Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577
Posted: 12:47pm 11 Jan 2021
Copy link to clipboard
Print this post
This idea keeps going round in my head and won't give me any peace so I decided to put it into practice and to the test.
Reading up on the much more sophisticated solar water heater Controllers last year I came up with the idea of simply pulsing a Mosfet connected to some caps to keep panels on their efficiency Curve when driving a mains rated element.
What I have set up is an arduino driving a Mosfet for turning the 240V, 3.6 Kw element on and off so the caps are either charging or dumping into the element. After a few days of getting my head around it again and remembering the more I had forgot than remembered, Today I got it working, set up 4x250W panels and hooked it up. I can't remember the size of the cap bank i'm using but from memory it was around 12-1800Uf. I taped it up real well to avoid nasty surprises.
After figuring out after a couple of hours the thing WAS working correctly, just my testing was stupidly flawed ( It is NOT easy being Dumb and most frustrating let me tell you) I set to " Tuning" It by measuring the voltage coming from the panels. One thing that did come out of this, I -may- have found where I went wrong with Tony's board he made me. I robbed the cap bank from that so when I'm done with my simpleton setup, I'll retry the intelligent designed one again and see if as I think, the testing by the idiot was flawed not the board at all.
So far what I have which was done in the late afternoon, is a Discharge time of 5/1000ths of a second ( can't figure that out in Hz :0( ) and a charge time of 250/1000's of a second ( 4 Hz? ) seemed to put the voltage where I though it should be around. I was seeing a low of 115V on the meter and a high of 128 with 132 Open circuit and a stated MPPT on the panels of 30V so 120 all up as should be the sweet spot. Never tested panels yet that came out at the stated numbers so i'm not worried about a few volts off.
I'm sure the meter reading isn't accurate at the speed of the switching but I was also seeing down to 50V with my initial guess setting of 100/ 1000ths on the discharge and 200 on the charge so I think I'm in the ball park.
By varying the numbers I could see the voltage changes on my Multimeter which I guarantee is way too slow However I think it's fast enough to allow me to see when I was hitting the upper voltage coming from the panels unloaded and when it was also bottoming out. I'm seeing a swing of about 10V which may in reality be a lot more but it's a start and I do not know any other way to do the tuning.
I was thinking of putting an Incandescent light bulb in parallel with the heater thinking perhaps the brighter I can keep that going the better. It will be interesting to see what readings I get in more midday sun tomorrow as it was pretty late this afternoon time I got things sorted.
I chose 4 Panels because they work out to be the best for direct Ohms matching to the element. I am trying to see if I can better the direct ohms matched connection which I will try to set up another 4 identical panels I have tomorrow and test them side by side but I'm wondering if I'm flawing the test doing that?
Perhaps I should be using 6 or 3 panels and testing for non matched Ohms? I don't think the power out of 2 Kw of panels direct would work well but perhaps that's where this dumb switch might have an advantage? That said, I did direct connect the panels and saw a bit under 50V where as what I was seeing with the setup running was well over 100. From this I take it i'm on the right track at least.
If I can find 2 Identical buckets ( Refuse to go to bunnings and wear a BS face nappy for the stupid population control measures we have here atm) I'll set up another 4 panels and the other identical element I have and give them a run and see if I can do better than the direct connection with the best panel config or it needs to be Not Ohm matched... which would still be OK. I think more practical to throw 2 KW at water 1 anyway.
I don't know what the power delivered is with 4x250W panels ohm matched to a 3600W element ( But I'd like to know from the people clever enough to work it out) but I bet it's pretty inefficient even still. I don't know what I could use to measure the power that I have or wouldn't cost a bomb but if there are any suggestions.... I did buy a DC powermeter but soon as I set it up on the test load I could see it was reading fantasy numbers and there is no way to calibrate the rubbish thing. I have the same one in AC and it seem very good.
Anyway, in line with the rest of this crude setup, I spose the only test I need to do which I can is back to back the " Controller " with a set of panels direct connected to an element and see which one makes the water hotter over a given time and different times ( morning/ Afternoon).
If this does show promise, I spose the next thing would be to make some water heaters out of 44 gallon drums so I can run from dawn to dusk and take measurements though the day and see which is the winner that way. Other thing would be which one wins in overcast weather. I -think_ the ohms matching might go off the rails a bit there.
I was looking to use some other timer boards for the pulsing but so far all I have found ( and setup) are ones that do 10'th of a second and that may be too slow. Still unsure about the speed I can charge and discharge these Caps taken from a Solar GTI and how many I need so as not to fill them and waste power as this setup is a constant pulse rate and does not take into account the voltage in the caps. I'm hoping it still may be better than straight Ohm matching and other pelicans like me could set one up for themselves. The arduino sketch is merely the Blink program re timed.
Anyway, any input appreciated and I'll report my faili.... findings when I get some.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 09:52pm 11 Jan 2021
Copy link to clipboard
Print this post
Within reason the heater load discharging the capacitors is not all that critical.
Obviously you need enough load to discharge into to recover worthwhile power, and a hugely excessive load will draw enormous current peaks, which would be inefficient.
A light load will have a much longer discharge time, and a heavy load a short high current discharge.
Likewise poor solar will require a much longer charging time, than full solar.
The optimum timing will change a lot, and larger capacitance will slow everything down too.
The basic strategy would be to charge up to a specific capacitor voltage, then connect the heating load, and allow the capacitors (plus solar) to discharge down to a lower capacitor voltage, then disconnect the heating load. The whole thing then charges back up, and the cycle repeats.
Its the voltages that should stay the same, and the timing self adjust to suit.
That could be done either with an Arduino, or the LM555 timer chip I used.Cheers, Tony.
InPhase Senior Member Joined: 15/12/2020 Location: United StatesPosts: 178
Posted: 11:16pm 11 Jan 2021
Copy link to clipboard
Print this post
Couldn't you just strobe the current as the maximum power point is exceeded? If you monitor the voltage and current from the PV you could turn off the FET when you exceed the rated knee current. By measuring the capacitor voltage on the output of the FET, you turn it back on again after the voltage has fallen below the knee voltage. I have no idea if that would work, but it sounds at least testable.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577
Posted: 11:16am 12 Jan 2021
Copy link to clipboard
Print this post
Yes, that is what the boards Tony made do. Measure the voltage each way and turn on and off accordingly. No question they are a much smarter and more effective approach but I really just wanted to see if a sticks and stone simple Idea a moron like me had could do better than the ohm matching technique. I think this is a bit more doable than other methods for those electronically challenged but may be more capable in just wiring things together. If I can do it, a lot of others can that's for sure.
I know this has a lot of inefficiency but then again, I believe the ohm matching approach may have more so it's just a hope for improving something to be a little less worse than it could be while still being not bear as good as it can.
I didn't get to do anything today, had a few things pop up a bit more important to take care of and then had a very inspirational start to try getting back into work again. Should be OK tomorrow ( if I can find some Buckets or containers) to pull out another 4 panels and set them up with the other heater element.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577
Posted: 11:55am 12 Jan 2021
Copy link to clipboard
Print this post
Well that was my first mistake, but I remembered what you told me before so I did come to work it out in the end. I was trying to use a 150W light bulb to get a visual Idea of when I was getting more power. Of course with a KW of panels, they ran the light at full voltage. Putting on the 3.6 Kw element changed things and I was able to get the voltage up where is should be to keep the panels happy at that time.
PLEASE correct me if I am wrong, but should not even this dumb system not waste any power PROVIDING the caps are not filled past capacity or the panels pulled down too far on the discharge Cycle? I have the caps permanently connected to the panels. I can't or don't know how to measure the charge time BUT, the way I see it, there should be no energy loss as long as the caps are not filled or the panels pulled down too far.
When the Mosfet is off the energy is saved into the caps and when the caps and panels are switched which they both are together, the energy is going to the element. As long as the over charge / under voltage parameters are observed, ALL the energy should go to the element.
I think if the cap is only 10% charged and switched, that 10% is used and if it's switched fast enough and released, the panels don't seem to have time to pull down too far either. I don't have the proper measuring equipment but seems to me they have some reactive power in that there are some Milliseconds before they drop too far even if cycled.
That's my possibly flawed theory anyway.
Yes, makes sense. I spose what I am aiming for with the timing is a bit like " Optimum" fixed tilt of solar panels. It's rarely in fact optimum, but a good all round Compromise. Obviously doing it your way is much better because it's a tracking system where I'm hoping this idea may be a bit more like a variable tilt rather than a true tracker following the sun and Improve on fixed panels that are the wrong tilt and direction for that time of the year... All year in effect as with ohm matching. A slightly better case than worst. :0)
Now that's something I have been thinking about. As far as I can imagine, Not filling the caps is not a detriment. Whatever is in them goes to use. The voltage should remain the same, it's only the amount of power which will vary. The undesirable outcome would be to fill them till they can't store any more -power which would then be wasted.
As such I'm thinking to over slightly over cap for the amount of panels for the timing set would be desirable. If only 80% or whatever charged, you still get all the energy generated in that time. If it's only a 10% charge, you get that too. If the switching time is not too long to sink the voltage at that time, all good and if the switching time is not long enough to drain them at peak time, whatever is left will go to the next cycle and all we want to do is not over fill them again.
If this is indeed the case, then seems to me the more caps the better because it would allow wider variations in panel input and we don't need to fully charge the caps at all.
Yep, just as your board does which I am also keep to get back to seeing if I can work out where I went wrong before and I have an idea where that may be now. The frustrating thing is I KNOW it's simple but still too damn difficult for me to work out. Like I said, it's hard being Dumb but I'm really hoping I can make the penny drop, Finally.
If I can get this to work, I'd then like to try and improve it by putting voltage monitoring on an arduino. I know this too would be simple for the smart people but probably a big challenge for me. Hopefully when the time comes I can fins someone who can help ( write) the code which I know will be simple but... I'll give it a go on my own and see if I can nut it out and if not.... well it will give someone a good laugh when they see what I have attempted! :0)
mab1 Senior Member Joined: 10/02/2015 Location: United KingdomPosts: 149
Posted: 06:05pm 12 Jan 2021
Copy link to clipboard
Print this post
The really simple system is Ohm matching which you've obviously worked out:- 4* 250w 30vmpp = ~120v ~1/4 power of the element, or 2*8* 250w 30vmpp for full power. But only works efficiently with more or less full sun.
I suppose with your adjustable on/off controller you can compensate for different levels of sunshine by changing the on/off ratio to match the ambient light, but that's quite laborious if your having to change it manually every time the light level changes.
You could also do 6*250w with a 75/25 on/off ratio (full sun), or 8*250w with a 50/50 ratio, which gives you more power options, but you still have to adjust for actual light level.
Trouble is you seem to have a working system that's 90% of the complexity of a voltage sensing system, but without the benefit of it being self adjusting to variation in the light.
Hence we keep coming back to voltage sensing. :)
mab1 Senior Member Joined: 10/02/2015 Location: United KingdomPosts: 149
Posted: 06:21pm 12 Jan 2021
Copy link to clipboard
Print this post
Thinking about your 4 panel test setup: you can't achieve max efficiency in full sun as the Vmp of 120v (I'm assuming your panels are 250w and exactly 30v vmp, Imp 8.33A) means the Imp will be >7.5A in full sun, and you can't achieve that without going above 120v Vmp even with 100% on time.
If you went to 5 panels Vmp 150v then full sun voltage on the element will be 133v nominal (89/11 on/off). At that point you should win vs ohm matching - as long as it's 100% sunshine. In theory :)
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 08:20pm 12 Jan 2021
Copy link to clipboard
Print this post
Dave, probably the best tool you can get for seeing what is actually happening would be a digital oscilloscope. That will clearly show the ramping, and the actual voltage levels reached.
There should not be any wasted power if you cycle THROUGH the max power point.
That is, allow the voltage to rise just above the max power voltage, and discharge down to just below the max power voltage. As the max power point is not a sharp peak, but a very wide hump, the tripping voltages can be set fairly widely apart.
Yes indeed. There will be some slight losses in the wiring and the mosfet heat sink that will show up as heat, but that should be very small in the great scheme of things.
It will really be a genuine self adjusting maximum power point tracking system, without requiring any fancy software. And it will follow very rapid changes such as passing clouds.
It just needs a few basic requirements to be met, and a little understanding how its supposed to work to set it up. But once running properly it should pretty much take care of itself. Edited 2021-01-13 07:15 by WarpspeedCheers, Tony.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577
Posted: 10:49pm 14 Jan 2021
Copy link to clipboard
Print this post
Did myself bit of a Mischief playing round with this yesterday. In the sun too long, sweating too much and came in and was not well the rest of the afternoon. Next time I'll set this up so I can put a gazebo up as a sun shade.
Anyhoo....
After all that experiment was a failure because the bucket that had the direct connected panels had a pin hole in the side and half the water drained out. The one with the oscillator did not seem impressively warm for the time it was out there so unsure about that as well.
I adjusted the timings to 50 /1000s dump and 100 Charge. I connected a 120W floodlight in parallel with the road and using that and measuring voltages arrived at this as a reasonable timing for the 8am power I was getting.
I am seeing around about a 10-15V swing on the multimeter as it jumps around which is from 130-133V ( full voltage0 down but only around 50V which swing much more on the Meter at the element. The direct connected panels are sitting around 88V.
This raises a question for me..... What should I be chasing, keeping the panel voltage up or the element voltage or is it a balance? My impression the goal is to keep the panels at VMP and the switching is probably just too fast for my meter to display accurately and voltage and power may be different at the element anyway.
I'll give it a couple of hours and see how it goes. My impression at this stage is the direct connection may win but I'll next try bumping to 5 panels and see how that goes. It will also be interesting to see if adding a panel reduces or increases the voltage on the direct connection once the ohm matching goes out.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 11:58pm 14 Jan 2021
Copy link to clipboard
Print this post
It needs to swing through the max power voltage. I think you said earlier that VMP was 120v, that sounds about right for four 24v panels in series.
Something like 10v above and 20v below might be suitable set points, so swing between 130v down to 100v perhaps. Power falls off much faster on the high voltage side.
Your directly wired panels are pulling the voltage way down to 88v which will be overloading the panels well below the sweet spot of 120v.Cheers, Tony.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577
Posted: 02:28am 15 Jan 2021
Copy link to clipboard
Print this post
Went and checked and found the direct panels had heated the water much hotter. :0)
Checked again later and found the little USB battery I was running the arduino with had Died. That may explain things. Talk about amateur hour. :0(
I wired in a standard 3 pin 240V socket on the output to the element. I tried plugging in a normal 240V to USB converter and it works. I can plug the battery into that to charge and the Arduino into the battery at the same time so it should be self sustaining. Looked at those little boards but there are none that have usb outlet so looks like this will be the clunky but effective way it will power itself. I'll move the plug to the panel side so it will get better power and self start with the sun if the battery is flat which it probably will be with the arduino running all night.
I Have adjusted the timing so it pulls down a bit lower. Might try and get it down a bit further if the high side is where it falls off the most.
Tony, Is there any calculation for caps charging? Say If I have 100V @ 5A, can one determine how long it would take to charge say a 1000Uf cap? Thinking if that's possible with round Numbers, that may also give an idea I can calculate what amount of caps I need for full output and timing and any lesser input from there should be taken care of with partial dumps.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 02:42am 15 Jan 2021
Copy link to clipboard
Print this post
Certainly possible to work out the charging time from a current source.
time in seconds = capacitance in Farads divided by current in amps x the change in voltage
T = 0.001 F divided by 5 amps x change in voltage (130v - 100v = 30v change)
T = .0002 x 30 = 6 millisecondsCheers, Tony.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577
Posted: 03:00am 15 Jan 2021
Copy link to clipboard
Print this post
Playing with timing, I got the element voltage to 106V which I thought was good. Checking what the direct connection setup was I got 107! That ohm matching seems pretty good!
Maybe this timing idea will only be effective outside of the ohm matching?
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 04:07am 15 Jan 2021
Copy link to clipboard
Print this post
Yes, If the load is perfectly matched to the panel, you cannot ever do any better than that.
But most of the time solar will be up and down, and sometimes down a lot. That is where a little bit of electronic black magic can make a difference.Cheers, Tony.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577
Posted: 01:55am 16 Jan 2021
Copy link to clipboard
Print this post
IT WORKS!
As if most of you didn't already know that.....
I combined the 2 arrays in series to take the setup way off ohm matching. With a direct connection to 78 panels I can get around 130V at the panels/ element. With the oscillator setup the panels are sitting around 245- 250V.
There is obviously a lot of lag in my Multimeter readings and the flood light came in very useful here. When paralleled to the direct connection, it looks as the voltage would indicate, about half brightness. When coupled to the element driven by the oscillator, it's definitely full brightness... and then probably some.
The other positive note I found with the timings was they do indeed work as well. If I increased the dump time too long the globe pulsed bright then quickly dropped down dimmer indicating when the caps had given up their power and the lamp was running direct and pulling the panels down as in a direct connection.
Similarly, when the charge time was shortened too much the blinking of the lamp was overall dimmer again indicating not enough charge in the caps and pulling the panels down.
I'm sure this is elementary to most here and it is certainly as I expected but it's good to see my theory was at least correct in it's limited application anyway and gets the results it should.
Now this leads me to maybe the real and more difficult question to test......
This morning is perfectly bright and sunny, optimum conditions. I left everything connected last night to see if it would fire up on it's own and it did which was good. The water was also very hot by 10 Am when I came back from running some errands and first checked it even though I got the timings a lot better when I played with them.
The question now to me is, with the timings set for optimal/ max power, how will they go early and later?
I figure if the dump time is long enough for the max power at this setup, it should be long enough for lesser power. The dump time I have is only 10 ( ms?) so it should not pull the the panels down very far given there will be some charge in the Caps as well. definitely thinking that a large cap bank with slower charge timing (currently 50 ) might take into account a wider range of inputs.
Anyway, theory is proven and this would allow much higher power input than just ohm matching which I think makes it worthwhile in itself. I would think this will be far better in less than optimal conditions of overcast where extra panels would far outdo the limited amount that one can ohm match. I'll now try going the other way with less panels than ohm matched and see how it goes with that.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 03:21am 16 Jan 2021
Copy link to clipboard
Print this post
Great stuff there Dave !!
With less solar (cloudy) or dawn/dusk, the caps will take much longer to charge up to full voltage, that is obvious.
Discharging time will be just slightly shorter, but probably not by very much. Although there will be exactly the same stored energy in the capacitors during discharge, there will also be less current being supplied direct from solar added to that, so the caps will discharge slightly faster into the same load when there is less sun.
The trick now will be to have it go into discharge when the capacitor voltage reaches the high trip point, and have discharging cease when the voltage falls to the lower trip point. It will then be self adjusting and just cycle at its own rate.
The value of the capacitor will not effect the total amount of power transfer or the efficiency, only the speed at which it cycles.Cheers, Tony.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 03:52am 16 Jan 2021
Copy link to clipboard
Print this post
It will probably not work nearly as well with a lot less panels, either direct, or through your capacitor cycling system.
The reason being there will be a lot less loading on the panels at much lower voltages, power drops to one quarter at half voltage with the same heating element load.
There may not be enough loading for the capacitors to dump enough energy, and the voltage will not be pulled down far enough to get it to cycle properly. It will very likely work better with direct permanent full time connection to solar under those conditions.
The system really needs a heating element big enough to be able to easily overload the panels, even with full sun, so it can cycle properly with a relatively short discharge time.
Earlier you had an ohm matched system and the cycling system did not offer any improvement.
If you reduce the heater loading even further, I suspect its not going to work at all.
This is going to work far better at higher voltage, or at least enough voltage so that the heating load will be heavy enough to readily overload the panels under full maximum summer sun.Cheers, Tony.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577
Posted: 05:44am 16 Jan 2021
Copy link to clipboard
Print this post
Thanks Tony. I very much appreciate the time and input you give a pleb like me and the great learning value I gain from you. You are a very good and smart man.
I understand what you say about the lesser power and slowing the cycling down with more caps. I am thinking that this being a fixed times system, more caps may allow slower timing on the high power end without filling and wasting the energy and on the low power end, the longer timing may allow more energy into the caps and not pull the panels down as much.
"There may not be enough loading for the capacitors to dump enough energy, and the voltage will not be pulled down far enough to get it to cycle properly. It will very likely work better with direct permanent full time connection to solar under those conditions."
This bit I am unsure of what you mean. This is a fixed timed setup for the on / off. It is dumb and does not know what state of charge the caps have, it just goes high and switches the Load in for 10 Ms and then switches the load off and charges the caps which are permanently connected to the panels for 50Ms before dumping the caps and repeat. I can see it cycling with any load, the 120W lamp or the 3.6Kw element or both together.
Could you elaborate on what you mean here please about being pulled down enough to Cycle??
"The system really needs a heating element big enough to be able to easily overload the panels, even with full sun, so it can cycle properly with a relatively short discharge time."
Yes, this was the initial Mistake I made just using the lamp as a visual indicator and I remembered you pointed this out to me before. I connected the lamp WITH the load and it worked very well as a visual indicator where the cycling is too fast to get an accurate reading from the Multimeter. In combination I can see where the panels are and get a reference to the energy input to the element.
My intention is for this to be connected to a 3.6 Or 4.8 Kw element. I would Imagine most people whom might use the system would not be putting the element rating of panels on their water heaters. Even if they did, the systems should still help with the morning and afternoon as well as poor weather performance as far as I can see.
Seems with Ohm matching you are stuck at a set number of panels, in this case 4. If you have say 6 or 8 you want to throw at the job for better heating, they become counter productive. With this system, one can use more panels and make more of them rather than dragging the panels down and getting less energy than what one would with more panels.
Now the sun is getting low in the sky, I'll go back out and see how my timings are going off peak sunlight.
Warpspeed Guru Joined: 09/08/2007 Location: AustraliaPosts: 4406
Posted: 07:23am 16 Jan 2021
Copy link to clipboard
Print this post
You will probably find that with a very low solar voltage, the panels really want to be continuously connected to the load for maximum power. Any time the load is disconnected (during charging) reduces the power in the load.
If the heating load is exactly ohm matched to the panels, such that the panels are operating right in the sweet spot, where the system voltage is spot on the maximum power rated voltage for the panels, that is the perfect situation. Nothing can improve on that.
Now if we reduce the load, by (say) fitting a higher resistance, lower wattage rated load, we will be cheating ourselves. The panels will be insufficiently loaded, and the solar voltage will be higher than optimum. Power is reduced because the load is just insufficient to draw enough current to be useful.
That is pretty easy to understand, no load, no power. We can increase the loading right up to the ohm matching point, and get more power as we go.
Now consider what happens if we have a large number of panels, all in parallel. Very low voltage, but a huge potential current available. your 3.6Kw element is going to look like a very small high resistance load, compared to what the panels COULD handle.
So the panels remain under loaded, and performance is poor.
That is the situation you will have if you reduce the panel voltage below the perfect ohm matching point. The best you will ever be able to do will be just connecting the panels direct to the load, or running your system in CONTINUOUS discharge, which is basically the same thimg. In other words, minimal charging time, maximum discharge time (like forever) will give best power, which is going to be be piss poor anyway.
So the hot tip is, work out the ohm matching point, where the loading is perfect for the solar panel voltage and rated power.
For the capacitor cycling method to work at all we need a heavy load and a high solar voltage, such that the load would be far too much and pull the panel voltage right down if direct connection was used.
The capacitor system then cycles REDUCING the effective load on the panels, allowing them to run at the sweet spot.
On a grey cloudy day, this will happen naturally as the load stays heavy, but the panels are very weak under those conditions. The capacitor cycling needs a very long charging time, and will dump into the load transferring all of the available power, without overloading the panels.Cheers, Tony.
Davo99 Guru Joined: 03/06/2019 Location: AustraliaPosts: 1577
Posted: 09:01am 16 Jan 2021
Copy link to clipboard
Print this post
OK, seems what I am doing atm. Panels are all in series (8) so the open circuit voltage is a bit above the element voltage but pulls down a lot. 2 Kw of panels on a 3.6Kw element so plenty of load.
I checked how it was doing at 5:30. Still with the timing I set this morning a bit before midday. The voltage on the panels was around 215V which isn't too bad from the 245 or so rated VMP with the controller connected. A little over 10% down. Some of the panels had a little shading too. Sun was at a pretty obtuse angle by then as well.
Direct connecting the element dropped the voltage down to 70V. This made the energy input either 3 or 1.5 times better. ( Half Voltage, 1/4 Power?) Connecting the lamp in parallel with the element confirmed the meter readings. Direct connected a barely perceptible dull glow could be seen. With the controller the the lamp was pulsing quite bright and pulsed but never extinguished.
Pretty happy with that. It seems the controller is giving the element increased energy input over a wider time frame than this non ohm matched configuration of panels. I think more is always going to be better because less ( than 4 ) just isn't going to create power for a meaningful amount of heating a useful amount of water in the first place. Be lucky to heat 50L of water to 70 with 3 panels and if it's cloudy, you are going to be limited on the cups of tea you can boil from that even :0).
Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
Print this post
