Heat: Panels vs MPPT


Ive notice something very interesting the last couple of days regarding my PV power generation.
Im in Strand, and last Friday and Saturday was probably the first 2 real summer days. Die kraaie het gegaap!!!

I have a MPII 3000vA, 250/70 MPPT and 3320W on the roof. (415W x8).

I’ve notice on those 2 days that my solar maxed out at 2791W. That a long way from the 3320w.

Ive made a DIY contraption with Cardboard and a gluegun to better the airflow. it currently have 2 fans. 1x 120mm to Pull the air from the back fins, buttom to top. And a 80mm to blow air upward over the front and at the same time, push it towards the fins.

Side note: We had a hell of a windy December, so on Saturday i cleaned the panels. Water and Soft broom. It went from 2513w to 2736w!! Instant upgrade, just add water!!! (could be that the panels was cooler, but the 2700w kept going for some good time!!)

So my question is:

  1. Will this be an result of the Panels max out due to heat, or the MPPT due to heat? The MPPT maxed out on about 51A.
  2. If above is true, will it then not be beneficial to get a bigger MPPT, as i read somewhere that the MPPT will only give 70% at max temp? in my case its 49A.

2800/3300 ~= 85% of STC. Not bad for a very hot day. I think it’s your PV modules, not the MPPT…

Typically such very hot days don’t have perfectly clear skies either, even if it looks clear to the naked eye.

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Thanks for the quick responds!
What is the max temp that these MPPT’s can go. Before i did the DIY jobbie, it was EXTREMLY hot, about 5 seconds before i have to remove my hand.
The things is, at about 2800w, the inverter can run at 2.4KW, and the battery get some charge!

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I have never tested this. Some years ago I ran a 100/15 MPPT on a grossly oversized array. The 100/15 MPPT has a plastic casing, and it ran so hot that you could smell it. It would top out at 14.3A, which is 95%.

But… officially the curve looks like this, starting at 40°C (the red one, the blue one is the Multi):


So I was perhaps a bit fast in blaming it solely on the panels. If it is uncomfortable to the touch, it’s probably around 50°C to 55°C, which could account for a derating to 60%, or just 42A.

In the words of my boss: If unsure, test it!

Thanks Plonkster. Would an IR gun be the only way of testing the temp?

This would be a really interesting to see if anybody else experience this. As most people would install the system in the garage? The garage is traditionally also the place in the house with the least amount of isolation agains heat and cold. Thinking about it, in a neighborhood, about 50% of people with a Garage, would be facing the afternoon sun… (in my mind that is). SO, then it would be wise to oversize on the mppt?

Or a thermocouple. Lots of (even cheap) multimeters come with a thermocouple.

thanks, i dont have one, but will do the test as soon as i can find one!!

I’ve seen ones cheaper than this, but that’s the cheapest one I could find on TaL today.

Electronic equipment doesn’t cope with heat well. They may state in the data sheet that the components can operate up to some rediculous temperature but heat stresses electronics.
It surprises me how high temperatures are tolerated. I recently installed a MPPT for my stand alone PV hot water system. I asked if these devices get hot and any advice regarding mounting: No clear answer.
As it turned out it was cooking so I installed a fat heatsink and it now runs fairly cool on the wall in the passage.

Actually, they can cope with heat well - if designed for that. The main problem is usually the actual (silicon) die temperature. Between that and the heatsink are numerous thermal junctions. This means that depending on the design, if the heatsink/case is at 60°C, the die might be at 120°C or 80°C. This all depends on thermal design like dissipation per die, thermal interface etc. Most consumer electronics are designed with the goal to keep the case safe for children to touch - so below 50°C? That might not be the case here. So you cannot really know the temperature of the silicon without having the actual design, and thus how that affects life.

Then there are also some strange things like some magnetic materials, like N97 that actually becomes less lossy at around 100°C (it is more lossy at both higher and lower temperatures).

Some components like capacitors you obviously want to keep at a lower temperature for longevity.

What size battery bank do you have? - is the max charge current set to 50a or managed that way by ESS?

Herewith Google on the subject:
All electronic components are subject to failure due to overheating. Any increase in temperature can result in a reduced lifespan. This includes increase in temperature due to ambient temperature of the environment, heat produced by the device itself, and the product’s efficiency at heat removal.
There are numerous methods of temperature control. It’s important that designers and manufacturers consider these methods when creating new electronic devices and components. Common cooling techniques include free convection cooling, forced air cooling, and liquid cooling. Each method offers its own unique benefits. The type of cooling technique used will depend on a number of factors based around the intended use of the finished product.

You might have missed the point. I agree that higher temperatures decrease lifespan. However, things might not be as they seem. For one device running at 60°C case temperature (uncomfortable to the touch) might be perfectly normal, with a life expectancy of >80000hrs. For another device a 60°C case temperature might mean <2000hrs. It is impossible to know without knowing the design.

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There, I fixed it …

That spot gets quite hottish in summer and the 250/100 gets freaking hot like I guess >60deg as per cheapie fish tank thermometer which maxes out at 60deg C.

Comes on at 10am and off at 5pm.

And it has a secondary benefit, it moves some air in the house.

At full speed, I swear one can use it to fly a plane …

But having sorted that problem, I’m contemplating mounting the MPPT away from the wall, on a bracket, that it has more airflow in any event.

Just hate to touch stuff that is not “broken”.

Victron MPPTs are designed to derate precisely to keep it reliable.

I’m no expert on this, but I read somewhere many years ago that 100°C is where things go wrong. Every 10°C above that halves the component life. But as @_a_a_a noted, we’re talking about the junction temperature there. Every contact point where heat is transferred to another point (junction to case, case to heatsink) adds a bottleneck.

From the chart above, it will switch off at 65°C.

Its all manage by the ESS. I have 6 year old LA batteries on them. The cells are in Table Bay… waiting…

I just had a look, and there is a relay built into the MPPT.
Now let me get this straight, im no expert when it comes to these things!!!

But going into the Settings, there is a High Temperature (dimming) option, and in the specsheet, i found the following:
Programmable relay DPST AC rating: 240 VAC / 4 A DC rating: 4 A up to 35 VDC, 1 A up to 60 VDC

So my question is:

  1. if possible, can i put a 12v fan on that, and it will turn on if the MPPT reached a certain temp?
  2. What is the temp?

found it:

  1. High temperature (Dimming). This option switches the relay ON when the charger output current is reduced due to high temperatures. Use this option to for example switch an external fan.

I see there is also an option for the BMV 702 aswell. Can use that as a fan controller for the batterybank?

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Forced cooling (a fan) isn’t the answer for some industrial equipment manufacturers. The reason for this is the unreliability of fans, especially if they run all the time.
This is a characteristic I can vouch for since I have seen many dysfunctional fans in my time.
My preference is for forced cooling when equipment reaches high temperatures.