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Solar panels + cold = A potential problem

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Re: Solar panels + cold = A potential problem

#41

Post by saghm »

geocar wrote: post #29
teiferer wrote: post #25

Maybe they should just improve their product to make it more resiliant, rather than blaming customers for thinking that 148 V is below 150 V? Not everybody buying these has a Ph.D. in physics and if it says 148 V on the label and 150 V on the other label then it's your product that has a problem, not the customer. And no matter what happens, customer support should help the customer, not blame them.

> Not everybody buying these has a Ph.D. in physics and if it says 148 V on the label and 150 V on the other label then it's your product that has a problem, not the customer. Idk. I don't have a PHD, but 220V sounds like 240V to me. I wouldn't do this. I feel like getting advice about how to wire up electronics should not be so hard. > Maybe they should just improve their product to make it more resiliant Adding "re…

To me, 220 sounds 20 like lower than 240. I have a hunch that this might be a common perception.

Re: Solar panels + cold = A potential problem

#42

Post by saghm »

syntaxing wrote: post #13

> 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. I don’t think this analogy works. The solar input works like Diesel or Gasoline in different temperature. It’s pretty unreasonable to assume the consumer knows when depending on temperature unless the explicitly state in the manual (I’m willing…

Agreed. No one needs to change which type of gas they use because it happens to be a warm sunny day.

Re: Solar panels + cold = A potential problem

#43

Post by uyzstvqs »

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 marketing, and it'd make this article manipulative, false blaming of the customer.

Re: Solar panels + cold = A potential problem

#44

Post by unglaublich »

nenenejej wrote: post #20

Why isn't there code/regulations for tbis. Why do you need blog advice. It is like using too thin wiring to your oven or something. Because you based it off how you typically use the oven not is max draw plus decent margin. Which is why you get a qualified electrician who knows or get qualified yourself.

Okay, but the oven tells you: use at least 8mm^2 wire, and then it goes up in flames because hey sometime you actually need 10mm^2...

Re: Solar panels + cold = A potential problem

#45

Post by taneq »

What we’re seeing here is the mismatch between component level specs and end user ratings. A device which is rated to 24V input power will probably tolerate up to 32V and it surviving 60V would not be uncommon. A component with a Vmax of 24V probably explodes if it sees 25V.

Re: Solar panels + cold = A potential problem

#46

Post by xg15 »

teiferer wrote: post #25

Maybe they should just improve their product to make it more resiliant, rather than blaming customers for thinking that 148 V is below 150 V? Not everybody buying these has a Ph.D. in physics and if it says 148 V on the label and 150 V on the other label then it's your product that has a problem, not the customer. And no matter what happens, customer support should help the customer, not blame them.

This feels a bit like the logic behind "do not put hamster in microwave" warning labels.

I think if you work with electrical or electronic systems in practice, you learn pretty quickly to respect tolerances and that data sheets are a map, not the territory.

Also, electrical installations are usually seen as a field that should be done by trained personnel, not arbitrary laymen home owners. So I think the appropriate reaction would be to remind people that they should hire an electrician to do the installation, if they don't have the necessary specialized knowledge themselves.

Re: Solar panels + cold = A potential problem

#47

Post by taneq »

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…

What does “maximum possible voltage” mean for a solar panel? Do you include things like cloud edge effect (which increases incident light beyond direct sunlight?) What about installs with a nearby window reflecting light onto the panel? Do you include ultra-cold environments (which will reduce the resistance and therefore often increase voltage, although admittedly not, I think, Voc)?

Re: Solar panels + cold = A potential problem

#48

Post by harvey9 »

xg15 wrote: post #46
teiferer wrote: post #25

Maybe they should just improve their product to make it more resiliant, rather than blaming customers for thinking that 148 V is below 150 V? Not everybody buying these has a Ph.D. in physics and if it says 148 V on the label and 150 V on the other label then it's your product that has a problem, not the customer. And no matter what happens, customer support should help the customer, not blame them.

This feels a bit like the logic behind "do not put hamster in microwave" warning labels. I think if you work with electrical or electronic systems in practice, you learn pretty quickly to respect tolerances and that data sheets are a map, not the territory. Also, electrical installations are usually seen as a field that should be done by trained personnel, not arbitrary laymen home owners. So I think the appropriate…

I have the impression these are consumer products so I would them to be designed to be installed by people who do not normally work with electrical systems. If they are only sold to tradesmen that would be different.

Re: Solar panels + cold = A potential problem

#49

Post by objectcode »

BobbyTables2 wrote: post #2

Why would lower temperatures lower the maximum voltage? Sure, diode forward voltages change a little but seems like something else is going on…

I think it works this way but I could be wrong: 1. The forward voltage across a diode depends on the current, and the graph is r-shaped. For a certain diode, 0.01A might make the voltage across it 0.4V, 0.1A might be 0.6V, 1A might be 0.65V. 2. The forward voltage also depends on the temperature of the diode. For a certain diode, per °C decrease there could be a 0.002V increase.

Let's say with certain current there is 0.687V. If two diodes are connected in series i.e. (point a) → diode 1 → diode 2 → (point b), and each has a 0.687V voltage across, that's 0.687 + 0.687 = 1.374 V between point b and point a.

For the solar diodes, the "current" depends on how "strong" the sun is. If at a certain "current", across each diode is 0.687V, you'll need 216 diodes in series (between two points) to get 0.687×216≈148.4 V.

If there is 0.002 V increase per diode per 1°C decrease, with 216 diodes, that's a 0.002×216=0.432V increase per °C decrease, so with a 4°C decrease it exceeds the MPPT's limit.

Another thing about solar that differs from how diodes are "normally" used in circuits is that the "true" voltage depends on the max current achievable with the how bright the sun is right now, instead of the "true" current. When the "true" current is 0 A, the voltage across each diode might be 0.687 V. When the "true" current is 0.5 A, maybe 0.65 V. 1A, maybe 0.6V. 2A, maybe 0.3V. Try to get more "true" current, the "true" voltage drops. Try to get more "true" voltage, the "true" current drops. Power is voltage × current so when full speed charging, the MPPT uses an algorithm to find the (possibly) best minimum (not maximum) input voltage based on the temperature etc and trades voltage for current at the output. If there is no minimum input voltage restriction, solar will follow the battery's terminal voltage + cable drop instead, and instead of something like 111V, there could for example be a ~4x less powerful 25.5V (if the battery is a "24 V") with just 10% more current.

At the MPPTed min input voltage for full speed charging, maybe 111V, all might seem well even with low temperatures, but when the battery is full and there is approximately nothing using electricity from solar, the real input current will be ~0 A, so there will no voltage "sag", so the solar will realize the full voltage corresponding to the temperature and the illumination, potentially >150 V...

Re: Solar panels + cold = A potential problem

#50

Post by xg15 »

harvey9 wrote: post #48
xg15 wrote: post #46

Earlier quoted context omitted.

This feels a bit like the logic behind "do not put hamster in microwave" warning labels. I think if you work with electrical or electronic systems in practice, you learn pretty quickly to respect tolerances and that data sheets are a map, not the territory. Also, electrical installations are usually seen as a field that should be done by trained personnel, not arbitrary laymen home owners. So I think the appropriate…

I have the impression these are consumer products so I would them to be designed to be installed by people who do not normally work with electrical systems. If they are only sold to tradesmen that would be different.

Yeah, it would be important to understand who the company is intending to sell to or do the installation.

Though the lines are often blurred, because I guess most companies would like to sell directly to end customers, even if their product requires a professional to install.

Even IKEA does this. You can go in and buy an electric stove and oven, grab them from the warehouse and take them home with you right there. But it's a bit of an illusion: You're still supposed to call an electrician to actually connect the things.

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