Can someone comment on the use of Schottky diodes on each string of solar panels. I have not used them in the past as I was using multiple controllers for the different types of panels but now I have most of the strings connected to a single classic. My concern is about the First Solar CdTe panels having a reverse flow from the other panels. I have some late day shading mostly affecting the First Solar panels and have read on their website cautioning about damage from reverse flow.
Strings:
4 ea. Siemens M55 36 cell mono in series X5 v.m.p. 69.6. V.o.c. 85.6
2 ea. Suntech STP-280/24/Vd. 72 cell poly in series. V.m.p. 70.4. V.o.c. 89.6
10 ea First Solar FS-275. 154 cell CdTe. In parallel. V.m.p. 69.4. V.o.c. 92.0
Tecno
You will not be getting reverse flow. All three strings should be combined in a combiner and separated by circuit breakers. That is for fire protection. All three strings will be at the exact same voltage when connected together.
By the way, the combiners job is to stop reverse current flow into a bad string. So if one of your panels shorted, the other two strings will gang up on it and reverse current would flow. Since there is a fuse installed in each string, the theory is that the two good strings will have enough current to blow the fuse and take the bad string off line, thus stopping reverse current flow.
Do not use diodes. They are terribly inefficient and not high enough voltage. As I remember, Schottky diodes are not high voltage diodes.
Thanks robin. That is what I was thinking....all 8 strings (5 strings of Siemens) hook to a MNPV-12 combiner with each series string having its own breaker but the CdTe panels are all in 2 groups of 5 panels in parallel at the panels with two feeds to the combiner box with two 6 amp breakers, slight economy on my part, the CdTe panels also have a fast blow AGC fuses right at the panels.
The good Schottky diodes are 50 piv but there are 600 v and 1000 v ones on Amazon but it is possible that they are not Schottky diodes, hard to tell by part numbers
I won't worry about it , I don't want to join the smoke um club
Tecno
Quote from: Robin on December 05, 2013, 02:07:40 PM
By the way, the combiners job is to stop reverse current flow into a bad string. So if one of your panels shorted, the other two strings will gang up on it and reverse current would flow. Since there is a fuse installed in each string, the theory is that the two good strings will have enough current to blow the fuse and take the bad string off line, thus stopping reverse current flow.
There are two possible functions for the breakers in a Midnite combiner. One function is to act as a switch and disconnect a string. The other function is the one you mentioned: overcurrent protection from reverse current flow through a faulted string.
I notice that the polarized breakers in the Midnite combiner are connected with their (+) side wired to the (+) side of the PV string. This is the orientation I would expect if the breakers were intended to function as switches.
If the breakers were to be used for overcurrent protection of a reverse current flow, their polarity should be the reverse of what the combiner box instructions call for.
--vtMaps
Quote from: Robin on December 05, 2013, 02:07:40 PM
Do not use diodes. They are terribly inefficient and not high enough voltage. As I remember, Schottky diodes are not high voltage diodes.
Respectfully, I disagree.
I have 6 arrays, each of 6 series-connected panels. On trackers.
I have breakers on each array, and individual current monitoring and logging. And because I had something bizzare happen once and blew all the diodes in one array when it was initially connected to the rest of the arrays (I think DV/DT did it), I bought a bunch of DO-220 mounting, 200V, 10A schottky diodes. Each string has its own diode. Sure, I waste a very small amount of power, but they are not "horribly inefficent" (half a volt at 7 amps is 3.5 watts). I think my diodes cost all of about $1.50 each.
Quote from: RossW on December 05, 2013, 06:42:48 PM
Quote from: Robin on December 05, 2013, 02:07:40 PM
Do not use diodes. They are terribly inefficient and not high enough voltage. As I remember, Schottky diodes are not high voltage diodes.
Respectfully, I disagree.
I have 6 arrays, each of 6 series-connected panels. On trackers.
I have breakers on each array, and individual current monitoring and logging. And because I had something bizzare happen once and blew all the diodes in one array when it was initially connected to the rest of the arrays (I think DV/DT did it), I bought a bunch of DO-220 mounting, 200V, 10A schottky diodes. Each string has its own diode. Sure, I waste a very small amount of power, but they are not "horribly inefficent" (half a volt at 7 amps is 3.5 watts). I think my diodes cost all of about $1.50 each.
I think the point here is that using diodes is more wasteful than not using diodes. Diodes are not necessary in typical
PV combiner operation. Of course, it also depends on your definition of "horribly ". In my past years discussions, it seems that
most off gridders fight for every last watt they can get.
The higher voltage "Schottky" diodes do not have the nice and low forward voltage drop that the lower voltage Schottky's have.
They're almost as bad as a regular silicon diode. However, their on voltage goes down as their temperature goes up, which is
what is going to happen to a certain extent when they dissipate power which is in your favor. Less semiconductors also mean
less to break, especially something that can be so close, electrically to lightning strikes.
Ross, I suspect the reason your diodes broke was because the modules were not designed correctly.
What kind were they ? How old ? There have been bad batches of certain modules.
Diodes in parallel with a PV module should not be subject to high reverse breakdown because
the forward conduction voltage (Voc) of the PV module will (should) clamp that way before the diodes'
reverse rating is reached. That is another reason to suspect bad modules.
boB
Quote from: boB on December 06, 2013, 02:08:49 AM
Ross, I suspect the reason your diodes broke was because the modules were not designed correctly.
What kind were they ? How old ? There have been bad batches of certain modules.
Diodes in parallel with a PV module should not be subject to high reverse breakdown because
the forward conduction voltage (Voc) of the PV module will (should) clamp that way before the diodes'
reverse rating is reached. That is another reason to suspect bad modules.
Bob, I got 30 panels in one lot. All identical.
Being the typical, impatient, offgridder, I would build a tracker, get the panels on it, and connect it ASAP.
Usually this meant I connected them near the end of the day with little sun.
The final array however I got finished just on lunch time. So I had already 5 arrays connected, in full sun, making full power. I connected the last array and went around plugging in the panels together (I know, wrong!). As I put the connectors together for the last connection, there was this popping and tinkling sound above me.
(http://house.albury.net.au/26apr2010/100_4398.JPG)
(http://house.albury.net.au/26apr2010/100_4397.JPG)
The PV cells all survived. The supplier was going to replace the modules, but was happy I was more than happy to just (try) replacing the diodes, which he sent me by international express next-day-delivery. Replaced them all (over 3 1/2 years ago now).
My gut feeling is that the 150V "instantly" applied was enough to punch through the diodes.
After adding the diodes, I've never had any concerns about anything, and I also see zero reverse leakage overnight.
Ouch !
I had this happen about 2 years ago at a small energy fair in Oregon.... We had a small 50 watt panel
and one small-ish 12V car battery. Our table was outside and I hooked up the module directly to
the battery so it would charge. Normally this is just fine BUT the manufacturer (Chinese) had
marked the polarity wrong ! Bang went the diodes just like yours. I quickly discovered it was
marked backwards, removed the two broken diodes in the J-box and connected it up the other
way and voila... It worked.
Right on the leakage especially if you are using a charge controller which should be the case.
Again... Ouch ! But luckily all was still good.
boB
Ross,
So this was a complete panel string of bypass diodes that blew apart? Was one of the panels faulty? Did you suspect that the diodes, which look like rectifier types, were somehow below spec or wrong types?
Did you then replace all of the bypass diodes in all of the strings since they are identical panels?
I think tecnodave is talking about blocking diodes but why fast schottky types. I always thought these would be unnecessary when each string is combined via breakers.
dgd
Quote from: dgd on December 06, 2013, 04:29:55 AM
Ross,
So this was a complete panel string of bypass diodes that blew apart? Was one of the panels faulty? Did you suspect that the diodes, which look like rectifier types, were somehow below spec or wrong types?
Did you then replace all of the bypass diodes in all of the strings since they are identical panels?
I think tecnodave is talking about blocking diodes but why fast schottky types. I always thought these would be unnecessary when each string is combined via breakers.
I have 6 modules in series per array.
Something roughly like this one which was the first.
(http://house.albury.net.au/17apr2010/100_4336.JPG)
This was the final array to come online. 6 modules, 2 diodes per module, only 2 diodes didn't explode. I replaced them all.
They were indeed schottky, and they were there for (I presume) "shaded cell" bypass. None of the diodes in any of the other panels has given problem, and none of the replaced diodes have given problems.
I too am talking about adding series "blocking" diodes at the "combiner".
Yes, I have breakers. One for each array.
But breakers don't stop one array being potentially "reverse biased" if it is in shaddow. If the rest of my arrays are in sun, I could have close to 150V "on the bus". An array in partial shade (or full shaddow, as a cloud passes) might be making as little as 30-40V, but in a hardwired scenario with breakers, it will have 150V across it, while making only 30-40. Leakage current is a given.
It's changed since this picture was taken, but the "metering" box (wide open), above the DC breakers. Schottky diodes are the half dozen DO220 devices bolted to the copper busbar in middle of frame. The very thin red wires from connectors to diodes are "fusible links" in the event the worst happened.
Is it standard practice? No. Is it best practice? I don't know. Would I do it again? In a heartbeat.
(http://house.albury.net.au/30may2010/100_4478.JPG)
Ross,
Thanks for posting those pics. That looks like the backs of moving coil meters, ammeters I assume?, for each string and on the right side another? Is that an A to D device on back of meter, you are using the meter as a shunt? ( i think I remember you said this some time ago).
I have been using an MN-EDC quad box with 10A breakers on +ve only inputs from my 4 pv arrays of 5by 140w, 91v @ 7.85A
but want to change to dual pole breakers for the arrays.
I divert two strings to water heating via SSR. I found that one bypass diode in one of the strings was burnt out and I suspect one of the strings was badly shaded and the other was full power when this happened. Possible because these strings are 50 metres apart. The PVs kept working and nothing seemed damaged so I just replaced the diode.
Looks like placing some blockers may be a good idea, those to220 packaged types look a good idea and I like the fusible wire idea too.
dgd
dgd.
I was talking about blocking diodes. They look the same as the ones in RossW's pic of his blown diodes. These were field installed in my Siemens panels when I bought them used. These panels have 2 junction boxes having a total of 2 shaded cell bypass diodes factory installed and 1 field installed blocking diode in each panel. (Blocking diodes sloppily crimped and soldered) They were used when I bought them from a ham radio operator, he said that they were from a 2 meter mountain top repeater in Southern California. I originally used them with my Chinese tracer controllers, removing these blocking diodes as they were in 2 strings of 4 panels (440 watts each 390 watt controller) I use Multi-9 din rail breakers to switch in 5 first solar CdTe panels (375 watts) in parallel with the Siemens strings to boost power in foggy conditions. The first solar panels each set of 5 panels in parallel each feed 2 breakers one goes to the controller the other to a set of switch mode T-8 fluorescent lamps to keep the panels loaded at all times. Only one breaker for each CdTe string is on at a time. The amount of power in full sun would be too much for the tracers and the fluorescent lamps are to dummy load the CdTe panels in full sun as per the manufacturers recommendation not to let the panels go to v.o.c. I have never heard of anybody else saying any such thing but it is covered in a white paper on their website. The original buss bars in the MNPV-12 Combiners are not used as the breakers feed separate controllers and the fluorescent lamp bank dummy loads.
I recently reinstalled the blocking diodes and now have drastically reduced power output. I will need to remove them again to restore power as I am dropping to 50% s.o.c. sometimes
The tracers now do other duty as I recently bought a classic 150 to replace the 3 tracers.
RossW. I like your metering setup.....I'm doing sort of the same thing with brainy deal digital volt ammeters 0-200 volts/0-200 amps with shunts on each string......cheap on Amazon....but I had to futz with them and power the driver electronics with a 7809 regulator chip to get reasonable accuracy.
I'm still looking for a way to post some pic's but my iPad has too high a resolution for the allowed file size.
EDIT: the fluorescent lamp ballasts are Sylvania Quicktronic nominally rated 120-277 volts a.c. 50-400hz. and in very small print 65-165 volts d.c. They work fine with the 69 volt CdTe panels directly connected.
tecno
dgd
Those look like copper buss bars to me......two rows of 3 meters each.....nice busses
Tecno
Quote from: dgd on December 06, 2013, 06:02:22 AM
Ross,
Thanks for posting those pics. That looks like the backs of moving coil meters, ammeters I assume?, for each string and on the right side another? Is that an A to D device on back of meter, you are using the meter as a shunt? ( i think I remember you said this some time ago).
They are indeed inexpensive but "adequate" 10A DC moving coil meters, and yes, I'm using them as shunts for my logging. I like the meters as they're instantly meaningful. (I have made prettier labels since this pic!)
(http://house.albury.net.au/23may2010/100_4452.JPG)
tecnodave has it right, there are copper busbars to join the meters. When I took this picture I had not finished building my logger.
(http://house.albury.net.au/23may2010/100_4448.JPG)
(The stuff on the right hand side was leftover rectifiers from my turbine, but that's all in another box now)
Quote from: tecnodave on December 06, 2013, 06:53:38 AM
... These were field installed in my Siemens panels when I bought them used. These panels have 2 junction boxes having a total of 2 shaded cell bypass diodes factory installed and 1 field installed blocking diode in each panel. (Blocking diodes sloppily crimped and soldered) They were used when I bought them from a ham radio operator, he said that they were from a 2 meter mountain top repeater in Southern California. I originally used them with my Chinese tracer controllers, removing these blocking diodes as they were in 2 strings of 4 panels (440 watts each 390 watt controller)
..sorry a bit off topic but..
1997/8 I bought new about fifty of the Siemens M55 panels, they came boxes of 4 about $2500 per box. I thought these were excellent mono pvs, wired in pairs to an Heliotrope CC120 24v, they would work near max power. The junction boxes at each end for +ve and -ve were ok, the diode in each was crimped in.
It was only a couple of years later I found a pair was at zero, on close inspection the tape/traces at one end going to JB were blackened and one was dissolved.. dead panel. After general panic mode set in I got the ladder out and went inspecting the rest and many were ok, looked normal, bright silver traces BUT at least six were various shades of brown. I also noticed on some good ones lots of little holes in the solder that appeared to cover the traces.
Other issues I had was water getting under the junction box as the white glue dried and powdered away. The flat tinned copper trace to the junction box then corroded away. Fixing was not always possible without stripping away the tedlar backing to find some buried tinned trace.
WHat an absolute ballsup they were, warranty worth nothing as dealer vanished
Took me 3 months to dispose of the lot and get BP panels, 170watt types at over $2k each. ANother disaster but another story :(
I hope your's are ok and reliable
Quote
I use Multi-9 din rail breakers to switch in 5 first solar CdTe panels (375 watts) in parallel with the Siemens strings to boost power in foggy conditions. The first solar panels each set of 5 panels in parallel each feed 2 breakers one goes to the controller the other to a set of switch mode T-8 fluorescent lamps to keep the panels loaded at all times. Only one breaker for each CdTe string is on at a time.
Do you get fog very often? Seems like a nuisance having to manually switch in/out pvs like this :-X
Quote
The amount of power in full sun would be too much for the tracers and the fluorescent lamps are to dummy load the CdTe panels in full sun as per the manufacturers recommendation not to let the panels go to v.o.c. I have never heard of anybody else saying any such thing but it is covered in a white paper on their website. The original buss bars in the MNPV-12 Combiners are not used as the breakers feed separate controllers and the fluorescent lamp bank dummy loads.
This would put these panels in the
too complicated, avoid at all costs basket for me. I have never heard of this requirement for PVs before. I see they are thin film type PVs, are they so delicate that going OC in bright sunlight will damage them? they must be somehow optimised for poor light conditions.
dgd
dgd
The whole system is way too complicated but I started on a shoestring as my local utility is very unreliable in the winter, I live way out of town and need small power for a medical device.
Most of the system was scrounged from recycle, the CdTe panels were from a forklift dropped pallet of new ones, most did not survive. They were free. The Siemens were bought at scrap price and do seem to work ok. For $30.00 each I have got my use out of them. The Suntech were the best deal at $60.00 each for a brand new 280 watt panel, left over from a 25 house construction project, so I have built my system from junk and leftovers. I paid full price for my Tracer controllers which is the worst investment but they have paid off as well. I am in the situation where the building inspectors will not let me do anything without a $70,000 permit, so the whole solar setup in on an old worn out motorhome which my house plugs into, seems that they can not do anything about that, not that they didn't try. The whole thing plugs in with an OSHA compliant tempower cord. NEC only covers up to the cord and plug. I am building the system here in California to take to Alaska with me in a few years. There are many things that I would like to do better but I am regulated out of California.
I no longer have to switch panels as the Classic easily handles the power of all the banks. I have been doing electricity since 1965 including communications and computers so I will do things way different than the norm but everything is safe and meets the national safety code.
The CdTe panels will be the first to go but they work very well in low light and fog, on that I have locally dense fog April through July so I need every watt I can get. The Seimens will probably go to Alaska with me. I am constantly tinkering the system as I am still new to solar but not to electricity. I have done DC to microwave professionally. I am a commercial electrician but I do not do solar at all commercially.
Have you ever heard of panels that will not be warrantable if left at v.o.c.? I'm stumped at that but First Solar actually has a part of their warranty that states that you must notify them if you let the panels go to v.o.c.! These are not meant for small scale use, they were developed for Multi gigawatt power plants in the desert. For free I will use what I get my hands on, I have a pile of dead panels that I picked up on speculation.
I just got a power out service call so I need to go as a storm is moving in off the pacific.
tecno
dgd
Reread your comments again, I see that you had never heard of that unloaded issue, stumps me not one other article or manufacturer has never said anything like that.
The CdTe panels are way different , they are 2 2 foot by 4 foot sheets of 3.2 mm glass vapor deposited with Cds/CdTe then bonded together, no frame, just the sheets of glass. Junction box bonded onto glass with epoxy with two 5 mm pigtails with MC-3 connectors.
I find them very useful besides working in fog very well , I burn sulfate on off battery cells with them directly connected to two stainless steel probes that I insert through the vent caps to the individual cell plates. They are very high v.o.c. and have high internal resistance so that they work as regulated current supplies, still experimenting with this and it will be the subject of another thread as I have done apprenticeships at Alaska Husky Battery Co. In Fairbanks, Alaska ( they make batteries that will start your car at 70 below!) and at Trojan Battery back when they were a local outfit out of San Francisco. I will cover Tungar Bulb chargers as well as other hidden secrets in the battery industry, but that deserves a thread of its own.
I am having junction box issues that you describe in your post and have seen evidence of water seepage at the junction boxes. I just checked the panel shunts this morning and found two dead strings, no time to check it today as I have a laundromat to finish and the storm is moving in. More time on the Onan, not the cheapest on fuel but they always run! First crank every time!
tecno
Quote from: tecnodave on December 05, 2013, 01:32:26 PM
Strings:
4 ea. Siemens M55 36 cell mono in series X5 v.m.p. 69.6. V.o.c. 85.6
2 ea. Suntech STP-280/24/Vd. 72 cell poly in series. V.m.p. 70.4. V.o.c. 89.6
10 ea First Solar FS-275. 154 cell CdTe. In parallel. V.m.p. 69.4. V.o.c. 92.0
Tecno
I looked up the First Solar FS-275
Data sheet says they don't have any bypass diodes.
Is that common for all CdTe modules ?
boB
Quote from: tecnodave on December 06, 2013, 11:56:20 PM
I burn sulfate on off battery cells with them directly connected to two stainless steel probes that I insert through the vent caps to the individual cell plates.
Wow. I'm very impressed. You must have nerves of steel. And no fear! --vtMaps
tecno,
Good to see you are taking advantage of free and low cost PVs, even better to know that the Classic has no problem dealing with this mixed bag of panel types although you have properly configured them in series to get almost identical voltages.
The eTracers are really popular here is NZ, every little PV dealer and his dog seem to sell tracers to match their PVs. One dealer I know has about 20 or more 10 to 60amp Tracers including the MPPT eTracer 60A models in their junk bin. No tech support at all, replace is only support, after 12 months, your loss.
Those M55s must be at least 17 years old now, I'd think near the end of their useful life.
WIth the real low PV prices now and the Chinese apparently dumping panels at giveaway pricing, its just so easy now and cheap too to put together a several Kw array of identical panels. Even planning arrays too large for the Classic to allow for poor weather days.
Sorry to hear about the planning and building issues but love your solution to use a motorhome
dgd
boB
I think that is true for all of the types like the First Solar. GE , BP , & Siemens make almost identical panels,they are built with Cds/CdTe vapor deposited on the glass, 154 cells about 2/3" X 2' wide, bonded between two sheets of glass. Very cheap way to make panels, about .40/watt production cost. No way to put diodes between the glass. They do specify landscape orientation if there are any shading issues. I do measure reverse current through them, so I just turn them off and dummy load them during days of good sun. I had some CIGS panels that were wired the same, no cell bypass diodes and no blocking diodes, hard to do with bonded glass panels. Their voltages were not compatible. Have you ever heard of panels that are not to go to v.o.c.? I never heard of such a thing! Oh well they were free so I will get what use I can out of them.
vtmaps
Quote from: tecnodave on December 06, 2013, 11:56:20 PM
I burn sulfate on off battery cells with them directly connected to two stainless steel probes that I insert through the vent caps to the individual cell plates.
Wow. I'm very impressed. You must have nerves of steel. And no fear! --vtMaps
Or just plain nuts & no fear. Or something like that. I did time in battery building shops, have melted a few things! I got knocked across the room doing a 12 kW FM broadcast transmitter 5kv DC to the final amp, got great respect for electricity! Do illegal power upgrades a lot, Deal with live utility wires, 120/240/480 3 phase, no it's about focus, focus, focus, one big mistake is all it will take. Shorting 240 volt within 50 feet of 25 kva transformer can produce 70,000 amps. Even if you sag the 240 down to 120 that's still 8.4 megawatts for 400 milliseconds until the utility fuses blow.
Read my upcoming post about burning sulfated cells and you will know just about nerves of steel, if you are not comfortable doing it, don't even think about it!
dgd
I too have several dead tracers and many other cheaper Chinese controllers but I got them dead, I opened them to attempt salvage but they are throwaway. No marking on the chips, etc, well built but very limited. Their universal answer to any technical question is "How many units do you want" Well at least they are consistent......lol. I looked at the eTracer 60 amp but here they are $489. USD and The Morningstar TS MPPT 60 is $485. No way I am going to pay more for Chinese than well made American product. I paid $610 for my Classic 150 from NAWS and it is probably one of the best buys of my system. Well I paid $950 for 4 Interstste L-16's 380 ah so I'll not complain there, and Suntech poly 280 watt for $60 each, I'm laughing! The Siemens are at end of life, but it have 2 Arco M75's that are even older, burnt bronze, and still produce full power. At least 25 years old, used in the Arizona desert for an earthquake monitoring station.
On the motorhome, well our building department is a work! Any way I can stick my thumb in their eye. Almost 99% of the construction jobs that I do are done without a permit! they force you to do it.
I still remember the inspector who tried to outlaw my 40' Gillig bus workshop,registered as a motorhome, he could not find any regulation against it. Stormed off my place, furious that he could not do anything. Wanna be cops! Oh well!
tecno
You do hear hear storys about commando raids on these calfifornia desert backlots. For the horendous crime of having a shipping container or something. Whats the deal, why so twitchy?
zoneblue,
Yeah that happens here....locked gate....they can't come through that!
It's all about money, Santa Cruz County has the second largest building department in California, second to only Los Angeles county, our neighbors in Santa Clara county have 5 times our populations, but a building department only half the size. It's $70,000 for permits here before you turn a shovel. Just to change a $19.00 flex connector on your water heater it's $80.00 for the permit and if you do that they will find something else to cite you on. Major cash cow, the building departments here. San Mateo county's new head building inspector went before the county board of supervisors to request red lites and sirens for the inspectors cars. Got laughed out of chambers! I live on a small farm which dates to the 1920's so I am largely exempt but that doesn't mean they won't try. My new workshop is a 8 X 40' shipping container and I pay a permit fee for that. I have cashed in on it as I have a row of new electrical panels mounted on a fence row pre weathering them so I can do upgrades and not look brand new, did I do that, I have no recollection of that. Ollie North syndrome! The permits are more than the parts and labor! It's funny how when you get older that it is convient to forget things that don't matter. My neighbors can appreciate that as I do live wire upgrades without the government getting in there. Genuine utility crimps and seals and all! Lol! Government in California is out of hand. I can actually charge more than the total on a permitted job! Some folks have waited 10 years and more for their permit process! Moving to Montana soon, gonna be a dental floss tycoon.....lol
Tecno
Quote from: tecnodave on December 07, 2013, 07:58:40 AM
boB
I think that is true for all of the types like the First Solar. GE , BP , & Siemens make almost identical panels,they are built with Cds/CdTe vapor deposited on the glass, 154 cells about 2/3" X 2' wide, bonded between two sheets of glass. Very cheap way to make panels, about .40/watt production cost. No way to put diodes between the glass. They do specify landscape orientation if there are any shading issues. I do measure reverse current through them, so I just turn them off and dummy load them during days of good sun. I had some CIGS panels that were wired the same, no cell bypass diodes and no blocking diodes, hard to do with bonded glass panels. Their voltages were not compatible. Have you ever heard of panels that are not to go to v.o.c.? I never heard of such a thing! Oh well they were free so I will get what use I can out of them.
Nope. Never heard of a PV you can't open circuit. Also don't know of any babies that were born with clothes on.
I don't believe there is a spec that says you can't open circuit one. It would sure make it very hard to unbox
one of those, assuming it was short circuited in the box, and then install it.
Also, bypass diodes do not have to be embedded inside the glass. They put them in the J Box. At least one diode.
Series blocking diodes should not be necessary for PV arrays using like modules and the same number of modules per string as long as you are using a combiner with the proper series fuse or breaker rating for strings more than 2 in parallel.
boB
boB,
I have not heard that anywhere else but it in in their installation guide for the FS-2 and FS-3 panels , I will sent it to you for your reading including a pointer as to where it is in their documentation. There is also a white paper somewhere on their website. The white paper talks about copper substrate migration as a result. It does not say ever, just no extended exposure to full sun during construction for more than 90 days. No operation at v.o.c. And no short circuit operation. The panels need to be covered during the installation process. Also they specify MPPT controllers only.
My foggy season is April thru July, in the past that is the only time I have used them for battery charging. In full sun I do not need the extra power that they provide so I cover them with 1/8 inch plywood or dummy load them.
I could not sent as an attachment here but will email it.
tecno
There is a fair amount of internet info about Cadmium Telluride thin film solar panels. I can't find anything about their application where special care is needed if left OC.
They sure do tick all the right boxes for me..
- Use Cadmium, one of the 10 most toxic materials, (we just need more Cadmium mining :-\)
- Telluride is rare, China appears to be main source but deep sea mining possible
- First Solar cant get regulatory approval (RoHS compliance) and dont seem to want it as its too difficult to achieve.
- Recycling CdTe PVs looks uneconomic so more toxic landfill?
- Damaged PVs mean immediate health hazard and need specialist HazMat clean up/treatment
- Apparently panels are safe in fire as glass melts/seals in the cadmium ::)
- Recommended for large PV applications only where they can be managed ???
dgd
Quote from: tecnodave on December 06, 2013, 11:56:20 PM
... I have done apprenticeships at Alaska Husky Battery Co. In Fairbanks, Alaska ( they make batteries that will start your car at 70 below!) and at Trojan Battery back when they were a local outfit out of San Francisco. I will cover Tungar Bulb chargers as well as other hidden secrets in the battery industry, but that deserves a thread of its own.
Thats a thread I look forward to reading.
For some unknown reasons my Century Yuasa FLA circular plate design 1080Ah 24V bank has just kept going for near 15 years now.
The only SOC monitoring I do is observing the voltage, maintenance is watering and making sure terminals are clean and an occasional wipe down with a damp cloth to get the dust away.
Yet in the 1990s an 880Ah 24v bank of R220s was dead within a year, ok 4 parallel strings of 4 series connected R220s, learnt the hard way about parallel strings :-[
Again with Australian SunCycle 2V 800Ah cells in one string of 12, this got under 2 years as bad design allowed terminal posts to rise up from top of cell and capacity/voltage sagged. One cell actually reversed its polarity -incredible! Of course warranty wqs a laugh, company just was not interested.
I briefly saw a post, was it from you?, about root cause analysis? Did you get to the root of the stiction on the st225? :)
dgd
dgd
First Solar used to sell to resellers for the public market, they are unavailable now. They focus on Gigawatt power plants, they have just signed a deal with Japan to install PV plants equal in size to two of the nuclear plants which melted at Fukushima. There is a environmental certification document from French government certifying their environmental suitability, They have a recycle program that takes back damaged panels from users without question. Somewhere in their white papers is where they get their cadmium as a byproduct from some other mining operation.
That said I would not buy these new due to the toxic nature of cadmium , I scrounged mine from a forklift dropped pallet ,only 10 of 60 survived, I did not know the nature of the panels at that time, only that they were free solar panels and my first large set.
I had been using the Arco and Siemens panels for years at communication sites that I had maintained for General Electric, Motorola , and others and am much more familiar with Monocrystalline technology having worked in crystal growing in the semiconductor industry as well.
My system is totally mixed bag with few products purchased as new as this is part of a learning process for me besides not wanting to support nuclear , coal, oil etc. I do have utility power but just don't use it unless absolutely necessary.
My largest mistake was buying more than one tracer, I should have just leaped to better technology but medical issues take priority so I limp along with a cobbled up system. My next purchase will be 12 matching 250 watt panels. Looking for Suntech Wuxi poly 72 cell panels.
Looks to me that Warren Buffet is looking to buy big in solar to do a deal with Japan.....Suntech Wuxi will be coming out of bankruptcy court any day now....warren Buffet buying?....waiting to see.
dgd
I did indeed work at Slavegate in pre-production prototype root cause failure analysis, but the ST-225 predates me, The ST-225 family of drives was already out of production by the time I got there.
My charge was the read/write channel of the 9XXA and 3XXA lines of notebook and 3 1/2 inch drives.
As I remember I was on the team that grew the 9150A 150 mb drive to about 4 gb and the 3XXA drives from about 400 mb to 8 gb. before i left there. Lots of learning there but I am a sun worshipper, I hate being locked in a cage with no sun, could not wait to get back in the field. Had to sign non-disclosures and never talk about my work as the disk drive industry is very competitive.
I will be sharing my battery experience but I am somewhat reluctant so as to not endanger people.
Many dangers there......hydrogen gas burns at 5600 feet per second....remember Three Mile Island Nuclear power plant meltdown. Quote. " We had a rapid Hydrogen Burn". Rapid hydrogen burn , my butt, damn thing exploded, jellied the entire containment dome....but we can't talk about that can we? Fukushima power plants exploded when the zirconium cladding of the fuel rods flashed into hydrogen gas at 550 degrees Fahrenheit ..same exact thing that happened at Three Mile Island, loose cooling water, temperature rises, gets to 550 degrees oops......bang......total meltdown follows.....Russians 1.....USA 1........Japan.......3 maybe 4........but nuclear power is safe....yeah right.
On batteries,
Parallel strings never work out....just can't divide the current correctly as the cells age......I have seen cells reverse polarity...rare....but it does happen! There are a lot of battery companies who will sell you product, not that many that will back them up.
Gotta go, some field service work to do
td
Well, sure enough, just like tecnoDave says, here is the part in their manual about not exposing them to
Voc for too long....
"Open circuit exposure may accelerate module efficiency loss and should therefore be minimized. First Solar requires that
modules not be operated in open circuit conditions for more than ninety (90) cumulative days to avoid a potential reduction
in energy output over the life of the modules.
Modules must not be operated under short circuit conditions for extended durations. Short circuit operation is not an
approved mitigation technique for open circuit exposure.
"
My question is, how close to Voc do you not have to be in order for the efficiency not to be reduced ?
If operating just near to Voc is not good for them, then this means that you should NOT get your
batteries full because the controller will run them near Voc when batteries are full if you have enough
power from these PVs.
boB
boB,
Stumps me but in my original setup with two tracers with 3 sets of panels on each controller (2 strings of 4 Siemens panels in series, 440watts and one set of 5 First Solar panels in parallel, 375watts) Two controllers I made a logic board which looked at controller v. in that would switch the first solar panels off the controller and on to the dummy loads at 76 volts. Probably too cautious on my part but I depend on these panels to power me through the foggy season
They do not really push these panels for off grid use. First Solar has built about 8 gigawatts of utility scale plants and just landed a major contract to replace the lost power at Fukushima with PV plants with a $100 million investment in Japan. I visited two of their facilities in Topaz, San Luis Obispo County, California (550 megawatts)and one in northern Arizona, truly impressive.
I read every bit that I can as solar is our future, sometimes I wonder just how much is baloney so I do further research on the subject. I studied nuclear so that I will know better how to oppose it.
tecno
Quote from: boB on December 07, 2013, 06:43:37 PM
"Open circuit exposure may accelerate module efficiency loss and should therefore be minimized. First Solar requires that
modules not be operated in open circuit conditions for more than ninety (90) cumulative days to avoid a potential reduction
in energy output over the life of the modules.
"
My question is, how close to Voc do you not have to be in order for the efficiency not to be reduced ?
If operating just near to Voc is not good for them, then this means that you should NOT get your
batteries full because the controller will run them near Voc when batteries are full if you have enough
power from these PVs.
boB,
Would the KID not be an ideal controller for these PVs?
With the load used as a voltage Clipper that increases a resistive PV load as the battery gets full and pv voltage rises.
dgd
boB,
I just sent you 2 data sheets on the FS-2 Modules. The one in English is close but the one in Dutch or German has the exact electrical specs as the most of the ones that I have that were made in USA but I have one made in Asia that has slightly different specs.
I can not find any I-V curves in my data collection or on their website.
There is an abnormality in their data as follows:
Panel type. V.max. # cells. V/cell
FS-2 series. 69.6 116 .600
FS-3 Series. 47.5 154 .308
For comparison
Siemens. 17.4. 36 .4833
Suntech. 35.2 72 .4888
Now if they reversed cell count
FS-2. 69.6 154 .45
FS-3 47.5 116 .41
Basic physics: the voltage of a cell is directly dependent on the junction in that cell.
No proof but I think I count 154 cells in the panels in the panels that I have, real hard too see as the panels are black and cell traces are hard to see, ah the mystery of it all.
First Solar is not real responsive to data requests.
FS-2 Imp is 1.04 Isc is 1.20
I went and looked for that white paper but I could not find it.
td
boB, dgd, vtmaps, & others
Results of a side by side comparison
System One:
Two strings Siemens M-55 mono in series 69.8 v.max. 440 watts
Tracer 3215RN controller. 30 amps 150 volts max
4 X L-16 battery at 60% S.O.C.
System Two:
5 ea. First Solar FS-275 in parallel. 69.6 v.max. 375 watts
Tracer 3215RN controller. 30 amps. 150 volts max
Same battery set as above. (Controller outputs in parallel)
Conditions , heavy ground fog, cannot locate sun in sky, noon, no shading, 100 % humidity
System one. Net 78 watts. % of STC. 17.7%
System two. Net 116watts. % of STC. 30.9%
This is why I futz with these cantankerous panels
tecno
I think that what I actually did in my in the fog comparison I swapped the setups where I normally have two sets of Siemens (440 watts) and one set of First Solar (375 watts) on each controller to the test setup where I had all 4 banks of Siemens (880 watts) on one controller and both banks of First Solar (750 watts) on the other so that skewers the % of STC values to half of the values in the previous post, 8.8 % for the Siemens and 15.5% for the First Solar. This was done last May during our foggy season, aw the value of good notes, I should have been documenting more.
I struggle for every watt through the foggy three months here, need to top off every week with the Onan. I was running the Suntech panels on a Tracer 4210RN controller 40 amps 100 max volts, 1080 watts. Don't have the notes on their output as the panels were in parallel and a different controller used with these panels with a different conversion ratio was used for them.
Quote from: dgd on December 07, 2013, 08:23:47 PM
boB,
Would the KID not be an ideal controller for these PVs?
With the load used as a voltage Clipper that increases a resistive PV load as the battery gets full and pv voltage rises.
dgd
Yes, you're probably right here.
That should work just fine.
boB