Solar panel exceeding controller rating

[RogerIvy]

If I have a 20A MPP solar regulator and on a very sunny day my panels produce 350w (21A), will I simply lose the extra to never-never land or will it potentially damage my controller?

TIA
Rog

 

[Lenny HB]

Depends on the regulator but shouldn't be a problem.

 

[Gromett]

Depends on the controller. A good quality one will have some overhead and thermal overload protection.

Cheaper ones may not have protection and could overheat/catch fire...

Personally I would upgrade to be sure.

 

[pappajohn]

Is 21amp the rated output of the panel or the actual measured, with a multimeter, output?
350w panel may output 250/300watts at best.

 

[RogerIvy]

Is 21amp the rated output of the panel or the actual measured, with a multimeter, output?
350w panel may output 250/300watts at best.

Not measured it. We're changing over to LifePO4 and want to change the charging system to compatible kit. I'm simply not sure at this stage if I'll upgrade my panels, and wanted to future-proof just in case and if feasible. When in Sunny UK no problem, but what happens when we're down in Spain or Portugal on a hot summer day.

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[EzeeRider]

Depends on the controller. A good quality one will have some overhead and thermal overload protection.

Cheaper ones may not have protection and could overheat/catch fire...

Personally I would upgrade to be sure.

I agree upgrade to be sure. The maximum controller current from a 350w panel is of the order of 24A, ideally that requires a controller capable of handling of 32A below this energy will be lost in the form of heat.
ezee

 

[RogerIvy]

Thanks for the replies, decided to go with a "Epever MPPT Solar Charger 12/24/36V/48 V, 40A, Input 150V, LCD UI (XTRA4415N)"
That 40A should give us a bit of leeway.

 

[eddie]

Make sure that whatever you buy has a Lithium profile if you intend to install Lithium

 

[RogerIvy]

Make sure that whatever you buy has a Lithium profile if you intend to install Lithium

Yep, this is what Ive ordered:

EPEVER MPPT Solar Charger 12/24/36V/48 V, 40A, Input 150V, LCD UI (XTRA4415N) | GWL Group

EPEVER MPPT Solar Charger 12/24/36V/48 V, 40A, Input 150V, LCD UI (XTRA4415N) - Demonstration video of wiring MPPT tracker Solar charger controller made by EPsolar is DC/DC charger with integrated advanced MPPT technology. It adopts the water-proof design with IP32 class and increase the professiona

shop.gwl.eu

 

[Gromett]

Is 21amp the rated output of the panel or the actual measured, with a multimeter, output?
350w panel may output 250/300watts at best.

You shouldn't look at the rated output of the panels. A charge controller is rated on it's output to the batteries.

A solar panel may put out 18.62V (Maxp) @ 8.057A ( Imp). When the solar controller converts this to a battery charging voltage the voltage drops but the current increases.

Never look at the specs of a solar panel and use them directly to spec the charge controller. The total power matters but you need to consider the output current.

The simplest way to do this is to use the nominal battery voltage of 12v and divide this into the wattage of the panel. So for a 100 watt panel 100w / 12v = 8.3 Amps.
I do it this way because it gives a safety overhead. the actual charge voltage could be as high as 14.5V so 100w / 14.5 = 6.9 Amps. But if you switch a high load on that pulls the battery down to say 11.5 Volts (inverter powered item) then the current can reach the max pretty easily.

I do this so the charge controller has some overhead AND in normal use it will run a little cooler extending it's lifespan.

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[cmcardle75]

The Victron MPPT ones claim to just dump the excess power with no ill-effect. I plan to use this as I prefer the slightly smaller one than the maximum power I'm planning (as it has a programable load output and is cheaper) and, quite frankly, I don't care if it wastes power when there's plenty about, as long as it doesn't waste a bean when they're running at 5% nominal.

 

[Gromett]

The Victron MPPT ones claim to just dump the excess power with no ill-effect. I plan to use this as I prefer the slightly smaller one than the maximum power I'm planning (as it has a programable load output and is cheaper) and, quite frankly, I don't care if it wastes power when there's plenty about, as long as it doesn't waste a bean when they're running at 5% nominal.

It is not excess power that is the issue. If your battery is full then any solar controller will simply not be able to push any current into the battery.
However, if you underspec a solar controller when your batteries are low the solar controller won't be able to push all the current coming from your panels into the battery. This is just like putting a bit of black tape over your panels. You are not getting the maximum out of your system.
IF you underspec your solar controller you may as well get smaller solar panels as well.

 

[Metamorfosis]

Bimble solar in the UK sell epever. They also stock a dual battery version of that controller so you can keep the starter batter trickle charged too.

30A Dual Battery 12v/24v MPPT charge Controller - EPever DuoRacer DR3210N-DDS - 100VOC PV - LCD Meter

www.bimblesolar.com

 

[autorouter]

Having 'excess power', ie more power available than it needs, is perfectly normal for a solar controller. If your MH was in storage, the battery would be more or less fully charged all the time, and the solar panel might be receiving enough sunlight to make its full output. The solar controller handles this, giving out only a trickle charge to the battery. That's just part of its day job.

Your mains charger, working from EHU, has 16 x 240 = 3840 watts available to it. Does that cause a problem? No, it only takes what it needs.

 

[cmcardle75]

However, if you underspec a solar controller when your batteries are low the solar controller won't be able to push all the current coming from your panels into the battery. This is just like putting a bit of black tape over your panels. You are not getting the maximum out of your system.
IF you underspec your solar controller you may as well get smaller solar panels as well.

It is very different. Yes, your 400W panel array might only be able to pump 300W in under bright sunlight. This I don't care about, but because 300W is way more than I need to charge batteries and keep up with my usage.

However, in a more realistic scenario in late autumn, these panels might be able to produce 30W, which will be a useful extension of my non-EHU capability.

If, instead, I reduced the panel array to 300W to match the controller, the low light capability goes down in proportion to 22W. This is a significant reduction in off grid time.

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