Victron mppt sizing

[1967bowesj]

Upgrade time so looking on the victron web site wizard for which mppt, it’s confusing me so need the collective fun advise.

Have two 175w roof mounted panels, which I was thinking the 100/30 mppt but the victron wizard is suggesting the 100/20.
Not wanting the mppt to be flat out all the time in summer so looking for advise.

John

 

[WESTY66]

Upgrade time so looking on the victron web site wizard for which mppt, it’s confusing me so need the collective fun advise.

Have two 175w roof mounted panels, which I was thinking the 100/30 mppt but the victron wizard is suggesting the 100/20.
Not wanting the mppt to be flat out all the time in summer so looking for advise.

John

My very limited knowledge would have me fitting a 100/30 Bluetooth MPPT at least

 

[Carpmart]

100/30 would be my choice… that’ll give you headroom (just about) for another matching panel in the future.

 

[AdrianChen]

I used the spreadsheet version but does the same thing - I have two of the 175 Victron panels (Mono) and like you it recommended the 100/20, but there was a note to say power limiting in low and high temps, to eliminate both of those those it required a 100/50 - cost difference around £130 vs £70.

Doubt in most UK weather it would make any difference, but went for the 100/50 anyway.

 

[Carpmart]

I used the spreadsheet version but does the same thing - I have two of the 175 Victron panels (Mono) and like you it recommended the 100/20, but there was a note to say power limiting in low and high temps, to eliminate both of those those it required a 100/50 - cost difference around £130 vs £70.

Doubt in most UK weather it would make any difference, but went for the 100/50 anyway.

The 100/50 is way overkill IMHO…

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[1967bowesj]

I find it a bit odd the site down grades the controller, I’d have expected it to go up a size.

 

[Lenny HB]

I have 2 x 175w panels and fitted a 100/30 the 100/20 is only rated at 290 watts of solar. I know you are never lightly to get full power from the panels unless on the equator in June but there is only a few quid difference in price.

 

[AdrianChen]

The 100/50 is way overkill IMHO…

Probably you're right, I played around with the default module temps, and perhaps in winter Norway/Summer Morocco there can be an impact, but doubt I'll meet the extremes in the UK!

 

[Gordo]

PM me if youre after a 100/30 - i just swapped mine for a 100/50 after I’d chosen the wrong one (4x130w panels).

 

[AdrianChen]

I find it a bit odd the site down grades the controller, I’d have expected it to go up a size.

I think 100/20 will be fine, and even if you were in conditions where the "limiting" came in to play, would it be critical?

So the fact that the calculator says accepted on a 100/20 means Victron are good with it, so not downgrading at all.

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[1967bowesj]

I think 100/20 will be fine, and even if you were in conditions where the "limiting" came in to play, would it be critical?

So the fact that the calculator says accepted on a 100/20 means Victron are good with it, so not downgrading at all.

Must have critical then as you went 100/50, it maybe acceptable to victron but why waste the throttled available solar and limit the potential to store energy.

 

[AdrianChen]

Must have critical then as you went 100/50, it maybe acceptable to victron but why waste the throttled available solar and limit the potential to store energy.

Yes, but things like this just bug me! I had plans to go to Norway, etc so though for the incremental cost why not! From memory when I fiddled with the calculator it was around 1.5amps ish on the low temps, which is the range I was interested in. Would see little or no difference in the UK summer I expect.

I guess it's similar to someone with a small wattage panel upgrading from PWM to MPPT, small gain on a small panel - will it make any difference in practical terms?

At 100/30 it's only the cold element that might clip, so perfect for anyone who tends towards the warmer climate areas so Lenny HB will be fine - and happy he hasn't spent the extra £££. (Got that FB PI working yet Lenny HB?).

 

[Raul]

If it was my choice, with 2x175W panels, I would not hesitate and fit the 100:30. The 100/20 will clip too much.
I know the panels are flat, but, from my experience and my real life monitoring, even flat panels can produce the nameplate value, sometimes even over that if you have a big enough controller. From spring to autumn at-least 2 hrs at noon can give full panel power even on flat roof, so I would go 100/30.

 

[Lenny HB]

(Got that FB PI working yet @Lenny HB?)

Finally got the UART to USB Hub they had been out of stock & printed a case for it, bought a new touch screen went for a 5", got to make a bezel & case for it.
Spent a lot of time play with the waste this week gave up trying to fit an actuator internally my valve was to stiff to work reliable so fitting an external valve. Then back to the Pi.

 

[Raul]

Have a look at PI shop for screen box, sometimes they have this in stock.

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[Lenny HB]

Have a look at PI shop for screen box, sometimes they have this in stock.

I'm having fun printing my own.

 

[Guigsy]

Counter argument is that if you're managing to max out the 100/20 for an extended period, then there's probably so much sun at the moment that you weren't that empty anyway, so your battery will be full by 1pm. If you had the 100/30, you'd be full by 11:30 instead. So in any reasonable situation, it would be pretty unlikely that you'd get to the end of the day with more Ah in the battery with the larger unit.

 

[Raul]

Counter argument is that if you're managing to max out the 100/20 for an extended period, then there's probably so much sun at the moment that you weren't that empty anyway, so your battery will be full by 1pm. If you had the 100/30, you'd be full by 11:30 instead. So in any reasonable situation, it would be pretty unlikely that you'd get to the end of the day with more Ah in the battery with the larger unit.

Yes and no; is all dependable on the weather, that is not always guaranteed wall to wall sunshine. In the event of having a cloudy day, and sun to show up 2-4hrs, then you want to gobble in as fast and as much you can for that short window of time. In this case the larger controller will win.

 

[Guigsy]

Yes and no; is all dependable on the weather, that is not always guaranteed wall to wall sunshine. In the event of having a cloudy day, and sun to show up 2-4hrs, then you want to gobble in as fast and as much you can for that short window of time. In this case the larger controller will win.

The chances of it being the peak of summer, you're camped up off-grid, you've not moved (so no B2B charging), and it's been really cloudy for days (so your battery is low), then completely cloudless skies for a couple of hours around midday, then going cloudy again... is pretty unlikely.

The reality is that there's only a few quid difference, so yes, I'd get that 100/30 if it were an option. But I wouldn't bother changing if I already had the 100/20.

 

[tonka]

Another vote for the 100/30.
I have 2 x 170 panels and use the 30amp one.

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[RogerIvy]

I find the Victron MPPT sizing site to give some unexpected recommendations.

Generally I approach the decision in two steps:
1. Add up the voltages (if in series) as this is critical, give yourself 5-10% leeway (you will need to know your panel voltages - most Victron up to 185w are around 20v)
2. Calculate the maximum wattage and divide that by 13 (13.2 is also usually fine)

So two 185w panels would be roughly 20x2 =40v
185x2 =370w, 370/13 =28.462A
So a 100/30 would be the correct one

 

[WESTY66]

I find the Victron MPPT sizing site to give some unexpected recommendations.

Generally I approach the decision in two steps:
1. Add up the voltages (if in series) as this is critical, give yourself 5-10% leeway (you will need to know your panel voltages - most Victron up to 185w are around 20v)
2. Calculate the maximum wattage and divide that by 13 (13.2 is also usually fine)

So two 185w panels would be roughly 20x2 =40v
185x2 =370w, 370/13 =28.462A
So a 100/30 would be the correct one

Wow, I guess I got it right from the get go uncle Lenny HB will be so proud of me, my electrical knowledge is coming on no end

 

[Lenny HB]

Wow, I guess I got it right from the get go uncle Lenny HB will be so proud of me, my electrical knowledge is coming on no end

Pure luck son, you still haven't got a clue.

 

[Guigsy]

I find the Victron MPPT sizing site to give some unexpected recommendations.

Generally I approach the decision in two steps:
1. Add up the voltages (if in series) as this is critical, give yourself 5-10% leeway (you will need to know your panel voltages - most Victron up to 185w are around 20v)
2. Calculate the maximum wattage and divide that by 13 (13.2 is also usually fine)

So two 185w panels would be roughly 20x2 =40v
185x2 =370w, 370/13 =28.462A
So a 100/30 would be the correct one

You are correct. And I too would go for the 30A. But the difference in yield for most people will be negligible. Pretty much every situation where you'd get the full 28A, you'd have filled the battery about lunch time... Because you're clearly in Spain in June to get full power. So even with the 20A limit, you'd probably be full about an hour later. So pretty much every time, it won't make a difference.

 

[mikash]

You are correct. And I too would go for the 30A. But the difference in yield for most people will be negligible. Pretty much every situation where you'd get the full 28A, you'd have filled the battery about lunch time... Because you're clearly in Spain in June to get full power. So even with the 20A limit, you'd probably be full about an hour later. So pretty much every time, it won't make a difference.

It's an hour less of baking your van in the direct sun though.
I think perhaps the Victron app is more geared towards fixed installations where maximizing peak yield is less crucial and tolerating some clipping might be more cost effective?

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[Guigsy]

It's an hour less of baking your van in the direct sun though.
I think perhaps the Victron app is more geared towards fixed installations where maximizing peak yield is less crucial and tolerating some clipping might be more cost effective?

You move your van in the day to be out of the sun after it's charged? If the sun's that strong, it might be better to be shaded at midday, and collect the photons in the morning and evening. In which case, clipping won't be an issue.

You might be right about fixed installations. A big cost for them can be the wiring. Trying to keep your peak amps down so you can spec a smaller guage wire might save a lot. When the run is only a few metres in a van, it doesn't make so much of a difference.

 

[RogerIvy]

You are correct. And I too would go for the 30A. But the difference in yield for most people will be negligible. Pretty much every situation where you'd get the full 28A, you'd have filled the battery about lunch time... Because you're clearly in Spain in June to get full power. So even with the 20A limit, you'd probably be full about an hour later. So pretty much every time, it won't make a difference.

We tried an undersized MPPT controller on our show trailer. By undersized I don’t mean the voltage (if you undersized that you’ll most likely blow the controller). When you undersized by amperage the controller keeps trying to charge and cuts out. So basically you get nothing because it spends more time waiting to reset than charging.

In 2023 we had this controller at the Newbury show, and we had near-perfect conditions for solar. We had virtually zero yield under those conditions. We changed the controller (sizing it correctly) and what a difference.

I agree that for most of the year we won’t reach the limit of the controller. But for those sunny days when we do … why save a few £ on the controller to get no solar yield worth writing home about?

For the benefit of those reading this: when you undersize your amps output the Victron MPPT simply cuts off and waits a while before it tries again. It doesn’t reduce the amps to its maximum output specification. So if you install a 100/20 and you have some nice sun that yields 23A (by experimenting we think there is a little margin for error but this is not official) you will get a few seconds here and there in between resets. This is especially true of Victron solar panels which yield more than their stated capacity under ideal conditions (our 915w actually yielded around 1000w on that particular day in Newbury 2023).

 

[mikash]

You move your van in the day to be out of the sun after it's charged? If the sun's that strong, it might be better to be shaded at midday, and collect the photons in the morning and evening. In which case, clipping won't be an issue.

Sometimes, yes.Might work until lunch, then move the van to shade some time after, to avoid the worst of afternoon heat, for example. Next van will probably have about 400W solar on roof. With estimated daily consumption at around 1.5kWh, getting every Wh possible out of the roof panels will help when deploying portables is not possible. It's not a necessity by any means, but I like to have the option.
The extra peak power will also help with AC consumption when I need to leave the dog in the van and the van in the sun while doing shopping for example.

 

[Raul]

We tried an undersized MPPT controller on our show trailer. By undersized I don’t mean the voltage (if you undersized that you’ll most likely blow the controller). When you undersized by amperage the controller keeps trying to charge and cuts out. So basically you get nothing because it spends more time waiting to reset than charging.

In 2023 we had this controller at the Newbury show, and we had near-perfect conditions for solar. We had virtually zero yield under those conditions. We changed the controller (sizing it correctly) and what a difference.

I agree that for most of the year we won’t reach the limit of the controller. But for those sunny days when we do … why save a few £ on the controller to get no solar yield worth writing home about?

For the benefit of those reading this: when you undersize your amps output the Victron MPPT simply cuts off and waits a while before it tries again. It doesn’t reduce the amps to its maximum output specification. So if you install a 100/20 and you have some nice sun that yields 23A (by experimenting we think there is a little margin for error but this is not official) you will get a few seconds here and there in between resets. This is especially true of Victron solar panels which yield more than their stated capacity under ideal conditions (our 915w actually yielded around 1000w on that particular day in Newbury 2023).

I have spent many many thousand's of pounds upgrading the house solar. When a controller bounces of limit due to overpaneling, a way round that is to set the controller 1-2 amps lower than its rating, to keep it going. Sometimes works, sometimes overshoots the controller and resets again. If irradiation is constant, it works, if you have a cloud pass, as it disappears and sun pops up, it can overwhelm the controller.
Fit a larger controller and job done.

 

[mikash]

For the benefit of those reading this: when you undersize your amps output the Victron MPPT simply cuts off and waits a while before it tries again. It doesn’t reduce the amps to its maximum output specification. So if you install a 100/20 and you have some nice sun that yields 23A (by experimenting we think there is a little margin for error but this is not official) you will get a few seconds here and there in between resets. This is especially true of Victron solar panels which yield more than their stated capacity under ideal conditions (our 915w actually yielded around 1000w on that particular day in Newbury 2023).

That is really odd behaviour and contradicts both the controller manuals and Victron training vids.

In that video they even go so far as recommend always overpaneling by about 30%.

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