[Cymen]

Also missing solar heating from diodes:

> This topic seems to be broadly misunderstood. It is 100% verified fact by both myself and others (including university researchers) that diode strings can produce more heat (or watt-hours, BTU) from a given solar panel than a bare resistance element.

https://www.youtube.com/watch?v=42XIbHA9Dv0

[labcomputer]

TL;DW: Isn't that just because the diode matches the PV array's max power point, assuming they both use the same technology (e.g., silicon)?

It seems like that depends on the diode string and PV array remaining at approximately the same temperature as heat is dumped into the diode.

[ErroneousBosh]

> It is 100% verified fact by both myself and others (including university researchers) that diode strings can produce more heat (or watt-hours, BTU) from a given solar panel than a bare resistance element.

In some of my early experiments with little radio transmitters some 30-odd years ago I managed to burn my fingers to an astonishing degree with little plastic transistors like ZTX300s and BC548s.

I remember my late father also commenting around that time "How come a 2N3866 which is rated for a couple of watts can get so hot it melts all its legs off when it's running off a half-flat PP3 battery?", astonished as yet another 2N3866-based amp got a bit lively and melted its legs off despite only running off a half-flat PP3 battery.

So yes I can believe a string of diodes would be a more effective heater than a resistor.

[Retr0id]

Intriguing, but wouldn't it be even more efficient to just paint something black and let the sun heat it directly?

[cwillu]

At the cost of very efficiently radiating that heat back out into space at night.

Making electricity and then using that electricity to heat something elsewhere lets you insulate, effectively allowing you to create a box that heat energy can only pass one way.

[jaggederest]

We have a one-way diode technology for heat, it's called "glass", and it'll bump your efficiency by about 25% versus uncovered flat plates on a still day. More in windy conditions etc, lots of hand waving assumptions about spherical cows in a vacuum etc.

[b00ty4breakfast]

You'd need some kind of storage for the heat, something with a large thermal mass that doesn't readily give up it's heat to the surroundings. Sand or water or even big rocks or a thick slab of concrete.

[Scoundreller]

depends how hot you want to get something

[petermcneeley]

where is this 'extra' heating coming from?

[labcomputer]

I suspect (didn't watch) it's just that a diode makes a crude MPPT tracker (since a PV array is just a bunch diodes arranged to collect photons at the P-N junctions). The benchmark is probably "non-variable resistor".

[Tuna-Fish]

You suspect correctly.

For people who don't know much about solar panels mystified about this:

Solar panels are not ideal voltage sources, their internal impendance varies depending on temperature and the amount of light falling on the panels. Because the point of maximum power in the circuit is achieved when the internal and external impendances are matched, a simple resistive circuit is inefficient and results in the panel converting less light into electricity. If you had a variable resistor, you could adjust it over the day to match the panel, but it is of course easier to use a semiconductor device that does this for you. Any halfway decent battery charger setup or PV inverter has one, but if you are building your own heating system, just stringing together a bunch of diodes might sound stupid, but totally works.

[Scoundreller]

my thought was that a diode removes all the current from its voltage drop (aka: why your LED will burn out if it gets uncontrolled current). A resistor will never remove all the current going through it.

Maybe we're saying the same thing in different ways.

[nandomrumber]

From the misleading sound-bites themselves, they’re know to increase conversation metrics.