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Solar panels + cold = A potential problem

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Re: Solar panels + cold = A potential problem

#131

Post by namibj »

guerby wrote: post #75
uyzstvqs wrote: post #43

Sounds to me like someone is misrepresenting their products. A solar panel's VoC should be its maximum possible output in ideal conditions (open circuit). If that's under your product's maximum input voltage, it should be no problem. Ever. Is EcoFlow advertising a higher input voltage than their products can actually take, assuming most people won't actually reach it due to temperature inefficiencies? That'd be false…

All solar panel datasheet have temp coefficient, eg for one random ecoflow solar panel: Temperature Coefficient Specifications TKPower -(0.39±0.02)%/k TKVoltage -(0.33±0.03)%/k TKCurrent +(0.06±0.015)%/k source https://websiteoss.ecoflow.com/cms/upload/2022/10/15/-139121... STC ("standard testing conditions" for solar panels) is 25C so if it's freezing 0C you have 25 multiplied by 0.33 Volt = 8.25 Volt more than STC…

Not to mention a fail-safe MPPT would/should just crowbar the input if there's any potential for overvoltage.

Solar panels are current sources that waste their power into a long string of silicon PIN diodes that eventually reach their forward voltage and begin to eat up all that juicy current. You can just take the current and keep the voltage as low as you want, just make sure to take all the current or it's voltage will rise to let the diodes take the current you aren't using.

Re: Solar panels + cold = A potential problem

#132

Post by marcosdumay »

franciscop wrote: post #7

I was going to comment on the manufacturer's safety margins, but then I found a graph [1] on the variability of voltage vs temperature and it seems to be a lot steeper than I thought/expected, to the point that I'm wondering how these do not require either training or a voltage regulator to install and operate properly: https://www.researchgate.net/figure/Module-voltage-current-v...

The part that they are warning about burning out is a voltage regulator.

Those things are normally built to handle a nominal 115 V assembly of panels. There's probably something on the manual about this, but when you put a giant label saying your device supports 150V, people are not going to read the manual.

Re: Solar panels + cold = A potential problem

#133

Post by namibj »

numpad0 wrote: post #55
_9ptr wrote: post #53

Earlier quoted context omitted.

Obviously you include everything, otherwise it wouldn't be a maximum. You can define a minimum temperature for this, of course, but the customer should know about it.

There's no theoretical maximum voltages for solar panels like there kind of is for batteries. They're just giant array of photodiodes and they just generate whatever voltage potentials proportionate to amount of lights received. You could produce a "max voltage flying low earth orbit over Gobi with no shadows from Starlinks" value, but that's just the value for circumstantial most absurd situation you happened to hav…

They produce current until the diodes start conducting given the forward voltage, as they'll take any current you don't extract off of your hands.

Of course if you want to extract maximum power you have to balance the higher worth of the current you take against the loss of current to the diode forward conduction.

Re: Solar panels + cold = A potential problem

#134

Post by namibj »

syntaxing wrote: post #82
franciscop wrote: post #7

I was going to comment on the manufacturer's safety margins, but then I found a graph [1] on the variability of voltage vs temperature and it seems to be a lot steeper than I thought/expected, to the point that I'm wondering how these do not require either training or a voltage regulator to install and operate properly: https://www.researchgate.net/figure/Module-voltage-current-v...

Another post commented but that’s exactly the point of the MPPT. Not only is it temperature dependent but solar incidence angle matters too (how the sun angle is relative to the surface). MPPT works by changing the internal impedance to match the ideal charging voltage. But there’s a limit to how much it can regulate but I think it’s very fair that a consumer would expect nominal voltage times panels in series is les…

There's a reason people don't install electric equipment without training.

This is just like not upsizing wire gauge if you have a bunch that are loaded simultaneously buried together in a somewhat insulating wall. Without the burying under plaster, everything would be fine. But combine that with simultaneous loading during summer, and you fry/roast the PVC insulation.

Re: Solar panels + cold = A potential problem

#135

Post by namibj »

sowbug wrote: post #111

I can imagine future solar panels sending spec data to the MPPT using Power Line Communication (PLC), allowing the system to shut itself down gracefully rather than dying. Rapid-shutdown systems already send keepalives using PLC today. But then it goes all Black Mirror, with manufacturers restricting solar-panel operation to approved devices only, and UIDs being used to enhance shareholder value through recurring sub…

The MPPT could just short them out and it'd be fine; solar panels are a current source with a huge string of non-light-emitting diodes wired in parallel with the output happy to soak up any excess current around their forward voltage.

(Technically the current source in question is _within_ the diode's junction capacitance.)

Re: Solar panels + cold = A potential problem

#136

Post by namibj »

dhosek wrote: post #12

When I got solar panels for my (former) house 15 years ago, as I recall, the best practice was to have panels in parallel (each with its own microinverter) and not in serial as serial would cause loss of efficiency when there was partial blockage of panels. (I could be misremembering all of this).

That's only relevant if you're so starved for panel area that you can't put them into places that have each sub array sufficiently homogeneous and only partially shaded during sunrise/sunset.

Re: Solar panels + cold = A potential problem

#137

Post by namibj »

dotancohen wrote: post #73
bob1029 wrote: post #35

I never tried the solar charging on my ecoflow so this fragility surprises me a bit. I've been able to run laundry in a machine with a 1/2hp motor using the inverter side on multiple occasions. No smoke or funny smells. My 2200w generator would trip out the instant the spin cycle tried to start.

Slightly OT, but how big of a capacitor would be needed to smooth out those current spikes? Solar-friendly could be a selling point for some appliances. I wonder if such a capacitor could even be retrofitted.

Don't bother; at that point just plug them into 200~300 V DC right to the battery (with just fuse and meter between, no need for any conversion, the washer motor controller that'd be needed to utilize a capacitor for smoothing these spikes would do just fine on a reasonable battery charge/discharge voltage spread.

Re: Solar panels + cold = A potential problem

#138

Post by 1970-01-01 »

>Plugging in four 400w solar panels in series is similar to filling your gasoline powered car with diesel and wondering why the car manufacturer isn't replacing your new car.

Ok, that is a very bad answer. Diesel fuel contains more amounts of energy per drop as gasoline, but that doesn't mean engine damage will result. Diesel fuel will not damage an engine if you were stupid enough to get it wrong at the pump. It will simply refuse to cycle until the diesel fuel is pumped out and the correct fuel is pumped in.

Re: Solar panels + cold = A potential problem

#139

Post by majorchord »

hyperhello wrote: post #125
immibis wrote: post #97

Earlier quoted context omitted.

But they want you to have to buy another one.

Why does this kind of comment get downvoted that pinpoints the actual motivation? We just pretend that planned obsolescence is history.

At least in parent's case, probably because the vast majority of their comments are black-and-white hot takes that are always downvoted regardless. And they basically never respond when asked for any sources.

Re: Solar panels + cold = A potential problem

#140

Post by namibj »

avidiax wrote: post #10
mindslight wrote: post #3

Why does the Delta Pro not have a fuse on the input, with the MPPT limiting the max voltage to 150v (by upping the current until the voltage sags and/or the fuse blows, or even a straight crowbar circuit). This is a premium consumer brand selling a mostly complete product, and protecting the input from overvoltage would be straightforward. The frustration at the warranty weaseling isn't surprising.

You might think that the voltage rise could be too fast for most protective technologies to save the downstream electronics, but the general case is that the temperature slowly drops and the sun slowly rises. So the voltage should slowly approach the limit. Adding a normally-open relay and a voltmeter and a microcontroller should fix this. Relay won't close on startup unless the voltage is safe. Microcontroller will…

No the DC/DC converter could just turn it's transistors to short out the panels and rely on the fuse you want anyways to handle idiots paralleling more panels than allowed.
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