Solar to mineral accretion underwater!

[Solar_Marine]

Hi Guys,

I am brand new to this forum and am really looking for some advice,

Here is the back story; I am a marine biologist working in Fiji, basically I am setting up a mineral accretion system, commonly known as BIOROCK, the idea is you run a low current/voltage to an anode (+) and cathode (-) underwater, cathode in my case being a steel rebar structure (normal for this technique) and I am using an aluminium anode. What happens is the reaction taking place at the cathode promotes coral growth and creates an alkaline environment via OH-, the anode errodes, lost of information about this via the net.

My problem is more to do with my power delivery system, which is why I am posting here....

I am using a 50w solar panel, max amperage at 2.93, max voltage is around 20v. Now i am running around 60m/197ft of 16mm copper cable. Ideally at the structure I want around 1 amp. Now Fiji is nice and sunny so I connected up my panel to the cable first, tested it and I was getting around 19v from the panel through all the cable.

I have connected everything up now to the anodes & cathode and it does seem to be working (the anode is bubbling as it should and looks like it is corroding) GREAT! BUT, the cathode is not doing anything after 3 days, I should be seeing something.

Now it is all connected when I test the voltage at the panel in full sun I get around 1.5v, am I right in thinking the anode/cathode 'load' coupled with distance travelled is causing this huge drop....? If i am getting 1.5v at the panel does that mean 197ft away is seeing very little voltage or is 1.5v the whole system?

I haven't tested the Amps in full sun but did it in cloudy conditions today at the panel and was only 0.06 on a 20m setting on my multimeter!!!!

Can someone please confirm my huge drop in amperage and volts is due to the distance and the anode/cathode causing load (they are a load correct?)?

I am a but stuck of what to do next basically, should I get another panel, should I move the panel closer to the structures (very tough), should I buy a battery to be cooer to the structures (easier).......

I really hope somebody can shed light on the problems I am experiencing from the PV point of view,

Any help would be greatly appreciated,

Thanks,
Luke

[myfriendSUN]

I have connected everything up now to the anodes & cathode and it does seem to be working (the anode is bubbling as it should and looks like it is corroding) GREAT! BUT, the cathode is not doing anything after 3 days, I should be seeing something.
What's the voltage output of the panel at the beginning, 19V ???

Now it is all connected when I test the voltage at the panel in full sun I get around 1.5v, am I right in thinking the anode/cathode 'load' coupled with distance travelled is causing this huge drop....? If i am getting 1.5v at the panel does that mean 197ft away is seeing very little voltage or is 1.5v the whole system?
It would be either one of the following cases:
1) Your panel only output 1.5V. Disconnect the load and check panel voltage output (open circuit output).
2) The resistance of load changed after 3 days. It's a very low resistance now and it draws down the voltage and the current should be high, not 0.06 mA!!!
Is it possible that the anode and the cathode were short circuited???
The panel cannot handle the load.
According to your readings, Panel Power Output = 1.5V x 0.00006A = 0.00009W

[Sunking]

Problem is a Solar Panel is a Current Source and not a Voltage Source like a battery. Salt water is highly conductive, and with your anode and cathode in sea water is shorting out which it should do. If you measure the current, you should something in between Imp (current maximum power) and Isc (current short circuit) depending on angle of the sun and intensity.

The 1.5 volts you are seeing is a result of current flowing through the total resistance of the cable, anode/cathode, and sea water path. If you want to know what that resistance is measure the voltage and current and R = voltage / current.

[Solar_Marine]

Thanks for the responses guys,

myfriendSUN;
the open circuit voltage was around 19v yes, sometimes hitting 20v,

Sunking;
I am not sure i totally understand

So is it possible we have the anode and cathode too close together underwater causing a short circuit which is why the amp reading was what it was?

The ideal voltage I want at the structure is 1.23v

The 1.5v I am getting fluctuates a lot, sometimes 0.6v up to around 2v, this is testing with a multimeter at the panel with everything connected.

[Sunking]

the open circuit voltage was around 19v yes, sometimes hitting 20v,

I believe you but like you said Open Circuit meaning no current flowing through infinite resistance.

I am not sure i totally understand

So is it possible we have the anode and cathode too close together underwater causing a short circuit which is why the amp reading was what it was?

The ideal voltage I want at the structure is 1.23v

The 1.5v I am getting fluctuates a lot, sometimes 0.6v up to around 2v, this is testing with a multimeter at the panel with everything connected.

A Solar Panel is a Current Source, and the current is directly proportional to the amount of solar radiance striking the surface of the panel or sun light intensity. The angle, cloud cover, humidity, time of year, time of day etc all affect the amount of current the panel produces at any given moment in time. It would be a very rare event to ever see a solar panel generated it rated Imp and Isc. In other words you have an unknown source of current. So you have a 50 watt panel and if you look at the specs you should see Vmp = roughly 16 volt, and Imp = roughly 3.125 amps. At 100% solar irradiance of insolation striking the panel will produce 3.125 amps through a resistance of 5.12 Ohms will develop 16 volts and generate 50 watts of power

Voltage = Current x Resistance. What you are seeing is a voltage developed as a result of a unknown amount of current is flowing through a unknown amount of resistance. The resistance is the wire, plus the anode/cathode, plus seawater.

Bottom line is you need a Voltage Source like a battery or generator. Basically you want to make hydrogen and oxygen, and that takes quite a bit of power.

[Solar_Marine]

Suking, again thank you for the reply,

Ok so it makes sense to me, I am not with the panel now so cannot give you the exact figure but is one in that region, I believe the max V was around 1, the max amp 2.95.

Anyway most people that setup the biorock system don't use a battery or any kind of controller, just direct from the panel as this method can work with 1v up to 12v,

1.23v is the most effective voltage though,

Basically I am stumped as to why my aluminium anode is creating oxygen/maybe even chlorine and looks like it is corroding, however my cathode is not doing anything,

The voltage coming out the solar panel fluctuates from 1 - 3v, so to me it should be working/looks like it is working but no CaCo3 yet!

Can I ask which maybe a daft question, if put a multimeter at my solar panel and check the voltage coming directly out, is that the same voltage more or less that is hitting the anode/cathode? (my 1-3v I am recording directly at the panel)

Thanks,

[Solar_Marine]

max voltage 17 (sorry)

[sensij]

Can I ask which maybe a daft question, if put a multimeter at my solar panel and check the voltage coming directly out, is that the same voltage more or less that is hitting the anode/cathode? (my 1-3v I am recording directly at the panel)

Thanks,

Yes, the voltage at the panel should be close to the voltage at the other end of circuit, especially when the current is low. 10 A at 12 V through 197 ft of 16 mm2 wire would show a voltage drop of around 10%.

Really, measuring the current throughout the day is necessary to offer more suggestions as to what might be going on. Do you have the ability to do this?

Edit... actually, what is the wire size? I guessed 16 mm2, but did you really mean 16 mm as you wrote? That is heavy stuff! If it is really 16 mm2, then the voltage at the anode/cathode will be almost nothing after the drop through the wire if the panel is operating at 2 V.

[Solar_Marine]

sensij,

Thanks, yes I will measure it today and report back my findings,

[sensij]

If you aren't familiar with it, here is a characteristic I-V curve for a 50 W panel.

IV.jpg

You can see that if the circuit resistance is low, your current tends towards Isc and your power delivered drops. If the voltage is low and the panel is making Isc, the voltage drop 197 ft away could be significant... in other words, almost all the power is going into heating the wire.

If at mid-day in bright sun you are measuring 2 V at the panels, the current should be close to 7 A. In those conditions, with 16 mm2 wire (5 AWG) there would only be 1.1 V at the anode and cathode, or about 8 W delivered to your Biorock system.

[Solar_Marine]

sensij,

Thank you,

Ok so I have just had it checked again, full sun and 12:17pm here, the readings are not promising
Voltage was 0.6v at the panel
Amps was 0.2-0.3 reading on a 20m setting on a multimeter

I am not an expert at all which is why I am asking here, is this due to a connection or short circuit? Why so low?

A bit more background, once the anode and cathode were connected first and not put in the water to check the voltage it was reading around 18v in full sun, not sure that helps as it seems putting the structures in the water has lowered voltage and amperage drastically,

[Sunking]

Yes, the voltage at the panel should be close to the voltage at the other end of circuit, especially when the current is low. 10 A at 12 V through 197 ft of 16 mm2 wire would show a voltage drop of around 10%.

Sensi I think you are over looking one very important element? What is the load resistance? What if the load resistance is say .1 Ohm with 3 amps flowing = .3 volts right? What would the voltage be if say the resistance was 50 Ohms? The voltage be higher than Vmp but less than Voc and the current much lower than Imp because at that point the panel behaves as a Voltage Source right?

Marine guy the way to make this work is using a 2 volt panel so it behaves like a voltage source. Instead of a panel of 36 cells is series to make a 18 volt (12 volt battery panel) is to use a panel with 3 cells in series (1.5 volts) with X in parallel to equal the current needed to flow through a resistance. There maybe other ways to do this as it is out of the norm, but I am not familiar with the application. The trick is you need a panel to operate between Vmp and Voc so it behaves as a voltage source. Anything from Vmp to Isc behaves like a current source. To pull thi soff you will need a panel with multple times more current than normal operating current to make it behave like a voltage source.

For example let's say the distance between electrodes yields .5 Ohms, and you want 1.5 volts. Current = 1.5 volts / .5 Ohm's = 3 amps. One would think all you need is a 4.5 watts panel but you would be dead wrong. You would want at least a panel of 50 watts with a Imp of 33 amps or more, and a Vmp of 3 volts and Voc of 4 volts.

The only other way I can think of to make a standard 12 volt battery panel to work is to use a Buck DC to DC Converter which steps down the voltage and boost the current to make the panel behave like a Voltage Source. But none exist for this application and would be a custom build specifically for the purpose.

[bcroe]

That setup is extremely inefficient, with very little of the panel power getting to
your load (rods). The wiring run may have too much resistance, and the panel
voltage (16 Vmp) is around 10 times what the load requires. If it meets your
needs that's OK, but you could get perhaps 5 times the load current with an
efficient design. That might matter more when the sun isn't ideal.

First thing I'd do is find out the resistance around your loop of wire. Look it up for
that gauge, multiply by the round trip length. If you get 1/2 ohm, 3A from your panel
will lose 1.5 V of your 16V. You could just make sure the wire is big enough to
deliver say 3A under full sun. 16V minus 1.3V for the rods leaves 14.7V to lose
in the wires. R = V divided by I = 14.7V divided by 3A = 4.9 ohms. If your wire is
more like 10 ohms, you could use heavier wire. OR put another 50W panel in
series. Then 16V X 2 - 1.3V = 30.7V. 30.7V, divided by 10 ohms gives 3.07A

If you want a lot more load current, esp with reduced sun, you could use a
"DC Transformer" next to the load to multiply the output current while dividing the
output voltage. It would still require relatively efficient wiring. The DC Transformer
would take the form of some sort of switching circuit. Switched capacitor (may 6:1)
would work, but perhaps a magnetic switcher would be easier. The simplest & most
efficient could be a buck switcher with about a fixed 5 off to 1 on duty cycle. A
little adjust could get you a little below the panel's Vmp. Don't go over or you will
lose power fast. Bruce Roe

[sensij]

sensij,

Thank you,

Ok so I have just had it checked again, full sun and 12:17pm here, the readings are not promising
Voltage was 0.6v at the panel
Amps was 0.2-0.3 reading on a 20m setting on a multimeter

I am not an expert at all which is why I am asking here, is this due to a connection or short circuit? Why so low?

A bit more background, once the anode and cathode were connected first and not put in the water to check the voltage it was reading around 18v in full sun, not sure that helps as it seems putting the structures in the water has lowered voltage and amperage drastically,

To verify the panel functionality, disconnect it from the Biorock system, short the panel's + and - lead together at the panel, and measure the current.

[sensij]

Sensi I think you are over looking one very important element? What is the load resistance? What if the load resistance is say .1 Ohm with 3 amps flowing = .3 volts right? What would the voltage be if say the resistance was 50 Ohms? The voltage be higher than Vmp but less than Voc and the current much lower than Imp because at that point the panel behaves as a Voltage Source right?

Marine guy the way to make this work is using a 2 volt panel so it behaves like a voltage source. Instead of a panel of 36 cells is series to make a 18 volt (12 volt battery panel) is to use a panel with 3 cells in series (1.5 volts) with X in parallel to equal the current needed to flow through a resistance. There maybe other ways to do this as it is out of the norm, but I am not familiar with the application. The trick is you need a panel to operate between Vmp and Voc so it behaves as a voltage source. Anything from Vmp to Isc behaves like a current source.

Yeah, high voltage and low current I can understand, or low voltage and high current, but not low voltage and low current, which is what is being reported. Agreed that using a 12 V panel for a 1.5 V application without some kind of controller is inefficient, and unlikely to result in a very consistent process.

Edit: Running a 1.5 V source over 200 ft is also kind of a loser. OP says other people run these systems without a controller, but are those system using panels that are located so far away?