MPPT conversion on a 40.2 VOC to 14.4 volts question

[Bryn23]

Well I’ve been looking for a better quality solar panel, I’m put off buying another eBay 12 volt panel after my broken unit and also the semi flex panels after seeing how a lot of people are having problems with them.

(The Solbian semi flex panels are around the $1000 mark here for 100 watts in Aus!!!)

So I started to look at what is available locally in a hard panel, there is a lot of crap out there!

I can get my hands on a LG 330 Watt solar panel with will work with my Votronic 350 MPPT, as it can handle 350 watts and a 50 VOC.

Now, does anyone know a calculation to work out the amps from a 40.9 voc to 14.4 volt charging rate..

I’m aware the MPPT with take the higher volts and produce more amp’s

But the question is how much more???

Surely it cant be as easy as 330 watts % 14.4 volts = 22.9 amps

Anyhow, if anyone can advise me, on what amps I should be seeing then that would be great.

Cheers,

Bryn



LG Panel Specs

Maximum power at STC (Pmax)
330
MPP Voltage Vmpp (V)
33.7
MPP Current Impp (A)
9.80
Open Circuit Voltage Voc (V)
40.9
Short Circuit Current Isc (A)
10.45
Module Efficiency (%)
19.3
Operating Temperature (°C)
-40 ~ +90
Maximum System Voltage (V)
1000
Maximum Series Fuse Rating (A)
20
Power Tolerance (%)
0 ~ + 3
*STC (Standard Test Condition): Irradiance 1000 W/m2, module temperature 25 °C, AM 1.5.
The nameplate power output is measured and determined by LG Electronics at its sole and absolute discretion.
The typical change in module efficiency at 200 W/m2 in relation to 1000 W/m2 is -2.0%

 

[Chrisfraser05]

Peak as you suggest would be 330/14.4 or 22.9a

 

[Bryn23]

so it was as simple as that..

I didn't think a MPPT would be as efficient as that.

 

[Chrisfraser05]

Ah, what are you using to step the voltage down though?

There will be losses in that too

 

[andys]

What problems have you seen with the semi flex panels? I was thinking of getting one of those.

 

[Bryn23]

Ah, what are you using to step the voltage down though?

There will be losses in that too

The Votronic MPPT steps it down, thats the difference from PWM solar reg to a MPPT Regulator.

Just not sure on the amount of loss from the MPPT from 40.2 to 14.4 volts..

It would have to be at least 10%

 

[Bryn23]

What problems have you seen with the semi flex panels? I was thinking of getting one of those.

I've seen heaps of people on the T4 Forum having issues with these semi flex panels over the last year..

Upspec only recommends Solbian (correct me id I'm wrong Upspec) I'm assuming he is still on here.

Having to pull one of these off after its been Sikaflexed on doesn't appeal one bit.

I really hate removing Sikaflex.

 

[Pauly]

Think the rating will not be that high
Pmax/V(mpp) = more like 10 amps @ panel voltage

Short Circuit Current Isc (A)
10.45

Then you need to factor in losses in conversion and battery resistance/cable length etc etc
I think using a decent panel and MPPT controller you could expect around 10-20% losses in optimum conditions but then how often are you going to achieve optimum conditions ?

Depending on weather and panel orientation i dont think its unreasonable to only achieve 50% of that output in real world conditions, your personal situation is probably beneficial being in Australia im assuming you can get some decent sun compared to our UK weather but there are lots of factors that affect output

Not trying to be negative but trying to calculate solar output is virtually impossible and is always a best guess given the multiple factors

 

[andys]

I've seen heaps of people on the T4 Forum having issues with these semi flex panels over the last year..

Upspec only recommends Solbian (correct me id I'm wrong Upspec) I'm assuming he is still on here.

Having to pull one of these off after its been Sikaflexed on doesn't appeal one bit.

I really hate removing Sikaflex.

Thanks, good to know.

 

[andys]

Upspec only recommends Solbian (correct me id I'm wrong Upspec) I'm assuming he is still on here.

Holy crap, they're expensive!

 

[Bryn23]

Thanks Pauly,

I didn't take it as negative, There are a lot of factors, just trying to get an general idea of performance.

If it was a 12 volt nominal panel which are between 17.8-23 volts then it would be easy, its just the high volts change things without knowing the formula.

even though we have lots of sun, its also bloody hot, the panel ratings are a 25 Degrees, and for each degree over you lose watts.

So it wouldn't be uncommon to have 40 degrees just on the roof in summer. they panels work better your way than here, but we have more sun light hours so it evens out i guess.

Ill have to keep hunting for a high voc to 12 volt system calculator to give me a rough guide.

As i don't believe it will be as high as 22.9amp, but id like to think its more than 10 amp, or i might as well spend more time looking for a 12 volt nominal panel.

But these are rare, as all the good quality panels over here are for 24/36/48 volt solar systems.

 

[Pauly]

The 10 A i listed was at panel voltage not battery charging voltage, once this voltage is reduced through the MPPT the current will go up as per your calcs above
I wasnt disagreeing with the maths (its correct) just trying to point out that manufacturers figures are generally fantasy in comparison to real world measurements

If i was looking at this for myself i would rate the panel at 300 do the maths then subtract 10-20% for losses and expect this to be the highest gains in best case optimum conditions = 16-19 A @ 14.4V

 

[Bryn23]

Yeah Pauly, everyone seems to overstate there panels.

I just managed to find a Excel Calculator, through Victron, that calculates all the specs to give a guide.

I've looked quite a few times and couldn't find what i was looking for..

and I've applied the "Panel Specs" in the calculator.



I've just gone through the spec's and I'm limited to 21 Amp on my Controller...

So even though this is with hot weather I'm looking at 23.5 amps..

Damm, i though id overspecced my MPPT when i ordered it.

The search continues, ill be doing cals all night until i find something, or go and buy a new controller.

 

[Davenjo]

The maths and techie stuff above is beyond me but, maybe a stupid question, how big are your leisure batteries, i.e. will you have sufficient capacity to cope with storing the amount of power generated via your 330w system or will the controller just shut down and waste it?

 

[Bryn23]

Im not planning on any 240 volt Hook up, it'll be of limited use for where i like to camp.

Any decent AGM over 100ah will allow up to 25 amps safely.

Rule of thumb for RV here in aus, is to have twice as much solar than battery, and to try and recharge around lunch time

Im looking at around 80 amps of usable power at the moment, so that will require 160 ah AGM with a 50% DOD or a 100ah Lithium with 80% DOD.

Leaning towards the 100ah lithium LiPo4 (12-13kg) as it can accept up to 50ah charge and will accept it all the way up to full, where as AGM, it will resist at around 80%, plus it will fit in where the aux battery is at the moment.

I was only looking at the 330 watt as it was a good brand to replace the broken 250 Watt i had, it was a bit overkill after i realised that it would exceed the amps allowed on my 350 watt Votronic solar reg

I've found a supplier today in Aus, of what appears to be a good quality Semi flex panels made to their spec and just for them, genuine A Grade Maxeon Gen III cells and certified, All Panels are tested for EL (electroluminescence) micro cracks.

He seems to provide good advise and from what I've read from others also good support, so that helps

They are more expensive than generic eBay units, but cheaper than Soliban units.

Id rather put it up once and be confident.

Although the roof my midroof it isn't flat its ribbed, so i'll have to fab up a aluminium 1.6 or 2mm thick support sheet as it'll stop the panels drooping in between the rails.

I done the calculations and it would only add 5 kg to the weight, plus it would allow a air gap for the panels.

 

[Davenjo]

Have you seen the PV Logic flexi panels - I don't know how the spec compares (or even if they are available in Aus) to the ones you are looking at but they include a layer of aluminium to provide a heatsink and a bit of rigidity.

 

[Bryn23]

Haven't seen the PV Logic semi Flex over here.

Im not sure I'm correct, but I'm sure it was the aluminium layer backed in the early years 2011-15 within the semi flex module, that caused micro cracks within the cells causing them to fail.

The Poly based backing seems to be the go know as there isn't as much thermal expansion.

Even if it was a aluminium backed within the module, i'd still need reinforcement due to the span of the ribs.

I've been advised that even putting one of these newer poly backed semi flex modules, is that the adhesive or tape has to be flexible or a similar thing may happen due to the difference material expansion rates.

That goes for putting it on a aluminium substrate, Lexan, acrylic or other substrate with difference thermal expansion properties.

You can't beat a good old glass panel, tried and trusted, but also heavy compared to the flex.

 

[Davenjo]

Time will tell - my panel was purchased and installed late last year and is working well - hopefully I don't have to ever find out how good the 20 year (80%) performance and 5 year product warranty is. The panels are actually quite rigid and, whilst sold as flexible, are only meant to be bent one way with a maximum 3cm curve per metre of panel length - guessing going beyond this and/or flexing against the grain could lead to the micro cracks problem you mention??

As an aside; I notice from your build thread that you have gone for a CRX65 fridge - this is the same one we have and it works very well. However, prior to getting the solar panel sorted we noticed that after a relatively short space of time the compressor on the fridge would refuse to run (service light flashing) after less than a couple of days even though the fridge light was still coming on - there was also sufficient juice to run our water pump, lights, etc., without problem. Turned out to be a supply voltage issue and, by design, once the battery drops below a certain voltage, to protect the battery, the compressor wont start. With the 100w panel and a 75ah AGM battery my fridge is now running 24/7 - interesting to see what happens as winter approaches and we get less hours of sunlight. Might have a bearing on the amount of power you need to store overnight as well as making sure you use a decent (6mm?) and short as possible supply cable?

 

[Bryn23]

I really do think time will tell, hopefully you never have an issue.

I'm sure even the really expensive once have issues, it all comes down to how they handle the warranty.

Its a good point you brought up about the voltage issues, I have heard a lot of the low voltage problem with Waeco/fridges.

Its funny how it doesn't seem to effect other things like lights and pumps, but then again they don't have the voltage cutoff limit, my Waeco portable CF50 is the same as it has the battery saving voltage system

I've already done the voltage loss calculations for my electrical plan, sizing and distances.

And the fridge requires 6mm2 to bring it within .11, so that is well under the .20 limit and the fused supply is close by.

I have all the Aussie made marine tinned wire ready to go, i always use marine tinned wire as there is less corrosion issues, plus i do believe locally made wire is better than the sightly cheaper Chinese made cable.

Having said that, chinese made stuff can be world class, it just depend on if the importer wants them to make it and spend the extra coin to make it world class.

But importers want to make more money than spend the small amount extra to do that

 

[Ads_Essex]

I think someone touched on it on another thread (FML I’ve read so many different forums in the run up to my build that they all blend in to one) that someone mooted the idea of using the rear offside window as a location for a solar panel. I think the issue was that it’d look pants unless it was made to the same sizing as the glass panel (and it wouldn’t pick up enough solar power through a glass pane).

For those unable or unwilling to store stuff up top, a fake rear window panel doesn’t sound like too bad an idea if a trickle charge is all that’s needed.

Now, where’s that Dragons Den application..