Author Topic: Intro and questions, if I may  (Read 4143 times)

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Offline ksouers

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Intro and questions, if I may
« on: February 01, 2012, 05:26:31 am »
Hello everyone.
I’ve been lurking around for about a week and decided to join your friendly little group. I have a question or two, but first I’d like to introduce myself.

My name is Kevin. I’ve been using solar on my sailboat for many years. I have settled on a single panel set up that works quite well for me. I’m also interested in wind power and I’ve lurked on the “other” site off and on for quite some time (years). When I was much younger, in the 70’s and 80’s, I had dreams of living off-grid with only wind power and passive solar for my basic needs. As in many things in life, that dream never fully developed.

I’m older now and preparing for retirement, though that is still many years away. I’ve starting taking some of my energy needs off-grid a portion at a time, starting with the garage and my hobby machine shop. I’m starting with what I’m familiar with, solar, and I’ll eventually add a small (micro?) wind turbine or two. I have a terrible site for wind power; the lot is on a hillside surrounded by lots of mature trees and tract houses. Small wind is about the only way I can go, and summer here usually means NO wind at all (except for the twisty ones). I’ll be satisfied with a few hundred watt/hours or so a month from a small turbine. I have no illusions about taking the house completely off-grid. Just the satisfaction of knowing at least my hobbies are completely independent of the utility companies is enough for me. Perhaps later I can find a halfway decent wind site to retire on.

Now on to the questions:
I’ve taken some of the “surplus” equipment I’ve had laying around from the sailboat projects and applied them to the garage project; a 25 watt panel, a 5 watt panel and a Blue Sky MPPT charge controller. I also have a 1000 watt Harbor Freight inverter that is used a few times a year in the car for another hobby. The battery bank is two group 27 batteries in parallel. Yesterday I added an 85 watt panel for a total of 115 watts, and just like the wind dying when a new turbine is flying, the skies clouded up shortly after the new panel was hooked up to the array. I’ll add another 85 watt panel before summer and perhaps another before the end of the year.

 The inverter has been idling continuously for several days (also cloudy) ready to run the garage door opener and lights with the 30 watts array keeping the battery voltage just above the 50% mark through the clouds. Yesterday was supposed to be clear in the morning, and it was for a while, the battery bank was showing 12.19 volts just before sunrise. It looked like a great test day for the new panel. As the clouds started moving in early I did see a steady charge of 1.5+ amps with several minutes of 3.5-4 amps during breaks in the clouds. Still, the batteries were only charged up to 12.33 volts. I would have expected a better charge than that, even on a mostly cloudy day. This is what I would expect just from the 30 watts array.

As it’s a 12 volt system all the panels are hooked up in parallel with individual leads to the charge controller. Is this perhaps not a good thing? Should I take the smaller panels out of the array and just run the 85? Or were my expectations too high? Should I give it more time before making a judgement?

I know you guys can’t judge the sunshine we had here yesterday, but I expected a little better performance from a potential 115 watts of panels. I didn’t get to watch the controller all day, I did have work to do, so the cloud cover could have been worse than I observed, perhaps I just happened to see the better parts. I’m more worried about the mish-mash of panels and possibly causing some damage.

Whew! That’s a rather long winded setup for just a couple questions! Sorry about that.

Thanks,

Kevin
As far from the city as I can get but still keep my job.

Offline bj

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Re: Intro and questions, if I may
« Reply #1 on: February 01, 2012, 05:38:12 am »
   There are many here better qualified to answer you Kevin, so for now, just let me say
   welcome!
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Offline WooferHound

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Re: Intro and questions, if I may
« Reply #2 on: February 01, 2012, 10:47:57 am »
Hey There and welcome
You seem to have a good start on a decent system and you're gonna have fun with it.
You left out an important piece of information. To answer you properly I would need to know your Battery Capacity.
I have a 150 watt solar power system (see link in sig). Each individual panel passes through a blocking diode to prevent power from backfeeding the panels when they aren't producing. Your charge controller may be doing this function for you. These diodes also help prevent the panels from backfeeding themselfs if some of them are shaded and others are not.

My batteries are 225 amphours. I use the 12 volt power directly off the batteries without an inverter. My loads are rather small and I max out at around 4 amps when I have a lot of stuff turned on, so My batteries will last over 10 days without Sun before I start to get worried about the voltage going down too low. But when the Sun returns after that amount of time, it takes a few days to pull the battery voltage back up to a 14.7 volt full charge. Also it seems that even in full Sun, the voltage will rise steady to a point and then stop rising and remain steady and unchanging even with the Sun beaming. It rises slowly through the 13 volt range and then it seems to rapidly rise past 14 volts and on up to a full charge. After a full charge and at night, the batteries will settle back down to 12.6 or 12.7 volts without any load on them.

So what is your battery size ?
How much power does your inverter pull when you aren't using any power from it ?
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Offline ChrisOlson

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Re: Intro and questions, if I may
« Reply #3 on: February 01, 2012, 03:10:01 pm »
So what is your battery size ?

Group 27's are 95 ah.

Edit: I might add that to match solar capacity to battery capacity, you really only need to replace what you take out.  But assuming a daily load that draws the batteries to 50% SOC every day, the usual recommended solar capacity would be 10% of the amp-hour rating of the bank.  Or for for 190 ah, 19 amps @ 12 volt nominal would be about 225 watts of required solar capacity to get the bank thru bulk and absorb during the available daylight hours.

If there are normal loads on the bank during the charging process, those normal loads must be added to the above so the solar panels can carry both the normal loads and handle the charging requirements during available daylight.

You would typically want about 1% of the ah capacity, or about 1.9 amps, to maintain float.  1.9 amps @ 13.2 volts is 25 watts.
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Offline ksouers

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Re: Intro and questions, if I may
« Reply #4 on: February 01, 2012, 06:14:14 pm »
Thanks for the warm welcome, guys.

Woofer: The charge controller does keep the batteries from back feeding into the panels. The batteries are 90 ah, I think. A little on the smallish side for group 27's. I need to get some T-105's, but this is what I had on the sailboat and will serve until they are dead or repurposed elsewhere. The inverter pulls 1.4 amps when idling.

Chris: Thanks for confirming that. I knew it intuitively from experience but seeing someone else explain it helps a lot.

My main concern was the mix of different sized panels. I've never run panels in parallel before, on the boat each battery had it's own panel charging it while it was off line. I'm concerned about the wide disparity between these panels causing some damage. The open voltage between the panels is within half a volt of each other, so logically I didn't think there'd be a problem. But I don't have the experience to believe it to be so. I'd rather be using all matched panels, but that will happen in time.

I don't have diodes on the individual panels. I've read where people recommend they be used, but I've also read reliable sources that say they are not necessary. I just don't know how much, if any, a lighted panel will back feed into a shaded panel. And yes, I do have that situation at my site with trees casting shadows in the morning.

While I'm thinking of fixing those things that are not great, can I mix T105's with the group 27's? I know they'll have to be in pairs. 4 T-105's at one shot is not going to be cheap, was thinking about doing it in pairs, though.

Update:
Today was mostly clear, only some sparse high cirrus. I checked on the batts when I got home and voltage was 12.87 and still had .7 amps going in. I'll check again after they've had time to rest, but I already know it'll be a solid 12.7 volts. The inverter was turned off. I had to go to the office today so didn't get to adjust the panels, just set them facing South. Yes, a tracking system is already on the list. Also on the list is a smaller standby inverter for the door opener.

Now that I've got a good charge I can see if this is going to run the lathe :)
Baby steps, it's all baby steps.

Thanks,
Kevin
As far from the city as I can get but still keep my job.

Offline ChrisOlson

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Re: Intro and questions, if I may
« Reply #5 on: February 01, 2012, 06:20:46 pm »
My main concern was the mix of different sized panels. I've never run panels in parallel before, on the boat each battery had it's own panel charging it while it was off line. I'm concerned about the wide disparity between these panels causing some damage.

Kevin, the different size panels don't matter a bit in parallel.  If you are using a MPPT controller with panels hooked in series, then you will want/need matched panels.
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Offline rossw

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Re: Intro and questions, if I may
« Reply #6 on: February 01, 2012, 06:50:46 pm »
I don't have diodes on the individual panels. I've read where people recommend they be used, but I've also read reliable sources that say they are not necessary. I just don't know how much, if any, a lighted panel will back feed into a shaded panel. And yes, I do have that situation at my site with trees casting shadows in the morning.

I would have agreed, once upon a time.

I have a moderate PV install. 6 arrays each of 600 watts. 4 of them on trackers.

A horrible little tale for you. When I installed the last array, it was about mid-day that I was ready to go. Just like the other arrays, as I got them done, I plugged each array in in parallel with the others. Each other time this was usually late afternoon. This time it was peak production. Well, I plugged in the cable and..... there was crackling and snapping and popping all around me.

Every panel (6) on this last array had to come off. Inside their J-boxes looked like this:


And a handfull of little rattly bits fell out, like these. Do you recognise them?


At the time, I was gutted. I was lucky, the company I purchased the panels from (in china) couldn't help me enough. Concerned and wanted to send me replacement panels, was delighted that I thought it was just the diodes and sent me replacements by overnight international courier.

All the panels came back working once I'd replaced the diodes (thankfully). It is my belief that it was the instant connection of around 120V DC to the array that caused a cascade/avalanche in the schottky diodes, allowing them to pass very substantial current. (The rest of the arrays were producing around 2.8kW at the time).

Since then, I added (as I should have in the first place) - series schottky diodes for each array.
I bolted each of them to a copper busbar for both electrical interconnect, and thermal dissipation.
The thin wire on the leads is very short. It is thin so it doesn't have a tendancy to break the leads off the diodes, and it will make a fusible link in the event of some catastrophic failure.


I now get zero current flowing back into any array, regardless of which ones are in shaddow (clouds moving past, arrays shading each other, etc), and I will never get another incident like this and blow up a panel.

Offline Watt

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Re: Intro and questions, if I may
« Reply #7 on: February 01, 2012, 06:54:20 pm »
My main concern was the mix of different sized panels. I've never run panels in parallel before, on the boat each battery had it's own panel charging it while it was off line. I'm concerned about the wide disparity between these panels causing some damage.

Kevin, the different size panels don't matter a bit in parallel.  If you are using a MPPT controller with panels hooked in series, then you will want/need matched panels.
--
Chris


I would have to be careful with this myself. 

The following numbers are just examples not of actual panel output.
If that mppt controller is holding the mppt voltage at say 52 volts due to the Vmp and VmI of one panel which is a better producer and the second panel in parallel is hooked to this same controller with Vmp and VmI 4 volts less than 52 volts, ( Say bulk charge for 48v battery group)  that one panel will not be producing as much power into the system ( if any ).  Will that work, yes but with limitations.  The two in series, if the VmI is very close between the two, series may be a better option.  If the current is way different and the Vmp is too far off for parallel, two mppt controllers may be required or three or four or just direct connect.   
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Offline Watt

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Re: Intro and questions, if I may
« Reply #8 on: February 01, 2012, 07:02:45 pm »
I don't have diodes on the individual panels. I've read where people recommend they be used, but I've also read reliable sources that say they are not necessary. I just don't know how much, if any, a lighted panel will back feed into a shaded panel. And yes, I do have that situation at my site with trees casting shadows in the morning.

I would have agreed, once upon a time.

I have a moderate PV install. 6 arrays each of 600 watts. 4 of them on trackers.

A horrible little tale for you. When I installed the last array, it was about mid-day that I was ready to go. Just like the other arrays, as I got them done, I plugged each array in in parallel with the others. Each other time this was usually late afternoon. This time it was peak production. Well, I plugged in the cable and..... there was crackling and snapping and popping all around me.

Every panel (6) on this last array had to come off. Inside their J-boxes looked like this:


And a handfull of little rattly bits fell out, like these. Do you recognise them?


At the time, I was gutted. I was lucky, the company I purchased the panels from (in china) couldn't help me enough. Concerned and wanted to send me replacement panels, was delighted that I thought it was just the diodes and sent me replacements by overnight international courier.

All the panels came back working once I'd replaced the diodes (thankfully). It is my belief that it was the instant connection of around 120V DC to the array that caused a cascade/avalanche in the schottky diodes, allowing them to pass very substantial current. (The rest of the arrays were producing around 2.8kW at the time).

Since then, I added (as I should have in the first place) - series schottky diodes for each array.
I bolted each of them to a copper busbar for both electrical interconnect, and thermal dissipation.
The thin wire on the leads is very short. It is thin so it doesn't have a tendancy to break the leads off the diodes, and it will make a fusible link in the event of some catastrophic failure.


I now get zero current flowing back into any array, regardless of which ones are in shaddow (clouds moving past, arrays shading each other, etc), and I will never get another incident like this and blow up a panel.






Wow, thanks for sharing this post with us Ross.  That's an eye opener for sure.  So, did you get to keep the replaced set on top of the replacements?
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Offline rossw

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Re: Intro and questions, if I may
« Reply #9 on: February 01, 2012, 07:12:57 pm »
Wow, thanks for sharing this post with us Ross.  That's an eye opener for sure.  So, did you get to keep the replaced set on top of the replacements?

No, I only asked for (and received) the diodes.
There was no damage (that I could ascertain) to the rest of the modules.
Since the man in China was so eager to help out, and sent me 15 diodes (I needed 12), without any hassles, and wouldn't take any money, AND sent them international overnight courier, there's no way I was going to try to screw him for more panels.

I fixed them with his parts and my labour, and was happy to come to such a resolution so quickly and with so little out-of-pocket expense.

Offline ksouers

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Re: Intro and questions, if I may
« Reply #10 on: February 01, 2012, 07:18:11 pm »
Thanks Chris. I won't worry about it any further then.

rossw: Thank you for relating your experience. I'm sure glad you weren't hurt! I know I would have had a dirty diaper at the least! Also glad everything worked out well with the vendor. I'm always afraid dealing with Chinese vendors. I've only dealt directly with a Chinese vendor once and all was well. Usually a US vendor will make good on a Chinese product even if the manufacturer won't. But then I only buy from established businesses, ebay scares me. I much prefer doing business where the owner is right there on site. It may cost a little more but I know where to go when there is a problem, no email tag with someone halfway round the world.

I will add diodes. Must they be schottky? I know they are low-loss, but that's about all I know. My thinking was the cells already have diodes on them to prevent loss and back current for shadowing and dead cells, therefore diodes weren't needed on the pig tails.
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Offline rossw

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Re: Intro and questions, if I may
« Reply #11 on: February 01, 2012, 07:29:43 pm »
rossw: Thank you for relating your experience. I'm sure glad you weren't hurt!

I was doing it all "safely". There was never any risk to me, which is more than be said for the panels.
I'd honestly never heard of or thought about the problem. I've had diodes avalance before with DV/DT so I SHOULD have considered it. But I just didn't. More fool me.

Quote
I'm always afraid dealing with Chinese vendors.

I purchased quite a bit from this guy, and was in regular contact with him by skype.

Quote
I will add diodes. Must they be schottky? I know they are low-loss, but that's about all I know. My thinking was the cells already have diodes on them to prevent loss and back current for shadowing and dead cells, therefore diodes weren't needed on the pig tails.

Do the math.
A typical schottky diode with 8A through it will drop around 0.5V Power = V*A = 4W. Typical junction to heatsink and heatsink to air thermal resistance with a modest heatsink area but without forced air cooling is probably around  10 degC/W. So with ambient temperature of say 40 degrees, add another (4*10) = 80 deg C. Not so bad.

A typical rectifier diode will go close to 1V, so power = 8W, and now we're up to 120 deg C.

*PER DIODE*.

Offline Watt

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Re: Intro and questions, if I may
« Reply #12 on: February 01, 2012, 07:29:59 pm »
Wow, thanks for sharing this post with us Ross.  That's an eye opener for sure.  So, did you get to keep the replaced set on top of the replacements?

No, I only asked for (and received) the diodes.
There was no damage (that I could ascertain) to the rest of the modules.
Since the man in China was so eager to help out, and sent me 15 diodes (I needed 12), without any hassles, and wouldn't take any money, AND sent them international overnight courier, there's no way I was going to try to screw him for more panels.

I fixed them with his parts and my labour, and was happy to come to such a resolution so quickly and with so little out-of-pocket expense.

Sorry Ross, I should have realized they may not want to deliver whole panels next day for free and never thought about repairing them even though you said they were all fixed.  OOPS, taking foot out of mouth now...
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Offline ksouers

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Re: Intro and questions, if I may
« Reply #13 on: February 01, 2012, 09:01:15 pm »
Thanks Ross. I love learning this stuff.
I can dwiddle bits with the best of them (I'm also a grumpy Unix admin, AIX flavored) but electronics makes my head hurt.

Kevin
As far from the city as I can get but still keep my job.