Author Topic: More panels!  (Read 6352 times)

BruceM

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Re: More panels!
« Reply #30 on: March 04, 2018, 02:16:53 AM »
When the difference in temperature between the heatsink and the ambient starts getting small, then blowing more and more air (with an exponential increase in fan power consumption) will do less and less...that's the point you noticed experimentally where more air doesn't seem to help.

I got my new PV current regulator assembled and soldered today.  Now for a rough night with a whopping headache from the solder fumes.  I thought I dodged them but apparently not.



glort

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Re: More panels!
« Reply #31 on: March 04, 2018, 02:28:43 AM »

Bruce there is a trick I learned from a shooting range I used to go to. They had strong airflow coming from behind the firing line at your back. As the firearm was held in front of you, the smoke was always moving away.

I do this with different things I want to avoid fumes with just by putting a fan or blower behind me.  Moves everything away from you and minimises if not eliminates  the exposure you get.
I have also used a household vac and put it outside when sitting near a window and drawn the fumes out from what I was doing so they were discharged outside.

Would be interesting to see and hear some more details of the controller you came up with.

BruceM

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Re: More panels!
« Reply #32 on: March 04, 2018, 04:47:16 AM »
This new PV current regulator  is really a simpler version of the one I've had in service for the last 8 years or so.  It's just a big linear series regulator. It's set up now for 0-5V current as control (through an opto-isolator) = 0-16 amps output (limited by the max output of the PV arrays).  It uses seven 350V NPN Darlington power transistors (BU323) that are tough buggers designed for automotive ignition systems.  It is a "low side" regulator, the PV negative is below the 0V of the 120V battery bank. 

So it's really 3 different boards to do the charge regulation;
1. A Battery Regulator board; float, bulk and equalize, temp compensated 12V shunt regulator for each battery (10 total), with shunt current feedback.  This lets me charge a large series string but baby each battery individually; that means adding only a gallon of water to the set of 10 every 2nd year.  It's designed for AGMs, which I may use for my next battery set depending on prices at the time.

2. PV linear current regulator; just a linear series regulator for the 120V nominal array (120-220VDC).  0-5V in for 0-16 amps current.  The previous design did fixed net charge selections of 0.5 amps (float), 2.5 amps (absorption), and max (PV limited to about 5.5 amps).  The new BBC (see below) charges with a continuous adjustment of current as the batteries come up to full charge so will charge faster. Much faster with larger PV and AGM batteries; the cheap marine batteries I'm using now have moderate internal resistance and can't really absorb high charge currents as AGMs could.

3. Battery bank charge controller (BBC).  This is a 3 year old newer all analog (op amps) design.  that computes the real time minimum charge current to keep all the battery shunt regulators just barely regulating without exceeding the 3 amp shunt current limit and automatically transitions from bulk to absorption to float.  It does this smoothly despite fast shifts in load or PV charge (sun). It also does the equalize timing. 

Other projects in the works- updating my generator- DC charger to a fixed voltage  (150VDC) 10 amp design that feeds into the PV regulator.  The current design uses a homebuilt motorized variac and adjusts itself via PICaxe controller as the charge current tapers off.  Charging is so infrequent that I may simplify this and ignore the minor loss of fuel efficiency of regulating via the PV charge regulator.  I only charge about 2-3 hours per winter, total. With the new PV capacity that will lkely be zero.

Lastly, the newer (3 year old) analog battery bank controller board has room for expansion with an added embedded microcontroller.   I may add that to continue to be able to use my remote terminals (LCD plus buttons) in the shop and house to monitor and control.  I'd use this controller to for my low EMI inverter control and power management like pumping the well or pumping air when sun is available and demanded loads are low.   

I'll take some pictures of the new boards on my bench tomorrow.







 


glort

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Re: More panels!
« Reply #33 on: March 04, 2018, 09:39:28 AM »

Look forward to seeing the pics. Might help me understand a little better. some of it is over my head. I am certainly jealous of your electronic skills. I always wanted to get into electronics even as a kid but I never had the smarts or the concentration for it. Still seems like a black art to me full of magic and mystery.

I did something Different today, I bought another solar setup!   :laugh:

This one is a 1.7 kw, 10X 175w panels and a not too young 2KW inverter.
Fairly good deal, $200.  Guy selling it initially wanted $1000 but I was able to negotiate over a few weeks and with the lack of any other offers, I think he just wanted it out the way in the end.

I was going to just re sell the panels, Probably keep the inverter but I might just take it all up to Dads and throw it on his roof.   They aren't going to go with anything I have and too small for me to bother with.

There are a couple of other systems I'm keeping an eye on. 
If I can turn a few over to make some pocket money and the Mrs can see them coming and going, all will be good.

BruceM

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Re: More panels!
« Reply #34 on: March 04, 2018, 03:29:00 PM »
I wish used panels were available here; I'd add one more set of 5 vertical panels for late in the day "sundown" power.  A set of 175's would be just dandy. 

BruceM

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Re: More panels!
« Reply #35 on: March 04, 2018, 06:46:38 PM »
Here's some photos of my new boards for my custom 120VDC off grid power system. 

The power regulation is all linear, both on the Battery Regulators, and the PV current Regulator. 

The new Battery Bank Controller is also all linear but has the option to add a shielded processsor module via filtered DB25 connector.  It uses Microchip 5v micropower op amps so it's all up power use is about 6 ma. The processor module will add another 5ma.  We're talking tiny, tiny power use.

The PV current regulator uses 7 parallel BU9323 Darlington power transistors.  So for my intended max of 16 amps at 146V (2336W), each would carry only 2.2 amps.  It will be mounted on the back of a large 24x10.1x2.8" finned aluminum heatsink on the outside wall of my power shed.  The heat losses during throttling of PV output is does not affect charge or direct use efficiency.

The Battery Regulators (one for each 12V battery) can shunt up to 3 amps of current but in practice, that never occurs for a well matched set of batteries.  Repeated cycling with individual battery regulation makes the batteries match very closely so the Battery Regulators tend to serve more as a very small correction for battery impedance matching. The battery regulators each have a external thermal sensor that is attached to it's battery negative post.

Definitely not the way things are normally done these days but phenominally low EMI and quite efficient.  Bulk charge losses are very low- diode drop plus 0.8V at 20A power.  Winter PV efficiency is down around 17% due to mismatch of panel array voltage (higher than necessary).  Size and cost of throttled (linear instead of rapid on/off switching) charging is certainly significant but that was lowest on my design priorities.

Sorry for the "soft focus" photos- I'm a shaky today but was too lazy to get out the tripod.



« Last Edit: March 04, 2018, 06:48:13 PM by BruceM »

BruceM

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Re: More panels!
« Reply #36 on: March 04, 2018, 06:55:37 PM »
Here's a photo of my prototype system- some while still in test and development in 2009.  I'm still using the same boards now.  Time flies.


carlb23

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Re: More panels!
« Reply #37 on: March 05, 2018, 12:31:55 PM »
Glort,

How many Kw of solar do you have now? 

glort

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Re: More panels!
« Reply #38 on: March 05, 2018, 02:15:26 PM »

Ummm,  Not that much up on the roof still, 8.5 KW.

I have 9kw worth still to put up.  The system I bought yesterday I thought was only 1.7 but when I looked at it today it's 2 KW which is a bonus.
I'll definitely take that up and put it on my Dads shed roof and knock his bills down a bit.  2 Kw of panels, 2 KW inverter, all the rails and brackets to mount them and even the wiring.  That's got to be good value.  I did notice 2-3 Panels have the connectors cut off by the lazy arse solar people but I just bought 20 of the connectors for less than a buck each off fleabay so not a problem there.

The setup I got yesterday also came with rails and brackets I want to put rails from another set on my House roof.
Been debating where to put the 4KW array, on the south side of the shed or the west side of the house.  Even though the shed would give me a bit more power, putting them on the house will be a lot easier to wire up and direct the power to the water heater and AC.

I have noticed the 3 Kw on the south sie of the shed does not seem to be performing well. I'll have to get up and have a look at what is going on.
There are 2 strings joined so maybe there is a bad connection.
I have also noticed on the other array which I can switch the seperate strings in and out that 1+1=3 rather than 2.
Have each string kicked in and you may on an overcast day or late in the afternoon get say 1 KW from each side. Switch in both strings and you get closer to 3 KW rather than 2.  Must have something to do with minimum thresholds and inverter efficiency I guess.

The 8.5kw I have now seems to be keeping up with things including the AC and the hot water I have been running off it for a few weeks.  I have had a meter on that and it's used less than 40 KW in the last week.  I expect this will go up when winter comes as the yeild from the solar drops.
This is why I want to add the extra panels on to give me a buffer for winter when there is less solar energy to be gained yet power consumption with heating will go up.

From now on I'll probably just keep a look out for bargain panels to buy and re sell.  I have developed a strategy with this that seems to be working well so I might see if I can earn a few bucks out of it. I'll look to standardise all the panels I have as 250W and sell off my lower ones as I can find the 250's.

ajaffa1

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Re: More panels!
« Reply #39 on: March 12, 2018, 11:45:54 PM »
An interesting development, my neighbour is building a homemade off grid solar set up. He has been gathering second hand equipment for months. I have volunteered to assist in the hope of learning something useful.
It appears that he has got his hands on a couple of battery packs off forklift trucks, should provide good storage.
With his permission, I will try to post some photos and information once we get started.
Bob

glort

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Re: More panels!
« Reply #40 on: March 13, 2018, 09:42:21 AM »

In the bit of research I have done into battery's, forkliftpacks are by FAR the best bang for the buck.
I contacted one company and they were most helpful and happy for their product to be used this way. Reckoned it was a lot easier on them than being used as they were intended... in forklifts. I can well see why.  Stationary setup with probably a much lower DOD than people would do with mobile application.
The people I spoke to said they would gaurantee their packs for 5 Years IF the automatic watering system was fitted. For $200, sounded OK to me.

They said that in the systems they had done before, 10 years was pretty much a minimum if they were in a really harsh climate or really flogged with deeper than usual discharges.  they admitted they weren't the lightest or most compact or anything else new and trendy but they were a tried and proven technology that was not the most reliable and the cheapest storage available on a watt per $ basis.

I would like to have a go at one of those DIY powerwalls with the 18650 laptop batteries. You'd need a DAMN good supply of them though.
I am watching a couple of YT channels and my question of how do you know even after all the testing and conditioning the things won't go belly up in short order. Seems the answer is you don't and several of the people on the channels I'm watching have had this happen.  Not the end of the world I spose but would be interesting to see how many times this happens over a few years. Easy enough to swap them out but if you are doing it every few months, could get to be bit of a drag.

One thing is for sure, these guy are getting some SERIOUS storage going. A  tesla battery holds 10Kwh. These guys are starting with 20KW, going to 50 and after that seems to be easy to go to 80 and 100KWh. One guy has just hooked up 120Kwh. That is a LOT of energy storage and several tens of thousands of batteries he's mucked around with to get his capacity that high.


I am told there are other and better sites but i have found the PVWATTS  site very helpful and informative in planning out the positioning of my setup. It tells you the amount of power panels will generate in different locations at different angles and orientations.  Very hand when you are not sure if the south  ( worst in the northern hemisphere) roof which is very flat is better than the west roof at the supposed better angle and what their outputs will be at different times of the year. For me the near flat south side is better but I have never come across a site yet that would tell you that.

Like about everything else I have learned through the net, the approved practices and advise taken as the correct gospel have holes you could drive a truck through. Sideways.

The " Optimal" angle of latitude for instance is very often not the best angle at all!  I was trying to work out how best to mount my panels and what I was going to build my mountings with to get them to the correct angle. I decided to throw them on the shed roof which is 5 and 13o pitch and I wondered how much that would kill my generation. Much to my surprise I found having the things near flat yelded me significantly more power over the summer from nov to Feb than the " ideal" angle would.  The over all for the year laying them direct on the shed rood was so little that there was no way to justify the cost, effort and risk of having the panels kicked up a foot at one end rather than lying them flat on the roof and much less susceptible to the high winds we get here.

Came back to my old solar efficiency rule, cheaper and better to add generally a couple of panels to the ones you have to get better production than try and make them more efficient.  The gains are generally small with optimising, the costs are usually high and no improvement in making an array more efficient works as well as just having more panels on a cloudy day.

That site and I imagine similar give you the opportunity to crunch numbers and see what would be best and moreso, suit YOUR ( or your neighbours) needs best.

The other ones I'd recommend looking at but are a bit variable and tend to err on the side of overcaution are the cable length/ size/ power calculators.
If these panels are not going above where the power will be used and there will be a decent cable run, these are very helpful even if conservative.
I have changed my plans to a degree with my setup. Going to locate the panels closer to where I want the output rather than the best yield possible. Again, for what i'm buying panels for ( and geez I'm slipping, haven't bought any in almost a fortnight!) it's cheaper to throw a few more on the less than optimal roof than run the required cable to where they would make a bit more power.  I have a heap of roof so no problem space wise. If I covered the roof in panels, I'd have to have the cable back to the power pole upgraded..... and they might have something to say about that!  :laugh:

I'm going to invest in a roll of 6mm. won't need it all but a sparky mate uses it and say he'll buy whatever I have left over.  Then again, probably end up using more than I damn well think!
I am going to cheat a bit and put one solar array on the water heater circuit. I have moved that from the off peak already and been testing with my voltage monitor relay to kick it in.  had a couple of days where it was cloudy and I don't think it got any juice but the system is a 400L which is well beyond our needs and stays hot enough for about 3 days showers etc .
That is a 20A circuit already and I will tap into it near the heater anyway. When the solar is generating and the heater kicks in, the load on the wiring will be minimal because most of the power will go about 3 ft to the heater and not all the way back to the board.  When the heater isn't active there will be plenty of headroom for the solar array.

It's getting easier to mount all the panels than it is to run the power they generate somewhere. I am looking forward to a very cosy and cheap winter though. ironically it will be cheaper to run several fan heaters than it will be to run the reverse cycle... not to say we won't use that as the main heating to get the place up to temp then use the fan heaters to maintain it in the rooms we are in.

I have learned a lot with solar and I find it very fun and enjoyable.  There is a fair bit to take on board but it is all fairly logical and straight forward.  I'd say rely more on your own findings and don't put an over amount of weight on what commercial sites say but you can rely on the calculaors which tell a different story with the numbers plugged in to what the sites, even the DIY ones tell you.  Might be a case of trying to be all things to all people but certainly paying attention to YOUR circumstances gives far better results that worrying about what best suits other people 10K km away in a totally different climate.

One tip i'd give is when dealing with used stuff, pay attention to connectors. I have bought several systems and none of them came with the inverter AC connector and they can be difficult and expensive to get.  I don't bother with them now. I just open up the inverter, take the connector away and run heavy cable through a grommet or strain relief right to the board.  Probably Kills their IP rating but I don't want them out in the weather anyway.

Other thing is tell your neighbour to order about 20 Pair of MC4 connectors through flea bay.  This the last ones I got the other week were about .70c pair.  at places like jaycar, they want $12:50 for the bastards! I can buy a whole bag of them sent to my lettterbox for $15 and I have not had any trouble with them yet.
Often the slack arses that take the old panels off jus chop the wires and the last lot I had they must have just reefed on them till they seperated one way or the other. I found a couple of panels which tested OK but the array was open circuit. Traced that back to the conductor being pulled too far back in the connector housing and failing to meet up with the opposite conductor. Couple I undid and reseated them correctly, another couple were chop and replace jobs.  Pays to have those Mc4's on hand. And get some of those little plastic connector tools as well. Some of them can be near impossible to disconnect without them.  Dollar odd each on fleabay.

I'm sure your updates on the project will make for interesting and satisfying reading and look forward to it. Don't forget lotsa pics!  :0)

BruceM

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Re: More panels!
« Reply #41 on: March 13, 2018, 04:03:07 PM »
I'm very skeptical about DIY internet claims for lithium battery banks that have no cell management.  Even minor corner cutting on series cell voltage management as the Nissan Leaf has done has resulted in many premature battery failures, and that's starting with new matched cells.  As you know, Tesla is no cutting edge, new tech company; electric cars are 100 years old and their car has no "new" technology other than fancy electronic displays and other ancillary computer features.  Instead they have been wise adopters and refiners of proven, existing technology. They use the Texas Instruments lithium cell voltage management IC's so that no series cells are left voltage-uncontrolled.  Reports are that they do have very reliable battery life because of this. 

Even 48V wet lead acid systems could have better battery life by incorporating individual battery management, but no one does because it would add cost and people are more interested in today's cost and not the expense of battery replacement.  In fact, just talking about battery replacement cost would be bad for business.
« Last Edit: March 13, 2018, 04:12:44 PM by BruceM »

ajaffa1

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Re: More panels!
« Reply #42 on: March 14, 2018, 02:24:23 AM »
Hey Bruce. when you say that individual battery management is not used because of cost, how complicated/expensive would it need to be to significantly improve life expectancy? Is this something that could easily be cobbled together out of cheap or second hand components?
Bob

glort

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Re: More panels!
« Reply #43 on: March 14, 2018, 02:44:28 AM »
Bruce From what I have seen, the guys building the DIY battery banks from 18650 cells are using individual pack management if not individual cell management.  Tesla uses 18650's in it's cars and power walls and to the best of my knowledge, they are managed in packs rather than individually as well.

I was watching a local blokes vid a few nights back that was showing on his battery management system where 2 of his packs were down. he has a computer screen with bar type graphs showin the state of every pack. I think he has around 30 now.  A pack is about 80 cells and the little monitors are attached to every one and give a visual LED warning to the packs health as well as more information back to the central monitoring PC.

Have a look at this and later vids from the same guy.

https://www.youtube.com/watch?v=Md4l9bFDOtc

This vid gives a good look at the BMS he uses.

https://www.youtube.com/watch?v=pYmu8CnnuNk


Tesla is nothing but over hype and empty promises to me with a lot of slight of hand to divert attention to whatever Elon wants the public to believe when 95% of the time the reality is completely different.  I was reading an article that went into their accounting practices. The slight of hand as to how and where they move money, the way they allocate and bury debt and the measurements they hold out as a measure of their success are farcical if not illegal.
Really, the only thing tesla do exceedingly well is Hype and bullship.  Unfortunately, that isn't unique and will only bring so many $$ in for a limited time before that falls over as well.

BruceM

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Re: More panels!
« Reply #44 on: March 14, 2018, 07:43:37 AM »
This Aussie guy doing his own DIY powerwall is using full (parallel) cell level monitoring, as far as I can tell.  His presentation glossed over the technical details but those packs look like all series cells are monitored for over/undervoltage.  Alas, it appears his charging system isn't automatically balancing the cells since he's talking 2 days to equalize his cells.  That's NOT how cell management is supposed to work.  It should divert power from charged cells to the slower cells and thus keep them well matched on every charge cycle.  If his system can't do that, and is requiring regular extended equalization that's not so good. Since he's selling stuff, it may be hard to get an honest answer about service life of his cells/packs.

I would not touch lithium right now myself...I'll wait until the price beats lead acid for stationary applications where light weight is not important.   By then, you'll likely see cell management integrated into the packs and standards will emerge so that things are not so proprietary and expensive.  Hopefully other more enlightened nations will pick up the ball and run with it.  It's hard to imagine that racks of 1000's of tiny laptop batteries are really the best we can do...though obviously for now, it is.

I'm sure if you google around you can find more in the way of lithium cell management systems.  I'd have to look hard at the TI IC solution...I don't like dirtying up my power with a bunch of unshielded embedded processors scattered throughout the battery bank but given the fan out and total numbers involved, their bussed serial communications are ideal.  Many of the newer AVR and PIC processors have multiple I2C serial ports available to help with the fan out. 

It's not a trivial piece of engineering, but given the price of a few thousand lithium cells, it's obviously worth it.


« Last Edit: March 14, 2018, 07:55:34 AM by BruceM »