Astronergy CHSM6612P)

Planning to run 2s2p is due to a lack of understanding on my part about keeping voltages down relative to the charge voltage (and already running wire).  I will definitely look at the 1s4p wiring and if I can make it happen.
With a ~50ft run my most likely scenario would be to run two parallel sets, and combine again at my charger since I already have 6awg in place and would be more likely to run another 6awg set vs removing what I already have run and replacing it with #2 or worse wiring. Given space constraints and the difficulties of wiring the boat I am not totally sure I can get more conductors run up there at this point in order to run 4 parallel. How big a deal would that be?
I expect shading on my initial 4 panels to probably be pretty consistent, probably not spotty - all four are up front in the same orientation. Just more likely that the sun will be up, but I will have terrain shading me, limiting my total sun hours either making recovery in the morning slow, or cutting off charging input earlier in the evening right as loads will really start to pick up.


Ron: What do you think about going above the 1.2 sizing- six panels would be 1.5 in lab conditions, but probably pretty far from real world. Summer temps will regularly be high 90s to low 100F probably peaking around 104F. As far as cold days, maybe 3-4 a year (barely) below 32F, hyperVOC calculated out at like -250F so probably safe there.



Really appreciate the thoughts/help. This stuff is complicated.


Edit: Panels will be mounted flat on a roof.
« Last Edit: April 12, 2019, 07:13:47 PM by bldr »

Ron Swanson

  • Jr. Member
  • **
  • Posts: 79
Re: Oversizing PV for Classic
« Reply #4 on: April 12, 2019, 09:19:09 PM »
Just that experience tells me they never perform all the way up to nameplate even when angled to the sun.  80% is a good figure.

When flat they are going to be even lower performing.

And if the input to the unit goes over rating, it can throttle itself back just like when the batteries are approaching full.

The recommendation for all parallel is because if you shade little parts of an array that is series/parallel the output really falls off for the whole array.  If it is all series or all parallel the loss is a lot more in line with the amount of shading, less interactions.

Resthome

  • Hero Member
  • *****
  • Posts: 1140
Re: Oversizing PV for Classic
« Reply #5 on: April 12, 2019, 11:59:43 PM »
Ron’s correct, you typically get 80-85% of the manufacturers rating.

Your temps are similar to mine and once you hit 90 the temp on the panels are a lot higher and output drops.

Also really think about voltage drop in you 6g wire running 50ft. For DC you have to double that distance to calculate voltage drop. West Marine has a good chart for different gauge wire and distance.  I’m 20ft from my combiner to controller with 4g marine wire that is a little larger that standard 4g and I still get about 0.8v drop.

Your battery bank at 200ah seems like you plan on a lot of loads other than charging the batteries. I’m charging a bank of 840ah with 1400 watts of panels.
John

10 x Kyocera KC140, Classic 150 w/WBJr, Link10 Battery Monitor, 850 AH @ 12v Solar One 2v cells, Xantrex PROwatt SW2000
Off Grid on Houseboat Lake Don Pedro, CA

bldr

  • Newby
  • *
  • Posts: 6
Re: Oversizing PV for Classic
« Reply #6 on: April 13, 2019, 02:01:28 AM »
Resthome  - definitely will see similar temps to you as this is all headed for Oroville
Good to know about the big drop in output once you hit 90s that is a lot of the time spent up there.

For estimating production I took the panels down by 80% from label rating and then applied that wattage against the solar radiation averages for the area which I think provides for a reasonable figure. For example I am trying to assess charging capacity such that during an hour with 700w/m2 (1pm on the first of July last year) of illumination my planned 1340w of panels would get to the charger something around 745w. Should I expect summer temps to pull that figure down further?

200ah - water pumps, music, lights, fans, etc. - is probably a bit light for a busy weekend, but trying to balance good enough and timing. Can always charge with the generator in a pinch, and save up cash for a move to a bigger battery bank. At one point I was looking at doing 12x300w-ish panels and 48v200ah in order to run a mini split A/C. Decided to start smaller and simpler for this year.

For wiring I was using https://www.renogy.com/calculators#tab_solar-cable which I beleive uses the one-way distance as an input.

Part of my concern about switching to all parallel is not having enough conductors already in place or room in the existing conduit for them plus deadlines and competing priorities.

Resthome

  • Hero Member
  • *****
  • Posts: 1140
Re: Oversizing PV for Classic
« Reply #7 on: April 16, 2019, 12:39:46 AM »
Bldr,

With similar panel wattage to what I’m using. I don’t think you will have a problem. I’m using 10 - 140 watt panels 2S5P due to size limitations on installing them on my canopy. I have 6 mounted on the forward area and 4 mounted on the rear stern end of the canopy. Also want to be able to clean them as bird crap is a big problem. Slight angle on each side so not perfectly flat but not at a large angle. Don’t have any shading issue other than my VHF antenna casts a small shadow for a short period of time. But I do believe I see that drop in output on some of my graphs. So I think shading is going to be your biggest problem. Temp effects output for sure but shading more.

My deficit in AH is almost all after sunset. I can handle laptop, phone chargers, VHF, TV, Dish Antenna and DVR, stereo, pumps, inventor and swamp cooler during the daytime with solar power. Usually don’t turn cooler on until around 10-11am and I can be in float by 11am. I use end amps to terminate Absorb and that is around 2-2 1/2 hours. We are conservative at night with lights as I have never converted them to LEDs. I typically only draw SOC down to 85-90%. But that is for a 840AH battery bank.

Would think their calculator calculation for wire size is doubling the length. 

Oh and use Midnite panel mount breakers as they are rated at full capacity and can be used as disconnects for panels and batteries and are not polarity sensitive. DIN mounts are okay for combiner use. I used marine grade wire every where in case insurance wants marine survey. They tend to write up non marine wire.

And on the mini-split AC would not advise it unless you are on marina with shore power. They suck a lot of juice from an inverter. What ever AC amps spec you see see on those units multiple by 10 for a quick guess as to what your inverter would have to pull from batteries to run it. Lots of boats have them at Don Pedro but they are all on Marina with shore power. Us buoy field folks don’t have that luxury.

Good luck and enjoy the lake, looks like they will all be full this year. If you have any questions feel free to ask.
« Last Edit: April 16, 2019, 01:22:25 AM by Resthome »
John

10 x Kyocera KC140, Classic 150 w/WBJr, Link10 Battery Monitor, 850 AH @ 12v Solar One 2v cells, Xantrex PROwatt SW2000
Off Grid on Houseboat Lake Don Pedro, CA

bldr

  • Newby
  • *
  • Posts: 6
Re: Oversizing PV for Classic
« Reply #8 on: April 18, 2019, 12:17:58 AM »
Resthome,

Thanks for all the feedback. The overhead canopy & 3600w system got shelved for this year (time, money, complexity). I figured shade would be the biggest enemy and based on my calculations of charging and usage the evenings is always where it will get tough with everybody back from playing, the loads will skyrocket as production tanks. Swapped everything for LEDs last year to help the car batteries and the 70w panel limp along which should be helpful. Also so far the boat is a phone/computer/TV free-zone.

The non-shore power mini-split was probably a pipe-dream. Figured it was going to take a lot of panels + 150ah @ 48vdc of battery, and would likely still require a generator on the really hot days that don't cool after sundown.

Back in the water end of the month, so just scrambling to wrap up the stuff that is a thousand times easy out of the water vs in.

Thanks
-Jordan

Resthome

  • Hero Member
  • *****
  • Posts: 1140
Re: Oversizing PV for Classic
« Reply #9 on: April 18, 2019, 02:06:30 AM »
Jordan, I hear you on wanting to get out of the boat yard, I was there last year. Think this was my six trip and I hate the place. Always there longer than I plan and spend twice what I think it should cost.
John

10 x Kyocera KC140, Classic 150 w/WBJr, Link10 Battery Monitor, 850 AH @ 12v Solar One 2v cells, Xantrex PROwatt SW2000
Off Grid on Houseboat Lake Don Pedro, CA