Mixing and matching panels (with Solis AC Inverter)

Charge Controllers (MPPT, PWM)
41

This is how I would ask the question if someone tells me I’m 100% fine going 5S:
If you say I can go 5S on my panels, and the MPPT blows IF it ever goes over 250v due to weather conditions, will you cover the replacement out of your pocket?

I’m 100% with Victron for making sure they don’t have to cater for that, cause if there was a 1/2/5/10v “margin”, then that would have become the “new norm” on forums like "Don’t worry, there is x margin built-in … ".

A line must be drawn in stone somewhere … not in the sand.

So, anyone who says I’m 100% fine with 5S for ±840w extra, MPPT will NEVER reach nor pop IF it does hit 250v accidentally due to weather conditions, then “put your money where your conviction is”, and guarantee me that financially. :smile:

If not, then it is MY risk to mitigate as I have NO idea what happens at the panels, temp wise, on a very cold sunny Cpt day with a cold North Easter/Wester blowing “unchallenged” over them … and cloud effect enters the equation.

Simple as that.

42

I think we can agree that the hardware has margin. The issue would be warranty. If an MPPT does blow and the voltage did exceed 150V, there would be no warranty. That’s probably a gamble you can take though.

Also, I did show earlier that by my own data, there is a substantial difference between the coldest ambient temperature, and the actual response from the panel.

I also suspect that a ground mount out in the open would be more susceptible to wind-chill than one on a roof. So as in all things in life… your mileage will vary.

43

If I tell the client that its safe, and it blows up, I have to take care of the damage, and I am covered for that…

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46

I saw a clip of someone opening up a Victron 150 MPPT clone and the capacitors were rated at 160V.

Edit:
And google says:
“Common working DC voltages are 10V, 16V, 25V, 35V, 50V, 63V, 100V, 160V, 250V, 400V and 1000V and are printed onto the body of the capacitor.”

If that follows then the 250V MPPT, may use 250V capacitors.

47

An I think here is a good point!

  1. We as installers need to spec and supply in our comfort zone.
  2. We need to except that the hardware is built for world wide distribution (Sahara and Canada in winter)
  3. Each installation is unique and needs to be planned as such - therefore a competent installer (and therefore solar solution design)
  4. We need to accept that some companies could market then product as “bigger and better” but choose to manage their reputations more careful and so don’t over-promise (rather over-deliver).

So both arguments have a lot of merit.

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48

Guy came back with another interesting story on the community…
I feel I want to share this as this fits in well with what i have personally experienced in the field.

Guy 2
Guy 2718×431 32.8 KB

On the one side, us blue supporters always try to tell the whole world how wonderful and robust our recommended equipment is, and then in this thread some of us create the impression that some Blue equipment might fail miserably at the slightest over voltage conditions…

I will stick to my guns, based on personal experience, Blue equipment is much more forgiving and robust than some people claim it is…

57

As per usual , way late for the prom… What am I missing here
To recap -

  • The main concern is that one could blow the MPPT if you max out the voltage of your array in low temp conditions.
  • What about that silly thing that we find in the high veld - “solar edge” where we have these Big cumulus clouds passing by and as they pass the sun you get a “spike” in production… but before I derail the original question too much…

Back to the question at hand, for the layman that is not up to speed with the solar jargon:
5s/3p - I assume implies 5 Strings of panels at 3 in a series , if this is correct lets look at the math’s (I cant see any of that in the previous posts)

Current setup :
3p = Voc 46.6v * 3 = Max Voc of 139.8 v Seems within the specks
Optional addition:
As I understand it the additional array of panels will be “pulled” down to the lowest voltage of the total array. So if the new addition that you want to add has a higher Voc than you current config. You will “loose” the additional potential. In this case
2x panels has a Voc of 46.8 and the last 48 ( So on this individual array the 48v will be pulled to 46.8v.Thus 46.8*3 = 138.9 v ) But then the current array is 139.8 so you will loose 0.1 v on the array
So unless I have the math’s or theory wrong the answer will be :slight_smile:

Yes you can add that mix of panels but you will loose some potential as a result of the different voltages.

*** The theory being - Solar production - Voc in a Series array will always be “pulled” to the lowest voltage of the mixed array of panels. PLEASE correct this if I am wrong and are misleading a “New to Solar” reader who stumbles onto this thread

58

Derailment Threads and responses to it was deleted. Please refrain from derailing any threads and please keep to the point.

59

5s3p is 5series, 3 parallel.
I made the same mistake when I first did the calc in my head, but you should be looking at the 4s that he wants to change to 5s to calculate the voltage.

60

Ah , one lesson learned thanks.
So then 46.6v * 5 = 233v that is till below the 250v mppt (I assuming that you have a 250v mppt)

61

Let me recap.

This is what I’m looking at:

image
image665×637 133 KB

Now Cpt that low has happened once in a very long time, but in other comments, I don’t know how cold my panels can get high up in the wind/sun on a cold sunny day with cloud effect, as the wind can cool them quite nicely underneath too, as I have seen my 4.2kw array spike to 5.750 watts a time or 2 on those cold sunny days … never checked the volts at the time.

Then I also asked a Victron dealer. They also said it is a close call, doing the calculating using the temp coef.
image

Err on the side of caution, they said, it MAY never happen but IF it does, fluke/bad luck the one day, there is no warranty. Victron says 250v, maybe they have a bit of spare built-in, but it matters none, if it goes out at 250v that is MY risk. Also what I’m looking at, the weather is changing. Colder, wetter, hotter.

Then I thought, for 3 more panels, 1050w - 20% = ±840w, is it worth it? First the cost, then the “risk”?

Then I started a thought on using a Solis to take care of the geysers, to add like 2/3kw more to take care of them, then the 4.2kw array primarily deals with the 560ah bank, the spare on the Solis adding to the charging before and after heating the geysers.

No risk, lots more paneling, and a 10-year warranty in some cases.
Or I get another MPPT and a 2nd array … the Solis is cheaper though.
And IF, IF CoCt major says he wants to buy power from homeowners and makes it sensible … let the Solis do the lifting.

62

OK, I hate to beat a dead horse. But here goes.

I’m not an electric engineer, my experience is merely of the “working with it on paper kind”. My practical experience ended with 335W modules on my own roof, which has a comfortable Voc of 45.5V. 10% margin.

So let me use an example. The capacitors in your car radio will be 16V. In my personal opinion, that’s being CHEAP. The kind of ripple an alternator puts into an electrical system, especially with a bad lead acid battery, can approach that kind of level already. A good car radio should come with at least 25V capacitors (the next step up), in my opinion. But my opinion aside… despite the caps being 16V and occasionally getting a hammering (think about temperatures and bad lead acid batteries), car radios do not generally blow their caps within the normal design life of the unit. And that is because it happens infrequently.

Another point: Capacitors are rated to do their work at a certain max voltage and also a certain operating temperature. If you FREQUENTLY run it at the top voltage, at the rated temperature, you will get a certain number of hours out of that cap (cheap caps are 1800 hours if I recall) before it fails.

Then you have ESR (effective series resistance), something which also degrades over time, increasing your ripple components, which then affects other components. This is something that the earlier Voltronic inverters frequently suffered from: The caps degraded, causing the FETs to blow later.

Then you have ripple. This is a switch mode power supply. You have to deal with ripple, which means the peaks might already be higher than the DC you are pushing in.

All of this has to be fitted into the safety margin, and keeping it under the worst component in the box.

The manufacturer doesn’t want warranty returns, so he picks a low-ish number that is good for everyone and everything.

On the other end, the panel maker likely errs on the side of picking higher numbers, because 1) better for marketing, and 2) you also don’t want someone to complain that your modules blew something up because it exceeded the stated specs.

The result is that there is probably a lot more room than we realise, and practical testing bears that out.

So if you have a system that has been working well for years, and your installer is backing it, then you can relax. I am terribly sorry if I caused people to panic. @calypso , if that 146V you saw was on a cold day, I would not worry. If it was on a hot summer’s day, then absolutely, get that array reconfigured asap :slight_smile:

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63

From my side, I 100% understand that.

But I think the part that is being missed, as this is my thread so I may crit myself here, is this teeny bit: 1050w - 20% = ±840w more.

I thought I had space for 4 more panels … till I checked and verified. :man_facepalming:

So even IF I “risked” it all, everyone else is right, me just being super over-cautious having a Doctatorial Masters in “WTF Not To Do”, well, I still can’t get past that teeny gain.

64

go get a beer and wait for the idea to pass

65

Seems I need min 2kw more, the 840w is a drop in the bucket.

66

I can also add some weight to the “get a PV-inverter instead” argument. They are typically 95% efficient, and they don’t derate like your Multi does. They are by far the best way to get energy onto the grid for those day-time loads where you are specifically targeting savings and not backup.

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67

EXACTLY my thinking too!

68

Even if you are forbidden to export to the grid, I find sizing a PV inverter to cover your existing daytime standing load to be noticeably more efficient.
Just to be clear about what I mean by standing load?
I mean the things that run constantly, that level of load that you just can’t seem to get under, the router, the freezer, the fridge, the telly, the security system and even the multiplus’s own standing load etc. All these sub-100W things add up.

What I don’t mean is the heavy hitters like the toaster, kettle and the like.
Use the Multi’s capability to cover the heavy hitters.
That gives you the best of both worlds.

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69

YES! I WAS there, coupled with lifestyle changes, I could run all with ease including 2 x 150l geysers during peak sun hours.

The system was balanced. Batts recharged.

Then three things changed:

  1. I noticed the last year and a half the weather. More clouds in Cpt in summer, and rain.
  2. Kids moved back … with a newborn.
  3. I got a 560ah battery bank … that maybe I still sell half of it.

So the “standing loads” aka geysers, the lowest hanging fruit to “solve”.

EDIT: AND I can shave more evening watts off the grid IF I can recharge the batteries.

Looking at it in a different way, I could literally be “off-grid”, or close as damn, with Eskom as a backup/generator.

70

Geysers are not standing loads, they are heavy loads that are not constantly on, just like a kettle or a toaster you have discretion when to switch them on.
Standing load is the sum of loads that accumulatively are on all the time.
I mean those things that are always plugged in.
This might be 300W - 800W in an average household I imagine.
It can also include a very slow small charge towards the battery, I suppose, but really minimal.