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. FACTS: 1) Diodes are not "Ohmic" so we cannot use Ohms Formula to calculate I/V/R as one would for resistance element. You could certainly try the maths, but they don't really work for diodes. Interesting exercise at least. 2) Diodes drop a roughly constant voltage (of course it's not perfect and does vary some) 3) Therefore a string of diodes will drop a roughly constant voltage equal to the number of diodes in the chain 4. Therefore diode strings can be matched to the vMP region of a solar panel, and they will drop roughly the same voltage all day, while the current rises in the morning, peaks at noon, and falls back away towards evening. This generates behaviors similar to an maximum power point tracking circuit, although it's not. 5. The diode string operating in the volts-max-power region nearly all day easily beat a bare resistance element. It's obvious - the diode string is holding a nearly steady voltage in the vMP region nearly all day, Volts x Amps x Time = watt-hours, diodes win hands down as they stay at or near vMP. MPPT charge controller does something very similar, no wonder they are so popular... 6) Resistance elements are linear (I/V/R) and will appear in the morning almost like a dead short to the theoretical solar panel producing almost no heat. The diodes will already be warm and operating at a much higher voltage. As the sun comes up, the resistance element will pass more and more current, but at a higher and higher voltage, generating a peak up to noon and falling down towards evening. At some point it will enter the vMP range, but it cannot stay. And current (amperage curve) will also look similar with a "peak" which is the expected behavior. 7. Diode strings connected to a solar panel create a "flatter" voltage curve - verified fact by multiple researchers - and it's obvious on it's own, because the diode is not Ohmic and just drops roughly constant voltage, we don't really see a diode string behaving like a resistance element - in general. 6. Bare resistance elements create a "peaked" voltage curve - again verified and obvious fact - in fact I've been verifying it for years by operating multiple resistance loads directly off my solar panels, heating water and heating my house :) 8. Diode string elements connected to a solar panel produce a "quite flat" voltage curve - again verified and obvious fact - verified by myself and multiple researchers in universities. 9. A diode tends to flow current exponentially versus the voltage flowing across it. 10. A diode tends to pass voltage "logarithmically" versus the current flowing across it. 11. #9 and #10 can help explain why diodes behave so differently and just so happen to match solar electric heating applications well. 12. Diodes aren't perfect, and sometimes do exhibit certain linear behaviors, depending on the type of diode, it's quality etc. but overall behavior matches what I have described in this video and in practice (and reality) in bench tests and real-world testing - not only theory. Diodes do some times have some Ohmic properties, for example due to the connecting wires and leads connecting the diode package. 13. Under changing solar conditions, which is reality, the diode string will far out perform a resistance heating element. The reason is the diodes keep the voltage up near vMP, but the resistance element swings the voltage significantly greatly reducing it's power output as the sun dims or cloud cover blocks the sun. 14. Thinking in terms of watt-hours, a string of diodes will produce lots more watt-hours (which can be thought of as converted to heat) versus a bare resistance element, because the diodes can stay near vMP under changing conditions. But the resistance element reacts noticeably to changing solar conditions, causing voltage to drop significantly and losing overall power. This I have repeatedly verified for years by watching the voltage of solar panels connected to various electric heaters with bare resistance elements. [I may update this list later as time permits] DD

@solarpoweredge I really like this concept, but there might be a mistake in your graph. I could be wrong, but in the morning when the sun is rising, the voltage starts at zero and moves up to the vmp (let's say 17v). Anything less than the voltage drop of the diode means that no current is flowing. That means that you are not gaining the full morning's losses in wasted heat. Once the voltage hits the vmp set by the diodes, the flat part of the chart would then start. But, nothing happens before that. The rest of the graph looks good to me. Still a definitely more efficient than a resistive load.

Nicely done! You have me headed to my electronics component draw to dig out diodes and see what I have in stock!

But still very interesting part would be to make Buck Boost converters at different voltage stages..."small step boost AND Buck" Converters is far, far even by magnitude. more efficient than a 2V-48V vs a 2V-3V Boost.... You are really one to somthing here... I really need to find a way to efficient transfer power from a 12V battery bank To a 48V House system ;) And balancne at the same time... Lol, i think you just solved the problem with efficient balancing different voltages and charge, as everything. you also can use ZenerDiodes to limit Currency ? MPPT for Battery paralelling...

Love your channel! Brilliant idea! When i began experimenting with PV I used a "MPPT" tracker that actually didn't track. It just tried to keep a preset voltage. I considered it useless and bought an actual MPPT tracker. But as the years go by, I, too notice, that even good MPPT trackers don't do much more than keeping a constant voltage. Yes, in low light conditions it tends to be 15 V while in bright light it tends to be 18 V. But really...is that worth all the electronics? You are also saying: As long as you run any PV to load circuit and you put in one of these diode heaters you can then also run other consumers in parallel at a constant voltage in almost MPP. Lastly: I appreciate your efforts to express as precisely as possible by adding comments to correct yourself.

Have you ever considered a peltier based PV DC powered device ? A different semiconductor device than the diode. Wired enough of them together .. and you could get a direct PV DC to DC cooling device similar to the direct PV DC to DC heating devices .. for things like cooling the inside of a fridge or such. And for heating you might be able to get a little above a COP of 1 .. the heat taken from the 'cold' side (air or liquid) of the peltier is added to the resistive heating (from supplied electricity) on the hot side. Although the trade off would be I don't think they would do the MPPT like function you describe in this video.

very cool

I'm very excited by the work you are doing with this! I've been trying to figure out a distributed heater for a thermal sand battery and this just might do it!

Interesting stuff, I gonna look into it for sure! Maybe it's not developed because it's not a commercially "viable" product! If it doesn't break you have to buy it just once😊! It's too effective!

Can you post specs on axial diodes used voltage and amp rated. I want to buy some on Amazon for testing

So each diode drops 0.7 volts and say its a 17 volts supply so each diode would generate 12 watts of heat. Makes sense a resistive heater will vary its resistance as it gets hotter and cooler and cant be segmented. Clever idea Does it work with diodes in parallel although that might be less efficient

see my reply to "tryget-.." below I think you could spend more time on how it is desirable target a certain point on the curve to impedance match the PV power source for maximum output... THEN explain how the didode dropper chain allows this to happen ... and also explain how it won't happen with just a resistor. Then I think it will be more clear to people.

Can we connect solar panels direct to nichrome wire for heating sand?

I like the idea of this. But I would guess that diodes haven't been used as heating elements because they give off toxic fumes when they are max overheated. And could possibly burn or catch fire.

I could balance my 18V Ryobi Battery against my 48V Hose bank? (80-100kWh) If so!!!!!!!! (Or my salvaged 12V lead ) Makes me wonder....

First of all Love your videos!!! But if we talk efficiency those pesky lavs of thermodynamics come into play...(Hate them) A resistor is pr defenition 100% effective... If you put your Diodes and my recisitive wire into two diffferent thermo flask i bet we both will win or be tied..(A solar panel will produce the same amount of energy if you do a short cucit , even at....Zero Volts, it will still heat up the leading wires and internal panelsnwires until somting "cooks" and desolder/burn off. Maybe and im think you are rigth in some sense You can make a really more efficient Battery charger .But not shure if it can do this unregulated? Regulated at different Voltage maybe? Btw: at really cold summer mornings ,just before sunrise my solar panels give 240V on each strings..but just 6W... At 12AM i get 8kW from each string.. You need to check average given energy...as in your "paper" curve and do the same regarding a resisitive heater.. And you also got a really interesting point using Diodes like this because you can work loads at higer Voltages and skip the cost of enourmus sized copper cables....I really do! Btw, I use solar/Battery to run my house heating by tading electrical energy int a Heat Pump At 0C i give it 2kW and i get approx.5kW heat Regards from really cold Norway

From what I can see 10a diodes are cheaper .For example 10A2 from DC COMPONENTS

Audio!

You stud diodes into heat sinks that would be a better way to get the heat out of them

They are acting like a regulator.