East/West Facing Solar Panels

[ChrisOlson]

We bought 2 more kW of solar capacity last month (eight 250 watt, 30.8 Vmp panels made by Helios Solar Works in Milwaukee, WI).  I got four of the panels installed and hopefully this weekend if we get nice weather I can put the rest up.

I put the panels on the east and west facing slopes of the house roof.  Right now I got two 250 watt panels on each roof slope.  But I think when I put the others up I'm going to put six panels to the east roof slope and have only two facing west.  That will give us a bigger morning boost to get thru the water heating time and get the bank to absorb.  Our system is typically floating by afternoon and we can't use the power then, so I feel more west facing panels would be wasted.

I bought a XW-MPPT60-150 controller for the panels but I never hooked it up yet.  I got the panels wired two in series for 61.6 Vmp and they are hooked into the combiner and direct to the bank thru the array disconnect - no charge controller.  I was surprised to see that this works fine.  I have a Doc Wattson with a 100 amp external shunt to measure power from the panels and the east/west facing panels have been making the same kWh/kW installed capacity as the much larger 3.75 kW south-facing array on the Classic 150 for the whole month of March.

I think I'm going to leave them that way, with no controller.  They can barely get the bank to absorb voltage (62.0V) on a good day and they seem to be at their peak output when they're "loaded down" to around 56-58 volts or so.  Which happens to be perfect for the morning boost to get the water heaters hot and get the bank to absorb.

Probably a bad idea to not use a controller when I got one laying in the box, brand new.  But it works so well direct hooked, I don't know what good the controller would do.
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Chris

[Wolvenar]

I am assuming the controller is an MPPT?
If so, wont it give a boost to the performance of the panels?

[rossw]

I think I'm going to leave them that way, with no controller.  They can barely get the bank to absorb voltage (62.0V) on a good day and they seem to be at their peak output when they're "loaded down" to around 56-58 volts or so.

If their Vmp is 61.6V and you're bank is running 56-58V I agree, you're wasting so little power as makes no difference.
Usually the panel Vmp is more like 17V, 34V, 51V, 68V and the battery is charging at 12, 24, 36, 48. So the difference between 4A @ 61V (244W) and 4A @ 56V (224W) isn't worth chasing. However if your batteries were at 48V and Vmp 68V then there's 80-odd watts per panel you're throwing away, and it's a whole different ballgame.

[Wolvenar]

Thanks for the explanation Ross, makes sense now.

[ChrisOlson]

However if your batteries were at 48V and Vmp 68V then there's 80-odd watts per panel you're throwing away, and it's a whole different ballgame.

We sometimes have that situation early in the morning.  After I read your post I got curious.  Our bank is about 49.4 right now.  I shut off the disconnect and checked the Voc of those panels and it is 75.1V.  I think their "official" Voc is 36.7 per panel, but it's a little cool out this morning - only 12° F.

Maybe I should hook the controller up as long as I already got it.  It's a strange thing because the east panels come up to full power really fast in the morning.  The sun is barely above the horizon right now and the east/west panels are producing 197 watts already, or 19.7 % of the installed capacity.

At the same time the south facing array is producing 88 watts, or only 2.3% of the installed capacity.

The sun is just slight north of due east when it comes up this time of year.

The solar installer where I bought the panels said we wouldn't get good power production by putting them east and west.  In the winter, I agree, they wouldn't work good.  But this time of year it is working fine.
--
Chris

[rossw]

However if your batteries were at 48V and Vmp 68V then there's 80-odd watts per panel you're throwing away, and it's a whole different ballgame.

We sometimes have that situation early in the morning.  After I read your post I got curious.  Our bank is about 49.4 right now.  I shut off the disconnect and checked the Voc of those panels and it is 75.1V.  I think their "official" Voc is 36.7 per panel, but it's a little cool out this morning - only 12° F.

Vmp is the important parameter here, far more so than Voc.
The greater the difference between your battery voltage, and Vmp, the more benefit your MPPT will make.

Maybe I should hook the controller up as long as I already got it.  It's a strange thing because the east panels come up to full power really fast in the morning.  The sun is barely above the horizon right now and the east/west panels are producing 197 watts already, or 19.7 % of the installed capacity.

At the same time the south facing array is producing 88 watts, or only 2.3% of the installed capacity.

The sun is just slight north of due east when it comes up this time of year.

Assuming they're mounted substantially vertically I can well believe it.
If the sun was as little as 12 degrees south-of-east and your south-facing arrays were facing perfectly south, you would get a mere 2.4% of the available light striking them due to the cosine error.

The solar installer where I bought the panels said we wouldn't get good power production by putting them east and west.  In the winter, I agree, they wouldn't work good.  But this time of year it is working fine.

The installer either doesn't know what he's talking about, or doesn't understand what you're doing. (Either way, don't ask his advice on stuff he clearly doesn't get!)

I posted this elsewhere, but I'll put it here too because it makes the point so clearly...
We're just on the winter side of the equinox here now, so this is FAR from the summer "WOW!" state:


The red line is a tracking array, facing 30 degrees above east at sunrise.
The yellow line is an identical array facing north (your south) at the optimum angle for this time of year.
Just look at the difference in the first couple of hours of sun...

[ChrisOlson]

Ross, your graph for that tracker setup is exactly what I'm seeing with the east facing panels in the morning.  They come up to full power really fast and provide a big boost in the morning when we need it most.  That's why I'm thinking about putting more of the array on the east roof slope and less on the west.

I got the rest of these panels to put up, hopefully this weekend.  Plus got more rails in the shop




--
Chris

[ChrisOlson]

I put two more of the panels up before we got snow, and the snow actually drove me off the roof when I was hooking up the wires to the last one, so I got three east and three west





I hooked up the XW-MPPT60 and that didn't work.  It struggles to get the bank to absorb (62.0).  So, since I got three panels on each side I wired them three in series east and three in series west for 92.4 Vmp.  That works great.

But now I got another problem.

The Classic controllers are networked so they all operate at the same charge stage.  The Classics decide absorb is done so they all drop into float.  Due to differences in the clocks and how the Classics count down for the absorb time vs how the XW-MPPT60 does it, the XW-MPPT doesn't think absorb is done yet so now it tries to hold the bank at absorb while the Classics are in Float and the Classics all shut down their solar arrays and wind turbines.  And now the XW-MPPT60 don't have quite enough juice behind it to maintain absorb so its counter stops running and the bank is in limbo - above float voltage but not quite to absorb, and it stays there all day unless I manually force Float on the XW-MPPT60.

So I ordered another Classic controller so it can network with the rest of 'em.  And I'll sell the XW-MPPT60 to somebody else that has a XW Power System.

Now I got another problem - I'm short one panel.  I bought 8 and now I need 9 of 'em.  I'm going to put 6 on the east roof slope and leave the other 3 on the west.

But other than some slight glitches with the mismatch between controllers and having to rewire for 90 volts instead of 60, it works great.
--
Chris

[rossw]

But other than some slight glitches with the mismatch between controllers and having to rewire for 90 volts instead of 60, it works great.

*smirk*.   This, from "Solar is utterly useless up here, not worth even having!"  Keep going, Chris! Glad things are working for you!

[ChrisOlson]

Well, if them solar panels provide the boost to run our new AC unit in the summer I'll be happier than a pig wallowin' in mud and I'll never complain about snow on solar panels again.   
--
Chris

[oztules]

The lower Vmp panels are the right choice for you, and my solar pumping systems. Higher VMP suits grid tie.

By the time your installed solar kw = installed wind kw, you will turn the wind off until winter.

I have found the same as Ross with the E and W panels. In summer, they actually run very well, as the north panels don't do much until 10am, as the sun rises south of east and sets south of west, so solar drops off early in the day.

Sometimes I wonder if the fancy controllers are thinking too much for wet batteries... low Vmp panels with a good watering system will do pretty well.... would not try this with sealed batteries though.

When you get up to 10kw solar like the gent that moved to the Daintree forrest in Nth Queensland  (wapokol or similar), you will be able to run AC all day and night like he does, and maybe the mills will run them through winter for heat ( except for icing up I guess on the condenser).

I prefer the seat of the pants inverter I have, as it does not intimidate me with gadgets.... I'm just simple like that though..

My little 6kw/18000kw inverter ...     http://www.anotherpower.com/board/index.php/topic,780.msg7495.html#msg7495

Nice setup... but another 5kw  ($5000) of solar will be the best money spent yet, and spread then across the sky.



....................oztules

[tomw]

My little 6kw/18000kw inverter ... 

Hey oz; your kidding right?
18000 KW is 18 Megawatts. That is monstrous surge for a 6 KW inverter!

The battery cables must be the size of telephone poles...

Sorry could not resist.

Tom

[ChrisOlson]

By the time your installed solar kw = installed wind kw, you will turn the wind off until winter.

Actually, with the new solar capacity we put in I am running the turbines.  But I have one solar Classic that activates its AUX1 port in Float and that turns on a mechanical relay.  That relay turns on the voltage clipper relays for the turbines and shuts them down when the system drops into Float.

It's got a bug in that function in the Classic so that when it drops out of Float into Float MPPT it cycles the relays on and off really fast like PWM.  I talked to boB and Ryan about it and boB is going to add a delay and hold timer to that function so it works better with mechanical relays.

But otherwise, yes, you are correct oz - it's no sense to running the turbines when the solar works.  There's no place for the power to go so may as well shut them down instead of letting them scream unloaded up against their voltage clippers.

We had a snow storm here this morning and the turbines hit 47 kWh by 10:00 this morning.  There was only about 140 watts of solar power coming in but the system dropped into Float and it shut the turbines down.  It had them shut down for several hours until we came in the house and threw some loads on and then it let them go again.

So it works pretty good.  But the solar won't let the turbines run anymore if the system is floating.
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Chris

[oztules]

System is coming along fine from the looks Chris, and I do understand you live down a black hole in the winter


..... yes Tomw, 18000kw is only 3 orders of magnitude out of kilter, if our govt could only get that close... sigh...



................oztules

[ChrisOlson]

It is really strange.  I got my Classic Lite and installed it.  But on (just another) cloudy overcast day it doesn't do what I expect.

I seem to get more power from the panels on a cloudy day from what I call "Cloud Shine" with one controller than with two.  I've verified it twice today.

I left the high voltage wiring from the one Classic installed into the high voltage DC disconnect so I can swap them around in just 30 seconds.  I was getting 1340 watts from the shop array (south facing, 3.75 kW) and 565 from my new east/west roof panels (still just six up there - weather has been bad to install the other three panels).

That adds up to 1905 watts.

I shut down the roof array and quick wirenutted the wires to the input of the other Classic to try it all on one controller (all wired for ~90 Vmp).  Flipped the breaker on and it came up to 2160 watts.

WTF?

So I shut it down and rewired it again quick into the Classic Lite and turned it all back on.  Same as before, except showing 1344 and 561 = 1905 watts again.

Why am I getting a ~13% "boost" by having the total capacity on one controller on a cloudy day?  It doesn't make sense.
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Chris