Solar panel setup questions

The_Fat_Controller · 2019-10-20T10:34:10.000Z

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

maukka · 2019-10-20T10:42:50.000Z

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.

The_Fat_Controller · 2019-10-20T12:33:04.000Z

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 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 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

youtube.com

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Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.

ImA4Wheelr · 2019-10-20T12:49:33.000Z

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

Barkuti · 2019-10-20T13:50:12.000Z

The_Fat_Controller:

…

Here is another good cheap TRUE mppt

Boost Mppt

…

Sort of nailed it, :-) 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:

…

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.

The_Fat_Controller · 2019-10-20T14:18:59.000Z

Barkuti:

The_Fat_Controller:

…
Here is another good cheap TRUE mppt
Boost Mppt
…

Sort of nailed it, 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

Barkuti · 2019-10-20T17:08:41.000Z

The_Fat_Controller:

…

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

YouTube

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 :-D 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?

The_Fat_Controller · 2019-10-20T19:25:47.000Z

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 (Enclosed)

hank · 2019-10-20T20:48:26.000Z

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.

Barkuti · 2019-10-21T01:25:10.000Z

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

The_Fat_Controller:

…

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:

…

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.

Barkuti · 2019-10-21T04:01:28.000Z

The_Fat_Controller · 2019-10-21T11:30:50.000Z

[quote=Barkuti]

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

[quote=Barkuti]

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

Barkuti · 2019-10-23T02:48:57.000Z

The_Fat_Controller:

…

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 :-D 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…

The_Fat_Controller · 2019-10-23T14:09:07.000Z

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!

Where as the manufacturer of my Gel batteries quote 2000 cycles with my above setup and gave me a 6 years guarantee (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

The_Fat_Controller · 2019-10-26T21:25:28.000Z

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

Barkuti · 2019-10-27T01:16:29.000Z

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.

snakebite · 2019-10-28T16:22:05.000Z

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.

volchyonok · 2019-11-14T16:41:26.000Z

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 (price)

The_Fat_Controller · 2019-11-14T16:50:32.000Z

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

volchyonok · 2019-11-14T18:03:23.000Z

The_Fat_Controller:

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 QB 26800, 6800mah, 30A - Страница 3

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 QB 26800, 6800mah, 30A - Страница 4

Such a discharge device can also be purchased on ali-express 30.09€ 27% OFF|150W Konstante Strom Elektronische Last 60V 10A Batterie Tester Entladung Kapazität Tester meter 12V 24V 48V|discharge capacity|battery testerconstant current electronic load - AliExpress