Anotherpower.com Forum
Renewable Energy Questions/Discussion => Solar (heating or electric) => Topic started by: ChrisOlson on April 02, 2013, 11:47:52 pm
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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
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I am assuming the controller is an MPPT?
If so, wont it give a boost to the performance of the panels?
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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.
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Thanks for the explanation Ross, makes sense now.
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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.
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Chris
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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:
[attachimg=1]
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...
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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
[attachimg=1]
[attachimg=2]
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Chris
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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
[attachimg=1]
[attachimg=2]
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.
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Chris
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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!
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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. :o
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Chris
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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
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My little 6kw/18000kw inverter ...
Hey oz; your kidding right?
18000 KW is 18 Megawatts. That is monstrous surge for a 6 KW inverter! :o
The battery cables must be the size of telephone poles...
Sorry could not resist.
Tom
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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
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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
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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
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30 seconds is a life time in cloudy conditions. It will pay to try it on a clear day where the solar insolation does not vary at all in a 30 second block... impossible to guarantee in clouds.
If it still varies considerably, then you will have to think algorithms in the classic are not linear, ie behave differently as the power increases.... likely to do with the power curve of the panels, and where the programmer thought you should be on that power curve for the voltage they see... ie depends how they calculate the MPPT point, jump table or fuzzy logic perhaps.
If their MPPT is real time fuzzy logic, then they should be the same, as max power is max power.... if they use some other formula.... then all bets are off.
Failing that.... maybe we will never know??
............................oztules :-\
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The thing is, though, I did it twice and got pretty much the same results. I didn't write down Vmp as showed on the controllers though. Forgot to do that. But I think it was right around 90 in all cases anyway, give or take a couple volts.
They got three different things in the controller for solar arrays. One they call "Fast Auto & Timed I-V PV Sweep". That's the default and what I am using.
But they also got "Legacy P&O" and "Dynamic" you can choose from. I've tried them other ones and can't see much difference.
I guess they do have a fourth one too where you can choose your own operating voltage as a percentage of Voc. I've tried that before too, and by playing with the percentage value can get it close to the output of using "Fast Auto & Timed I-V PV Sweep". But it don't stay constant and all it takes is for a cloud to go over and it's way off. So I never use that.
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Chris
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I agree with Oz about clods, or those days when the sky is all exactly the same shade of gray. It changes too fast to get anything very meaningful.
Clouds and angles can do some strange things to PVs.
I tested matched pairs (as matched as possible, consecutive SNs, or at least from the same case) of smaller panels for Commanda. The test was to see how balanced real PVs were for a large project of her's.
Amorophous, mono and poly. 12V. Wired 2 in series for 24V, so the same current. Measuring the voltage of each panel shows whats what. Tried it both with fixed resistances, and batteries.
One always did better than the other, which I expected.
Almost always, the one that did best in full sun didn't do as well as the other in overcast conditions.
At an angle, usually one dropped considerably more than the other.
The output voltage even had some effect.
The percentages were a lot larger than I expected.
I would think all that variation would have some effect on MPPT logic... somehow... not sure how.
G-
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I would think all that variation would have some effect on MPPT logic... somehow... not sure how.
My interest in it being somewhat piqued, I tried a different experiment a bit ago. We have grey overcast with some sleet coming down. I know spring is around the corner - just haven't seen it yet.
I wired the roof array into the single Classic 150 thru its disconnect breaker. So I can shut off either the roof array, or the shop array while watching the screen on the Classic.
Very poor output, as would be expected in these conditions - 526 watts and the Classic is running the arrays at 87 volts in the poor light. This is 100 watts/kW installed capacity.
Shutting off the breaker for the house roof array causes it to drop to 352 watts output and the Vmp does not change. This figures out to an output of about 94 watts/kW installed capacity. Turning the roof array back on makes it come up to 525 - about the same as before. Shutting off the shop array makes it drop to 143 watts and the Vmp showed 88. This figures out to an output of 95 watts/kW installed capacity for the 1.5 kW east/west roof array. Turn everything back on and it came up to 530 watts and 87 Vmp, so no basic change from all three readings with everything on.
So if I add those figure up for the individual outputs; 143 + 352 = 495 watts. This is vs ~525 with everything on. That's a 6% boost today with the grey sky and some precipitation coming down. Not the same as the ~13% that I measured yesterday with what I call "Cloud Shine", but still get more power with the entire works on one controller.
The other thing I noticed yesterday is that with the whole works on one controller I was still making 68 watts after the sun had set for the day! If I turned off even breaker in a combiner the Classic would go to zero output and not come back. Flip that breaker back on and it went to 68 watts with the sun below the horizon. LOL!
I don't know what the explanation is, but I am concluding there is some sort of "boost" from connecting multiple arrays together as one big unit. On the perfect day I will get less power by doing this because the Classic can only handle about 4.8 kW on a 48V system, so it's going to amp-limit itself and "waste" part of the array. But the thing is, on those days I don't need the power because the bank is floating by 2:00 in the afternoon anyway. I want to optimize output on the less than perfect day because that's when we need the power the most.
The Classic's power measurement to the batteries is very accurate - in the neighborhood of +/- 1% with the type of shunt they use in there. So I'm satisfied that it's not erroneous readings. I'm going to leave it all on one Classic for now and shut off the individual breakers from time to time over the next few days in various conditions and write down what I get. If it proves out that I can get even 6% more on the bad day, it's worth it to take the "hit" on the good day simply because on the good day the controllers would have the whole works throttled back in Float anyway.
I'm thinking it has something to do with the arrays being combined, being able to collect more available light, and sending it down one pipe, eliminating the losses in an additional MPPT controller. But that's just my theory on it.
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Chris
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Maybe the controllers back down because with both working because the apparent battery voltage is higher to each from the incoming power from the other?
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Maybe the controllers back down because with both working because the apparent battery voltage is higher to each from the incoming power from the other?
I don't think that's the cause of it, Wolv. They adjust for battery voltage even if that was the case. And a power input of 500-600 watts with our bank and loads is like peeing in the ocean. So it just doesn't change it. These are the types of average loads our system carries almost 24 hours a day, with daytime peak loads sometimes 4-5x that, and nightime average loads around 500-800 watts.
[attachimg=1]
So basically, two controllers supplying 500 - 1,000 watts is like insignificant and doesn't change the bank voltage, or voltage that the controllers "see", by even .1 volts.
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Chris
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So if I add those figure up for the individual outputs; 143 + 352 = 495 watts. This is vs ~525 with everything on. That's a 6% boost today with the grey sky and some precipitation coming down. Not the same as the ~13% that I measured yesterday with what I call "Cloud Shine", but still get more power with the entire works on one controller."
Grey sky and precipitation... and still getting 10% is what I like to see........ 500w is the average my house uses over a 24hr period..... for you probably 1kw plus a bit.
Our previous discussion about solar is starting to have some teeth.... for the cost of your new inverter, you could spring for another 5kw, and see 1kw power on grey rainy days... and that starts to make a difference to the power input required even in inclement weather.....
Cheap solar really makes the difference now days.
Still don't know why your seeing the differences, unless the classic is a bit heavy on the idle current, and that makes it look better with a larger output.... bit like that inverter I modified from 200watts idle to 20 odd watts idle.... but I can't see how a buck would use up magnetizing currents like that.....mystery
All power is good power, and the powers that be and must be obeyed, will find a use for it .....have no doubt.
....................oztules
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Our previous discussion about solar is starting to have some teeth.... for the cost of your new inverter, you could spring for another 5kw, and see 1kw power on grey rainy days... and that starts to make a difference to the power input required even in inclement weather.....
Yes, I certainly could. But on the other hand the wind turbines pretty easily produce 3-5 kW on those grey rainy days too because they normally associated with sort of front that makes the wind blow hard. So I'm trying to build a balance of systems that works well in all weather and minimizes our generator run time in the long term.
With careful design and selection of components we're able to use a very small generator for our primary standby, compared to what most would consider necessary for a 30 kWh/day off-grid all-electric home. That has saved tremendously on fuel in the generator. We use it primarily for peak load management in combination with Generator Support, which saves on buying extra inverter capacity to run big load, and saves on buying batteries to run the big loads.
At the same time, using the Gen Support takes the load off the batteries and RE system so it can do the job of charging batteries instead of using a generator to charge batteries. Using a generator for on-demand peak load is quite efficient, actually. The gen power goes right to the loads, and properly set up, it runs the generator at its prime power rating where it's the most efficient. Using a generator into an inverter charger to charge batteries that are at best 85% efficient, then converting it back to AC to run the loads is horribly inefficient use of a generator.
Over the long term, after getting this set up, I only recall three times since the first of the year that our inverter has started the gen for battery charging. And in the new inverter I got a STOP V trigger set so it shuts it off when the bank voltage reaches 56, and from that point let the RE system do its job.
So that's what I've been trying to do - find that balance of systems that's the best for us. We're getting there, and this summer will tell if we have the need for more solar power yet.
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Chris
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I got all 6 kW of solar capacity on a single Classic 150 with 3.75 kW facing south at 30° tilt, 1.5 kW facing east on a 22.5° roof slope, and .75 kW facing west on the other 22.5° roof slope. Today was the first perfectly clear day we've had in weeks. I logged the output from 7:00 AM to 5:00 PM with the Classic and graphed the CSV export from the Status Panel in Excel. This is what it looks like, with some comments on it below.
(https://lh3.googleusercontent.com/-aqhAGCcBRMc/UXND2UhjxfI/AAAAAAAAG1c/gLVQBNWhBy8/s703/Solar+April+20%2C+2013.xls+4202013+84046+PM.jpg)
From about 8:15AM to 8:45AM there's a dip in the power due to shading on the east facing array from a wind turbine tower.
That same tower causes a dip in the output from 10:30 AM to 12:30 PM due to shading on the south-facing array. Today the turbine was running and the blades caused shadow flicker on the south-facing array, which really screwed it up for about two hours as the shadow moved across the array, knocking out series strings of three panels one at a time for two hours.
Damned 90 foot tall wind turbines. But this won't be a problem as we get into summer more because the sun is at higher elevation then and the shadow flicker from the rotor on that turbine doesn't affect the south-facing array then.
The bank went into absorb at around noon and was done with absorb at 3:00 PM where the big dip in amps occurs. Although the controller did hit darned near 90 amps (about 5,400 watts) for a very brief time, the FET's got hot and it de-rated pretty fast. Then you can see the arrays being "throttled" most of the afternoon in absorb - the bank and loads didn't require the full output of what it could do. At about 2:20 PM you can see a spike where it goes up to 88 amps or so. That was due to me doing some welding in the shop and the big load on the system caused the controller to put out max power for a little bit.
The other up's and down's are caused by varying loads in the house - 'fridge and freezer starting and stopping, wife doing whatever - turning her stuff on and off, etc.. And that's why the morning curve is smoother - it was basically requiring everything the arrays and controller could put out - right up to where the turbine tower caused some problems. In the afternoon, with the arrays "throttled", the controller would adjust output as necessary to meet charging requirements and loads on the inverter.
So I'm going to say putting the whole outfit on one controller works fine. 28.4 kWh from it and it could produce more if we had the loads for it today.
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Chris