Solar panel setup questions

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Barkuti
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Solar panel setup questions

A close friend recently inquired me concerning a strange question. He started asking about aquarium water pumps and the thing ended up in that, apparently, someone is interested in the installation of an aquarium “in the middle of nowhere” (!), I mean, somewhere in the countryside but… without access to power lines.
Beyond my amazement, I've searched for whatever would be required to keep a 20W water pump running all day long without interruption.
According to my math, to cover ≈16 hours of a day at ≈23W, which is the 20W consumed by the pump plus DC/DC converter losses, 368Wh are required (total power consumption per day would be 552Wh). This means big battery, no less than 552Wh in case of a li-ion battery if the aim is to just use ≈70% of its capacity by charging at a lower maximum voltage, to ensure absolute maximum cycle life. I've also thought in using deep cycle lead acid batteries, but after looking at certain VMF DC18-12 datasheet I'm not impressed with their cycle life.
The climate here is pretty sunny all year round, this is good news but, in any case, there may be a cloudy day or two. To prevent having to install an insanely big battery, I think the smart option is to install maybe a couple 100W solar panels. In a sunny day both panels should at least average 60W/hour for no less than 8 hours, this is ≈960W raw input power. But I honestly do not know how much performance will the panels give in cloudy days. If the installed battery has, let's say, 560Wh useable capacity, certainly some power has to go in in a cloudy day if the aim is to withstand a following night (we've not taken into account charge controller losses, although they should be slim). Suffice to say I have 0 experience with solar panels, and this is the reason I am asking.

Some of the components I wishlisted:

And of couse some cables and other thingamajigs like a buck controller for the pump.

 

Well I think this is more or less nailed as far as my knowledge goes, yet suffice to say it's going to cost a good deal of money once the battery pack and the installation is taken into account… 

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The panels can power the setup during the day the battery is for times when the panels dont produce power. So you need to have enough panels to charge the battery and power the setup.

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I have a single 100W panel. For three days in a row now, it has produced <10Wh. Of course this if Finland, but I wouldn’t trust a solar panel for devices that absolutely need to be powered on 24/7 without a huge battery.

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maukka wrote:
I have a single 100W panel. For three days in a row now, it has produced <10Wh. Of course this is Finland, but I wouldn't trust a solar panel for devices that absolutely need to be powered on 24/7 without a huge battery.

Pssst! Maukka see my signature (your image doesn't meets mobile friendly standards). Big Smile

Thanks, that was enlightening. Looks like the above panel only worked at a good pace for a single day out of 7, with another two honorable mentions.

 

Spoke a bit more with my colleague. Apparently the pump setup is to move water between adjacent ponds or bogs, and doesn't need to be powered 24/7. This is quite a difference.

The above graphic is pretty useful, lets me know the panels will only be able to power up the pump setup for a few hours a day, if anything, without a battery. I can now see the problem much better, namely because it is not coral, fish and squid life critical. 

Sat, 10/19/2019 - 11:11

The_Fat_Controller
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Get the Max Watts to Dollar you can find, S/H 250-300w grid tie panels are ideal giving 3 times the power of most 100w panels for the same price, what ever you think you need triple it

cheap PWM controllers can cut panel watts by up to 50%! (look up MPPT) its a tuned buck conversion far far more efficient

Lead acid is ok if you get GEL batteries , lion is better but massively more expensive.

On a good day my little hobby system produces around 1kw for 5-6 hours generating roughly 6Kw/h it stores 2.5Kw/h of that for night time and sends the surplus to the Grid tie.. on a bad day it can make as little as 0.2kw/h for the entire day, during the winter i don’t even bother to cycle the batteries i just fully charge them and switch panels directly to a grid tie.

230AH 24v Gel Bank / only cycled to 50% dod giving 2000+ cycles.

Here’s what a winter week can look like!

Wind turbines can help, there are some quite reliable kits coming out of china that can hit around 400w Turbine Video review

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The_ Fat_Controller That is a beautiful solar setup. Done neatly and efficiently. Good work!!!

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Also:

https://www.google.com/search?client=firefox-b-1-d&q=solar+panel+failure...

Quote:
… Quality issues get public attention
Nobody likes to wash one’s dirty linen in public. And that’s the case in the industry as well. Reason why you rarely see publicized product failures neither the names behind, like in the case of the “revamping” in Italy. That being said, there has been some articles in the last years, in international newspaper, highlighting publicly issues around solar panels quality like in the New York Times and Bloomberg.

The paper of the New York Times features industry insiders testimonies raising their concern over solar panels quality, especially in a context where the price pressure on solar panels and a low margins environment can prompt actors to cut the corners. …

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Hello again. Smile

My colleague told me the “potential customers” aim to lay some fresh water fishes in the ponds (!), and they will see how much will it go without water circulation. The stuff will have maintenance every two days at least. I am no aquarium expert, so don't know how senseless or senseful this is.

Yes very nice setup The_Fat_Controller, that should allow you to save quite some money in electricity bills. Thanks for pinpointing the above concerning MPPT controllers (so much abbreviations which God knows Facepalm what they mean without proper context).

The above panels are good, or so it looks to me (the bulk of this message was writen before hank's latest contribution). The question here is more like how many of them will be required, either two or three for the time being.

In the meantime I looked for some no-frills, affordable MPPT controllers:

I aim to DIY the battery pack out of either 18650 li-ion or 32700 LiFePO4 cells, at least for the time being (I may change my mind). 

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Things to be aware of with cheap controllers , Many sellers lie about them being MPPT most are in fact PWM there are many fake Mppt modules

there are also some good cheap controllers which really are MPPT
here is one example
Real budget MPPT
You can tell because internally it has Inductor

the other give away is the conversion if you feed mppt say panel voltage 24 1amp.. you will Get 2amps at 12v , with PWM you will just get 1amp 12v

Here is another good cheap TRUE mppt
Boost Mppt

The issue you will face with most of these is not conversion efficiency but very restricted charging options, many do not have voltage sensing and reliy on preset values with timers ok for floaded lead acid but not much else

Others such as the Epever tracer Tracer Series offer more control and can be setup for custom charging routines I believe these can be setup to safely and correctly charge lion cells they also support load shedding and remote access, the epever is a good controller and i used one for quite a while (there maybe better options available now)

The Victron controllers are probably the best they have full customisation of the charge routine and can be programmed for any type of cells such as Tubular Gel li on, lifepo4 etc , bulk absorption float etc and it is all monitored on battery voltage with full customisation

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Victron is surely the way to go if you just want it to work and make configuring easy. It’s very handy to monitor locally or over the internet with a Raspberry Pi running Victron’s Venus OS.

Mine is just in the testing phase, since I don’t have a good location for the panels.

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Bottom line with panels is Watts are watts and the more you can get per dollar spent the better , being more efficient simply means a smaller panel gives the same watts. but if it costs you 3 times as much per watt its pointless. Large industrial panels are built to last many years mine tested to 275w each (300w rated) and cost about 100 bucks each Smile The ones you point out on alliexpress are not bad if they really give 200w for 120 bucks but id check the reviews on them not all panels are created equally and price doesnt always mean a lot

NOTE: you will almost never see the full rated output from panels unless they are below 25C. people always assume you get max power in really bright hot sun but this is not the case. as semiconductor temperature rise efficiency drops (solar companies neglect to mention this)

I love the victron Its very good controller but OWch! the Price sucks!!

PS: for good cheap inverter option PURE SINE , look into APC Smart UPS Smile can be controlled vier Virtual load output on controller. (Epever also) I used this method initially but found grid tie inverter to be more suitable for my needs but if i was going offgrid I would go straight back to the APC

There is a guy on Youtube by the name AverageJoe , he has many detailed videos on making and protecting Lion packs as well as balancing & monitoring well worth a watch

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I don't have any direct experience with this pump.  The PV version of it can be connected directly to solar panels without separate controllers or batteries. 

https://www.thesolarbiz.com/el-sid-sid10pv-10w-pv-direct-pump.html

 

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The_Fat_Controller wrote:

Here is another good cheap TRUE mppt
Boost Mppt

Sort of nailed it, Smile thanks. For just a tiny bit more money than the aforementioned Sunyima it offers better interface and looks like a better overall machine, even though it is fan cooled… 

And I really mean just a tiny bit more expensive: https://www.aliexpress.com/item/32931442381.html

The panels are a bit more expensive , I see €142.16 for a pair and €209.49 for a 3-pack @ solarfactoryretail.

ImA4Wheelr wrote:

https://www.thesolarbiz.com/el-sid-sid10pv-10w-pv-direct-pump.html

What the… wow! That pump is @#$% expensive! 

 

Thanks to everyone, for now I have plenty of data to start with. This project will load the battery with buck or buck-boost converters and DC pumps but pretty sure I'll take a look at the inverter thing sooner or later. Many of the “high end” device suggestions will come into play once I am more familiarized with the stuff, I presume. 

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Barkuti wrote:

The_Fat_Controller wrote:

Here is another good cheap TRUE mppt
Boost Mppt

Sort of nailed it, Smile thanks. For just a tiny bit more money than the aforementioned Sunyima it offers better interface and looks like a better overall machine, even though it is fan cooled…

No worries , those little 7210a’s really are excellent for the price only issue is they are boost so battery bank needs to be higher voltage than panel but its ideal if you want to run a 24v bank with an 18v pannel

here’s a review

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The_Fat_Controller wrote:

No worries , those little 7210a's really are excellent for the price only issue is they are boost so battery bank needs to be higher voltage than panel but its ideal if you want to run a 24v bank with an 18v pannel

here's a review

Wellp, while I am more or less fluent in read and written english language, the same I cannot say concerning spoken english understanding. I may have certain negative beliefs in this regard, forged at an early age.

Despite this, looks easy to understand. In red is the input voltage from the source (panels, wind turbines, mini-stellarator or mini-tokamak, etc.). In purple, with yellow V is the settable battery output voltage, and with yellow A the settable maximum output current. Below and all in yellow is output power in watts. In cyan colour figures battery capacity can be specified (what the point is right now I don't know), and a timer count whose point is also sort of pointless Big Smile to me. At the right side column I see a diskette icon with a two digit counter, I presume that is a writeable¹ array of memory presets…

I also have a small concerning doubt with the MPT-7210A, will it be able to support 16.6̅7 amps of input? I know I should stay below 10A at the output (for such I thing I would choose no less than a 9S li-ion battery for 200W of “18V” panels, and a minimum of 13S for 300W), but no figure I've found yet concerning input limit. The above Sunyima boost controller specifies 16.7A maximum input current, for example.

¹ Would you say writeable or writable? 

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Generally the max current is regardless of voltage , as such most controllers will handle more watts at higher voltage

For example my victron is rated for 30amps , if i run a 12v battery bank my PV max will be 440Watts , but if i run in 24v @ 30 amps i can have upto 890w of PV and so on

the MPT-7210A is 10amps max input or output ,so you’d need to go 48v (13S) bank and run your solar panels in series to give 36v that way you never go above 10amp on the charge controller.

The issue then is getting from 48v back down to the voltage you need for the pump so you’ll need a converter

Buck Step down

48v to 24v

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Quote:
as semiconductor temperature rise efficiency drops

And vice versa. If you live in an area where winter sunny day temperatures can drop well below freezing, be aware.

An old friend living off-grid once boiled his lead batteries dry in such cold conditions because his solar panels got so highly efficient.

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Well, for now I can say this thread gained a lot of momentum. It's been a busy Innocent weekend.

The_Fat_Controller wrote:

For example my victron is rated for 30amps , if i run a 12v battery bank my PV max will be 440Watts , but if i run in 24v @ 30 amps i can have upto 890w of PV and so on

Guess that arithmetic is maximum charge voltage times maximum current, yet these are maximums and you don't want to be pressing the pedal to the metal frequently, or do you? Long term reliability matters.

The_Fat_Controller wrote:

the MPT-7210A is 10amps max input or output ,so you'd need to go 48v (13S) bank and run your solar panels in series to give 36v that way you never go above 10amp on the charge controller.

Well, I discern the MPT-7210A is then not really well suited to handle 2 × 100W “18V” panels in parallel, as they can give out in excess of 5.5A each.

Given this and considering I may go with up to 4 × 100W panels, the better affordable solution as I see it is to choose 2x (Sunyima) CTK-EV-300 charge controllers, each one fed by 2 × 100W panels.

By the way, looking into this I found the following page with specifications for quite a lot of the devices discussed here: Product list @ Nanjing Longline Electronic Technical Co., Ltd.

 

I really like the DPS3806 boost-buck converter, affordable and flexible device. Found a video of it made by the same Julian Ilett fellow which talked about the MPT-7210A above:

 

 

 

SEPIC topology maybe? They're easily parallelizable. 

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Barkuti][quote wrote:
Guess that arithmetic is maximum charge voltage times maximum current, yet these are maximums and you don’t want to be pressing the pedal to the metal frequently, or do you? Long term reliability matters.

Well… in reality it is very very rare that you will ever see the maximum from a solar panel unless as someone else said it is Freezing cold and you have very very strong sun , the ratings they give for Pmax assume absolute perfect conditions, Most sensible controllers are also current limited so they will simple draw up to their max rating rather than self destruct

Barkuti][quote wrote:
Well, I discern the MPT-7210A is then not really well suited to handle 2 × 100W “18V” panels in parallel, as they can give out in excess of 5.5A each.

correct it would be 2 panels in Series.. Parallel would be to much current also no head room for later upgrade , it is always better to get a larger controller if you can

There are some very nice Boost buck up & down converters around you dont need to spend alot of money to get the power out of the panels, the issue is as i said earlier going to be safely charging lithium batteries

Im not sure of the requirements for charging Lithium cells … for my Tubular Gel batteries they require a current limited 3 stage charge , Bulk Absorption & float and each voltage has to be temperature compensated (if you cause a gel battery to GAS) it is ruined and capacity lost so they must never be equalised

Im no expert on lithium but id imagine at the very least they will need Balancing, current limiting & over voltage protection , I think i also read somewhere they must not be charged if temperature below 0

I would have preferred lithium but cost was an issue and price difference big 80ah at 12v Lifepo4 , VS 110ah at 12v Tubular GEL ..

Leoch GTP

Lifepo4

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The_Fat_Controller wrote:

I would have preferred lithium but cost was an issue and price difference big 80ah at 12v Lifepo4 , VS 110ah at 12v Tubular GEL ..

Leoch GTP

Lifepo4

Lead acid batteries cannot offer anywhere close to their 20 hour ratings if discharged fast, much less the above 100 hour rating albeit this may be inconsequential due to battery size versus average power consumption. I also wonder about their actual lifecycle performance, but looks like they're still the most affordable technology.

I've already built a few small li-ion batteries with modern 18650 cells (LCO and NMC chemistries), going as far as binning and grouping cells to maximize series pack balance and lowering maximum charge voltage to boost cycle life too. No issues with them, guess it is too early to say anyway.

If you are willing to take a chance with some cells from china the price for li-ion can be lower, although it requires battery pack assembly skills. Take a look at my top choices at this moment:

 

https://www.aliexpress.com/item/4000197218968.html

This is a cell from a still unknown to me OEM, and rewrapped by some. Here's a review of it: Queen Battery QB26800 6800mAh 20A - the big guy! @ Thunderheart Reviews

By charging that cell to slightly above 3.9V still above 20Wh per can can be extracted at a low C-rate, which is pretty interesting.

 

https://www.aliexpress.com/item/32795814865.html

As far as I understand this other cell is from Heter, it is used by some Ukrainian fellows in their DIY e-bikes and unorthodox tests. Tester Henrik will soon publish a review (lygte-info.dk).

 

A problem I face with cell balancing is that commercial balance boards are designed to do it at very high voltage, above maximum permitted voltage. This is not ideal, in my honest opinion. It probably is better to install switchable voltmeters at each battery stage together with pushbutton enabled bleeding resistors (inexpensive flashlights with linear drivers would probably be a nice idea Big Smile for such role), and do balancing by hand from time to time.

 

By the way I've noticed that DC solar cable can be somewhat pricey. I wonder if some beefy silicone wire could also do good… 

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Lead acid batteries are indeed wasteful both in discharge due to Peukert Law but also during charging much energy is wasted for example to recharge 1kw/h used will generally take 1.5kw/h there is another problem as battery state of charge increase rate of charge decrease so they only really fully use the panels when they are at 50% dod this is why my system is Hybrid & sends the surplus power to the inverter when batteries are no longer pulling full power from the panels it is also important that the batteries are always fully recharged to avoid Sulfide buildup and capacity loss. (memory effect)

Life cycle wise , Floaded & AGM have very short life 300 cycles maybe.. But Deep cycle GEL has long establish high service life many many cycles if Depth of discharge is kept to 50%

I totally agree Lead acid is not the best technology for this application but the cost of large lithium battery bank and all the additional technology needed to charge it safely is still very high

I generally keep my discharge rate to 20H giving a theoretical 45AH per battery assuming a 50% DOD totalled up this gives fully consumable 90AH at 26v (2340 W/h) note that 24v would be fully discharged….

When i built system a few years back the cost of good (3ah high drain) 18650 was 10 bucks each! and i calculated i then needed 220 of them to make up the same 2300 watt hours and to make matter worse cycle life was only 200-500 depending on discharge rate! Sad

Where as the manufacturer of my Gel batteries quote 2000 cycles with my above setup and gave me a 6 years guarantee Cool (I will be counting)

But now you can buy 5ah 26650 from Liitokala for just 3 bucks.. Perhaps tables have now turned it really depends on the cycle life

Those Liitokala 3.7V 26800 7200mAh you posted look very good, I wonder if anyone has tested them properly?? if that cycle life & capacity is true then it is certainly a better option and may even work out cheaper than lead acid! I may have to order a few for testing Big Smile

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Ordered a few of those Liitokala 3.7V 26800 7200mAh you posted will let you know if they are any good… and if they are i may have to make the switch from Gel to Lion

id still need 98 of them assuming A 7AH capacity to match my current setup so its a not without costs

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The above 26800 cells are made by a good chinese OEM this is nearly for sure as far as I know (it may as well be Heter, but God knows).

In order to get high cycle life out of li-ion certain life-prolonging practices are due. Check BU-808: How to Prolong Lithium-based Batteries @ Battery University. The article is somewhat old and, while still valid, it may not be required to restrict the maximum charge voltage as much. I say this because I get excellent cycle life out of my smartphone batteries, charging only up to ⅔ of max or ≈4V with minimum load according to 3C Battery Monitor Widget (yes, I give 'em thousands of cycles), and also from what I can fathom out of documents like this Samsung INR18650-35E datasheet from Orbtronic (check page 14/19 table, Electric Storage Systems/Uninterruptible Power Supplies). Could select 3.95/4.2V just to be safe, still 20+Wh out of each of the above 26800 cells.

Yes, you will have to solder cells for a while. 

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whatever you calculate for panels just go ahead and double it.
or triple.
i have solar setup here and its not uncommon to get long stretches of low production.
upsizing the battery has its own set of issues one of which is cost.
i overpanel and find something to do with any overproduction.
like heat water.

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I am also interested in these 26800. In this store, QB26800 can be bought much cheaper than asking for Liitokala 3.7 V 26800 7200mAh. However, QB promises 6800mAh against Liitokala, which promises 7200mAh. In appearance of the “positive” output, these are elements from one manufacturer and I think that Liitokala is simply lying about such a large capacity, because the QB26800 shows less results (when discharging a current of 10A to a cut-off voltage of 3 volts, the best batch reached 7000mAh, and The same ‘the big guy! @ Thunderheart Reviews’ with a similar discharge current of 10A received only 6568mAh). Where can there be 7200mAh from? Is this another fantasy from a famous liar named Liitokala?

QB26800

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Well i ordered 3 as a sample, I cant do accurate test but i will certainly post what i get from my charger

(When they eventually arrive)
I think they are being shipped by sea turtle

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The_Fat_Controller wrote:
Well i ordered 3 as a sample, I cant do accurate test but i will certainly post what i get from my charger

It will be interesting if you do not have a simple household charger (with very low currents), but there is such a high-precision four-wire electronic load (discharge current up to 10A), with which, for example, the QB26800 test was performed on this forum https://electrotransport.ru/ussr/index.php?msg=1664948

When discharged with a current of 10A and before the cut-off 3v, this person received a maximum of 6900-7000mAh, but the results for other people were somewhat more modest, since his party with very fresh elements was the most successful https://electrotransport.ru/ussr/index.php?msg=1733829

Such a discharge device can also be purchased on ali-express https://aliexpress.com/item/32725711985.html?spm=a2g0s.12269583.0.0.74c8...

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volchyonok, be sure both QB26800 batteries (datasheet) and LiitoKala 7000/7200 (cough!) are manufactured by the same original equipment manufacturer. The OEM sells his cells to whoever can buy the MOQ (Minimum Order Quantity) which can be a few thousand pieces, but other than this it is a relatively simple thing to do for a business or society (like Vapcell or LiitoKala whoever it may be).

The effective capaciy for the 26800 cells may be a little bit higher when using BMS systems with lower than 3V cutoff; this is common and I really doubt it would in practice be really detrimental for the batteries. 

P.S.: to be accurate any testing device needs some sort of calibration. I, for example, took the time to properly average all my Lii-500 channels and obtain channel correction indexes. In my experience Lii-500s tend to very slightly underestimate capacity, at least mine does.

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Barkuti wrote:
I, for example, took the time to properly average all my Lii-500 channels and obtain channel correction indexes. In my experience Lii-500s tend to very slightly underestimate capacity, at least mine does.

This is not a matter of calibration, but of the strength of the discharge currents, which are mandatory as an orientation for choosing the suitable elements, which then will have to work under high loads in the battery for electric vehicles. Given the estimated number of parallel cans in each cell (3P …. 5P, etc.), one should bear in mind the ability of each element to hold a load in the region of 10 amperes and know exactly what capacity it can give to the ‘common boiler’ (“Joint boiler”). Your household charger, even if it is treated with high-grade pure gold, does not work with discharge currents greater than 1 ampere, so its informational value in the case of selecting batteries for a powerful battery has no value. A discharge device is required with the ability to load an element with a current of at least 10 amperes, even if its main load is a current in the region of 5A.
The_Fat_Controller
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Last seen: 2 hours 35 min ago
Joined: 09/13/2019 - 07:34
Posts: 236
Location: England

The cells for a large solar battery bank do not have to be identical, they do however have to be protected & fused individually , it is inevitable that in a pack containing a few hundred cells some will fail over time and degrade at different rates so redundancy and protection has to be built in to accommodate it

This is why i ended up going with Tubular Gel, The costs involved even if you build your own Lion bank by the time you have factored in all of the extra bits you need to make it safe , the cost of the cells BMS fuses & protection boards etc you end up spending just as much money and life time of the pack is really no better, The real advantage for lithium in a solar system is that it accepts high charge rates , there is no tail off like there is with lead acid

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