211–220 of 228 posts
Earlier quoted context omitted.
I see, thanks.
The problem would not even be making it initially, the problem would be to keep it safe in the long run. I am not a huge fan of all these embedded Lithium-Ion batteries, they're flooding the market (and our homes) and they are disproportionally large factor in house fires.
Earlier quoted context omitted.
The article presents it oddly, it's not that the converter maximum input gets lower, it's the solar panel output that gets higher from the nominal quoted value (which is not a maximum, and not really intended to be used as such). Derating your converter is equivalent for the purposes of ensuring margins, but it implies the issue is in the wrong place.
Open circuit voltage is _very much_ widely considered to be the maximum. If its not spec'd openly as " at temp X" then it's reasonable to expect it to be invariant. "Voc 37v @ 25*C" Vs "Voc 37v" Edit: Isc is the same- max current.
E.g. choosing a random Jinko datasheet: https://jinkosolarcdn.shwebspace.com/uploads/JKM600-625N-66H...
V_OC is specified at both STC and NOTC, and the datasheet clearly states which environmental conditions accounted for in those test conditions.
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I believe the vendor here produces both the device and the panels being plugged into it, and while they also supply other vendors' panels, they seem concerned primarily with customers who buy all components from them and then experience this failure. I agree the labeling is an issue here, but the solution must come from the wider industry or regulatory bodies; the alternative is for vendors to switch to their own pse…
Why not label the panel with the maximum possible voltage that it can produce? Or even have a little table showing the maximum possible voltage at various ambient temperatures. It's not as if there isn't room on the back of the panel for a big enough label.
The label on the modules themselves tend to also provide these ratings at STC, e.g. this label from Jinko specifies the Open circuit voltage and also summarizes the conditions assumed for STC:
https://image.made-in-china.com/202f0j00LURcYuatWIqH/Jinko-M...
While I agree that the label could also add the temperature coefficient, I'm not sure if it's reasonable to expect that specialist electrical equipment details all of its operating parameters on an attached label without the expectation of consulting a datasheet or manual. For specific products that primarily target non-specialised consumers however, a different labelling approach may be warranted.
I am surprised that open circuit voltage is specified at 25°C and increases dramatically as the temperature goes down. Seems backwards! I'm looking at the Ecoflow spec sheet right now and fair enough, it's got the open circuit voltage and then the Temperature Coefficient of Open Circuit Voltage (-0.35%/°C) right next to it. Great, guys, how about you go ahead and multiply those two numbers for me, since you're the on…
> how about you go ahead and multiply those two numbers for me What are you going to fill in for the third number, though? With an open-circuit voltage of 37.10V at 25°C and a coefficient of -0.35%/°C it can theoretically go up to 75V at absolute zero. And that open-circuit voltage is with an irradiance of 1000 W/m2, should we also account for the possibility of someone building a heliostat around it? There's no one-…
42-48 is not a big enough range to give up over. My impulse is to arbitrarily pick -40 and say the normal max voltage is 45.5 degrees. Now it's nice and obvious that you can only hook up 3 to a 150 volt input, and you'll have a 9% margin of error left over. On that "first cold and sunny day" you'll output 120 volts instead of 160.
And no don't worry about a heliostat.
I am surprised that open circuit voltage is specified at 25°C and increases dramatically as the temperature goes down. Seems backwards! I'm looking at the Ecoflow spec sheet right now and fair enough, it's got the open circuit voltage and then the Temperature Coefficient of Open Circuit Voltage (-0.35%/°C) right next to it. Great, guys, how about you go ahead and multiply those two numbers for me, since you're the on…
> Great, guys, how about you go ahead and multiply those two numbers for me, since you're the ones writing the fucking spec sheet? No time. Busy writing blog posts blaming customers.
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…
I think this is where the confusion arises - what do you mean by ideal conditions? Ideal conditions for solar generation are not necessarily at the same time as the highest voltage operating conditions. VoC tends to be specified at Standard Test Conditions which has light-levels representative of a sunny day (1000 W/m2) and a cell temperature (not ambient) of 25 degrees C, which is already a lot cooler than most panels would typically be at that level of irradiance. So really, the label is already specifying a voltage higher than what you would typically experience during times of max generation.
However, the max voltage could exceed this rating at times when there are cold ambient temperatures with enough light for the module to function, but not enough sun to meaningfully heat the cells. So in this scenario you may have maximum voltage, but you're far from maximum power nor at 'ideal conditions'.
Can anyone comment on the "You can exceed the amperage specs" ? I made myself a little case study using 4x1W panels and using them in series and parallel. I got the distinct impression that running panels in parallel is better in not so bright conditions compared to a single panel. Whereas a serial configuration made it worse. Since the sun doesn't shine here that much. Running in parallel seems to be preferable, but…
This is what MPPT controllers do, as this maximum power setpoint will change as environmental conditions change.
Earlier quoted context omitted.
Open circuit voltage is _very much_ widely considered to be the maximum. If its not spec'd openly as " at temp X" then it's reasonable to expect it to be invariant. "Voc 37v @ 25*C" Vs "Voc 37v" Edit: Isc is the same- max current.
But that's not true - V_OC for PV modules is nearly always spec'd at STC or NOCT, which is clearly stated on module datasheets along with the temperature coefficient of that voltage. E.g. choosing a random Jinko datasheet: https://jinkosolarcdn.shwebspace.com/uploads/JKM600-625N-66H... V_OC is specified at both STC and NOTC, and the datasheet clearly states which environmental conditions accounted for in those test c…
> 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…
(certain fuel systems components will be degraded by high ethanol gasoline)
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I don’t know about the components they’re selling, but with electronic components, it’s on the buyer to properly read the data sheet and understand what the quoted nominal specs mean. Unless it’s safety critical, you usually don’t want a system with a bunch of active electronics to prevent someone wiring it up wrong, because those components will interfere with whatever you’re hooking it up to, such as the MPPT, the…
In your AA batteries analogy, this is like saying that you do not need to state that the device exploding at 1.55V would do so, not about battery declarations (panels in this case).
Essentially the "nominal" behaviour is not the actual behaviour, it's just a quick way of summarising the characteristics in a way that someone familiar with the class of item will be able to understand what they're buying. Another similar situation is timber sizing, where a 2" by 4" is actually 1.5" x 3.5".
In the case of electronic components, the actual behaviour will be either documented in a datasheet or just common knowledge in the industry. For example if you're buying a standard li-ion battery with no active circuitry, you'll often find the datasheet quite lacking in details because you are expected to just know the characteristics of the li-ion chemistry provided the basic parameters are provided.
