question

wolfbarnsolar avatar image
wolfbarnsolar asked

Use Excess Solar to charge a second battery set

Started From Here https://community.victronenergy.com/questions/18866/solar-wattage-so-low-1.html?childToView=18887#answer-18887

So much depends on what sort of systems you have installed.

Ie if you had a victron multiplus or quattro unit then you could export to the grid and thus not waste the power.

but then you maybe off grid

there are lots of options but unless we know what systems you have, its imposable to advise or help

So please advise also please open a new threed and place this in the correct area , Modifications is not the correct area

So hopefully this is

When a system is in float mode & In my case for some 6 hrs + & the Panels can at times actually still be producing over 3000 Watts i need a way to use this WASTED PV power to charge another set of 48V Batts i have maybe via a second Solar Charger ?? No Hot Water Service

OFF GRID

5KW PV in 5 strings 48V Battery Bank, Solar charger 250/100 Multiplus 5000

Solar Panel
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3 Answers
Pat Davitt avatar image
Pat Davitt answered ·

Well, Wolfbarnsolar you have brought up the Holy Grail of off grid solar systems. I live in an off grid solar house and currently do it manually. If the batteries are in float, I look at the weather forecast and look out the window to see what the sun is doing. If everything looks good I manually turn on things like my irrigation pump, do the laundry, etc.

The trick is how to automate this functionality. I have an oversized solar array that can produce more power than is needed for bulk charging the batteries and covering the loads, if the sun conditions are favorable,

I am working on a project, utilizing a solar irradiance sensor to allow me to maximize the use of available solar power. I have a prototype that works but am not ready to activate it for my house.

Hopefully soon,

Pat

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wolfbarnsolar avatar image wolfbarnsolar commented ·

Have you considered a Light receiving Diode circuit powered up when in absorb to control a relay

https://electrosome.com/solar-tracker-system-using-lm358/

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Elimac avatar image
Elimac answered ·

Maybe stupid, I don't know, but will the folloing work ?

- Two different MPPT controllers connected to same PV array and different battery banks

- Controller #1 output relay will be connected to controller #2 remote input. This 2nd controller will be normally OFF unless MPPT1 is in float.

- Programm controller #1 to switch the relay when it becomes in FLOAT state, and from that moment on, controller #2 will use the PV to charge battery #2


Is this nonsense ?

We could even use different voltage batteries with same PV array.

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wolfbarnsolar avatar image wolfbarnsolar commented ·

good thought but believe reading the manual MPPT 250/100 the relay of a controller is open/closed on a Set Voltage Not a state of charge


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2019-05-25-09-24-26-manual.png (68.8 KiB)
wolfbarnsolar avatar image wolfbarnsolar commented ·

RE- Program controller #1 to switch the relay when it becomes in FLOAT state, and from that moment on, controller #2 will use the PV to charge battery #2

Can you advise how you intended to start up the second Controller via input Please

the programming parameters of the units is very different to the MASSIVELY OUTDATED MANUAL

indeed you can activate the relay on Float as an output but i see no inputs and the controller is powered by the battery

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Elimac avatar image Elimac wolfbarnsolar commented ·

Besides the relay output, my current 250/60 also has a two-pin input called "remote". And it has an external shunt by default to keep it in normal working state. I never tried, but I am assuming that if I take the shunt out the controller will be off. So, connecting a relay to this "remote" input should make possible to turn it on or off remotely.

This is just my assumption based on what I read, but if someone knows that this is incorrect, by all means please step in.

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wolfbarnsolar avatar image
wolfbarnsolar answered ·

Hi Pat

I live in an off grid solar self sufficient as possible small farm and currently do it manually to

Holy Grail ! Yes Looking out the window has Many missing Modern day uses good for weather reports also

The trick is how to automate this functionality Would using the grid function not automate this for you.

Just because your not connected may not mean you can not use output to grid feature of an inverter. EXPORT to Appliances"

The solar irradiance sensor is an interesting line of thought I dabbled with Parabolic collector tracking solar energy at one point.

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Pat Davitt avatar image Pat Davitt commented ·

The sensor I am using is an IMT Solar Si-I420TC-T which is a silicone sensor designed to be mounted on the array with the same orientation as the array. This sensor reports the Solar Irradiance in Watts per Meter Squared as well as panel temperature. Link to datasheet is below:

https://www.imt-solar.com/fileadmin/docs/en/products/Si-Sensor_2017_E.pdf

I then use this information to calculate, based on panel specifications, the maximum output the array could produce given the current irradiance and temperature. A tuning constant is used to fine tune the calculation. I then subtract the current PV output in watts from this maximum to obtain the excess PV power available.

Pat

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wolfbarnsolar avatar image wolfbarnsolar Pat Davitt commented ·

Ok So Similar to the one in this Weather Station

https://www.weatherlink.com/bulletin/47e63ffa-0673-4f91-adf5-d962bcdfbab1

Unfortunately the one in the weather station has an INACURATE Calculator & does Not account for Efficency of the Panel. ans at 100 watts a SQMeter its about 30% Acurate

Yours is Hopefully much better & is an interesting project I hope it comes to fruition for you.


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Pat Davitt avatar image Pat Davitt wolfbarnsolar commented ·

Am away from my computer. Will answer in detail tomorrow. But so far am seeing 1 to 2 % accuracy.

Pat

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Pat Davitt avatar image Pat Davitt wolfbarnsolar commented ·

The problem with "Weather Station" information is that it is generalized and as you stated does not know anything about your specific solar array. My system measures this information at my array and the calculations relate directly to the specifications of my array.

I think Victron is headed to supporting standard analog I/O for their GX products, but they aren't there yet. To give you a better understanding of what I am doing, below is a schematic of my system.

Pat

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solar-project-diagram-rev1.jpg (3.2 MiB)
Pat Davitt avatar image Pat Davitt wolfbarnsolar commented ·

Attached is a zipped spreadsheet with my calculation.

Patpowercalc.zip

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powercalc.zip (8.2 KiB)
wolfbarnsolar avatar image wolfbarnsolar Pat Davitt commented ·

Hi Pat

You have gone to a lot of work here congrats on the efforts

hope to get an update when finished

Martin

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