20 volt panels

[rossw]

If you don't mind me asking, what sort of actuator do you use?

36" linear actuators designed for satellite dishes. Not a particularly heavy-duty one (I think it's rated for 2500 lbs), and not particularly expensive. I got 6 or 8 of them for $50 each including shipping.

This picture is taken before I ran the heavier 4 sq mm (10 AWG?) wire and conduit etc, but should give you an idea...

[ChrisOlson]

36" linear actuators designed for satellite dishes. Not a particularly heavy-duty one (I think it's rated for 2500 lbs), and not particularly expensive. I got 6 or 8 of them for $50 each including shipping.

This picture is taken before I ran the heavier 4 sq mm (10 AWG?) wire and conduit etc, but should give you an idea...

Cool, thanks!  I figured one of those satellite dish actuators would work OK.  Like I said before, I know only enough about solar panels to hook them up and point them at the sun   

I got some steel coming tomorrow to build the mount - this will be the first time I've messed with a tracker of any sort.  Other than the Picnic Table Tracking Mount where you C-clamp a 12 foot 2 x 6 to the picnic table, lean the panels up against the picnic table resting on the 2 x 6, then go out and drag it around to line it up with the sun a few times during the day to test out your new panels.   
--
Chris

[ChrisOlson]

Some things I've learned about the 20 volt panels I got - tracking makes little to no difference in daily output.  The largest gains are when the sun is lower on the horizon in early morning or late afternoon.  If they're pointed due south during those times of the day they develop about 320 watts.  If I point them directly at the sun then the output goes up to about 500 watts.  I tested this at about 1-1/2 hours after sunrise, and 1-1/2 hours before sunset.

During the period in between those times the amount of power they make depends a lot on battery voltage.  When the bank is lower voltage in the morning they reach their peak output by about 10:00 with the panels fixed and pointed due south.  Turning them and pointing them directly at the sun at that time causes them to heat up more and their output doesn't change much at all.

Today, the bank reached fully charged by 10:30 in the morning (solar noon is at about 12:30 PM), and once the voltage of the bank is up to 28 the output of the 20 volt panels drops to about 650 watts and it doesn't make any difference if they're pointed at the sun or not.  I can turn them about 15 degrees away from the sun and they still put out about 650 watts.  If I put a good load on the batteries at around the noon time, then the output of the panels goes up steadily as the bank voltage drops.  Today I could only get them to about 850 watts at high noon with the air temperature at about 85 degrees F.

In the mid-afternoon, again pointing them at the sun vs due south makes little to no difference - only about 20-25 watts with the bank running at float around 26.5 volts.  If I put a heavy load on the bank in mid-afternoon, then I get more gain in output by pointing them at the sun vs due south.

I've pretty much arrived at the conclusion that being I have way more solar generating power than I can even use on a good day when the wind is blowing too, and based on the output results I got by moving them around on a good day vs leaving them fixed, that tracking doesn't make much sense for these panels.

In the winter the sun just makes a little short arc thru the southern sky and we barely get 7 hours of daylight here.  So I think they'll work fine and do what I bought them for just fixed due south, and inclined 55-60 degrees from horizontal.
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Chris

[ChrisOlson]

I discovered yet another thing about these "low voltage" solar panels - they deliver over double the power of my standard panels on a cloudy overcast day.  Yesterday it was drizzly and raining most of the day, and dense overcast.  The standard panels developed an average of about 48 watts.  The low voltage panels developed an average of about 125 watts.  Rated output capacity of the standard panels is 1,230 watts.  Rated output capacity of the low voltage panels is 960 watts.

So that means the standard panels only averaged about 4% of their rated output.  The low voltage panels averaged about 13% of their rated output on the rainy day.

This makes me wonder if MPPT, like a Morningstar TS-MPPT-45,  might be a good investment for my "standard" panels?
--
Chris

[birdhouse]

and once the voltage of the bank is up to 28 the output of the 20 volt panels drops to about 650 watts

that's pretty darn good!  so they're operating at 67% of rated output @ 28 volts.  most charge controllers are tapering off the majority of the power that the batteries see around that voltage anyways, so 100% rated output wouldn't even be helping anything anyways.   

i don't know how to answer why the 20v panels are outperforming the high voltage panels in overcast conditions.  may just be different cells/brands do better in overcast?  or maybe they're still just matching the load better? 

MPPT for solar would be really nice!  i find it hard to justify the cost.  last time i bought panels (laminates) i got two 245w laminates for $450 inc. shipping.  i think the tristar mppt is close in that price range but isn't going to increase your output by 490watts! 

it's kinda like oz-tules states-  better to buy a few more panels than pay for a tracking system.

anyways, i'm glad you're happy with the new panels!

adam

[rossw]

MPPT for solar would be really nice!  i find it hard to justify the cost.  last time i bought panels (laminates) i got two 245w laminates for $450 inc. shipping.  i think the tristar mppt is close in that price range but isn't going to increase your output by 490watts! 

I'd do it again in a heartbeat.

I only have a modest system - 3.5kW - but the MPPT (I got a FlexMax80) produces more additional power than what its cost would have got me in extra panels.

[ChrisOlson]

I only have a modest system - 3.5kW - but the MPPT (I got a FlexMax80) produces more additional power than what its cost would have got me in extra panels.

Ross, is my understanding correct that the MPPT will help the panels the most on cloudy days, or in conditions that are less than perfect?  And that on the really good days it won't make as much difference?

I wonder this, because in the winter we get far more days that are less than perfect than we do good ones.
--
Chris

[rossw]

I only have a modest system - 3.5kW - but the MPPT (I got a FlexMax80) produces more additional power than what its cost would have got me in extra panels.

Ross, is my understanding correct that the MPPT will help the panels the most on cloudy days, or in conditions that are less than perfect?  And that on the really good days it won't make as much difference?

Chris, it's difficult to answer in plain english - because conditions (like panels) vary so much.

As you have observed with your "low voltage" panels already, they are a much closer "match" to the batteries than normal modules, so with those I suspect you'd get less benefit than I do.

It is true to say though, that MPPT helps most when the operating conditions are furthest from perfect.

Example: a "standard" array that is dead square on to the sun, at midday, in cool weather, with your batteries at a low SOC. Lets use my monocrystalline for the calcs.
The panels will be producing their maximum power at 17.5V, around 5.7 amps. A battery at 12.8V can only "get" 73 watts from my 100W panel under these aparantly "ideal" conditions.
An MPPT will operate at the peak power point, 17.5V, get the 5.7 amps, less its losses (lets say it's only 92% efficient), can still deliver 92W to my battery at the same 12.8V out.
Only 19W more. But thats per 100W. 190W per 1KW.  665W more for my array.

If you wire your panels so they're a (much) higher voltage than your battery, you can still get useful power when illumination is low enough that a barefoot panel couldn't charge your battery. Again, with my panels, I have 6 in series. If I have reasonably poor illumination (dust, smoke, high cloud etc), I only need to get more than the battery voltage to get current flowing. In a 48V system, that's a little over 8 volts from a panel that would be (nominally) 20.5V open (17.5V MPP). So yes, with the MPPT, I make more power when conditions are "ideal" as well as when they're far from ideal.

[ChrisOlson]

If you wire your panels so they're a (much) higher voltage than your battery, you can still get useful power when illumination is low enough that a barefoot panel couldn't charge your battery.

Thanks for that info - I have been reading about the MPPT controllers and what they do.  It seems that for the roughly $400 that I can get a Morningstar controller for that it would be money well spent for my "normal" high voltage panels.  Those panels, much like yours, are rated at 17.something volts and I have them wired series for 24 volt.  So they really need to operate at much higher voltage at all times to deliver their most power.

The controller I am looking at can go up to 150 open volts.  The specs says the panel's open circuit voltage is 21.78 volts and I have 10 of them.  I was thinking that if I wire two banks of five in series, then parallel the two banks, the open voltage of the array will go to 108.9 volts, which is well within the limits of the controller, and it will probably help them to deliver their maximum power no matter the voltage of my batteries.

The more I study it, the more it makes sense that I should have one.  These low voltage panels have shown me what a better "match" can do for output with solar panels, and it can be quite dramatic under some conditions.
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Chris

[DamonHD]

Note that you have to ensure that Voc on the very coldest days (when Voc is highest) doesn't exceed the controller's max Vin.  My little Morningstar MPPT (200W@12V) is full of warnings to that effect, IIRC.

Rgds

Damon

[rossw]

Note that you have to ensure that Voc on the very coldest days (when Voc is highest) doesn't exceed the controller's max Vin.  My little Morningstar MPPT (200W@12V) is full of warnings to that effect, IIRC.

My Outback FlexMax80 has plenty of "warnings" about max input of 150V.
I just checked, and it's showing it's Max Voc = 162.6
My arrays are 6 series modules, each claims to be Voc of 21V, which is only 126V.
To get 162.6 means I have to have had 27.1V/module. I don't get anywhere near as cold as you guys do... -3, -4C but not with sun. Full sun, rarely see below 0C

Upside: Clearly the Outback doesn't let the magic smoke out at 150.1V

[Volvo farmer]

Thanks for that info - I have been reading about the MPPT controllers and what they do.  It seems that for the roughly $400 that I can get a Morningstar controller for that it would be money well spent for my "normal" high voltage panels. 

For $280 more, you could get a Classic    The Classic has this nifty "hyper Voc" feature which allows you to exceed 150V upon occasion if it's really cold or something, without blowing up the controller. My understanding is that you can exceed 150V by the battery voltage without letting the smoke out. You won't be making any power in hyper Voc mode, but you won't be sending it in to be repaired either.

If you didn't like the Classic for solar, you could always play with it on your wind turbines. Can't do that with a Morningstar. 

[DanG]

On the MPPT for low light, a gain 20% of 4% or 13% yields 5% and 16%... might noticeably keep the stand-by power source fuel usage down regardless of economics of just adding panels. The off-peak sun hours would also be money in the bank.

And those differences, the 4 vs. 13%, could that be partially from new glass?  Have you razor bladed the moss, lichens and mineral build up off the old array?

the Outback doesn't let the magic smoke out at 150.1V

No - but it does set a tell-flag at 140 (MX60) and 145 (FW80) that has proven to erase warranties for some. You are just lucky so far?

I just checked, and it's showing it's Max VOC = 162.6

Interesting! Damon - your roof mounted panels may see 3 to 7°C lower temperatures than a ground level recording, especially with your well insulated house!

If cloud edge, rain/snow reflections and clean panel glass just boost current... then it has to be temperatures?

[DamonHD]

I have MPPT for my little off-grid system AND for my grid-tie system (SunnyBoy inverters).

Generally I think load matching with MPPT is a good idea.

I'm limited for space so I can't just use more panels, and I'm not allowed to track anything.

Thus MPPT (plus Sanyo HITs on the roof) has made it possible (I believe) for me to get the house carbon neutral/negative and keep my server off-grid entirely for the space that I have.

Not everyone is space constrained, so different arguments will apply.

Rgds

Damon

[ChrisOlson]

My question is, how can I determine what the Voc will go to when it's really cold out?  I assume the specs on the panels are for STC?  Assuming I would wire for 109 open volts and the max limit of the controller is 150, it would seem "safe".  But I'd like to keep the factory smoke in the box if I can.

VF: I already got some Morningstar equipment and I like it.  I think they build good stuff.  Plus I already ordered it this morning, so it's a little too late to change my mind and get a Classic instead  

DanG: I don't think it has anything to do with the glass.  I think it has more to do with the fact that the lower voltage panels simply perform that much better when the bank voltage is low, it doesn't recover right away when we got no sun or wind, and the "normal" panels are operating quite a ways off their peak power curve.
--
Chris

[Volvo farmer]

Might try this

http://www.outbackpower.com/resources/string_sizing_tool/

[Dave B]

Chris,

  The 45 or the 60 ? We might be able to compare notes, I am looking at both of these as well. Mine would run as the specs on my panels show 88 VOC series / parrallel for 48 volt system. MPPT makes much more sense to me for solar than wind, things happen slow with solar. You don't have the runaway potential and clipper circuits needed to protect the controller and turbine by running on the edge of preset load points just to get high output. A bit more to the term MPPT real time with solar, tracking slow is comparitively easy.    Dave B.

My question is, how can I determine what the Voc will go to when it's really cold out?  I assume the specs on the panels are for STC?  Assuming I would wire for 109 open volts and the max limit of the controller is 150, it would seem "safe".  But I'd like to keep the factory smoke in the box if I can.

VF: I already got some Morningstar equipment and I like it.  I think they build good stuff.  Plus I already ordered it this morning, so it's a little too late to change my mind and get a Classic instead  

DanG: I don't think it has anything to do with the glass.  I think it has more to do with the fact that the lower voltage panels simply perform that much better when the bank voltage is low, it doesn't recover right away when we got no sun or wind, and the "normal" panels are operating quite a ways off their peak power curve.
--
Chris

[ChrisOlson]

 The 45 or the 60 ? We might be able to compare notes, I am looking at both of these as well

Dave,

I ordered the MPPT 60 because the 45 was a little too small for my array.  My array that I'm putting it on is 1,230 watts and the 45 is only good for 1,200 on 24 volt.  The 60 can go to 1,600 watts, which gives it a little leeway on capacity.  The 45 was $378 and the 60 was $478 at the place where I got it.  So I figured for the extra $100 bucks I can even add on two more 123 watt panels if I want at some point and it still won't be over the capacity of the controller.

On 48 volt the lady told me the 45 can go to 2,400 watts, so the 45 might work OK for your 48 volt system.  Either way the max input voltage is 150.
--
Chris

[DanG]

I understand the voltage mismatch; no need to skip the question - have you scraped the panels with a couple of years exposure? The film build-up will especially hinder low light performance. Not quite as fun as adding components but Windex won't touch lichens and your panels are going to live 30, 40 years. These things etch silica without fail and can survive being orbited in outer space so the high temperatures on the PV panel glass are laughable to them. The only reason they aren't more of a problem is the metal ions leeching out of the metal frames in rainfall arrest their 'visible' growth, but the months of frigid dry air and sun-warmed panels make a good nursery for colonies to attempt to start. Just a thought from someone interested in getting that last 1/2 of 1%

[Bruce S]

Chris Apologies on a slight tangent.
I would like to know where you found the 20V panels.

DanG;
I don't have near the number of panels you guys do, but even the HF panels had a film on them that I couldn't figure out what it was until I saw this posting.
I too have found these little buggers to be a pain in the Arse 
The one thing that I've found to help was the use of Cider Vinegar full strength. Even the RainX I was putting on mine to try to keep them clear was not helping.
The Vinegar trick does seem to be working.

Hope it helps for you too.
Bruce S

[ChrisOlson]

Guys, I must admit I have not scraped the glass with a razor blade.  I have cleaned them a couple times a year with some glass cleaner and they look nice and clear.  I have gotten over rated power out of them in perfect conditions from time to time, so I figured they are working normally.  Just for giggles it sounds like I should take a razor blade to the glass and scrape it to see if anything comes off, or try that cedar vinegar trick.

Truthfully, though, I think the MPPT 60 is going to "fix" it, just by observing how they work.  When the bank is low on voltage the 20 volt nominal panels pull the hardest, when the bank is higher on voltage the standard 12v panels wired series come to life.  If the MPPT works good on my standard array, I'll probably wire the new panels series and get another one (MPPT 45).  The new panels have been working really good, though, in the cooler weather we've been having lately.

Bruce, I got the panels from this outfit:
http://www.spheralsolar.com/products/Schott-240W-PV-Module.html

As it turned out, I couldn't get the Sharp panels I ordered because I have to order them on a pallet of 10.  But I could get these Schott poly panels because somebody else wanted some too.  So I split the pallet and took four and they took six.  The shipping was prompt - they came by Conway Freight - and since I split the pallet the shipping only cost me $150 from Colorado, although the total shipping bill was $300 on the pallet.

When I got these panels I went thru several ideas of how I was going to mount them.  They're over 5-1/2' long and about 40" wide.  I ended up putting two on the shop roof on a fixed mount and I was going to put the other two on a tracker.  After playing with them on the "picnic table tracker" (see photo) I figured out that tracking is not going to make a lot of difference with these panels in the winter.  So then I was going to put the other two on the house roof.  But when I considered how heavy they are I decided unless Jesse Ventura was coming over to help get them up there, they're not going on the house.  So I still got two on the picnic table mount and two on the shop roof.  I'm building another rack to put the other two on the shop roof where they'll be easy to clean off in the winter. 





I had a little trouble getting those two I got mounted on the shop roof.  It's a good thing my wife is six feet tall and she could reach from the bed of the pickup to hold them there while I hung on by my toenails on that steel roof, trying to get bolts in the holes to keep them from sliding out of the rack.  Those two on the picnic table tracking mount just might stay there for awhile   
--
Chris

[ChrisOlson]

The MPPT makes enough difference on my standard panels that I think it would be worth it for the low voltage panels too.  I had to hook the thing up and unhook (bypass) it several times to take different readings to make myself believe it.  I get 7.7% more power on a cloudy, cool (45 degrees) day with the MPPT.  In cloudless sunshine when the panels get hot it makes more difference - I get 14.3% more power.

Nowhere near the 20-30% claims they make for MPPT (might be able to get that under some conditions).  But enough difference to justify the cost of the controller over a year's time vs buying another couple panels and simply hooking them direct to the batteries.
--
Chris

[ghurd]

Been using MPPT at the shop for a few years now.
It is a "12V in / 12V out".  SB2512iX.  A higher voltage input rating would be more efficient.
At the time, it cost less than adding a 50W PV (PV, mounts, wire, etc).

Something nobody seems to mention is how they make a large difference in the winter and how it helps in the real world.
-  The battery bank voltage will effect the charging amps.  If the battery only needs 2A to maintain float voltage then a decent MPPT will only give it 2A because it is "controlling" the bank, even if a direct connected PV array will send in 3A.
-  Cold PVs make more voltage at peak power, and winter is colder.
-  Less insolation in winter, and more lighting demands, and more soldering (for us), mean the battery bank is always low.  The lower voltage battery combined with the higher voltage PV means the MPPT works far more efficiently.
-  Here, if the system is even semi-well designed, there is far too much PV power available to bother with MPPT in summer, but winter is off the bottom of the insolation chart at <0.5H/D.
-  It works best when it is needed most.

Wait to pass judgement until the bank is low, on a cold cloudless day.  You will be impressed.

Increasing the PV array at the off grid shop by ~50% this week or next.  Adding a 75W PV to the 180W array.
We never thought that much power would be needed, but it is nice the existing oversized MPPT can handle the increase!   
G-

[ChrisOlson]

Wait to pass judgement until the bank is low, on a cold cloudless day.  You will be impressed.

G-,

That's what I meant when I said it will probably get the 20-30% more power that they claim under certain conditions.  And in all fairness to the MPPT controller folks, I've never seen them flat out say that it will make that much more power.  They say it can make up to 30% more power and I believe it will after testing it.

Day before yesterday when it was sunny with fluffy clouds floating by, I saw more power out of my array than I've ever seen before.  The sun would go under a cloud and let the panels cool off.  Then the sun would pop out and I saw 1,412 watts from a 1,230 watt array for just a little bit until the panels warmed up again.  That gave me just a little idea of what they are capable of with MPPT on a cold clear day.

Edit--
Just went out to the utility room to look at the gauges this morning and what I saw is what I needed to see to convince me that MPPT is worth every penny you spend on it for solar panels.  The bank is down to 24.0 after overnight, the turbines are just idling on their towers practicing for when the wind picks up, so no power there.  We got dense fog with a heavy overcast.  My new low-voltage panels would normally be kicking butt on the standard panels under those conditions.  With the Morningstar TS-MPPT-60 on the standard panels they're kicking butt on the low voltage panels by almost double the power output!  64 watts from the low voltage array, vs 118 from the standard panels with MPPT. 

When I see that it makes me realize that wiring those low voltage panels in series for 144 open volts, and buying a MPPT-45 for them, would enhance my investment in those too.
--
Chris

[thirteen]

If they operate better when they are cooler is there any way to control their temperature to keep them cooler? Just wondering.

[defed]

each MPPT manufacturer has a string size calculator, you enter your panel model #, max/min temps, etc and it tells you how you can wire them.  my panels are only 44voc, which seems i could have 3 in series and be below 150v.  but if it gets to 0F, they are at 50voc, and at -10F they are at 52voc...it rarely gets below 0F, but it has, so i figured i better stick w/ 2 in series.  i didn't want to personally test the tolerances of the unit!

i have the xantrex 60a MPPT, i am probably switching to outback at some point (got an outback inverter), so if anyone is interested in a 1 yr old, gently used MPPT....

[ChrisOlson]

so i figured i better stick w/ 2 in series.  i didn't want to personally test the tolerances of the unit!

I put a Tristar MPPT 45 on my new low voltage panels, with all four wired series.  I seen it at 154.7 volts a couple days ago and it didn't hurt it.  When ever the bank is hooked up the PV voltage is never that high anyway - usually around 116 volts.  It only goes that high if I disconnect it from the load.
--
Chris

[defed]

true, i haven't run my panels thru a whole winter yet, but the highest voltage that i've actually seen out of a series pair is 80 some volts.  that's 40 some each, so even with 3, still under 150v...but, since the xantrex, outback and morningstar string calculators all say not to go 3, i just won't.  it might be, even probably be, fine, but it won't make much difference for me either way (except less line loss at higher voltage).  the things cost too much to bother risking it, to me anyway.

[ChrisOlson]

the things cost too much to bother risking it, to me anyway.

Yeah, that's true.  I got two Morningstar RD-1 relay drivers - one that controls water heating, and the other one shuts my RE system down in stages in the event of over-voltage when the turbines are putting out a lot of power.  When I put in the MPPT controllers I changed the RD-1 setup so it adds 2,500 watts of load to the system at 30 volts, then another 2,500 watts at 30.5 volts, and yet another 2,500 watts at 30.7 volts.  If the voltage still continues to climb (because of turbine output) the other RD-1 shuts both solar arrays down first, one array at 31 volts, the second array at 31.5 volts, then channels 3 &4 applies the brakes on the turbines - one at 32.0 volts, the other one at 32.5 volts.  That keeps the inverter online because I have that set to kick out at 33 volts.

On both solar arrays I changed the relays so it opens the high voltage circuit from the PV arrays when shutting down the solar.  That way the controllers just see zero PV volts when the RD-1 activates the over-voltage shutdown sequence.

When I was hooking that all up the other day I had the low voltage panels hooked up to the MPPT 45 with no load (battery) hooked up.  That's when I seen it at 154.7 volts.  But that will never happen in actual operation.
--
Chris

[rossw]

When ever the bank is hooked up the PV voltage is never that high anyway - usually around 116 volts.  It only goes that high if I disconnect it from the load.

I beg to differ.  You may have never *seen* it, but I bet the controller does (probably infrequently) reduce or drop load when it does a performance sweep. It may well also do periodic checks of panel open-circuit volts, or other tests. Like when a cloud goes over and the array output changes dramatically in a short time frequently triggers MPPT controllers to "re-scan" for optimum operating point.

At these times, you will see full V(oc)

[ChrisOlson]

I beg to differ.  You may have never *seen* it, but I bet the controller does (probably infrequently) reduce or drop load when it does a performance sweep.

Well, that may be true too - I don't really know how those controllers work.  So far it's been hanging in there and no problems with it.  I set up the RD-1 to disconnect the solar first when over-voltage occurs because I know for a fact that the controllers will let the panels go to full Voc when that happens because they think the bank is fully charged.

I never thought about that performance sweep thing under varying conditions.  I guess I'll find out how good the factory smoke is packaged in that MPPT 45.
--
Chris

[birdhouse]

chris-
pretty slick how you've got your controllers and rd-1's set up.  you mention all the 1/2volt increments as the changing points for shutting off solar ect.  are these voltages set in stone, or do the automatically vary based on a temperature sensor on the battery bank?

i know you can set the voltage points manually, just curious if the controller is capable of moving them around a bit based on the temperature of the battery bank. 

adam 

[rossw]

I never thought about that performance sweep thing under varying conditions.  I guess I'll find out how good the factory smoke is packaged in that MPPT 45.

Don't get me wrong - I'm not saying it will blow up, I'm just saying that we ALL need to be very very careful when we ASSUME things, without thinking of all the conditions and scenarios.

Your assumption that the voltage will always be held down because of the load is valid for that particular set of conditions - problem is, thats not the only condition