Finally, initial Electrocacus DSSR vs MPPT side-by-side/RW results ... and they're SHOCKING! lol

[Dhowman]

OK, so not CC

I was going to make a few more observations, but I see that Dacian has already made them in the comments in that youtube clip.

The only thing that I disagree with is his statement that a MPPT charger throws out 6% to 8% of the input power as heat. Unless you buy bottom shelf products that simply doesn't hold true. That could easily be over 80 watts. You'd need a really big heatsink to cope with that passively, but yet the heatsink on my passively cooled MPPT controllers does not become burning hot, which it most certainly would under that sort of power load.

Victron rates their SCCs as 98% efficient, ie dropping 2% as heat. Given the temperature rise I see with them, that is quite believable. The couple of Renogy (SRNE OEM) SCCs I have been testing lately fall into the same category.

Is it a revelation that MPPTs like a bit of headroom to charge a battery? No. It's stated in the manuals for decent ones, along with voltages required to start charging, and maintain charging once started. It's certainly something that has been mentioned on this forum several times. MPPT controllers really make the life of the system designer much easier and systems more flexible by removing the necessity to keep the array Vmp near battery voltage.

This is not to say there is anything wrong with Dacian's approach, it's just another option for people to consider, and that has to be a good thing.

Agree entirely except for MPPT efficiencies (isn't that a maximum efficiency rating? what's a typical range and what conditions do you need to stay near that max?) and the "not CC" ... DSSR20 simply passes amps from your panels (a CC source). Do the DSSRs regulate that current? No. Think that's all I was trying to say in reponse to the "not PWM-ish" reply.

So what's the point of all this heated agreement? I certainly didn't start this thread to convince anyone that one product is better than another. I started it because we've been dying for this kind of side-by-side. Why? Because I think there's a misconception that you need MPPT to sop up all the power you can out of your solar panels. In some cases you do, as the scenarios described above attest, but not all! You can absolutely design a system and get near or even better-than MPPT performance without having to buy one (or find a place to put it). Up to now, it's only been theoretical for a lot of us. Starting to get RW test results that bear it out is pretty damn cool.

 

[gnubie]

Yes, that would typically be the max efficiency but experience has shown me that unlike some suggestions elsewhere on the forum MPPT controllers do not necessarily (ie quality based) throw away 'lots' of power and let's not forget that the ED by pulling the panels off Vmp would be ditching perhaps 5%-10% of the panels potential output in the first place, for a well matched panel / battery configuration and well, the efficiency of the MPPT is no longer that much of a concern.

Being cheeky I could just say that if the <3% loss one can expect with a MPPT controller is a concern, just add another panel... but I think someone has already claimed that as an answer to Vmp vs battery for the ED

 

[Dhowman]

Yes, that would typically be the max efficiency but experience has shown me that unlike some suggestions elsewhere on the forum MPPT controllers do not necessarily (ie quality based) throw away 'lots' of power and let's not forget that the ED by pulling the panels off Vmp would be ditching perhaps 5%-10% of the panels potential output in the first place, for a well matched panel / battery configuration and well, the efficiency of the MPPT is no longer that much of a concern.

The results above seem to disagree, no? The PP tracking the MPPT is performing on panels that are already matched results in about a 6-10% reduction in power compared to not trying to track (aka the DSSR results).

Have to say, it's kinda confusing and probably impossibly complicated, given the myriad of variables, trying to do paper comparisons from panel, battery and MPPT specs rather than just looking at test results. Seems those point to a different conclusion, no?

 

[gnubie]

It's not rocket science, Dacian gave you the answer in the youtube comments

 

[Dzl]

This has turned into a great conversation, I'm hoping it continues, I'm learning a lot. I have a couple thoughts.

First, this guys videos aren't flashy, well produced, or super scientific or systematic, but they are some of the best videos on the SBMS0 that I have come across so far (and maybe the only videos of the DSSR20), and I really appreciate him taking the time to make them!

Second, I agree with whoever made the comment about n of 1. Its nice to get a little real world test data, but it leaves A LOT to be desired. As dhowman mentioned, a controlled side by side comparison over time, ideally a month or at least a week, in the summer and again in the winter, would carry much more weight. Throwing 2 or more brands of MPPT (and maybe a PWM controller) into the mix would help paint a fuller picture as well.

@Dhowman I think that you may be reading too much into the test results, they certainly bring up an interesting possibility (that the DSSR actually exceeds a cheap MPPT when PV is optimized for the DSSR), but I think it would be very premature to draw any broad conclusions from a test like this (a few minutes, on a single day, with a single off-brand controller, and many unknown and uncontrolled variables). It might well be that the results he saw, are accurate, but based on the video alone, I think its much too early to say.

Dacian, Bogart Engineering, etc, say that the advantages of MPPT are often overstated, especially after accounting for the DC-DC converter, and that in some situations non-MPPT is competitive with MPPT in efficiency, but I don't believe either has ever hypothesized that MPPT is actually less efficient overall. This leads me to believe that its likely that a more rigorous test might yield different results.

Its a large task, but I hope that someone will take it upon themselves to do that testing, it would be super useful information for a lot of people, and could have far ranging implications if in fact the DSSR exceeds MPPT efficiency overtime, or even if it gets close. Personally I'm still planning to use multiple small mppt controllers, but I really want to use the DSSR's with diversion, when the time comes I might buy both and do a comparison, the problem is that I would prefer 96 cell panels if I go the MPPT route which obviously would not be optimized for the DSSR's so I would need two sets of panels to optimize for both.

The ED has its niche, so do MPPTs.

And so does the combination of the Electrodacus BMS with MPPT in my opinion. A niche within a niche though further testing might prove this is not worth the added cost in some or all conditions, hard to say.

@Dhowman @KohalaJim

Where do you get most of your information on the DSSR's and SBMS, I still feel starved for info on Dacian's latest products, but I'm impressed with how much info some of y'all seem to possess.

 

[Dzl]

@Dhowman @KohalaJim

Where do you get most of your information on the DSSR's and SBMS, I still feel starved for info on Dacian's latest products, but I'm impressed with how much info some of y'all seem to possess.

You sneaky little bastards have been holding out on me! But I've caught you now ?


Today is the first day I realized the message board on Dacian's website actually exists. I've tried to check it, at least a half dozen times but its always just been a blank page. I even tried in multiple browsers. Turns out my adblocker or tracking protections was blocking the message board probably because its remote google content. I can't believe in the whole 8 page SBMS conversation nobody ever mentioned the message board, even in passing. I just had a big Aha! moment, I could never figure out how some of you seemed to have so much info beyond what could be found in the documentation, now it all makes sense, I've got some catching up to do!

 

[Dhowman]

I agree with whoever made the comment about n of 1. Its nice to get a little real world test data, but it leaves A LOT to be desired. As dhowman mentioned, a controlled side by side comparison over time, ideally a month or at least a week, in the summer and again in the winter, would carry much more weight. Throwing 2 or more brands of MPPT (and maybe a PWN controller) into the mix would help paint a fuller picture as well.

Well, technically it's an n of 2, but: a) isn't that where all experiments start? b) it's more data than we had last week, and c) they're 2 data points that are consistent and that beg for more to confirm it's a result worthy of this much attention.

@Dhowman I think that you may be reading too much into the test results, they certainly bring up an interesting possibility (that the DSSR actually exceeds a cheap MPPT when PV is optimized for the DSSR), but I think it would be very premature to draw conclusions from a test like this (a few minutes, on a single day, with a single off-brand controller, and many unknown and uncontrolled variables). It might well be that the results he saw, are accurate, but based on the video alone, I think its much too early to say.

This was all i concluded. It's just data that comport with the theoretical calcs, except that *maybe* the MPPT efficiency used in those was too gracious. But, yes, need more data. Kudos to this guy for getting a couple on the map.

The MPPT he used, btw, was an EPEver ... not really an off-brand MPPT.

 

[KohalaJim]

I asked Dacian to reiterate the MPPT off-grid arguments (suspecting he'd done this already because of his "no surprise" commentary)
And of course, this was in 2015:

 

[KohalaJim]

These (2) graphs are illustrative of what I suspected in prior editorials...
The higher the difference between the PV voltage and the battery, the lower the MPPT efficiency:

 

[Dhowman]

I asked Dacian to reiterate the MPPT off-grid arguments (suspecting he'd done this already because of his "no surprise" commentary)
And of course, this was in 2015:

Uh oh. @BiduleOhm

Might want to review a couple posts and replies to 'em to catch up on discussion that vid has already generated here.

• here
• here

 

[Bogart Engineering]

Sorry, couldn't resist the screaming tabloid headline, but this is VERY encouraging for DSSR users and starts to address, what until now, has been a heated, albeit purely theoretical, debate:

Our customers have known this for several years! When the panel voltage is properly matched (& panels wired in parallel) to the storage voltage, a PWM (essentially what the Electrodacus + DSSR is) controller is better for small systems. Our SC-2030 solar controller consumes less than 5 Watts while delivering 31 Amps to the batteries (12V or 24V).

Most MPPT controllers may advertise a peak efficiency of 98% but operate at 90-92% at the rated max current. The peak efficiency of 98% is when the current is 35-50% of the rated max. Add to this, loss in panel voltage due to cell temperature, any advantage an MPPT may have is lost for small systems. Most users often don't realize how large this is. To put it in perspective, it took about 4-6 years of R&D for the overall PV efficiency to increase by 15% ( 17.5 to 20%). All of this can be lost in one warm afternoon.

For RV rooftop mounted systems our recommendations have always been low voltage panels, wired in parallel & a good quality PWM controller. This offers the most reliable setup and is as efficient as any MPPT based system.

 

[Dzl]

Well, technically it's an n of 2, but: a) isn't that where all experiments start? b) it's infinitely more data than we had last week, and c) they're 2 data points that are consistent and that beg for more to confirm it's a result worthy of this much attention.

We are on the same page here, its a step in the right direction, and some data is better than no data, but I think its just a fraction of the data needed to confidently draw any conclusions from. I see in the comments section of the video that the author intends to do more testing, I'm definitely looking forward to that, but if he only has two panels, longer term testing might not be a possibility.

This was all i concluded. It's just data that comport with the theoretical calcs, except that *maybe* the MPPT efficiency used in those was too gracious. But, yes, need more data.

I suppose I was basing that comment of this statement "Seems to make absolutely no sense to use an MPPT with 60 cell panels in parallel on a 24V battery." and a couple others you made in response to Gnubie. But its entirely probable that I am minsinterpreting the broadness and conclusiveness with which you mean them.

In my eyes, these test results offer the first little bit of limited evidence that the DSSR when compared with a budget MPPT controller, can meet or exceed the output of a particular controller, in conditions where it was theoretically predicted to be most competitive. I would want to see more data before I accepted that as fact, but I don't have a hard time believing that, and don't have a hard time believing it might be true with top tier controllers as well. But to me this is not the area that needs to be explored. What needs to be explored is the performance over time, over the whole range of conditions. As I understand the advantage of MPPT has always been that it handles variable conditions better, so a short snapshot comparison in near ideal conditions, is not a very good basis for evaluating the difference between the two technologies since its the situation where the difference should be the least pronounced. As you said, his test results confirm the theoretical data, but the theoretical data also shows that the test conditions are where we would expect the DSSR to be most competitive, before making assumptions like "seems to make absolutely no sense to..." I think we would need to see testing from a wider range of conditions, specifically conditions where we would expect an MPPT controller to do well.

I agree with what you said earlier, I think a longer test over time, that captures a wide range of temperatures and both overcast, sunny, and partially shaded conditions would be much more meaningful. Personally I wouldn't be confident drawing any broad conclusions before that. And even then, because of the proprietary nature of MPPT algorithms and the

I suppose my point is mostly that jumping to conclusions (especially ones that confirm our preconceptions) based on a limited slice of data can be as bad as having no data at all. We should take this for what it is, one useful data point, that still falls far short of what is needed to make an informed decision, and that we should try to keep open minds until more conclusive data becomes available. If you go back to some of my first posts on this forum, you will see I was quite swayed by Dacian's logic re: mppt vs non-mppt in ideal conditions, but the big unknown to me is how would this calculation change in less ideal conditions (specifically partial shade and overcast or cloudy conditions), I think this question is still as unanswered as ever.

After writing all this I feel like I should apologize, I think I'm making assumptions about your perspective that I'm not entirely sure are accurate, so if i'm misconstruing your thoughts I apologize. I'm also not trying to be a debbie downer, I think that its totally reasonable to be excited about this test data, I just think its too early to draw conclusions.

The MPPT he used, btw, was an EPEver ... not really an off-brand MPPT.

I suppose what is and isn't off-brand is somewhat subjective, and maybe I'm being a solar elitist here but I definitely think of Epever as an off-brand (which isn't the same as saying its a bad product). Its a semi-unknown company based in China (with only a Chinese contact number and address listed) that sells mostly low to mid budget charge controllers to companies like Renogy and direct to consumers through amazon and aliexpress, and is semi-branded, but mostly unknown outside of niche communities like this (and our awareness is probably mostly due EPever being Will's reccomended budget SCC). I think its fair to say that in the broader market Epever is a fairly unknown brand, with a fairly unknown medium to long term track record, not sold by most solar retailers. To me this is what off-brand means. And with something like an MPPT controller, where the software and hardware are both quite important, this might make a big difference. But I can't say, that's why I think it would be useful to test multiple MPPT charge controllers (maybe a budget option like the Epever and a Victron).

 

[Dzl]

Hey @Bogart Engineering I'm really glad y'all are chiming in here. One of your articles very much influenced and helped shift my perspective on PWM vs MPPT (though full disclosure I'm still leaning MPPT), and your expertise here is appreciated.

I wonder if you can comment on one of the things I'm hung up on, and maybe share some test data if you have any.

I can see how with well matched panels in sunny wearther at near STC (or higher) temperatures PWM or the DSSR would stack up well against MPPT.

Of particle interest to me are overcast days, cold sunny days, and especially partial shade (for instance would you recommend your controllers for use on a sailboat or vehicle)?

Do you have any numbers you can share for non-ideal solar conditions, and/or longterm comparison data over multiple seasons?

 

[BiduleOhm]

Since @Dhowman tagged me I'll just add something who hasn't been discussed while I'm here: if you want to compare systems prices and efficiencies then you need to account for price and losses in the wires, especially for a home system with dozens of feet of wire.

 

[Bogart Engineering]

Hey @Bogart Engineering I'm really glad y'all are chiming in here. One of your articles very much influenced and helped shift my perspective on PWN vs MPPT (though full disclosure I'm still leaning MPPT), and your expertise here is appreciated.

I wonder if you can comment on one of the things I'm hung up on, and maybe share some test data if you have any.

I can see how with well matched panels in sunny wearther at near STC (or higher) temperatures PWN or the DSSR would stack up well against MPPT.

Of particle interest to me are overcast days, cold sunny days, and especially partial shade (for instance would you recommend your controllers for use on a sailboat or vehicle)?

Do you have any numbers you can share for non-ideal solar conditions, and/or longterm comparison data over multiple seasons?

Partial (or full) shade & PV don't mix! Wire the panels in parallel to make sure a shaded panel does not affect the whole system. If series wired, bypass diodes may help, but not always. The MPPT algorithm can be easily fooled by multiple (local) max power points that may occur in such conditions.

Amorphous and polycrystalline silicon panels are better under cloudy skies; poly-Si panels also tend to have a slightly better (lower) temperature coefficient for Vmp & Pmp.

We don't have long term data for non-ideal conditions. However, this is a well studied topic and a web search would dig up some.

 

[Bogart Engineering]

paper by Victron CTO (former?) - https://www.victronenergy.com/uploa...Which-solar-charge-controller-PWM-or-MPPT.pdf
does not appear to consider DC-DC conversion efficiency

 

[KohalaJim]

Since @Dhowman tagged me I'll just add something who hasn't been discussed while I'm here: if you want to compare systems prices and efficiencies then you need to account for price and losses in the wires, especially for a home system with dozens of feet of wire.

In the primary "financial" case being asserted in the video, the generalized number for wiring cost differences (parallel/series - voltage/current) was $100'ish or so... the power losses due to wiring runs are more abstract. The broader points on co$t savings was amortizing the ca$h outlay for MPPT over the the life of the PV panels.

All good stuff, and I continue to learn more relevant stuff through the continued dialog.

[EDIT]... here's the slide:

 

[Bogart Engineering]

Hey @Bogart Engineering

Of particle interest to me are overcast days, cold sunny days, and especially partial shade (for instance would you recommend your controllers for use on a sailboat or vehicle)?

Yes, we do recommend the use of our controller on sailboats & vehicles. A Santa Cruz, CA based sailboat with our controller & monitor has sailed to New Zealand several times over the past 6-7 years. The controller was one of the first production items.

 

[Dhowman]

I suppose I was basing that comment of this statement "Seems to make absolutely no sense to use an MPPT with 60 cell panels in parallel on a 24V battery."

There just isn't enough V difference between 60-cell/24V panels, especially when they're at STC or higher (which is most of the time and in most places?), and a 24V battery, so the MPPT is stuck with the power point the panel's already at or one that's not different enough from it to make up the overhead inherent in the MPPT itself. Intuitively this makes sense but it also seems to be borne out by the results above too, no? In conditions where panel's below STC, increased panel voltage may allow enough wiggle room to find a power point to make up it's overhead and get you a little more, but these seem like edge cases for most people. Dacian's remarked that for a panel in the sun to be at STC, the ambient temp need to be about 14F deg (-10C). Anything above that temp and you're maybe better off not relying on MPPT and its overhead and just going with the inherent power point of your panels ... or putting 'em in series to give it the voltage diff with your batteries that it needs.

 

[ADM]

Just chiming in here with something that seems to not be discussed when deciding on charge controllers.
Built in bypass diodes in PV panels, not all of them have them but many do. These panels would really only properly work with mppt charge controllers as they will drop voltage during partial shading.
Yes they do confuse the MPPT charge controllers and I can attest to that. I recently swapped out my older Tracer mppt charge controller for a new MPPT to see if it would overcome the inconsistent voltages the controller would hold the panels at.
Will post my findings after a couple weeks testing.