PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world test.

[mbuckhurst]

Re: PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world t

fwiw, we produce full 3d models of every building we install on and can estimate the shading impact very precisely on average for each hour of daylight for each month of the year, and use this to design the system to absolutely minimise the shading impact.

We actually don't use micro inveters though, as we've never found a situation where the figures stacked up to mean that their benefits outweighed the reduced efficiency of the micro inverters vs an SMA 4000TL, which with Optitrac global peak enabled will already greatly reduce any shading impact on a properly designed system to get the best out of the panels in built bypass diodes to bypass any shaded strings of cells.

Took us a fair amount of time, effort and scratching of heads to get to that point though.

I went through 18 installers, and not one, even the one we went through had any kind of 3D modelling.

On the efficiency situation, I'm not sure I'd agree, from my personal situation, you'd never be able to achieve a string big enough for an SMA inverter to work efficiently with one or more panels shaded, which would mean for the period the shaded panels are doing nothing, an SMA inverter would do nothing.

My main concern with the efficiency figure is the fact that everyone seems to assume all panels side by side produce the same output all the time, but when you have the ability to view each panel as you do with a microinverter, you get to see quite a variation, even simple things like vapour trails from aircraft can affect the output of a single panel - due to the fact I've got panels with a spread of 14m you can see the output change as the clouds move across the sky.

Unless SMA have managed to break the laws of physics there is no way they can optimise the power across a string so that the power output is the sum of the total, only the most efficient for the system as a whole.

In my case the difference between the side by side panels is larger than efficiency difference between the best SMA inverter and the Enecsys micro-inverter, but I only have 3 pairs of panels where they can be said to have absolutely identical sun.

This is what makes this kind of experiment very interesting, I'd like to see the same experiment, but looking at microinverters against string inverters, we all have our own beliefs, but no one seems to have the hard facts. My best guess is that in reality there's little difference between the two, so cost is the only factor, but in my case it actually wouldn't be possible to get a string large enough so it's not a choice.

Perhaps the most interesting fact is that I've got some friends, their roof isn't shaded, and points in the same direction as most of my panels, I do have a set of 4 pointing slightly more southerly, both ours and their systems are within 1% of the same output, and both have identical numbers of identical panels.

I should also point out, the installer I went for, was the only one to consider installing a very esoteric system rather than a slap it up as fast as I can to maximise my profits which pretty much the rest seemed to want to do. I think the avoidance of micro-inverters is in a large part simply because it costs the installer more to install.

mike

 

[Gavin A]

Re: PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world t

Unless SMA have managed to break the laws of physics there is no way they can optimise the power across a string so that the power output is the sum of the total, only the most efficient for the system as a whole.

no laws of physics being broken, they've just used a function that sweeps the VI power curve from top to bottom every few minutes to find the actual peak point instead of getting stuck on a false peak and riding that all the way down to nothing.

Basically what they're doing is making it so that the bypass diodes in the panels are used properly, particularly in situations where the shading rapidly impacts on several strings of cells at once, which often takes the new peak voltage outside of the range of the sweep of the standard MPPT tracking.

If the bypass diodes are enabled to function properly, then it allows the unshaded portions of each panel to output at their optimum point instead of being dragged down by the shaded parts of the system.

I'm not sure if I'm explaining this right, it's a bit late, but the bottom line is that it's surprisingly effective. Obviously you can only install on maximum 2 roof faces, and need a minimum of 4-5 high voltage panels per string, but frankly I detest the look of systems with panels dotted around all over the place, and am of the opinion that such systems will actually cost the customer money in the reduction to the houses value from the poor aesthetics, so for me it's not really an issue.

There is potentially an arguement for microinverters with sanyo panels as the sanyo panels have a +10% tolerance on them, and strings will always operate at the output of the lowest rated panel in the string, so if the variability really is this great from panel to panel, it could potentially have a greater impact than the +2-3% efficiency of the 4000TL vs enercsys. I'm dubious about this, but would be interested in some real world comparative data from panels on exactly the same slope, orientation etc if you had such data.

 

[Gavin A]

Re: PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world t

I think the avoidance of micro-inverters is in a large part simply because it costs the installer more to install.

mike

I don't know about anyone else, but if it costs us more to install, then the whole system would also cost the customer more, which is another factor. I don't know the exact figures, but if it were an extra £500 for enercsys, then it'd need to provide 5% benefit vs a string inverter just to cover that extra upfront cost.

tbh, I don't think there's much in it either way providing the system is modelled fully in advance and designed carefully to mitigate the shading impact.

 

[mbuckhurst]

Re: PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world t

I find this whole thing very interesting, my wife who has a degree in Physics and a PhD in electrical engineering, specialising in semiconductors explained it to me, how the MPPT could never achieve as much as treating each panel at an individual level, basically the sum of the parts will always be greater than the sum of the total because each panel is optimised or the whole system is optimised, but whether this was significant or not, who knows, what is very significant is the Physics involved in the conversion of photons to electrical energy, and this is where clouds can have a big impact as the shadow moves across the panels, but again, it's not measurable in any meaningful way.

Personally detesting the look in my opinion is only excusing a lack of willingness to consider the options, in my case, 9 panels are hidden from the front, and 8 of these sit on top of flat roofs that don't have any aesthetics to lose . But if aesthetics are important, surely the only option is solar tiles, which incidentally I did get a quote for, but it put the install, off the scale, for price.

I'd love to give meaningful figures but I've yet to find a way to record the Enecsys figures beyond the totals they show, for day, week, month etc. and this is looking at the data with sufficient detail. I have collected the odd snapshot throughout a single day to see what happens, but you'd really need to capture every reading for every panel throughout the day, to analyse it in any meaningful way. If a shadow from a cloud moves across the panel at the same speed, the effect on a micro-inverter system is for both panels to record the same total, if using a string, the effect is to lower the overall output for the duration of the shadow on either panel. But if you looked at the instantaneous readings, you'd see one panel was generating maybe 10 or 15W less for the duration of the cloud.

My best figures I can come up with, for 2 of the pairs that are in consistent conditions, and they're flawed for the reasons above:

Pair 1: Today: Same reading Week: Same reading Month: 18.37 vs 18.45 Year: 64.84 vs 65.17
Pair 2: Today: Same reading Week: 2.49 vs 2.48 Month: 19.14 vs 19.07 Year: 67.92 vs 69.88

Pair 2 is interesting as the panel that's achieving the most has swapped over.

Another interesting factor is temperature, and I suspect worrying about clouds and positioning is probably largely irrelevant compared to temperature, we know how much heat can affect the generation efficiency, so the middle panels in any array, could potentially be under-performing the outside panels due to heat build up. Now we're in the summer I'm seeing my flat roof mounted panels exceed the generation of the roof mounted panels by a much larger margin than any of the efficiency differences, which is probably mostly to do with heat. My roof mounted panels were always the best during the winter by 10-15% and this situation has reversed by roughly the same amount.

There are so many factors that could affect solar generation, I found it quite dismaying that micro-inverters were rejected out of hand by so many installers. I think the reality is as you say, the cost is more significant than any benefits, unless the system cannot function without.

I suspect my install is one of the most esoteric out there (and my reasons for maximising generation at whatever cost), and it would not be possible to design out any of the shading issues, simply because orientation of panels is largely fixed due to various factors. I would have loved a 3D model, but given the cost is nearly half that of fitting an extra panel, you'd wonder whether the suck it an see approach is just as valid as sitting there and trying to do the maths.

mike

 

[series530]

Re: PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world t

With my system the Sanyo panels were chosen mainly on grounds of yield per square metre. We could fit 3.5kwp on the roof without it looking like a chess board. I wanted something that would be, at worst, neutral upon the look of the house from the road. My feeling is that this is one of the few installs that actually enhances the look of the house as it gives it a slightly more modern feel.

The problem with going for something that looked reasonable was the fact that we have a large chimney on the front of the house and a chimney and aerial from next doors house causing difficulty first thing in the morning. Most installers just wanted to slap up panels in the middle of the house avoiding the shading from the chimneys. Our chosen installer suggested Enecsys and with a high up mount. Much more expensive but not outrageously so and virtually cash neutral when you factor in the twenty year warranty on the inverters and the fact that, at that time at least, a string would need replacing at some point.
His thought was that Enecsys would pull as much power out of the system as feasibly possible while string inverters would suffer to some degree. I'd read about clouds and I can see the effect of them, albeit delayed, on the monitor. I can also see the effect of the chimneys and aerials.

I will never know how much inefficiency exists within the micro inverter. All I have are the specs. Over 1.2M watt of production the Enecsys monitor is reading about 2.7% higher than the PV meter. meaningless I know, but it does give us an idea of the accuracy of the monitor.

One place where micro inversion does fall down with the Sanyo panels is bypass diodes. The HIT250's have a pretty high open circuit voltage and this necessitates the use of the higher tracking range Enecesys units. These also have a higher minimum tracking voltage for the MPPT and this means that the moment a panel reaches about 50% hard shade the inverter will shut down. We're this on a string the inverter would most likely keep the panel producing. This has proven to be something of an issue with our chimneys.

I've always taken the long view with PV. For me, it isn't about how quickly can I get my money back. I'm more interested in maximising my income each year. IT amounts to a similar thing but it isn't quite the same. Achievements so far show that the best performing panel (since November) has yielded 90kwh. Interestingly it is right in the middle of the array. The worst performing panel has managed 71.5kwh. This one is right behind the chimney. Now, I could have left a gap behind the chimney but the evidence shows that even the shaded panels will pay for themselves albeit over a 25% extended period or so. Now, given that the shading is far less at this time of year (nothing before 5.30pm) yet the sun is stronger, I suspect that the differential between the best and worst performing panels will reduce. I also suspect that the system losses of 2.7% will come down as the quiescent drain of power to run the inverters becomes less significant as solar yield increases.

If my system had been very low shade I am sure I would have taken a string based approach. As to if the micro inverter route was the best one... Who knows. provided I get close to or exceed my installers estimate (which offered a significant uplift over PVGIS) I cannot complain. It will take several years to compile enough data to be statistically meaningful... Certainly the data so far is not enough.

The upfront cost of Encesys is higher. That is a big turn off for both installers and customers. The fact that there is more hardware per panel install and the fact that even with a 20 year warranty somebody may have to come back several times and possibly install ladders or scaffolding is a turn off for installers. Some installers have a fear of something new. Some installers have a tainted vision given the poor reliability when Enecsys changed manufacturers. I can't blame installers for not advocating micro inversion. I cannot blame customers for reluctance to pay more up front.

Time will tell with micro inversion. I'm playing the long game and as long as my metrics are met, I'm reasonably happy.

 

[Mark42]

Re: PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world t

Originally Posted by Vegelen
The only way equal conditions can be found is by installing side by side.
Do you know a millionaire locally that will fund such an experiment?
I'd be happy to see the results.

As would I.

All I am saying is that to compare these two systems is not very good science, particularly when you understand just how much impact orientation, pitch and shading can have on a system.

To take these two systems and then to go and make a conclusion based on the results is not going to very accurate.

Gentlemen, I'm confused.

I'm the OP who, whilst not a 'millionaire' is running a side-by side experiment between Chinese and Japanese panels at my own expense (see early posts).

Please don’t derail this thread with details of other comparisons, where the systems are not actually ON THE SAME ROOF! It will confuse later browsers (including me).

Thanks

 

[Mark42]

Re: PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world t

I know its only nearly 3 months from fitting but do we have any conclusions/updates yet?

Hi Gary

Thanks for your continued interest. The data so far are most interesting. And surprising. There is a temperature factor at work, but it’s relatively minor. I’m not going to say anything more until I have enough data which encompasses seasonal variations.

I also don’t yet have any up-loadable information, since we’ve been stuck on the supposedly simple matter of getting a legacy RS232/485 serial port working on a Win 7 machine. All the data remains locked inside the inverters for now.

Cheers, Mark.

… I have a wife with a Ph.D. in semiconductor Physics so have an insider

Ha Ha! I live with a tame programmer/mathematician so clearly we share an interest not only in elec-trickery, by also in intelligent women

 

[Earthstore]

Re: PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world t

Cash and dash, we are all intrigued as to how they are performing, to be a fair test you want to run it for a year of that we appreciate, but could you give us any idea as to how they are against each other, just roughly would be great.

Many Thanks.

 

[danesol]

Re: PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world t

Been really picky, the only error I believe you have made is that you have installed the panels in specific groups at different parts of the roof, which could depending on environmental circumstances could cause some rogue results possibly. I think the better way for panel layout especially seeing its a comparison experiment, would of been 2 rows - 1 row of each make across the roof, one make above the other and/or crossed over 8 panels reversing make on top for make on bottom.... or if wiring would allow - mixup in an orderly fashion - a Sanyo panel then a Hengjji panel and so forth....

However apart from that I'm really looking forward to your findings - good work !

 

[Avontech]

Re: PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world t

With all the focus on maximising putput, one of the biggest areas people would benefit from is maximising usage, as mick says:

my reasons for maximising generation at whatever cost

I do hope mike, you've got a coolpower emma attached to that ...

Back to the OP's reasons for this, a real worl comparison over a year would be excelelnt - any chance of posting the data / hooking the inverters up to pvoutput.org?

 

[Mark42]

Re: PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world t

Been really picky, the only error I believe you have made is that you have installed the panels in specific groups at different parts of the roof ...

That's not picky at all, it's an obvious point, and I agree absolutely.

I didn’t do it for historic reasons: I’d already fitted all the rail and 4kW of Chinese panels before the idea of doing a comparative test crossed my mind. It was reading all the arguments on this forum about ‘which panel is best’ that gave me the idea.

I immediately sold 4kW of panels on EBay and ordered replacement Sanyos. Time was very tight since I was aiming for the 3 March deadline.

Plus the work involved chipping ice off a slippery metallic roof to get the panels on. Handling metallic objects at -5C is rarely fun, so the idea of taking off what we’d finished already did not appeal. I also didn’t have enough PV cable immediately to hand to do a checkerboard array.

Now it’s sunny, I’ve toyed with the idea of changing it around, but I doubt I’ll actually do it, there just so much else happening at the moment (any volunteers? ). At least they are side-by-side on the same roof, and I don’t think even that has been done before.

Due to the great disparity in price between the two systems, I am looking for a major difference in performance, way beyond any ‘Ah but that end is more shaded at 07.00’ type argument. Even allowing for the possibility of differing average illumination levels at each end of the roof, with a 50:50 chance of it disadvantaging the Sanyos, I would still expect them to provide statistically significant greater generation.

 

[Mark42]

Re: PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world t

Cash and dash, we are all intrigued as to how they are performing, to be a fair test you want to run it for a year of that we appreciate, but could you give us any idea as to how they are against each other, just roughly would be great.

Many Thanks.

Apologies for the suspense

But I'd better be careful: there may be liabilities attached to the results - they may well show that one type of panel has been mis-marketed, leading to all kinds of legal claims from previous buyers. The UK's Sale of Goods Act is pretty clear about manufacturers' claims. So before I release the data, and take full responsibility for it, I need to make sure that what I have is both irrefutable, and statistically significant. It might be big news. Or it might not. Kindly stay tuned

 

[Gavin A]

Re: PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world t

the last couple of days should have given a good indication of whether the sanyos are likely to start significantly outperforming the others through the summer.

FWIW I wouldn't have expected much different up to this point in the year, but most of the generation will be May-September, so it's the advantage at this time of year that really pays dividends.

I've probably said this already, but we work on around a 5% improvement with the sanyo panels in our estimates. I'm hoping this is about right, but wouldn't expect it to be much higher than this - probably slightly lower if panel voltages were the same (slight improvements in inverter efficiency usually from the slightly higher panel voltages).

 

[Earthstore]

Re: PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world t

I think you will be OK on that one because all panels are tested under stc, so that one can compare a panels performance to another tested in the same conditions, but what you are testing is real performance, in real conditions.

This test could possibly show opposite results if it were say in California.

But thanks from all of us (well most).

 

[danesol]

Re: PV Panel War: Sanyo v. Hengji. The ultimate side-by-side long-term, real-world t

Can we have somekind of interim results please.......................