Author Topic: Direct solar water heating and battery charging.  (Read 593 times)

veggie

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Re: Direct solar water heating and battery charging.
« Reply #15 on: March 15, 2020, 11:37:36 PM »

Would it make sense to use use variable resistors (dial pots)  for the upper/lower band setting?
That would allow the user to tune the system to the Array and Heating element.
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glort

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Re: Direct solar water heating and battery charging.
« Reply #16 on: March 16, 2020, 12:34:51 AM »

I thought of that but I have not seen trim pots with suitable power dissipation ratings needed. Trimpots I have seen anyway tend to be pretty low power handling.  It may be possible to put in base power resistors and use the trim pots to adjust over a voltage range  close by though.

What I was thinking was to have terminal blocks on the board and then people just select the resistors  they need which would be provided and labled and just connect them up like they would the wires to the board.

ATM I'm trying to work out the legalities of selling the things. I'm getting very mixed information even from official sources. Couldn't give a damn if the stupid BBQ themselves with them but don't want them or their families coming back to sue me out my house for their stupidity.

It seems there may be a lot of protection for me selling the thing as kits. What constitutes a kit, I have to find out.  It may be putting  the 2 resistors in and presenting it as a non working board may be OK but I get a feeling it may have to be  say at least 50% built by the purchaser ETC. The other thing is to sell it as low voltage only. I think that would cover me here and then I could state the thing was for use with 120V or under only unless it was legal in your country/ area to hook it up to a max of 350V DC.

Thing that makes me wonder is how do they get away with selling so many dodgy devises from China? Maybe I need to drop ship them and have a shelf company registered to my Cat or something?

I wondered why no one had come up with something like this before. I'm beginning to see why.

Zeppole

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Re: Direct solar water heating and battery charging.
« Reply #17 on: March 16, 2020, 06:33:15 AM »
Glort
 I would definitely be interested in trying out one of your prototype boards and/or getting more information on how to convert the battery board. I have played around with direct coupling solar panels to a water heater taking into account the resistance of the water heater element and the characteristics of the solar panels used. Like you, I found the results to be very good so long as there was direct sunlight but very underwhelming when there were clouds.
 I hope you will pursue this further. I would be willing to invest since I believe PV solar is the only way to go especially for off grinders of which I am one.  Used panels are incredibly cheap in the US.
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glort

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Re: Direct solar water heating and battery charging.
« Reply #18 on: March 16, 2020, 10:36:11 AM »

I have had a fair bit of input from locals and TBH i'm no wiser but far more confused than what I was at the start. Everything seems to conflict with different things and I'm only looking at the rules in Oz so far. Don't know how it would work other places. Still, other people sell things in a similar vein so....

I just finished doing a basic pulsed controller with a Mosfet instead of a SSR.
Good SSR's are both exy and hard to Find  where as Mosfets are the opposite. They aren't hard to set up, can't be if I did it, and the right ones will control a lot of power.
I'm driving this one with an arduino Nano and have gone to  great trouble, expense and effort Modifying the Blink program.  Well, I did change the on and off times :0)

I have also just used 1  1000 uF cap instead of 4 and shortened the cycle times to account for the faster charge time.  It's all a guess at this point but I think there is so much margin for improvement with direct connection you'd have to go to effort to get it just as inefficient.  Not possible to go backwards.

This setup will be rough in that it does not take into account the actual power being generated but with a fast Cycle time it should not matter in either bright sun when there is plenty of power the charge time will be fast or when there is less sun because it will be cycling faster than the power can sag at least in any worthwhile light that is.

I'm going to start with 50 Millsec off to charge the cap and 20 Ms on for the discharge.  I'll see what I can work out with an analogue Amp meter.  It bounces around a bit bit should give an Idea.  Might also put a cap with a diode  and a resistor on it to see if I can get a reading of the panel voltage as that bounces around.

Was hoping my boards and prototype would turn up today, Hopefully will come tomorrow.

I would like to see this go somewhere to help people particularly off gridders.  The gerbers for the boards will be in the public domain but The thing is I know there are a Lot of people out there like me that can do electrics but electronics is a very different thing and a lot of people wouldn't attempt it.  I could also do kits, better as they are very simple but I think what most people want is the Box they connect  their panel and heater to and off the thing goes.  Wether it is viable to do that or not without risking my house I don't know. Pretty damn sure it's not worth getting approvals and things for because The Chinese will probably copy it the minute it's certified and people take an interest.

As far as kits go, I could probably have the things made in china cheaper than I could buy the components unless I bought 1000 at a time.

I actually wouldn't care that much if they did.  I'd like to make something out of the effort and risk it would take to get it out there as a going thing but by the same time if it could get out there without me having to be put to any risk, that would be better still.


Zeppole

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Re: Direct solar water heating and battery charging.
« Reply #19 on: March 16, 2020, 05:06:14 PM »
Glory—

 I hope I’m not being presumptuous, but would like to make a few suggestions.

 Consider doing the bare board along with a detailed list of parts required to finish the unit and a very complete set of assembly directions. In the United States we used to have a company that made Dyna kits for preamplifiers and power amplifiers . These kids had a step-by-step assembly directions and were rather complex projects, but were very popular for those with basic soldering skills.

One of the benefits of selling a bare board is the minimization of any liability  in as much as you would be simply selling a component rather than a finished product. This coupled with a broad disclaimer of liability would seem to give you adequate protection.

The second benefit would be elimination of acquiring parts and ease of shipping since the board could be  shipped via ordinary mail at a relatively low cost.

Additionally, your profit margin could be quite high; for example, I would be willing to pay at least $50 for a bare board along with directions, etc. I am assuming that your cost per board is relatively minimal  and that this would allow you a reasonable profit. It would also discourage copycats since it would be limited to a fairly narrow market, i.e., do it your Selfer’s .   There simply wouldn’t be enough gross dollar profit involved to encourage copycats.

As you noted, if you develop and market a finished product, someone in China will copy the design and market it after you have gone through the tedious and expensive tasks of certification, etc.

 I think there would be a lot of interest in this type of product in the DIY community.  The only product that is readily available in the US is a PWM unit that has very limited capacity (1kw panel input max) sold by “Tech Luck” for a stupid high price of around $250.  It does not appear to be a robust product.

Hopefully your design/kit would accommodate at least 2 to 4 kw solar panel input. 

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glort

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Re: Direct solar water heating and battery charging.
« Reply #20 on: March 17, 2020, 12:03:31 PM »
Glory—

 I hope I’m not being presumptuous, but would like to make a few suggestions. 

Glad you did! There are a lot of good points in what you said.
"Production" wise, it would also be very practical.  Get the boards, provide a set of instructions with some detailed Pictures and maybe access to a password protected vid on my site , Bundle them up, send them off, no problems what so ever.

This is a VERY easy board to build, so easy even a moron like me can do it.  There are only about 16 Components on the board and 6 of them are resistors, 2 are mosfets and 2 are IC's. Then there are 4 terminal blocks and a couple of diodes and a pre built power module you just connect up. From there you add your cap bank and wires to the panels and your heater and that's it.   Very easy and the board is generously spaced as well which helps non builders with Sausage fingers like me a LOT.

I believe most people could build the thing just looking at pictures of it.  Diodes and IC's have to be aligned which you could see  on a good full page Image which would be about 4X magnification on A4 ( or could put links to real Hi res pics) but would answer the majority of build questions.

People in the states could probably source the components cheaper than I could buy them wholesale so that would be an advantage as well.

I like this idea a lot more now you have extolled the virtues of it.
I was thinking to do a complete prebuilt unit but the inept people that may try to use it and hurt themselves in the process rather than the board hurt them was my concern.  This would be GREATLY reduced by doing a kit because if they are smart enough to build it they are probably, in the main, smart enough not to grab hold of live wires.  No guarantees of course but I'll take the better odds.

Quote
I think there would be a lot of interest in this type of product in the DIY community.

Yes, these were the people I was thinking of.  I have mentioned the idea on another forum where to be perfectly honest, the majority of the members are inner city, latte sipping types that would struggle to change a light bulb and the rest of them would be sitting round citing  rules and regulations and crapping on with all sorts of bedwetting safety warnings and imploring the person to cover themselves in PPE before attempting such a risky proposition they should leave to a licenced tradesman.  Seems when push comes to shove and I wanted to find out about rules and regs they don't know jack in reality to what they make out.  Much to my pleasant surprise, I have had a few people express interest as well.

Seems those of us Real man that were brought up with a sense of self sufficiency and not afraid to get ones hands dirty are not extinct yet.
With current situations we may be the only ones left alive! One can dream I suppose.

Used panels are so cheap now and anything non grid connected escapes the rules and regs to a great or total degree and more over, the majority of useless pussy whingers.

Quote
  The only product that is readily available in the US is a PWM unit that has very limited capacity (1kw panel input max) sold by “Tech Luck” for a stupid high price of around $250.  It does not appear to be a robust product.

I just came from another board discussing that very product and said exactly what you mentioned.  The thing is really designed for small tanks and to heat the water to a temp that is Illegally cold here.  He have to have a minimum of 65oC to kill legionella bacteria. Seems on the tryyourluck site they go on as if 52o is molten lava.

Given the average size heater here is 250L and we would be on average heating the water to 70o ( Haven't seen any heater thermos I can recall go below that)  they are saving probably 70% of the energy needed for what I had in mind.
Trying to heat that with the 750W they actually recommend isn't going to get done even on the brightest summer day let alone a partially cloudy winters  one.

I also totally agree with the thought they don't look to inspire confidence in their longevity.  They use little caps which must be working hard. Caps are in my book one of the weakest things in electronics over time. They say it's  MPPT but I don't see how. There are components NOT on the board that far as I know would absoloutley need to be for it to be MPPT. They mention that, saying it's a Different kind of MPPT.
Seems to me like it's probably some sort of PWM. I'm not sure how that would work either given there is no provision for voltage setting I can see.  That's what the board I have is and that's fine, but I'm not telling everyone it's something it's not.  PWM is fine for this application and its set up to keep the panels in their happy place so there is no advantage over MPPT for a dumb resistance element anyway.

I was playing with an arduino today and just driving a Mosfet through a cap with that and observing what the various on and off pulse widths effects were on the output.  From what they say in the literature and in their vids, I have the distinct feel this thing is just the same.
Cycles the panels/ caps, pretty dam slow too it seems, and just feeds that to the element.  The fact they are paying attention to ohm matching makes me very suspicious.  I know about that and have tried it but in the design I have, doesn't matter a rats.

At a point  when I was playing around today, just so happened that the panel/ element / conditions all lined up and I couldn't really improve on a straight connection. wondering what was going on at first.  Even with my fixed pulsing the cap bank, normally I can make a BIG difference in the power going to the element and I am thinking this is just what they have done with maybe  a 556 timer or something.

From what I can see from pics and vids, It's not MPPT, it's not taking into account The Vmp of the panels or how much power it's attached to, makes me think it's just a pulsed switch.
That's a LOT of Money for something I can do with a  $5 Arduino Nanno or digital timing board and go a LOT better with a battery charger board that uses a Voltage divider to actually look at the voltage across the caps and vary the pulse accordingly.



Quote
Hopefully your design/kit would accommodate at least 2 to 4 kw solar panel input.

This design will take pretty much what you want to throw at it within reason.  Certainly whatever the heaters full rating is. In discussing it with people in the design we figured here about 2 Kw of input power would be good but if you wanted to add 4kw or even 6, no problem. One does get diminishing returns as you can still only get what the element is rated for and the controller will take care of that as long as the array is not grossly over volted like 20 panels in a string giving 600V or something. If you bought higher voltage rated caps, then it wouldn't actually matter up to the only limited thing on the board which is 380V. thats about 12 190/250w panels in a single string and would still cover our 380V 3 phase.  Drop in a voltage divider for that component and you could go all the way to 600, not I can see any point in not splitting the string and going 2 arrays in parallel at 300v. 
If however you series/ paralled the panels to keep the voltage down to about 280 -300 on a 240V element, you could run all the panels you wanted. Won't get the water hotter any faster but it will give you some extra backup to run the thing at full tilt in less than perfect weather when the panels production is down.

I have all my grid tie system double or more over clocked for that reason. Inverters make near as Dammit the same in winter as they do in summer only for not as long thanks to shorter days but still stay on the top of their output under a lot of less than ideal conditions. .

There are 2 Resistors which set the on and off voltages. They were worked out to be very simple to calculate.  1 K per volt.  You array of 6 has a voc of 180V, put in a 180K resistor.  The Vmp is 100, put in a 100K resistor for the bottom end.  easy as with no complicated calculations. It's all been done in the design to make it easy.  Also does not matter if you are using 12V panels or the newer 54V types.  Look at the voc, look at the VMp, multiply by however many you have, put in your resistor and that's it.
A trimmer could also be used but they are less resistant over time to dirt and humidity etc but if for some reason you had cause to change the array and the values, no real drama.


I had another thought today with these.
If the power went out and people had panels, they could hook up one of these units and power a bar heater to keep them warm in winter.
Controller won't give a dam, just another dumb resistance load. Could also power an electric jug, sandwich toaster etc.
Because it's a pulsed output, not going to fry anything when it turns off on a thermostat like a direct DC connection would.

Thanks for the input. Much appreciated and definatley good food for thought!

Zeppole

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Re: Direct solar water heating and battery charging.
« Reply #21 on: March 17, 2020, 04:46:03 PM »
Glort--

I think your idea of a password protected video on the web is brilliant -- I think a lot of us are visual learners as opposed to reading learners and a video would be perfect in conjunction with written directions.

I would certainly be willing to be a guinea pig if you would like input on taking a bare board through to completion.  At the end you would know that anyone can do it if I can!

The great thing about PV solar water heating is the very short pay back period -- with PWM controller and used panels I would estimate the pay back to be under 2 years for a DIY'er.
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glort

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Re: Direct solar water heating and battery charging.
« Reply #22 on: March 18, 2020, 08:57:11 AM »
Glort--

I think your idea of a password protected video on the web is brilliant. 

Well you inspired the Idea with your suggestion of a kit!  :0)
Seemed appropriate being I am a very visually orientated person myself.

When this thing was drawn out as a circuit it seemed a real Challenge to build to me. Just the physical construction would be something as I have no training in electronic layout. When I saw the board and you just attach the components, I was very pleasantly surprised at how easy this was going to be.  Like I said, I think a good, detailed picture thats close enough to see the orientation of the components and maybe a circled highlight or 2 of markings would be enough for most people to go from.



Quote
The great thing about PV solar water heating is the very short pay back period -- with PWM controller and used panels I would estimate the pay back to be under 2 years for a DIY'er.

Based on what we pay for power here, I'm thinking and planning it would be a payback of 6 months for a kit anyway. I'm not into this " Years"  thing, I'm greedy!  :o)

Like everything else to do with anything solar, the variables are wide and endless.
On another board I had a guy say wouldn't be worth it to him with just he and the mrs in their small house with small water heater and only paying whatever minimal amount of power it was.  Next reply was by a guy that had inlaws living with him and 6 Kids and was paying a fortune for power and hot water and said I'll take 3!

People in the UK, Ireland and Tasmania  may not get enough sun to make it worthwhile, people closer to the equator with endless sun may never have to pay for water heating again.


glort

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Re: Direct solar water heating and battery charging.
« Reply #23 on: March 20, 2020, 12:03:06 AM »
My pcbs arrived late yesterday along with the prototype.
They are things of beauty to behold.

Seeing them in the flesh im more confident of how easy they will be to put together.

I think ill set the first one up in an old solar inverter cabinet which will have provision to wire up connectors in the cabinet to make testing easy.

I'm going to try 4 250w panels first with a couple of 1000uf caps and go up and down in panels from there.  First thing i want to test is the ability for AC thermostats to switch without arcing.  Ill try some light switches first which will be much lighter duty than thermos so if they are fine everything else will be.

Had some more controllers of this type pointed out to me. One is a localy made finished unit . The element in the heater needs replacing with a 48v type, have to put a temp sensor in the heater, does less than 1500w, needs mains power and costs.... $1000!!!!

YA!  Makes mine look pretty damn good. No heater mods, will run 4.8 kw or whatever the element is and needs no mains power supply. Build the thing in maybe an hour for under $ 100.

Looking forward to testing!

EdDee

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Re: Direct solar water heating and battery charging.
« Reply #24 on: March 24, 2020, 10:44:51 AM »
Nicely done!!
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glort

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Re: Direct solar water heating and battery charging.
« Reply #25 on: March 25, 2020, 09:34:29 AM »

Would probably work pretty well in your part of the world Ed with lots of sunshine.
With the right panels, no reason why it couldn't be used to power an electric fence to deter Miscreants.  Unlike other electric fences, this one could literaly blow the shorts off those that came in contact with it by providing lower volts but MUCH higher amps than your normal fence.

I'm just finishing Building the thing into a suitable box. That's taking longer by far than building the board itself.  Still, I want to make it as decent as possible.

I have been playing around with an arduino nano as just a pulse driver and controlling a BIG Mosfet and it's worked well.  Forgot to put in a transient suppressor but hasn't blown up yet which is a positive sign.
I know nothing more than to change the variable on a cut and past Arduino program however the fact I can control the fet and put in voltage sensing makes the nanno perfectly capable of doing this job as well.  All that will be needed is a voltage divider the fets and the caps the same as the other board and should be a goer.

I'll have to thrash out the code or find someone who can do it for me but that will be the hardest part.  The smart people could add all sorts of Monitoring, temp sensing, wifi if they wanted and over complicate the whole damn thing as they liked!  :0)