Author Topic: Blasphemy..... Solar power.  (Read 66491 times)

LowGear

  • Casey
  • Hero Member
  • *****
  • Posts: 1905
  • What? My diesel had fries for lunch?
    • View Profile
Re: Blasphemy..... Solar power.
« Reply #240 on: November 10, 2017, 06:29:52 PM »
Does Australia receive FOX News?  Humor is where you find it.

I think this last page of posts underline Elon Musk's current criticism of Hydrogen powered fuel cell power.  When we have way more electrical power than we need then that tune will most likely change.
NPR Tipper/Dump Truck
Kubota BX 2230
Witte BD Generator
SunnyBoy 6000 + SolarWorld 245

glort

  • Hero Member
  • *****
  • Posts: 1720
    • View Profile
Re: Blasphemy..... Solar power.
« Reply #241 on: November 10, 2017, 10:56:10 PM »

Hydrogen is a feel good scam for the greenwashed to attract investment Dollars.
It's not an energy source, it's simply a storage medium.... With a hell of a lot of practical drawbacks that mean it will never see wide spread use.

LowGear

  • Casey
  • Hero Member
  • *****
  • Posts: 1905
  • What? My diesel had fries for lunch?
    • View Profile
Re: Blasphemy..... Solar power.
« Reply #242 on: November 11, 2017, 04:07:36 PM »
Good Grief

So how is the big solar storage thing going?
NPR Tipper/Dump Truck
Kubota BX 2230
Witte BD Generator
SunnyBoy 6000 + SolarWorld 245

glort

  • Hero Member
  • *****
  • Posts: 1720
    • View Profile
Re: Blasphemy..... Solar power.
« Reply #243 on: November 11, 2017, 11:38:28 PM »

I believe it's going very well to make Musk about $50m in cash and add to the hype of RE.

Great scam that was too....."I'll build it in 100 days or it's free but my mate who I cooked this up with, has to sign off on the connection before the clock starts which will take till I'm  3/4 the way through building the thing. "

Independent experts are confident it should have enough capacity to boil the kettles in every home in the state, once...... as long as 80% of them have gas.   ::)

If you think I'm solar Smitten as a save the world solution just because I'm using it and stuffing around in my own back yard, You'd be very wrong.

starfire

  • Sr. Member
  • ****
  • Posts: 256
    • View Profile
Re: Blasphemy..... Solar power.
« Reply #244 on: November 16, 2017, 10:40:18 AM »
Im pretty impressed with my Chinese solar panels. Have had 30 amps for 10 hours  a day now for nigh on a week, batteries are bulging with hot electrons. Lister hasnt run for the longest time in its history, its looking a little lost and neglected.
This is my first summer with a decent lot of PVs... they are pretty boring, no moving parts, no comforting exhaust note, and have never heard my batteries bubbling before because of the noise.
Just read an article, China is now leading in  electric vehicle , battery technology and solar panel manufacture.
My next battery bank will be a 2 kW Toyota Prius battery pack rewired to 48 volts. These are $3000NZ new, very competitive with a similar bank of lead acid.
Im sure a charge controller can be designed to allow car alternators to charge these correctly without damage.

mikenash

  • Sr. Member
  • ****
  • Posts: 316
    • View Profile
Re: Blasphemy..... Solar power.
« Reply #245 on: November 19, 2017, 09:38:22 AM »
Hey Starfire, re China and EVs

Dunno if you take any notice of the Nurburgring?  It's kinda THE forum to sort out the men from the boys when someone claims to be making a genuinely fast car.  Not just fast in a straight line, or fast off the mark, or fast through a set of tight bends - but genuine real-world point-to-point FAST

Last time I looked the fastest thing around the Nurburgring was, you guessed it, a 1400 HP, Chinese-built electric car

Way of the future perhaps?

BruceM

  • Hero Member
  • *****
  • Posts: 2103
    • View Profile
Re: Blasphemy..... Solar power.
« Reply #246 on: November 19, 2017, 05:40:54 PM »
Hmmm-  Prius cells are only 6.5 ah, so I'm not so sure about this approach. I don't know what kind of individual cell charge management they use in these Prius modules; some approaches don't lend themselves to parallel cells. I also wonder what the residual cycle life curve looks like after 80% depletion.





BruceM

  • Hero Member
  • *****
  • Posts: 2103
    • View Profile
Re: Blasphemy..... Solar power.
« Reply #247 on: November 19, 2017, 06:23:10 PM »
I did a bit more reading on the Prius battery packs. No wonder so many are available cheap-  they don't have a good cell management system so cells are drifting out of match and then failing prematurely.  You must then replace all of your mixing varying aged cells will result in very poor performance. They seem to be monitoring two blades of 7V in series but don't provide enough detail to know what the problem with their battery management system is. Individual cell voltage/charge management isn't use and I believe most EVs do that to avoid this type of problem.

http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.1028.2529&rep=rep1&type=pdf

They certainly aren't ideal for off grid power use.





AdeV

  • Administrator
  • Sr. Member
  • *****
  • Posts: 434
    • View Profile
Re: Blasphemy..... Solar power.
« Reply #248 on: November 19, 2017, 07:16:00 PM »
Quote
They certainly aren't ideal for off grid power use.

Certainly not as-is, if they're not doing per-cell management... but if you've got the electronical wizardry necessary (I haven't... but I do have a very clever friend I can ask who would be able to work it out), and you can modify the pack to do per-cell management, then you'd be able to rescue a cheap "dead" pack, quite possibly to near-original efficiency.

This used to be what killed laptop batteries off: The individual cells would drift out of sync, so when you charged them, the charger stopped when the most-charged cell reached capacity; but your battery would be "flat" when the least-charged cell discharged. Meanwhile, if the "most charged" cell still had 90% of its charge - tough! The battery was apparently flat. And charging the battery would only put (in this case) around 10% charge into the discharged cell before it stopped. Hence the "5 minute runtime" and the bad rep Lithium batteries got early in their lives. These days, all cells are individually monitored and charged, so laptop batteries don't degrade anything like how they used to. I do wonder, how many perfectly good LiIon or NiMH batteries got thrown away, just because they weren't being charged correctly?
Cheers!
Ade.
--------------
1x Lister CS Start-o-Matic (complete, runs)
0x Lister JP4 :( - Sold to go in a canal boat.

BruceM

  • Hero Member
  • *****
  • Posts: 2103
    • View Profile
Re: Blasphemy..... Solar power.
« Reply #249 on: November 19, 2017, 08:22:26 PM »
I concur, AdeV.   Same thing happens with lead acid batteries, but there regular equalization charging (adding water and sacrificing positive plate life for the best cells) is typically used to compensate for the drift in charge rate of individual cells and groups of cells (batteries).

The AGMs in the early EV days were dying very quickly until battery management was developed to reduce it. They could not be equalized for long periods or the electrolyte got dried up.  The simple individual 12v battery shunt regulator (limiting individual battery voltage) as used by Manzanita Power saved the day and is the approach I used for my 120V bank. It works surprisingly well; the batteries become more and more matched over time instead of less, kicking to absorption and float stages within half a minute of each other and a bad battery can be replaced without concern for matching.  Watering just a bit over a gallon every 2nd year doesn't break my heart either.  On my neighbor's upgraded version, we found equalization charging to match individual cells within a battery (checked via hygrometer) can be virtually eliminated by a slight increase in float voltage, since the batteries are typically in float all afternoon.  His system bulk charges at a higher current than mine so we watched things closely the first year.

I think even in 48V wet lead banks battery life could be improved by individual battery management. Yes, it adds cost and complexity, but over time, the ongoing replacement cost of batteries is the biggest component of your power bill. I haven't seen it offered in any 48V system yet.




starfire

  • Sr. Member
  • ****
  • Posts: 256
    • View Profile
Re: Blasphemy..... Solar power.
« Reply #250 on: November 20, 2017, 10:12:14 AM »
Interesting. I dont know for sure but this is what Im thinking.
Prius packs are packs of 7 volts that are seriesed to 210 volts or so.
The packs as received  are monitored at 1/3rd  sections, or at the 70 volt taps.
If they were  seriesed to two  x 15 paralleled, ie 14 volts x 15, to get a nominal 14 volts at  6.5ah X 15 = close to 100ah.
Monitoring parallel packs is easier than many  series cells, so runaway cells "should" be held down by the other paralleled cells.
By making two independent packs of 50ah, each can be alternatively 100 percent discharged so every charge cycle starts from a known start point.
As I understand it, they dont mind a hefty discharge cycle, but are fussy about charging.
If charging from a known low state of charge, then a simple watt hour meter will control /indicate a reasonable charge time.
If a fixed charge rate can be given, then a simple timer may be sufficient.
The charging can easily be kept below the 100 percent full without damaging the pack, or needing fancy charge controllers.
The encouraging thing with these, to get the equivqlent AH from lead acid requires  around 800ah to prevent excessively hard discharge cycling.
The size reduction and maintenance issues are also bloody enticing as well.
A low voltage detect will allow each bank to switch itself in and out when it needs to be charged.
Problems with inverters are likely as the bank voltage rises, if we have a "48 volt" system, the nearest pack voltage will be 7 volts X 8 cells = 56 volts, probably too high, or 7 volts X 6 cells = 42 volts, probably too low.
14 volts for a nominal 12 volt system is good, and the higher current drain suits these cells.
Thats my thinking anyway.
By using light intercell interconnections, a shorted cell will fuse itself automatically isolating itself from the bank.

BruceM

  • Hero Member
  • *****
  • Posts: 2103
    • View Profile
Re: Blasphemy..... Solar power.
« Reply #251 on: November 20, 2017, 04:32:48 PM »
I did some reading on manzanitamicro.com about their lithium battery regulators. I was dead wrong about paralleling of lithium cells being a problem; since voltage and state of charge are directly linked for lithium cells (unlike lead acid) parallel cells can be managed together.  Alas, series lithium cells MUST be managed separately according to literature at manzanitamicro.com and other sources.  So it would seem there there is no way to avoid series cell management if long battery life is desired.  Prius switched to the battery they used late in the game and it pretty well proves that short cuts don't work; their early failure rate is commonly acknowledged.  They are only monitoring current and temperature in pairs of 7v modules and are not doing cell voltage limiting.

Manzanita's scheme for lithium batteries is similar to their lead-acid; shunt regulators with thermal feedback to the charger to have it cut back on charge current as shunting current (heat sink temp) gets higher.  So rate of charge is limited by amount of current handling of the shunt regulators, keeping the best cells from overcharging. They use on/off switching of a shunting mosfet and power resistor to limit the cell voltage.

Other regulator schemes use more elaborate means- using the shunted power through a switching power converter to help feed the other cells rather than dissipate it all as heat.  The trade off being much higher complexity, and a lot of EMI generated.

All together, the individual cell regulators, monitoring equipment and variable rate charger that manzanitamicro sells is a fairly complex system-  but with our present battery tech, it's the best approach to get good battery life.  Tesla does something similar, but I have not studied their design. I don't believe they would add the extra complexity and cost unless it was absolutely needed. 







« Last Edit: November 20, 2017, 04:37:43 PM by BruceM »

BruceM

  • Hero Member
  • *****
  • Posts: 2103
    • View Profile
Re: Blasphemy..... Solar power.
« Reply #252 on: November 21, 2017, 12:42:49 AM »
I couldn't resist checking for information on Tesla's battery management scheme.  They don't provide any technical details but others have torn apart batteries to have a look and have reported their findings.  I had a couple hours entertainment searching for useful engineering info.

Their modules of cells use a TI battery management chip (bq76PL536A) which I could read the datasheet for.  It is stackable to 191 levels on the SPI bus and handles 6 series cells per chip. It has 6 dedicated outputs to drive N-ch mosfets with power resistors for cell balancing. It monitors voltages and temperatures so the main charge controller can adjust charge current, etc. 

A nice bunch of electronics to manage the Tesla batteries with their racks of small lithium cells, but they did it right.




starfire

  • Sr. Member
  • ****
  • Posts: 256
    • View Profile
Re: Blasphemy..... Solar power.
« Reply #253 on: November 21, 2017, 03:36:32 AM »
I think the longer a series string becomes, the likelyhood of mismatched cells/charging increases.
With low voltage  parallel strings, the problem diminishes.... I think.
However, 1000 AH of lead acid runs to $3000 here in NZ to give the 20 percent depth of discharge of 200ah and maybe 5 years of useful life.
For the same price we can have the equivalent in Lithium cells that will do the same job, smaller with no maintenance, and even if the lifespan is similar, they still have these advantages anyway.
One faulty cell in a series string limits the whole battery to that what the faulty cell can provide, one faulty cell in a parallel config will reduce the AH by a paultry 6/7 ah, everything else remains the same., both current and voltage.
This allows the battery to be micromanaged, replacing faulty cells only, not the whole thing.
It would be uneconomic to have a hugely fancy and complex charge controller, but if one was not required, the economics are there and make more sense.
The likes of Prius/Tesla, they have to consider fast charging, regenerative braking power inputs, output currents, temperature etc, this may explain the complexity,  but with off grid stuff, its a simple known current in, known current out thing.
Thats why I thought to divide the bank into two, and charge one while using the other, overcharging seems to be the bain of these type of battery, and unlike lead acid, will not be damaged by full discharging, and partialy full charging... maybe to 75 percent only.
The electronics to detect low voltage and when to switch out a bank is trivial, as is a timer to control charging time. Both sytems can simply control an old fashioned low tech change over relay even via the ubiquitous 555 timer..

The internet seems confusing at times just what these batteries need, but for off grid use, I think it can be kept quite simple. Even if each paralleled pairs were seperately and manually monitored with a voltmeter once a month by having shorting links, battery health could be monitored initially to see how its working out.
If there were a constant degradation then it would need looking into, but chances are they would perform reasonably well.
Even a real time battery capacity test could be automagically computed by monitoring output watthours, then charging the same bank with an added 20 percent or so, whatever the charge/chemical efficiency is.
The best scenario is just to connect and forget.
My lead acids have a few years left yet, but I do think these Prius packs are worth a try.

starfire

  • Sr. Member
  • ****
  • Posts: 256
    • View Profile
Re: Blasphemy..... Solar power.
« Reply #254 on: November 21, 2017, 04:13:29 AM »
And Bruce, thats a great bit of info you linked to, thanking you.
They appear to ground the center tap, and differentially compare the end voltages to detect battery malfunction.... the absolute voltages are ignored, only the difference will flag a battery error, this is a good way to do this. The charging/discharge current of 63 amps ( 63 x 210 = 13 kW) does give a very large total voltage change, but remember, this is  with all in  series .
The equivalent charge rate at the nominal 14 volts will be  well over  900 amps.... hardly likely in real life.
A 14 volt paralleled pack would change from approx 6.2 x 2 = 12.4 volts discharged to 8.2 X 2 = 16.4 volts during charging.... a tad high, but this would reduce at a lowered charging current.... most connected inverters would overvolt and shut down at this point.
By bank switching, this is not a problem however.
Its unclear if each module can be further disassembled to replace individual cells, but everything is possible.
The main cell failure mode seems to be shorted cells, or chemical degradation over time.
Looking at the figures, an off grid situation will baby these cells compared to what EVs demand from them.
Thats if I have interpreted the figures rightly.
As mentioned, shorted cells become increasingly manageable at low voltages and paralleled modules.