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Comment by franciscop | Hacker News Reader

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...

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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 )

Note it would be sufficient to shut down (short-circuit) a single panel, which is safe, to lower the overall voltage.

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.

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.

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

I’m not sure if I follow that logic and if your analogy follows. I would argue this is closer plugging in an appliance rather than running wires. If I run a 15A appliance on a 10A breaker, a normal person without training would expect the breaker to trip. This is like running a 10A appliance and the 15A breaker trips because the appliance is sometimes 16A when it works in the cold.

> If I run a 15A appliance on a 10A breaker, a normal person without training would expect the breaker to trip.

Would the breaker trip in this case? I thought in this case it'd be more likely to start a fire.

Edit: thinking about this more, I think I'm wrong. A fire would start if your wires were too thin for a given amperage. Breakers detect current flowing.

Yeah, you were wrong: 15A on thin wires would heat them up too much and could cause a fire after prolonged runtime.

A 10A breaker breaks the circuit much faster than it takes for the wires to heat up, thus stopping the current flow.

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.

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