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Solar Electric Heating Semiconductors Explained! Efficient Simple Powerful Diode chains #solarheat
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May 9, 2024
Diode strings are a very efficient and much misunderstood DIY way to get the most electric heat possible out of a PV solar panel array in a variety of solar conditions - far superior to bare resistance (Ohmic) heater elements. In this video I will explain how the technology works, and demonstrate it in operation on the workbench in my solar workshop. This is part 2 in a series about Solar Electric Heating with Solid State semiconductor heating elements. Solid State Solar Electric Heating (DIY video series) 🟢 Boiling an Egg with a 20 watt solar panel and diodes: https://youtu.be/CRhkZp6ECHk Part 1: https://youtu.be/6D0aUmkUQSQ Part 2: https://youtu.be/CVH2Cv84a94 (This video) Solar Hot Water - Early Tests: https://youtu.be/Xt7dKT8LIN0 It's hard to believe, but simple diode strings (or a diode chain), which are semiconductor junctions and some of the most basic electronic components available, can actually hold the approximate Voltage of Maximum Power (Vmp) of a solar panel array nearly all day. They act almost like an MPPT DC-DC converter circuit. And they can do this without any supporting electronics. They are a practical heating element for solar electric heating and PV-to-Load applications. But there are challenges due to the current package designs available off the shelf. Diode voltage is a logarithmic function of current passing across; or you could say the current increases exponentially with voltage. This happens to match very well with a solar panel when trying to extract all the electrical power as only heat. The end result is the interesting electrical behavior of diode strings as described in this video. PV-to-load is the concept of attaching useful loads directly to PV solar panel arrays, bypassing the traditional battery, inverter and charge controller setup. Operating heating loads directly off of solar panels makes sense as it saves wear and tear on expensive discrete solar power components and equipment. See videos below for more information about this concept. ---------------------------------------------------------------------- /// Parts List /// Supporting the channel: these are affiliate links, I may receive a small commission if you use them, thank you :) (If you don't want to use the links, just search the item keywords directly online) 20A Silicon Rectifier Diode https://amzn.to/4b3niOb
View Video Transcript
0:00
Hi, D.D. S
0:09
Hi folks, D.D. Solar here. In this video, which is part two and a follow-up
0:30
to my last video about solid state heating elements. Here's one of them here. I'm going to explain to you why this technology is so powerful and exciting
0:38
and really should be on the market and should be well developed. It's very strange that it's not
0:43
I'm going to show you the number one feature why these types of heating elements should be absolutely everywhere
0:48
Now previously there was a comment on my last video that said basically you should just use PTC heating elements
0:53
There's no point. Well that's not true. Believe it or not these diodes are like a pseudo MPPT tracking system
0:59
tracking system because these diodes are not resistance heating elements. These diodes are actually dropping a set amount of voltage. It is relatively fixed. I won't
1:07
say it's exactly fixed but it's pretty close. In this case I have a single 100
1:11
watt solar panel powering these diodes. The fan is powered separately and I'm
1:15
getting 14.93 volts, 52 watts. Now this moves around a little bit. However the
1:20
difference between a resistive heating element is that this voltage here is going to be all over the place. It's going to change throughout the day. It's going to start out
1:26
pretty low and it's going to go to a pretty high state and then it's going to go back down again
1:30
So you're going to have kind of like a mountain or a peak. However, diodes don't behave that way
1:35
These diodes will hold the maximum powerpoint all day long, more or less, and they do it without
1:39
any supporting electronics. To me, that's just amazing. This technology should be everywhere
1:44
Why isn't it being developed? Perhaps in the future we'll see heated appliances and space heaters that use semiconductors to produce
1:52
the heat and track the maximum powerpoint. Or maybe they'll find a more complicated way to do it
1:56
Who knows? In any case, let me show you using a diagram what I'm talking about
2:01
I'm simply going to diagram on a paper the distinct difference between PTC heating elements
2:05
resistive heating elements, and a diode stream. So I've got a sheet of paper here
2:09
I'm going to show you why a diode junction is so much better than a standard resistive
2:14
heating element. First let's start with a standard profile. Let's make a chart
2:21
Here you would have your voltage. Let's just do the voltage. be time. Okay, so I hope you can read that. Let's check the focus again. So we have a
2:35
chart here and typically with a resistive heating element, you would have your solar
2:40
panels and this is solar panel voltage. When you start in the morning, which would
2:47
be right here, your voltage is going to look kind of like this. It's going to go up and
2:54
it's going to go down. Okay, now this is not a scientific graph, but let's put DC here
3:04
But that's what it looks like, because here you have noon. Let's write noon here
3:12
So generally a solar panel driving a resistive heating element would look like this
3:17
However, if you plot a maximum powerpoint tracking charge controller on top of this
3:22
this is a resistive heating element. Here's the behavior you see. It goes up like this
3:27
and it stays pretty much flat, and it goes down at the end of the day
3:33
These are two different behaviors. Now, the current is going to vary as well
3:39
Now, an NPPT charge controller acts like this part here. So this is the voltage profile
3:46
and a resistive heating element acts like this, the one underneath. And all this area in here
3:51
is wasted power. Okay, this area inside the graph that I'm filling in, that's wasted power
3:59
Diodes don't behave like a resistance heating element. They behave differently. What they're going to behave like, believe it or not, is this line right here
4:08
I know that's hard to believe, but a string of diodes can do exactly what I'm showing you here
4:14
And in fact, I'm watching the meter right now in my heating element. It's staying right around 15 volts
4:17
I'm not having to do anything. I've been running it for quite a while now. and I'm just going to keep running it to test the idea
4:24
So the point is that a PTC heating element or resistance heating element
4:28
cannot stay with the maximum powerpoint of the solar panel. As the day goes on, as the voltage climbs
4:34
the resistance heating element is just a linear relationship between the voltage, the current, and the resistance
4:38
There's nothing you can do about that. You can add supporting electronics. You can certainly use an MPPT DC-DC converter
4:46
but that adds cost and complexity. Now it's worth pointing out that with an MPPT charge controller or DC converter of some kind
4:53
it's kind of funny that the voltage will look like this top part here, and your current will look like this part underneath
4:59
And that's what an NPPT charge controller does. The amazing thing is that a diode, a simple string of diodes
5:07
here's some diodes that I've been using, can do exactly the same thing. It will make the exact same type of chart
5:13
The voltage will be the one on the top. It'll be nice and flat. Most of the day, of course, then the same
5:17
beginning of the end of the day there are changes but there's nothing to do about that it's not really a problem because you don't get much heat at the end
5:22
of the day anyway and the little peak underneath this part of the chart is
5:27
going to be your current instead of the voltage so I'm actually using this chart kind of incorrectly let's diagram it again let's diagram a solid state
5:35
heating element and again we're going to use voltage here DC it's going to be
5:43
the same exact idea you're going to see the voltage climb up like this It kind of go like that and it towards the end of the day it start to go down to nothing What you seeing here this flat area this is the diode dropping pretty much the same amount of voltage Now admittedly it isn exact in its dropping of voltage but it going to be a little slanted It may
6:03
vary a little bit, but it really isn't that bad. Compare that to
6:07
a resistive heating element. It's never going to look flat like this
6:11
This flatness here looks just like what you would expect if there is an intelligent circuit regulating the voltage, but there isn't. There's just
6:18
diodes. It doesn't make any sense. But these diodes drop pretty much the same amount of voltage
6:24
They are not a resistance heating element. Okay, so diodes will behave in a certain way
6:28
They'll drop about a half a volt. It might be 0.6 volts
6:32
You know, it can vary based on temperature and other factors. Whereas a resistance heating element can't do that
6:36
And that is reason number one why a resistance element is not as good as a solid state heating element
6:42
Now I'm not saying they're no good because I actually heat my house with resistance heating elements
6:46
I use space heaters. I use PTC ceramic elements. But having just looked into this
6:51
and discovered that it works extremely well, I'm shocked that this technology isn't all over the place
6:56
You can cook food, it can heat your house, there's so many different things it can do. So I hope everybody understands first, before I move on
7:03
that diodes drop pretty much the same amount of voltage, and let's say you want to drop 17 volts, okay
7:12
And 17 volts DC might be a pretty common voltage for a solar panel, maximum powerpoint
7:19
We'll just say VMPP. How do you reach 17 volts VMPP? Voltage of maximum powerpoint. The way you do that is first of all understand a diode drops about a half a volt
7:33
You just need to put enough diodes in series to drop about 17 volts
7:37
That's it, that's all there is to it. Very simple. So 17 volts DC for maximum powerpoint
7:44
In order to reach 17 volts DC or to drop 17 volts you put enough diode
7:49
in series to reach 17 volts probably a dozen or so those diodes will drop about 17
7:55
volts DC pretty much all day long without any additional supporting electronics
7:59
so what does that mean well it means you essentially have a pseudo MPPt
8:03
algorithm or tracking system that's going to track about 17 volts all day using
8:08
nothing but diodes and so what's going to happen is it's your current that's
8:11
going to vary so throughout the day let's go ahead and add another chart this is
8:15
for a solid state element okay on this side. There's what your voltage profile will look like throughout the day
8:22
This is noon. Okay, now these are just estimates. Of course I'm not really
8:28
collecting any data here, but that's more or less what it will look like. It will vary. So solid state heating element, voltage DC, morning, noon, evening
8:37
it's going to look pretty flat. The current is going to look like this
8:41
Let's draw another chart. A for amps. It's going to look like this
8:49
That's what it's going to look like. I forgot to write time on there
9:05
So this is noon. Now as you know, volts times amps equals wattage, power, or heat, and BTUs
9:17
You can convert it to BTUs if you want to. if you want to. And this is all done with just simple
9:22
diodes in a circuit in series, and that's it. There's no MPPT
9:25
algorithm involved, really. There's no actual microcontroller or brain or anything like that
9:30
It's just diodes. That is why. This technology should be absolutely everywhere
9:36
It does this all by itself automatically. We don't have properly packaged
9:39
diodes for heating applications, unfortunately. But who's to say that if there's enough
9:43
demand for this technology, why those packages should not be developed? And I'm talking
9:48
for example this is called an axial package it's got a lead going right through
9:52
the middle axially this is just not ideal for solar heating applications
9:56
unfortunately but that's what we have the other package is called a T0220 it's a
10:00
little rectangle with a metal tab on it I don't have any of those but that's the
10:04
other kind what is the take-home message here what is this telling us what this
10:08
is telling us is that if you can hold 17 volts DC on this theoretical 12
10:11
solar panel pretty much all day with nothing but diodes you're gonna get anywhere from
10:15
10 to 30% more power more heat from the same solar panels than you would with a PTC heating element or a resistive heating element
10:23
That's a fact. And to me, that's, again, unbelievable. So getting back to the heating element itself, I'm running this thing and the whole time I'm talking
10:34
Here's my watt meter. I hope you can read that. I've tried to focus the camera manually
10:37
I think it's focused. It seems to be. So this heating element is tracking about 14.9 or 15 volts, really
10:44
It's about 15 volts, which is about what this solar panel normally would do. I can feel a lot of heat coming off here, and the diodes have been holding 14.98 or really 15 volts for a really long time
10:57
And I don't have to do anything. Unlike a resistance heating element, this voltage is going to change
11:01
Throughout the day, there's nothing you can do about it. It's going to start low, go high, and then go low again
11:05
That's all it does. But here where the diodes, know, is staying about 15 volts
11:09
And it's the current, which is over here, that's going to be varying up and down throughout the day
11:13
Now that we've covered why these diodes can sort of track maximum power point
11:17
of a solar panel, which resistance heating elements cannot and will never be able to do
11:21
because that just isn't how they work. I want to make one more point. A resistance heating
11:25
element is an omic heating element. It means that it's got a linear relationship between current
11:30
and voltage. Diodes are not omic heating elements. They drop voltage, and they drop a set amount
11:37
of voltage. I have to tell you that of course the voltage is going to vary over time, but it's
11:41
only a little bit. It isn't really that bad. Here you can see it is moving a little bit
11:45
and it probably will change towards the end of the day. and if the sun gets a little brighter or a little dimmer it might change a little bit However it more or less is going to stay stable unlike a heating element that just a resistance element Now I hope you understand at this point why this technology is so interesting and exciting to me and also incredibly useful
12:01
Now I want to tell you about yet another feature that is inherent in this type of heating element design
12:06
Now I'm going to show you the number two feature why this is so unbelievably useful
12:11
Believe it or not, what you're looking at here, it's not just a heating element. This is literally a variable power supply
12:16
This thing can charge a battery, it can charge your cell phone, it can run a fan, anything you want, and I'm going to prove it to you
12:23
In past videos I've showed people how to use PTC or positive temperature coefficient ceramic heating elements to heat their home using a small set of solar panels
12:33
And I was doing that for quite a while and was very successful. I heated my back room with it
12:37
It worked very well. One of the things I mentioned in both that video and also the video about solar heating for beginners using car, truck, and cab heaters, that's where you connect to
12:46
a cab heater directly to a solar panel. All these videos and topics are going to be linked in description if you want to look at them. I mentioned that heating elements
12:52
can actually be tapped at certain points to draw off a certain power supply, but a
12:56
heating element made out of resistive material isn't quite as stable. It's going to have
13:00
quite a variable voltage. Diodes, on the other hand, totally different world, because
13:05
once again the diodes are dropping a fixed amount of voltage, relatively fixed. That totally
13:09
changes the game. Let me show you how this works. Notice that the heating element
13:13
overall is receiving 14.9 something volts, really about 15 volts. And you can see that
13:19
the wattage is 54 watts and the current is about 3.6 a. Now the current and the wattage
13:24
are going to fluctuate, but the voltage stays pretty much bang on 15 volts. At this time
13:30
I have switched some of the diodes out of circuit. And I'm referring to these jumpers here
13:34
This jumper here is actually switching some of the diodes out of circuit. And this is
13:39
what makes this system so powerful. Not only can you, different voltages, you can also achieve different power dissipations by switching these
13:47
diodes in and out of circuit. You can also regulate the temperature of whatever you're
13:51
heating by simply switching some of the diodes in and out of circuit. What you're doing is
13:55
you're varying the heating power of this system. Okay, reason number two, why these
13:59
types of heating elements are so powerful and effective. In the upper left-hand
14:03
corner of the screen, you can see that I'm making the multimeter bigger so you can look at it. This is recorded in real time from a separate camera, and I wish to publicly
14:10
thank my brother who purchased the high-quality camera which is actually recording this multimeter
14:15
Now I've got my multimeter probes. They're going to that very meter
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And just to show you it's real time, here's my hand in front of the meter
14:22
Now, let me explain how this works. You've got blue, which is actually the positive fee
14:27
coming from the 100-watt solar panel outside. I'll attach a photo of that later in the video
14:32
And it comes in here, and it actually goes into this red test clip and jumps over to this diode
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So these diodes here are currently not hot. They're cold. Starting here, the voltage is going in this chain of diodes
14:41
and it's jumping and it's dropping voltage. all the way. By the time it gets down here, you have zero volts. So if I take my
14:49
multimeter probes, and I'm going to attach one of them to the green clip, which is negative
14:55
Just go ahead and do that now. Now it's connected. I have this positive part right here
15:03
This is the most negative of the heating element, so this would be considered ground or common
15:08
If I take my multimeter probes and I just measure ground or common, there's nothing
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Watch what happens if I jump over the first diode. .76 of a volt
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What if I come up here to this diode? Try to get a good connection
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Okay, let's jump up to one more. 5.3 volts. What you have there is your USB charging voltage
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You can literally attach a USB device from here to here and charge it
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And depending on the conditions, these diodes will regulate the voltage just fine
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What if I wanted 12 volts from this setup? As you can see, I'm getting 14 volts, 15 volts, really
15:57
What if I want 12 volts to charge a battery? Okay, let's go farther up the diode chain
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Let's try it right here. 9 volts. Let's try coming down, say, right here
16:09
There's your 12 volts. Well, let's back one diode off. There you go. There's 12.3 volts, power supply
16:17
All you got to do is connect your negative here and your positive here. You'll get 12.3 volts
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Now it's not perfectly regulated. Obviously there can be a little bit of variation in it, but if you're just charging a battery or you need a rudimentary 12-volt power supply
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you're looking at it. If you need a rudimentary 5-volt power supply, you're looking at that too
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This is shocking and amazing how simple this stuff is and how well it works. This is essentially entry-level and basic electronics that I'm teaching here
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Okay, so we've established. that there's different voltages present here. And the way this works is you're dropping a certain amount of voltage
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but you're creating what's essentially a voltage divider network. I'm not going to get too deep into it
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I think most people don't care too much for electronics, so I'm not going to go too deep into that direction
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But just understand that as the voltage flows over these diodes, it's getting lower and lower as it drops over each diode
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until finally you have zero volts. If you connect anywhere in between, you can have some of that voltage before it drops
17:07
and essentially it turns into a power supply. Now the final amazing feature of this technology
17:12
is what I'm doing here with these clips. these clips. As you can see I have one going here and then this red wire loops
17:18
around it goes here and it's shorting out these diodes. The reason for that is this heating element is segmented so that I can actually control how much power output
17:25
I'm getting. For example let's say I'm heating my food with this 55 watt system
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right here. By the way I can feel the heat just pouring off these diodes. It's a good
17:34
thing I have this fan. This fan here on the left is actually operated based on solar
17:38
turning off a different solar panel. The main feature of these clips here is ability
17:42
regulate the power output of this heating out So let say that you know 55 watts I got my hot water and I ready to make my coffee but I just want to keep it warm How would I accomplish that Well conventional wisdom would say go ahead and just turn the heating element off and then turn it back on and turn back off But I suggest a different way of doing it Instead what you should do is you should come down here switch a couple more diodes into the circuit
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Now you see the power just dropped to 39 watts. Or how about we come all the way down here
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23 watts. Is that not sure keeping warm wattage? Isn't that going to keep your drink warm? 21
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watts of heat should do the job. This heating element is so amazing because it can do three different things
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And it's very simple to do. You just need a switch. You can use a normal switch or you can use a
18:31
transistor to short out a certain number of diodes and vary the power. If I want to go back up
18:35
let's say the dream starts getting a little cold. I'll just undo what I just did
18:39
Let's try coming down here. 52-53 watts. Okay, there's my cooking temperature
18:47
I'm back on full power. All I did, literally guys, all I did was shore out some of these diodes
18:51
It's not complicated. It doesn't require a degree in electrical engineering. All I did was bypass some of these diodes and only use these
19:00
And that instantly changed the characteristics of the heating element. Okay, now I want to show you a short practical demonstration
19:06
of how you can power a load using a heating element like this. element like this. I'm going to start by connecting a test clip to ground or negative
19:16
Here's the other end of it. And I'm going to take a fan. Here's a fan, just some DC fan. I'm not actually cooling anything with it. It's just a demonstration
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So you can see that in the upper right hand corner right there. I hope you can see that. And I'm going to take the
19:34
ground side of the clip and I'm going to connect it to the negative part of the fan
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Okay, this being connected. Now I'm going to take my positive and I want to hook this up to a certain voltage
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Before I do that, I'm going to connect the other side of the positive clip to my fan, like this
19:53
Hope you can see that. Now this goes to my fan, the positive lead in my fan
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I'm making sure not to mix the clarity up and this can be very confusing, but you always start from ground or negative
20:05
At least that's how I do it. All right, so here's my fan
20:10
I'm getting 14.9 something volts. And somewhere on this heating element, there should be the proper voltage to run my fan
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Now, this fan is just a 24-volt fan. It doesn't really matter, but let's say I want to run it at 12 volts
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So let's take my meter. Here's the positive probe, the negative probe is already connected
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So let's take my positive probe here, and let's measure and find on this heating element a place where there's about 12 volts available to run my fan
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Let's just start here. In the upper left-hand corner of the screen, you will see the meter and
20:42
13 volts So 11.5 volts See, I'm gonna try here 12.3 volts. So right here is 12.3 volts
20:54
So now I'm gonna take my Test clip which is going to my 12-volt fan. Just check it again
21:02
12.3 volts. I got the positive and negative correct because this is the positive
21:06
side of the multimeter and it says it's positive so and look at that the fan turns on as you can
21:15
see the voltage is holding steady at about 12.3 volts that's amazing unbelievable I've never seen
21:23
such simple electronic components do so many different things at one time it's just mind-boggling
21:30
I hope this helps people understand the concept behind solid-state diode-based heating elements
21:36
in solar power. Remember, this is running directly off of a solar panel
21:40
There's just diodes and that's it. I don't have any secret tricks, there's no DC converter hiding somewhere
21:45
I assure you these wires go straight to the solar panel outside my shop. There are no tricks and games here
21:50
And I've showed you three powerful things you can do with just a string of diodes
21:54
Now these diodes can do more than just blow hot air. They can also cook food
21:58
My hope is that I'll have time to do that kind of research in the future. And I will most certainly post and upload any results if I have anything good to share
22:06
I hope this explanation of the different characteristics of this type of heating element
22:11
helps you understand what's going on here. It's a little bit complicated at first
22:15
When you think about it, this technology starts to make a lot of sense, and it's strange
22:19
how it's not absolutely everywhere in some form. The most important part of this video is actually these charts and drawings, and I would
22:28
suggest if you're having difficulty understanding the concept of why diodes are superior to
22:32
PTC heating elements and resistive heating elements, that you'll go back to the
22:36
to the beginning of the video and look at where I explain these charts. Because believe me, this behavior of diodes is everything
22:43
This means everything. This technology, these diodes and how they behave, completely changes the PV to load solar electric heating gain
22:50
Now I'm still going to use my space heaters, which I've shown in prior videos, all that's linked in description
22:55
But this has a lot of promise, and I'm going to put more effort into it. As time permits and as my health permits
23:00
and if I get anything really good going, I will definitely share and upload my results. In the future, I plan to have at least one, maybe two projects
23:06
done that are related to solid-state heating, running directly off of solar panels
23:11
Of course, those will take some time to develop. There's also a few more interesting
23:14
projects and videos that are on the way. It just takes time to edit. I hope you
23:18
enjoyed the new camera setup and this new capability where I can move things around
23:22
on the screen. Okay folks, thanks for watching and I'll see you next time
23:36
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