Solar Panel Controller Charge Rate query

[marchie]

We have a 180w Sunshine Solar Panel with a Victron 75/15 MPPT Controller that feeds our KS Energy 120Ah Lithium Battery. This in turn is linked to an Ablemail B2B and an Ablemail AMT12 Battery Relay/Charger that keeps the Vehicle Battery charged up very nicely

We are in Spain, where the temperatures have taken off for the last 4 days, with today forecast to peak at 35 degrees. The Solar Panel has slowed right down, and is still charging at Bulk, producing what seems to be a static 18w charge, 6 hrs 39 mins after switching on, keeping the Lithium at around 13.47v, when there's more than enough sun and clear view to the Panel to get the Lithium up to 14.22v. I presume that the Solar has throttled the power generation during the high temperatures to avoid damaging the Controller and/or battery? Yesterday we had a similar 'Go Slow' on the charging during the hottest part of the day, and the Absorption + Float phases occurred as temperatures fell and the Charge Rate increased in late afternoon. I would like to be sure that this is normal, rather than post in 3 or 4 days time that the Solar Panel has stopped working! All/any advice appreciated

Steve

 

[wildebus]

Initially I thought you had the situation where the Victron MPPT Controller is configured at the default "Adapative Absorption" setting.
What this means is there is a MAXIMUM absorption mode duration of 6 hours. However, depending on the voltage of the Leisure Battery at the time the Controller wakes up in the morning, that 6 hours could end up being 3 hours, 2 hours or even just 1 hour, after which time it goes to float mode until the next day no matter what the Leisure Battery voltage is (the greater the voltage at the start of the day, the shorter the absorption time).
However you have said it is in Bulk mode, so that would suggest it is not that though. If you go into the Batteries App, is there anything there which is suggesting the battery will not take a greater charge? Typically, even if a battery is full and so the solar cannot give the full power (as nowhere for the power to go), increasing the load would increase the solar harvest - any change if you put the TV on or something?

 

[marchie]

Initially I thought you had the situation where the Victron MPPT Controller is configured at the default "Adapative Absorption" setting.
What this means is there is a MAXIMUM absorption mode duration of 6 hours. However, depending on the voltage of the Leisure Battery at the time the Controller wakes up in the morning, that 6 hours could end up being 3 hours, 2 hours or even just 1 hour, after which time it goes to float mode until the next day no matter what the Leisure Battery voltage is (the greater the voltage at the start of the day, the shorter the absorption time).
However you have said it is in Bulk mode, so that would suggest it is not that though. If you go into the Batteries App, is there anything there which is suggesting the battery will not take a greater charge? Typically, even if a battery is full and so the solar cannot give the full power (as nowhere for the power to go), increasing the load would increase the solar harvest - any change if you put the TV on or something?

Thanks, David
We don't have a TV, and our recent power consumption has never exceeded 20Wh for the day. The air temperature has dropped by perhaps 7 or 8 degrees, and the Solar Panel started fluctuating as the air temperature began to fall, allowing a quite quick move to 14.2v for the Lithium. It's now getting a steady 4w in Absorption Mode (1 hr 28m), so I guess it will change to Float mode as the sun remains high but the intensity fades.
Sitting in the Fife gloom in January urging the Solar to action is bad enough; but the Spanish 13 hrs+ strong sun and a battery in Bulk mode is quite unsettling!

Steve

 

[nabsim]

Can you isolate the solar during the hot part of the day? It does sound like it is heat related, what gap do you have between panels and roof, do you know offhand? That’s just me being inquisitive so don’t worry if you don’t know. Personally I would start managing the battery’s manually the way I do in winter. Once you have above 80% SoC switch solar off, wait until you know you need some charge before you turn it back on. At 20Wh per day usage that could be quite a time.

Dave will probably put me right on this bit but I thought the mppt should come to life, see the battery’s are still charged then stop trying to put charge in although I think they may check again periodically. This seems to be what mine do?

 

[marchie]

Can you isolate the solar during the hot part of the day? It does sound like it is heat related, what gap do you have between panels and roof, do you know offhand? That’s just me being inquisitive so don’t worry if you don’t know. Personally I would start managing the battery’s manually the way I do in winter. Once you have above 80% SoC switch solar off, wait until you know you need some charge before you turn it back on. At 20Wh per day usage that could be quite a time.

Dave will probably put me right on this bit but I thought the mppt should come to life, see the battery’s are still charged then stop trying to put charge in although I think they may check again periodically. This seems to be what mine do?

We've done 6 cycles on the Lithium since mid July 2021 over 112 nights away, so you may be right re some time before power is needed ... Frustrating though because we're off grid and my rechargeable screwdriver/drill is breathing its last and I've some more drilling to do; oh to be able to run the Dewalt 10.8v charger from the Lithium in all this sun!
Hoping to visit David on the way back to Fife, so might be able to find a safe way to use some of the surplus power ...

Steve

 

[Admin]

Can I ask if the panels are clean?

 

[marchie]

Can I ask if the panels are clean?

As far as I'm aware, Phil. We've been away 7 weeks, and I don't have ladders to check, but we've had some downpours, the last 4 days ago, and that would have washed away grime etc. Carwash force for most of the day ...
The air temperatures have been a comfortable low to mid 20s for most of the trip and the Lithium has gone through the 3 phases every day. But the last 3 or 4 days has been really hot, peaking at today's 35 degrees (I almost passed out walking up the hill to Mercadona!), and these have coincided with the prolonged Bulk Charge phase. I only noticed the seemingly fixed 18v limit today (no fluctuating power takeup, fixed 18v and no hint of a flicker) during the really high air temperature, and, as soon as the Temperature fell back to about mid 20s, normal Solar Charging resumed, with the voltage changing by the second and the Wh generated clocking up like a metronome. Despite its siesta, the Solar churned out 280Wh today and went through the 3 phases after the earlier interruption to service! Living in Scotland, I've never had to worry about excess heat and too powerful a level of sunlight ...

Steve

 

[AndyGoPro]

The Victron 75/15 MPPT will lower the output over 40C

 

[marchie]

The Victron 75/15 MPPT will lower the output over 40C

Thanks, Andy. That fits with the behaviour of the 75/15, albeit the 'fixed' wattage varied each day as peak temperature was reached. Much cooler now and the MPPT is working without a break

Steve

 

[wildebus]

Does that mean the inside of your van was over 40C then? Toastie!!

 

[AndyGoPro]

In the history section of the MPPT app there is a section at the bottom for errors. That might show something useful, I don't have any errors to know what info is shown.

 

[rugbyken]

over the last 3 months there have been at least 3 instances of saharan dust storms crossing spain & portugal i cleaned my solar panel and the yield tripled i am unable to access the roof from inside my hymer & have to carry a telescopic ladder for that purpose ,

 

[nabsim]

mine have been in over two years now and showing 63 cycles on the BMV, I use them quite heavily as well. At this rate they will see me out lol

 

[marchie]

Does that mean the inside of your van was over 40C then? Toastie!!

It would have been without the sunshine roof vent wide open plus the 2 small roof vents and the sliding window behind the driver's seat .. The outside temperature on the day I first noticed the static charge rate was 35 degrees! Now back in southern France, 12 degrees and peeing down!

Steve

 

[nabsim]

Ha ha Marchie, currently in Fort William and it’s 26.5 degrees C in the van with roof open and a couple of windows. I have got a bit sunburnt today as well

 

[marchie]

Ha ha Marchie, currently in Fort William and it’s 26.5 degrees C in the van with roof open and a couple of windows. I have got a bit sunburnt today as well

I don't wish to know that, Neil, kindly leave the stage ... My tan is accumulated rust spots

Steve

 

[compost]

i am thinking solar panels give there best output on a cold sunny day heat does affect them if you think about it a cable when heated up increases in resistance so lees current flows i would think the same with solar panels
kevin

 

[rugbyken]

don’t think that applies to solar panels mine peaked in tune with the heat ie 25deg in the shade gave me 1.9 kw 16 deg 600w

 

[wildebus]

Out of interest, when a Solar Panel gets its Wattage rating, it is based on certain standards, one being the luminosity it is hit with - so an irradiance of 1000 Watts per square metre (W/m²) - and at a specific temperature - the standard one for measurement is 25°C.

So when the irradiance is lower, you lose power, but above that you can gain a little extra.
And with temperature, for each degree over 25C, you lose over1/3rd of 1 percent of power in thermal efficiency, so a 100W panel at 25C could be in the bright hot Spanish sun maybe a 90W panel when it is at >50C. And when lower than 25C, you can gain power in the same way.

Of course generally, the greater the irradiance (the sunnier it is) the warmer it is, so it is impossible in real-life use to seperate the two effects so best way is to just analyse your panel performance with a cold beer in the sun (or go to the Antarctic in December with the camper for maximum sun at freezing temps?)

 

[AndyGoPro]

i am thinking solar panels give there best output on a cold sunny day heat does affect them if you think about it a cable when heated up increases in resistance so lees current flows i would think the same with solar panels
kevin

don’t think that applies to solar panels mine peaked in tune with the heat ie 25deg in the shade gave me 1.9 kw 16 deg 600w

Using a Victron panel as an example, you will lose 0.45% output per degree C above 25C (I believe it's 25C, I think I'm reading the spec sheet properly)