Author Topic: Direct solar water heating and battery charging.  (Read 994 times)

glort

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Direct solar water heating and battery charging.
« on: March 02, 2020, 01:23:14 AM »

I have had a compulsion over the last year or so to work out a simple way to use panels  to heat  water  in a stand alone configuration without mains Connection.

It is patheticly inefficient to just hook the panels to the water heater as this pulls the panels off their power point and you get next to nothing out of them.  It's much like trying to drive a car locked in top gear. the thing has no power and if you can get it going the first hill you come to it will be lucky to do 20 Kmh when in the right gear it could easy do 100.

Pulling panels off their power point is exactly the same. They need to be kept in their happy place which is the power point voltage they all have written on the back with their rating and other info such as power output and amperage.
If one works out the resistance of the panels and matches the ohms to that of the heater element they want to use, better efficiency can be had but it's the difference between terrible and less terrible.  Under perfect conditions they can be OK BUT, they will be OK for a very short time and as the sun changes or a cloud comes over, kiss your generation goodbye.

In my tests I have hooked up 2 KW of panels and got around 200W out.  Best case I have ever got, briefly, was around 50% panel rating. IE, 1.25 KW of panels gave almost 500W. 

In order to keep the panels in the right " gear" to get decent output, a Controller is needed.  There are different Types, MPPT being the holy grail but for this job it's really overkill as is the price of the few controllers commercially available out there.  The ones I have looked at in the lower end use about $5 worth of components which are really quite over taxed in the circuit they are in and the cost of the board is nearly $400 au.  A complete and utter rip off that -might- last it's warranty period of 12 months but anything past that would be really good luck and nothing else.

There are some DIY designs for controllers on the net and some are very good but require a high level of expertise in electronics to build and set yup and some are just complicated and basicaly useless. These operate on low voltage, 60 V or less and have outputs of under 500W and well below that often.  Fine if like some of the people demonstrating them you only need enough hot water to wash up with or one person take one really quick shower per day but if you want a decent household amount of water, useless.
I have a large hot water heater and while I don't need to heat the whole lot every day, I wanted something useful not to be mucking round playing Tiddly winks with less water than I keep my tiny little play greenhouse warm in winter with. 

The function of a controller in this application is really very simple. All we need is a switch that turns on at a certain voltage, as the panels just pass power point and turns off when they drop below it.  Tests myself and others have done looking at this problem indicates a 10% Margin either way is quite acceptable and the efficiency fall off is not much either way as being mass produced, the same panels have a tolerance one to the other anyway and none are spot on rating as one would expect from a mass produced item.

There are an endless number of Chinese control type boards on different sites and they are cheap and for the most part quite reliable and do a good job. I wanted to use these as a base for a controller and make some simple modifications so they would work with practical power outputs closer to that of the mains voltage 240V elements standard in water heaters.
The boards are all low voltage but with some very simple electronic components and Mods, they can easily control mains power rated voltages and Currents.

  With so many different boards available and doing the same functions, the question once I worked out what I needed to actually have the things do was which one to use? Many will work but I wanted to standardise on a couple so I can do some vids on how to set these up so people with no electronic knowledge like myself can put them together without undue stress  and by follow the numbers rather than having to learn electronic theroy for 5 years before they were up to it.   

I have found some new generation boards that seem really funky and have an LCD display rather than the old '80's Looking LED figure 8 readouts.
These boards are like the others I have used, designed to be battery chargers.  They have a low voltage cut in setting and a High voltage cut off setting.  They work in stock for  from 6-60V so can be hooked to a panel direct and to a battery. This is a boon as it will work perfectly for keeping batterys float charged on equipment.  My Father spends fortunes on commercially available mains units but these things typically are cheap as chips and will work really well for me Keeping battery's charged in my machinery shed which has no power.



I have done setups before but they require a power converter and then the charge controller which is a bit clunky and costs more obviously.
These things simplify that and you can see exactly where your battery is at.

To use these things as a water heater controller, the mods are very simple. First thing is to create a supply voltage the board can handle. This can be done 2 ways, with a small transformer or with a voltage divider. I'm initially going for the transformer. This is a tiny 3W AC 12V unit that will also work off DC and will supply plenty of power for what the setup needs.
The next thing is to reduce the voltage to a level the board can handle to detect the panel voltage.  This is done with a Voltage divider. a Couple of resistors that will take the mains level voltage and reduce it to the 6-30V the board can read. Doesen't matter what it comes out at, as long as it is within that range then you can set it up to the panel type and number you have.

As the board will switch off and on at a rapid rate at peak power production, the will be a loss of power when it is off. To save that the panels are wired to a small capacitor bank and this is what the controller monitors.  When the caps charge up, the voltage rises, the controller switches a Mosfet or an SSR that handles the high voltage and amps and the heating element gets all the power generated.  This can easily happen at anything from half a hertz early in the morning and late in the evening to 100hz in the middle of a good day.

Because the panels are kept on power point, the efficiency is probably at very least around 90% of what the panels are generating at any give time and I'd expect it to be at the higher end of that.

The relay on the board can be removed and a mosfet or several can be added to replace the mechanical relay which is really slow and being mechanical, has a very limited life. They are rated at 10M cycles but when firing at 100 times a second, not going to take long for that number to come up. Plus the fact they are likely to fry switching High voltage/ amperage DC.  I'm initially trying a DC SSR as that will be the easiest thing for most people to work with rather than Mosfets which will require heat sinking and soldering etc.
Also using an SSR means the built in thermostat of the heater can be used to shut the system down when the water is hot enough or divert it to something else by switching the very low power low side of the SSR rather than frying the thermo contacts on the high power DC side which they will NOT handle.

The beauty of this basic setup apart from cheap, simple and readily available is it is adaptable to any amount, type or rating of panels and any element.  One only needs to calculate the max voltage of the string of panels they have, work out the resistors for the voltage divider with an online calculator and it's all the same. Add more panels later and -maybe- change the resistors ( although the same ones will work over a pretty wide range if calculated around 12V to start with) and that is it.

The caps can be salvaged from things like old solar inverters or bought off the net and as long as they have sufficient voltage handling capability, I recommend 350V as a minimum for mains level outputs, they are good to use.

If there is any interest in the water heating setup I'll come back and explain it more and once I have done more testing I want to do some vids using different boards. The board specifics are irrelevant, there are at least 6 I know of that could be used and that is just the battery charger boards, there are other boards for very different purposes that can be adapted as well using the same base setup. None will work better than the other I can see, just looking for cheapest and easiest to work with.

I think the LCD screen on these board is rather impressive. Shows how cheap and advanced this stuff has got. I also see there are IO ports on the thing one could connect and arduino or other such micro computers to if one wanted to actualy monitor the power output or other parameters.

The boards can be found here:

 https://www.ebay.com.au/itm/10-30A-LCD-Display-6-60V-Lithium-Battery-Charge-Protection-NC-Control-Module/163448947271?_trkparms=aid%3D555018%26algo%3DPL.SIM%26ao%3D1%26asc%3D225514%26meid%3D8aa2ead4657a4312a09bf2697a95a78e%26pid%3D100005%26rk%3D5%26rkt%3D12%26mehot%3Dpf%26sd%3D401629656034%26itm%3D163448947271%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv5PairwiseRecallReductionWeb&_trksid=p2047675.c100005.m1851









mikenash

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Re: Direct solar water heating and battery charging.
« Reply #1 on: March 02, 2020, 06:06:53 AM »
Glort I have lots of sunshine up at my "shed" property in the Bay of Plenty

I have the simplest-possible water heater:  My water supply is a spring that fills a tank up on the hill about twenty-five metres in direct elevation from my site - so delivers water at around 2.5 bar.  Off the line coming down from the spring I have a 20mm "alkathene" offtake and the alkathene pipe is wound in a flat spiral onto a piece of 8mm thick black plastic sheeting about 1400mm X 1600mm and it's stood up on an angle to catch the sunshine for all the world like a ground-mount solar panel.  Total cost $100 for 50 metres of black plastic pipe and the other stuff all scrap

The other end is attached to the hot tap of one of my showers inside.

When the sun shines the water in the pipe gets extra hot extra fast - hot-enough that you have to mix it with cold water to be able to shower in it.  It gives a long enough shower to have a good scrub-up, wash your hair (beard in my case) and stand around thinking "I'm clean but I don't want to get out yet cos the hot water is absolutely free . . ."

However, it, obviously has no storage capacity whatsoever.  Sunshine = hot water.  Overcast = none

I often think that if I was willing to use electricity to pump, I could select a suitable quantity of water to fill a big "solar panel" array, some plumbing and a big "hot water cylinder" of some kind - and just pump it in circles (thermostat/solenoid valve control yadda yadda) and watch it get hotter and hotter.  Take hot water off the top to use as whatever, and displace it with cold in the bottom.  Just as with any other HWC

Although you perhaps think of your extra watts as "electrical energy", they're really just the end result of extra solar energy.  You could put solar water panels in the places now occupied by some of the PVs (or elsewhere) and use some of the surplus electricity to pump it around in circles into some storage vessel - possibly "the bigger the better"

LowGear

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Re: Direct solar water heating and battery charging.
« Reply #2 on: March 02, 2020, 05:03:19 PM »
Wow glort.  That's some workup.  Pretty nice.  I'm beginning to think about direct PV hookups without any electronics myself. 

It started a couple of months ago when a friend told me about hooking one panel directly to a 12 volt battery that powers a small water pump to keep his distributed stock tanks full using a float switch on each tank.  It works for him - throughout the night as well.

I like the coiled black line for limited hot water applications like the work shower out on the garage.  My current understanding is that rather than collect energy directly to water that hooking PV panels to your grid - public or private - allows the energy to be collected when your hot water storage is at "Hot Enough" and more heat is not needed and lifting the temperature up an additional degree is quite inefficient.

Cheers,
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SunnyBoy 6000 + SolarWorld 245

glort

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Re: Direct solar water heating and battery charging.
« Reply #3 on: March 03, 2020, 01:41:28 AM »
I'm beginning to think about direct PV hookups without any electronics myself. 

Not sure if you mean without a Commercial controller/ inverter or nothing at all but if it's the latter, I'd say have some sort of electronics is absoloutley essential if you are going to get decent output effeciency from the panels and make your batteries if any were involved last a decent life.

Quote
It started a couple of months ago when a friend told me about hooking one panel directly to a 12 volt battery that powers a small water pump to keep his distributed stock tanks full using a float switch on each tank.  It works for him - throughout the night as well.

If you friend has no charge controller  which will stop the battery being over drained as well as over charged, his battery will have a very short life. It will be virtually boiled throughout the day and potential over discharged through the night.  It's all but gauranteed to be one or the other or both.  It will certainly work for a time, no two ways about that but It will work for maybe months instead of the years the battery would last otherwise.

I have a couple of radiator fans running of a couple of smashed panels on mmy shed roof. They sit in the window and blow air into the shed  which offly enough seems to keep it cooler than the outside temps.  Maybe because it's shaded but it certainly stops it becoming the over it would otherwise.  These are direct connected, just as they would be to a battery.  Even that is inefficient to a point.  I have them wired in parallel which poses a greater load to the panels and drags them well off power point. In this case I use it to my advantage.

The panels are around 37V open and 30.5 at max PPT. The fans are only 12V. This helps regulate the voltage which is what I want in this case.  When there is bright intense sun on a hot day, the things literally scream. That's OK, want all the air flow I can get. at other times they are self regulating. Cooler day, less intense solar radiation, the things are blowing much more gently and that's all that is needed.

I was playing with another set of fans and panels yesterday using them to dry the washing on a dryer rack my wife put out for some things she wanted done on their own. It was later in the afternoon and the fans weren't doing much. I measured the voltage and the panels were being dragged down to about 9V, way off their efficiency point.  I just re wired them so they were in series and the thing came alive.  By doing that, I halved the resistance and the things were now getting 27.4V, spot on a tad over 13.5 Each.
That made a BIG difference to how fast they ran and how much air they blew.

Being the panels are paralleled and don't have a max voltage much higher than that, it's safe for bright days as well. I will put them back the other way though because they are a lot quieter under driven than running flat our and as I usually have them just to move the air under the metal roof of the verandah which they do well, having them not run flat out is better.

I'm thinking to do some vids based on the solar topic and I think this would be a really good demonstration of the importance of keeping panels in their happy place as I call it. 


Quote
I like the coiled black line for limited hot water applications like the work shower out on the garage.  My current understanding is that rather than collect energy directly to water that hooking PV panels to your grid - public or private - allows the energy to be collected when your hot water storage is at "Hot Enough" and more heat is not needed and lifting the temperature up an additional degree is quite inefficient.

Cheers,

It is well known and well demonstrated although some are adamant one way or the other than Direct PV and electrical PV water heating are for all intents and purposes just effective as each other. Some people say that evacuated tubes leave electrical heating for dead but there are just no tests to prove that unless the electric system is not correctly set up such in the case of being directly wired.

It really comes down to the amount of area and the solar radiation falling on them.  Both are about as inefficient as each other.

 I completely agree with what you are saying with the utilisation of the energy when the water is hot enough.
A few years ago a friend of mine whom is very into environmental things spent a good amount of money on  evacuated tubes and set up a water heater.  To my surprise he only had it about 3 years and took it down and upgraded his PV system.  When I asked why he said it grated his nerves too much when he was home to see the thing venting steam at 10am  in the morning and doing so all day with all the energy and an amount of water going to waste.  He said he ran the numbers and by the time he ran the circulation pump  when it was heating and with all the losses ( he's a scientist so takes EVERYTHING into account ) of the pipe work etc, PV was better because that power could be used for other things he was running and using in the house and at very least, going back into the grid and earning him some money to reduce his bill rather than do nothing.

Not that long ago, even just 5 years back, everyone said do direct heating because it was cheaper with the price of panels being what they were then.  Now with them being so cheap and for things like this a ready supply of used panels available, it is not only much cheaper, more efficient but a Lot easier and more reliable to use PV.  Far easier and cheaper to run a wire than a pipe, nothing to leak, easier to hide for aesthetic appearances and about as close to perfectly reliable and maintence free as one can get.

And, when the water is hot, the system can be used for running everything else in the home.

A lot of homes here have plenty of roof space for more panels but simply aren't allowed to install them for a grid connected system and if they are, they have to meet the ever changing and increasingly BS standards designed to keep the industry going and the power co profits becoming greater every year. Even if one does put up panels that are redundant by midday having done their job only heating water, they are still saving money and getting an infinitely better return on their investment than what would be returned with the significant expense of Direct water heating.

There may also be other things that the left over power can be used for, heating or cooling the house, cooking, running some appliances and so it goes.  Quite a lot of things WILL run on DC as well as AC. It would depend on the setup and the power it was designed for as to what could be run or done with it but either way, If one spends $200 and has at least 80% of their hot water needs covered for virtual eternity and that's all that investment covers, it's a damn good investment.
Take into account the money it saves them buying power AND that an amount of the power from their grid system which is now freed from it's biggest single load, the fed back power would also earn them money offsetting that cost further. T hat's money real well spent.

Right now I'm trying to calculate the most effective amount of panels to put on such a system.  Water heating can be done over  the course of the useful daylight hours.  Thats a big range right there.  Here, in summer you have something like 12 hours of useful daylight where the PV generates worthwhile if not full power, in winter, 6 is pretty much the limit and that's probably being generous. One therefore needs to have enough power coming from the array to heat their daily ( or 3 day averaged) needs in that time... depending again on the size of their heater tank.

The average heater tank here in oz is around 250L. In US measurements, that's about 250 Litres.  :0)
A 30oC temp rise with 2KW will take about 4.5 Hours.  That's about where you would want to be here. To get that full 2 KW for that much of the day, I'd be suggesting 4 KW of panels would be what one wanted.
In summer of course, you have MUCH longer sunlight times and much stronger sunlight so it is entirely possible that by 10 am your water will be up to temp and the panels will be done for the day and sitting there roasting.
That's just the nature of the beast unfortunately.  If you reduce the size of the array much you would be having some cool showers in winter\ so it is a trade off.

Having more panels is always a good thing though.
I was just making a Cuppa and went out to feed the cats and checked on a couple of my inverters on the house.  This time yesterday I was making 9Kw between the 2 Being a lovely cool, heavily overcast day today, I'm making a whopping 1KW. 1/9th the amount I was doing yesterday. And that is another thing you have to contend with. 

Even if one does get a string of bad weather and a direct PV water heating system comes up short for a period of time, you can set it up to be powered from the grid.  Only regulations on what solar you connect to the grid, nothing saying you can't connect water heaters as one would presumably already be on a grid connected home.
You might pay more than you would with off peak those days or that week but at the end of the year, your water heating costs will be a fraction of what they were before, you power consumption from having more available to run your home will be down and your FIT will be up.  Win, win, win.

The only wrong thing one could do in this situation IMHO is to install batteries.  No matter which way you slice the numbers, Honestly rather than fudge them, batteries will NOT save money over their costs and lifetime.  I can't see they ever will.
Most effective way to save money on power is simply not buy it in the first place and where possible, send back all you can to get some credits on that which you must buy.  Even if that is at night, still more cost effective to buy it than buy batteries.

And if you have made it this far Casey, Congratulations on the HUGE improvement in your reading abilities and getting through not one but two Novels!

veggie

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Re: Direct solar water heating and battery charging.
« Reply #4 on: March 04, 2020, 05:23:35 PM »
This is my method of using PV to heat water.
It is a very small system with a 1500 watt, 120 volt AC element. Could be scaled up to a larger system I suppose.
Self modulating, and pushes power to the heating element only when the sun is shining and the grid tie inverter is making adequate power.
Arduino controller and AC wattage sensor from eBay.
It eliminates the need to control DC power with relays.
« Last Edit: March 04, 2020, 05:26:21 PM by veggie »
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glort

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Re: Direct solar water heating and battery charging.
« Reply #5 on: March 04, 2020, 09:38:17 PM »

That's a similar way to I have mine.
I use a Voltage sensitive Relay that Bruce here put me onto which monitors the voltage levels in the mains wiring.  When the solar is running at a decent power level, the voltage goes up and the relay kicks in powering the heater.  The relay switches another more powerful relay which can handle the 3600W heater element but that's rarely run flat out. I have a 4KW PWM controller on it so I can run the thing from about 10W to max output.

Sunny days I turn it up and the water is heated quickly, cloudy days I turn it down and let the thing heat more gradually. I did this initially to reduce the over voltage in my system but Now they have dropped the tap in the street and the voltage has come down and I had a real HD circuit put in, no longer a problem although I did notice an inverter tripped it's breaker a couple of times the other day which was curious.

A similar stand alone setup to yours could be done with an inverter, battery and PWM controller but that seems very clunky and bulky.
A guy I talk to on another electronics forum designed me a circuit and is having the boards made for it.  Only has 15 Components plus the cap bank and will handle any input and element size.  Will be very compact and easy to build and install.

A similar system could easily be made with an arduino and that was something I was looking at yesterday.  Just need a voltage Divider to monitor the HV coming from the panels and send a pin high to drive an SSR when the pre set voltage level is reached. Run one of those little voltage converters off a cap with a diode off the solar input. could also have a temp probe monitoring things so as to shut it all down when the tank was up to temp or fire another pin to divert the power else where.

I'm not very skilled at all on arduino so I'll have to find snippets of code and hash them together to make it work but I'm sure for the knowledgeable this would be a complete no brainer.

I found some different pre made boards yesterday, there are so many that can be adapted and I still want to do something with these to prove the idea to myself. The designed board won't be any more efficient but it will be more straightforward.
The idea we had was to be able to direct couple the panels to the heater as a stand alone so it could be used independently of a power source or off grid. Panels do need control for this.

Last couple of days here it has been overcast and I have run a line in the office from a panel outside and been testing things with it. I have a digital volt meter on it and it's interesting to see the behaviour.  In the mornings the thing ramps up very quickly, You can see the voltage meter changing all the time and it probably goes from no voltage to full voltage in 5 Min.  They pretty much sit at the open circuit voltage all the time despite the current levels and only change when a load pulls them down.  In the evenings they go from full voltage to nothing again in about 5 Min.   There is no half way with them voltage wise when they are doing more than a few hundred Ma.

It's also interesting to see how easily they can be pulled down under load. I have a USB converter hooked to the panel and in the overcast conditions, 2 Phones connected to the USB board to charge can pull the 190W panel right off it's power curve.  Shading which is what cloud effectively is, sure plays havoc with output that's for sure!

I also noticed that with cloud the output is very flat over the main part of the day. There is not much power to be had under these conditions but it's pretty obvious one could get a simple PWM controller, set it in the morning and it would have the panels very close to their power point for the majority of the day.  Sunlight I think will be more variable but still using a Fixed PWM rate would leave direct connection to a load from the panels for dead in the total output one could derive.

Got to set up a small array, a power meter and connect a PWM to an element and prove this but I'm very confident.  :0)

glort

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Re: Direct solar water heating and battery charging.
« Reply #6 on: March 08, 2020, 08:05:40 AM »

Today while impatiently waiting for my Boards to arrive  From Corona land,,,,errr, I mean China,  I decided to do a rough and crude test of my theroy that even regular and constant Pulsing through a cap bank would allow more power to be put into a heater system than a direct connect even if Ohm Matched. 

I made up my capacitor bank of 4x 1000uF , 350V Caps in parallel and used an arduino as a pulse timer wired direct to a DC SSR.
I set up 4x250W panels flat on some crates and wired them in parallel. Each panel has an open circuit voltage of 38v and  Vmp of 30 but for some reason the open circuit voltage was only 126. Might be a dud panel in the mix. They are all 8.XX amp@ Vmp
The water heater is 50L and has a 240V single phase 3.6 Kw element. The water temp was about 21 oC to start with.

I ran the panels through an analogue Amp meter with a shunt and measured the voltage on the panel side. The day was nicely overcast varying from mid range to looking like it was about to storm any second with about an hour of erratic sunlight. A good day for testing.

The Arduino  was first set up to run at .300th of a second on and off. This gave a wildly swinging amperage of around 6 Indicated and a voltage also swinging of somewhere around 100. Direct connecting the panels by shorting out the SSR gave a lowly 49V @ about 1.5A. Not enough to heat a water Bootle basically.

I let this run for about 90 min and to my surprise, got a water temp of .30oC which was much more than I expected and worked out at around 400W input.

I then loaded up a little Nano at twice the speed and let that run about another 2.5 hours over the darker weather over all but with the bit of half sunlight.  This made the amp reading ( still swinging all over) of about 4A but brought the volts up a bit.  During the sunny period the amps came up a little, maybe to 5 but the voltage was showing up to 12X regularly.

The caps not the SSR got any detectable warmth and I ran the arduinos off one of those single 18650 portable usb power pack things. I think they draw like 30-60 MA and the SSR is about the same.

Before packing up I tested the water again and even more to my surprise got a reading of 42oC .  Pretty impressive given the weather. I noticed my inverters were doing about 1/4 their clear weather output for this time of year before the heavier cloud rolled over.
Also before packing up due to the look of an impending storm, I noticed the average voltage had pulled down to about 80 ( still flickering) and the amps looked back down to about 4.

I shorted out the SSR again to see what straight Direct would yield and barely got 1 amp @ a lousy 22V.
Proof positive of the HUGE inefficiency of dragging panels off their power point and the gains to be had but arbitrarily pulsing through a cap bank to keep them closer to Vmp. 

Tomorrow is forecast to be a similar day so I'll experiment further with on and off times. I'm thinking of shortening the On time down to one 50 Thousandth of a second and leaving the on time for the caps to charge at 150 thousandths. Being the resistance of the element is constant, once the ideal drain time can be established, that just leaves the Charge time which will be the variable.  That said, if the element can be belted 5 times a second with a conservative 500W input, it will tally up a lot higher than a full second at 70W.

This is of course the worst case scenario.  When I get the  boards I have ordered and set them up, they will be fully self adjusting. The open circuit voltage for the array will just have to be set and the board will automagically adjust to the incoming power levels. Same thing could of course be set up in arduino. Forgotten  how small those little Nano boards are but they are plenty big enough in computing power for this simple job.

I really thing this is bit of a breakthrough in solar water heating. It just makes SO much different over Ohm matching or direct connection and one can use the cheap Mains power elements rather than the far more exy 24/48V types.


veggie

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Re: Direct solar water heating and battery charging.
« Reply #7 on: March 08, 2020, 03:02:30 PM »

Interesting experiment.
My understanding of what you are doing is limited.
Does your assembly do a better job of using power when the panels are not in the sweet spot?
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glort

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Re: Direct solar water heating and battery charging.
« Reply #8 on: March 13, 2020, 07:06:40 AM »

Sorry Veg, Missed your reply.

The setup I have done KEEPS the panels in their sweet spot under all conditions.  Even when the sun is low, instead of the laod pulling the output to nothing, it is able to utilise all the power that is available at the time.

I'm expecting some Boards  From China and the Prototype Hopefully on Monday.

I am thinking of seeing if there is any interest in the things and if so looking at doing a Limited batch run and offering them for sale.
These differ from anything else I have seen out there in that they are independent  of the grid and don't need batteries.
You hook the panels to the thing and it sends all the power be it 2 panels or 2o to the heater and you get a VERY high efficiency of the power the panels are developing.
If the Array is developing 500W in the morning, you are going to get about 497W of that in your heater. If it's developing 2KW at mid day, that's what it will run at and if you are getting 20W after sunset, 19.5 will be going to heat the water.

It can't make what's not there but it can use whatever is there Very effectively and keep the panels doing WAY more than they would direct connected.

Next step is to see if there are more people than just me interested in this or I'm the only nutter who could be bothered.

dax021

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Re: Direct solar water heating and battery charging.
« Reply #9 on: March 13, 2020, 07:29:52 AM »
I would be very interested, if the price is right.  Our Rand is not doing so well at the moment, so $1 US costs us about R17.  I would like to run a fan or two in my kitchen.  When the sun shines the fan must run.

glort

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Re: Direct solar water heating and battery charging.
« Reply #10 on: March 13, 2020, 07:43:20 AM »

I was thinking of motors but these are a different thing to a plain old resistance element.
There are also different types of motor. I believe a universal motor would be ok, A single phase motor with a starting cap would probly not work well and a 3 phase would be OK but you would probably need another controller.

I have some old fans up the back, I'll test it when I get a chance.

Depending on the application where you want the fans and asthetics, I have that setup already.
I have an old panel  driving car radiator fans.  Sun shines and the fans run in proportion. Works very well with twin fans wired in parallel to pull down the voltage of the panel. I also have a single fan blowing down onto my solar inverters to keep them cool. Harder the inverters work the harder the fan blows. again, very convenient.  Does tend to drive the fan a bit hard in bright sunshine so I have a 12V 100W Bulb on one which is just a resistor and stops the fan being over driven and on the other I have a small 40V, 5A Pwm controller. About $2 from Fleabay.  This is adjustable to any speed I want but not proportional, not that I need it.

I put one of these twin fans in the kitchen window when Doing renos to Suck the dust out which it did magnificently.  hardly got any dust in any other rooms because I Opened windows in them, Cracked the doors slightly so there was Negative air pressure in the Kitchen and all the outside air was being sucked through the other rooms stopping the dust going back in.

You could always pull the motor and fan blade off the radiator shroud and mount it on an old pedestal or make your own up and make it steam punk style.  With the PWM controller, instead of the normal 3 speeds you could have it 300 speeds.  :0)

dax021

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Re: Direct solar water heating and battery charging.
« Reply #11 on: March 13, 2020, 04:38:07 PM »
Was thinking of using 4 or 6 12V computer fans, wired in series or parallel depending on the panel, when I find an old one at the right price.  Would build them into a plywood bow mounted in the apex of the pitched roof.

glort

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Re: Direct solar water heating and battery charging.
« Reply #12 on: March 13, 2020, 05:42:09 PM »

You would be a heck of a lot better off using one Radiator Fan.
They can move an amazing amount of air and with the little PWM controller  you could turn them down as much as you liked or have them running hard as you wanted.  Pretty cheap to buy from wrecking yards.

veggie

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Re: Direct solar water heating and battery charging.
« Reply #13 on: March 13, 2020, 10:36:53 PM »
Hi Glort
How do you determine the best wattage rating for the heating element? Or does it not matter with your system?
- 6/1 GM90 Listeroid - Delco 33si Alternator
- Changfa R175 - Lease/Neville Alternator
- Kubota Z482 - 4kw
- JiangDong R165 Air cooled - 2 kw

glort

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Re: Direct solar water heating and battery charging.
« Reply #14 on: March 13, 2020, 11:45:42 PM »

The wattage does not matter.  It is important to match the voltage of the panels though to keep them in their maximum efficiency band.
10% either way does not matter and you can get a bit more on the high end as that self maxes out anyway.

If you have say 8 190W panels that have a Voc of about 30V and an open circuit voltage of about 38 v ( Most that size are in this range, some are different)  you set the voltage band on the board with 2 resistors, one high, one for the low end. The little power converter on the board makes things pretty easy to just use the upper value voltage as the nearest resistor value.

 In this case the voltage would be 304v Open so you would use a 270K Resistor ( being the nearest common value and a voltage under the panels max for that series array) which would trigger the circuit to dump around 270V.  It's not precise however but VERY close.  Panels are not going to be precise, the tolerance in the electronics like resistors are not precise, there could be cabling losses and resistance etc.  In any case It's going to be well and truly close enough with minimal losses.
The 270V does not matter if the element is 220-240V because the voltage will only be at that level for a split second and then it will fall. Also  it's the watts coming in that really matter and as 8x190 panels would only be 1.6 KW and a standard element ( here at least ) is 3.6, you are still not going to bother it in the slightest.  You could drive a 240V element at 400V in this scenario and it still won't care because it's not getting overheated internally. It's not the voltage you have to watch it's the watts.

For the bottom end, You would calculate about 10% Under  max power point of the panels which would be around 240V -24 = 216V so a 220K resistor to give around 220V bottom end.  More than close enough.   With this you have a 50V power band so as you can see, the values aren't critical, you just want to stop the array being dragged to to about 120V where it would be direct connection and maybe making 20% of it's power.

In that band in good sun, the thing may pulse at 40-70 hz and when the sun gets much lower it may be down to 5 Hz.  It doesn't matter, what ever the panels have to give the controller will keep them at their max efficiency just like a grid ties does and put whatever power is produced into the element. .

Now if you want to run say 12 Panels in series for around 450V, that would be about the upper limit as designed but if you wanted to go higher, all you have to do is make sure the capacitors you are using are 600V types.  By the same token, if you want to use 4 panels, You work out the open circuit voltage and the VMp,  install the appropriate resistor values and that's it.  Doesn't matter how many panels ( up to the voltage limit of the caps)  doesn't matter what size, doesn't matter what size element or it you want to run 2 arrays in parallel.
I don't even think it would matter if you ran odd size arrays.

I have been modelling on 4x1000Uf caps but there is no reason why 1 Cap could not be used or 10. Will just make it cycle faster or slower and that's something I'm going to test as well as with a much bigger cap bank.  I expect the outcome of my tests to make no difference what so ever.There are a few things not taken into account like the ESR of the caps but  unless they started getting very warm which is highly unlikely because if they were cycling that quick the circuit would probably be locked on and the switching speed of the Mosfet would probably be the limit anyway. 

The cap is only there to present a Light load to the panels and save that power till they reach the high end of the voltage band and then dump that power into the element.  At the same time, the panels are also connected to the element while they stay in the set voltage  margin.  If you have a perfect setup with enough panels, bright midday sunshine etc, The circuit may will stay on and not pulse at all because it will detect the cap is holding at the required voltage and that's  just what the controller is there for.  An hour later when the sun has fallen off and the array drops out of power point, then the pulsing will begin again to keep the panels from being dragged down and putting all the power they have to give into the element. 

Pulsing might sound funny as one may think the time is being lost between the pulses but it's not because the energy is being stored then dumped back in. The caps are always connected to the panels so whatever power they are doing is always saved and used.  They just dump their power very quickly and then the element is turned off till they recharge again so the panels are kept in their happy place not effectively crushed under the load and struggling. 

The board is NOT designed around the cheapest components but it IS over designed to have a VERY long life and to be simple as possible. For that you have to pay a little extra but for the money the board will cost and  the savings it will make, basing it on average bills of people I know and have been able to ask, I would say the repayment time was 3-6 Months depending on when it was installed.   Every little diverted or battery based stand alone system I have would take years and looking at the components even from pictures, I reckon the things would be a risk to even recover their cost in savings.

The mosfets could be substituted for some cheaper ones but it's a case of literally saving 5 bux for something that is likely to have a limited life or something that is under driven and by design, rated to last 100 years in its operating parameters.
It is early days yet, haven't even practically tested the things as built but even the rough tests I did with other boards show how extremely effective the concept alone is over any form of direct connection even ohm matching.  The problem with that is you have tuned the system for the best part of a clear day only. The ramp up, ramp down and a cloudy day or even passing cloudy and you would be lucky to get 10% efficiency.