Solar panels + cold = A potential problem

In both examples given you can have 2 panels in series.

So given that in almost all use cases, you can have 2 panels in series, they should just say “max 2 panels in series”. Simple.

A good product hides complexity from the user with sane defaults and optional advanced configuration. This feels like the same problem.

> 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 "resilience" usually adds to the per-unit cost. I think making a web page adds some cost too, but at least that can be amortised.

> And no matter what happens, customer support should help the customer, not blame them.

I think that's happening here: Making a web page to educate future customers seems like a really good idea. I wouldn't have thought that necessary until I saw it, but I'm always excited to learn something new.

The existing customers who did dumb should consider this a relatively cheap education in electronics; cheaper than a PHD at least!

Also, whether the company also gave them rebates or credits we don't know here, but telling "customer support" they "should help the customer" is also telling them they're not helping the customer, and you don't know that.

This is 100% on the manufacturer if they intentionally chose to highlight the "best case" 150V, rather than the 120V lower end. Especially without any additional safety mechanisms.

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.

> make it more resiliant, rather than blaming customers

Yeah, this sounds very much like "you're holding it wrong".

I read it as a problem with solar panel voltage going over declared threshold of 37v in certain meteo conditions.

That is the issue is with the wrong labeling of things that are being plugged into this vendor's device, not the vendor's own labeling.

Considering the electric code has an 80% rule for loads, anyone assuming they can use 100% of what is on a label probably should not be doing electrical work.

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 battery, or whatever else.

This is like how AA batteries have a nominal voltage of 1.5V but the actual open circuit voltage is 0.9V~1.65V depending on charge level, temperature, etc. If you connect an AA to something that’ll explode at a voltage of 1.55V, that’s on you.

Similarly if you buy a 470 ohm resistor, you will find in on the data sheet that’s usually at 20°C. To know what it’ll be at any other temperature, you’ll need to use the temperature coefficient to calculate it.

Maybe it would be a good idea to at least add a pair of MOSFETs (one for each rail, + and -) and a voltage meter? Like, the voltage doesn't rise to maximum instantaneously, there should be ample of time to detect voltage rising to a critical amount.

So say, the input is rated for 150V, spec the components to sustain 180V, and trigger the MOSFETs to disconnect the panels at > 160V.

And maybe also add a big ass buffer capacitor, that can be used to soak up a bit more energy in the case of an inrush spike before the MOSFETs actually disconnect.

High voltage, low RDSON FETs are (slightly) more expensive, and these products are cheap. A better design would use a higher-voltage rated input switch with poor (slow) switching performance, like an IGBT. Don’t design critical infrastructure around EcoFlow hardware.

> They shouldn't be that close to the absolute maximum voltage ratings on the components.

This appears to be a situation where the engineering team determined the absolute maximum input voltage and the marketing/product people put that number straight into the documentation.

Standard practice with electronic parts is to determine the absolute maximum rating, then to specify a recommended maximum that allows for some safety margin and variation.

Instead, this company determined the absolute maximum and then just shipped it.

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

I love a good analogy. This is not a good analogy.

a better fuel analogy would be to run e85 in a non flex-fuel car.

(certain fuel systems components will be degraded by high ethanol gasoline)

They do!

Basically anything that consumes solar power incorporates what's called a "MPPT", or maximum power point tracker.

Basically, it's a smart DC-DC converter that continually tracks the voltage/current output of a solar panel and adjusts the load to extract the maximum available power from the panel.

It's not uncommon to have issues with extremely high panel voltages in snowy climates, when they're first illuminated in the morning. If you are close to the maximum voltage your MPPT charger can handle in normal circumstances, extreme cold can even damage things during the initial morning transient. You then have to do oddball things like use a crowbar system to prevent blowing up your MPPT system.

(see https://en.wikipedia.org/wiki/Maximum_power_point_tracking )

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 less than the marketed solar input to work.

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.

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)?

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 in open circuit situation.

Unfortunately inverter manufacturers seldom document how many Volt will destroy the MPPT and up to how many Volt the MPPT will safely turn off by itself before breaking.

> A solar panel's VoC should be its maximum possible output in ideal conditions (open circuit)

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'.

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 open the relay if the voltage gradually nears the limit. Should be solvable for <$5 in parts.

Dark start (when the batteries are flat w/o grid power) will be challenging. There will need to be a small battery to power the voltmeter and relay, or a high-voltage tolerant supply to power the microcontroller and relay temporarily. A 9V should likely be sufficient.

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...

> Why isn't there code/regulations for tbis. Why do you need blog advice.

On pretty much every other device (domestic for sure, I don't actually know abount commercial) there is.

> 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.

Sure, but with all other electrical labelling the numbers are correct. Imagine if Neff said "you only need an 13A rated socket" for their oven, and then when you want to bake bread it draws more. That's very different to Neff saying "you need 45A", and deciding to install it on a 13A socket yourself because you don't need to make bread. The former is what's happening in this case.

Most household solar systems do require permitting and inspections before you can turn it on. There are some exceptions in a few states for very small systems now. Ecoflow provides equipment for these small legal unpermitted installs.

More importantly, equipment shouldn’t self destruct in a dangerous fashion when pushed over the limit.

you might be misremembering bypass diodes?

There are also power optimizers which are DC-DC and connected in series.

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.

It's the soul leaving the IC.

I’ve never heard it called magic smoke before, but a regular saying at one of my old jobs was “ah yeah we let the smoke out” in relation to 100% electric drive vehicles. Smoked many inverters, shorted 96v bus to a 24v bus, etc.

It was almost a rite of passage to “let the smoke out” in that org. That job was actually great because as a software engineer I happily spent a lot of time with a fluke, a wrench, arm buried in the bowels of a vehicle fishing out sockets, etc. Writing the software was not the hardest part of those programs, but being one of the handful of folks that knew the entire electrical, cooling, mechanical, and software systems made us the most valuable folks on the program. We had to know all those things in order to write the software correctly.

The presentation helps a lot too, the way I was told it was something like:

“Did you know that computers actually run on magic smoke? Once the magic smoke comes out though, it stops working.”

Devices run on magic smoke. When something bad happens the smoke escapes and thus the device no longer works.

This is proven by observation - the only thing you see charge is the smoke escaping.

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.)

Worth noting that the physics of electricity has an odd symmetry between voltage, power and current which means almost any circuit can be redesigned to effectively switch around all V's and I's and still work.

It is mere convention that we have decided that V should usually be regulated and constant and a property of the supply whilst I is variable and determined by the load.

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.

The solar panel with inverter does not have any inertia so it can survive power spikes more easily, can lower the voltage till it's over. The generator on the other hand has physical rotating parts that could be damaged by sudden torque asked by increased load. Of course it could be mitigated with additional "soft start" circuitry on the motor but that's usually not included. Not capacitor alone please, you risk more damage.

The problem is usually shading, not so much the capacity of the wiring, though, if you try hard enough you can exceed the rating of the final stretch of wiring to the inverter (or the little pigtail in the inverter if you connect all of the strings at max voltage/amperage). Shading can really upset the current flow in a set of parallel/series connected panels and can cause local hotspots due to overcurrent. Usually inverters are pretty smart about this and they'll detect that you are pushing it further than is responsible and they will just switch off. I've purposefully triggered such conditions to ensure my installation is safe and I was pretty impressed with how utterly painless fault detection, isolation and recovery are in modern inverters. I also had an older one and there it definitely wasn't all that friendly, to the point that the whole thing had to be hard disconnected from the grid before it would work again.

It be worth looking up the I-V curves of solar modules on a datasheet - a key factor is that the maximum power point of a solar module (for a given set of environmental conditions) is really dependent on the voltage that it is running at (whereas the current is more constant based on the light level, up to a certain voltage), so to get the maximum power out the resistance of the load needs to be matched to achieve that maximum power voltage (V_MP).

This is what MPPT controllers do, as this maximum power setpoint will change as environmental conditions change.

Maybe it’s different in the rest of the world (I doubt it), but the fuel nozzles for gasoline and diesel are different. You can’t put a diesel nozzle into the opening on a gasoline car, so it’s rather difficult to fill a gasoline car with diesel fuel.

The other way around is possible. You can fill a diesel tank with gasoline. Whether it destroys the engine or not depends on how much gasoline you put in. A gallon or two that is then diluted by filling the rest of the tank with diesel is not likely to cause any lasting damage. If you fill a tank 3/4 of the way with gasoline and try running it in a diesel you are probably going to need a new engine.

So yeah, the analogy is not good. Slightly exceeding the rated voltage and breaking the whole thing is usually not the same as putting a little gasoline in your diesel tank.

> 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.

A solar panel is like a normal silicon diode. The voltage over the cell goes up drastically with lower temperatures. In cold climates crowbars are usually added.

> 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-size-fits-all number they could possibly quote. It'll always depend on the environment, because that's just how the physics work. The best you can do is provide a figure for the standardized testing environment and the relevant coefficients - which is exactly what they are doing.

It’s not that it lowers the maximum voltage that the charge controller/inverter can handle. It’s actually that the panels become MORE efficient in the cold temperatures, resulting in a (potentially unconsidered by end-user) increase in voltage, overwhelming the downstream BoS components.

Solar panel voltage goes up as temperature decreases. The chart is misleading, it's stating something like an equivalent max voltage if you think of the solar cell voltage as staying the same (and presuming your temperature coefficient matches)

Lower temperatures increase PV max voltage output, not lower it. Conversely, when solar panel temperature increases, voltage decreases. So the headline specs/outputs assume to be valid at a particular temperature. As the temperature of the panels change, the realized performance changes.

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...

It's not that little given these diodes run between sun baked summer and cold soaked winter dawn.

I'm more surprised you managed to plug them in reversed; did you have good reason to avoid the polarized semi-pwrmanently-latching connects that most panels ship with?

The input max is for most inverters on the market now a setpoint where they will simply disconnect, stop generating power and go into an error state that you need to hard-reset if you want to use the inverter again. It's pretty typical to have a 1000V hard limit on a nominally 800V or 600V system. If you're going to ride close to the limit then on some days you will see overvoltage and disconnects. So it is something you simply should not do. But people think that if the label says 1000V then 990V total nominal panel voltage should be fine, which it obviously is not. Panels are analog devices, they will produce an open circuit voltage much higher than their nominal use voltage and when you're on a switched mode inverter that means that the average voltage may well be 'in spec' but the voltage from one millisecond to another may well be outside of that if the system was built 'on the edge'. And because inverters have to take the grid side into account as well (they are not allowed to exceed certain voltages) there is always the risk of not being able to load the panels sufficiently to get the voltage to drop. So you should side your system so that the open loop voltage of your panels under ideal conditions is still comfortably lower than the max input voltage of the inverter. 800V nominal is pretty close to that limit, 700 is better and 600 is playing it safe.

I think one of the main reasons why installers tend to overprovision voltage wise is that they count on the inverters switching off the whole string every now and then versus being able to make more power without a lot of additional wiring under normal conditions. The net effect of that is positive.

Low quality inverters (the ones without the ability to disconnect the HV side autonomously) should be avoided like the plague anyway, those are simply unsafe and as far as I am concerned should not be allowed for re-sale at all.

My own system can make 17KW on a very good day in March at 1 pm or so, but normally it is closer to 12KW even in the summer. So those peaks are actually substantially over the normal output. Over a given day the average is about 5 KW or so from sunrise to sundown, and those first and last hours hardly contribute.

To be honest I went into it half expecting it to be about papal elections[1].

[1] https://theconversation.com/conclave-the-chemistry-behind-th...

The subtitle is, though, and I do find a problem with it. There might be someone out there (possibly not sober) who thinks "Magic smoke? Let's see some!" It also somewhat distorts the original. It should be more like "unless you want the magic smoke to escape." The smoke's magic properties are gone once that happens. At least, nobody has ever proven the escapee smoke has any.

Thanks, we've updated the HN title to the article's main title now.

There are a lot of possible things. The question is which is the easiest to get financing for.

I don't think that addresses the thing that the article is actually about...