Watts needed

[cliffy49]

I have read where folks suggest any where from 1 to 2 watts of solar per ah of battery. My question, is this based on battery rating (ie 215 AH) or is it based on useable amp hours(105)?

All replys are greatly appreciated.

[BFL13]

I blame it all on the Watts! They hide what is really going on with Volts and Amps. When it says Watts or Power, beware! 🙂

[Huntindog]

BFL13 wrote:
Just from being flat you would lose more than 6 watts out of 720. Then add heat loss.

Heat loss might be a bit less with panels flat (not sun direct) so pretend you lose 5% instead of 10% 5% of 720 is 36 watts. Say 5% from being flat in June in Arizona for another 36 watts. panel output now 720 - 72 = 648w.

If panels were 720 out and wiring loss is 2%, 2% of 720 is 14.4 watts. It just doesn't work out right.

That 714 must be from something else. Whatever, your set-up is working. Not so sure about the readings for what is measuring what though.

The way I see it, if your method of figuring is correct, there is only one explanation. The Aims panels are putting out more than their specs. Remember that they were more than the Jaboni controller could handle, even though they were just under it's specs. That would explain both issues.

[BFL13]

Just from being flat you would lose more than 6 watts out of 720. Then add heat loss.

Heat loss might be a bit less with panels flat (not sun direct) so pretend you lose 5% instead of 10% 5% of 720 is 36 watts. Say 5% from being flat in June in Arizona for another 36 watts. panel output now 720 - 72 = 648w.

If panels were 720 out and wiring loss is 2%, 2% of 720 is 14.4 watts. It just doesn't work out right.

That 714 must be from something else. Whatever, your set-up is working. Not so sure about the readings for what is measuring what though.

[Huntindog]

Huntindog wrote:

BFL13 wrote:
Almost there? The Victron showed 923w output? But that has only 720w of panels.I guess I typed it wrong. The 923 was the total of both systems according to the Victron shunt

Where was that 714 watts at?The Victron controller

Controller output goes to load and remainder to battery. Any load is included in the controllers' output.

Can we get the output of the Victron only and compare that with the 720? I don't believe it can be 714 out of 720. No way. That is what it said. I took a screenshot of the screen.
One possibility is that the Aims panels are exceeding their specs. That could explain why they were too much for the Jaboni controller

See the voltage loss co-efficient per degree of C temp above 25C on your panel specs. Usually panel is about 20-25C above 25c ambient (50C when ambient is 25C is worth about a 10% loss in watts due to lower voltage--amps stay up despite the heat-even go a bit higher)

You are losing me here.... I am not so sure that the Aims specs are accurate at this point.

[Huntindog]

DP

[BFL13]

Almost there? The Victron showed 923w output? But that has only 720w of panels.

Where was that 714 watts at?

Controller output goes to load and remainder to battery. Any load is included in the controllers' output.

Can we get the output of the Victron only and compare that with the 720? I don't believe it can be 714 out of 720. No way.

See the voltage loss co-efficient per degree of C temp above 25C on your panel specs. Usually panel is about 20-25C above 25c ambient (50C when ambient is 25C is worth about a 10% loss in watts due to lower voltage--amps stay up despite the heat-even go a bit higher)

[Huntindog]

BFL13 wrote:
Thanks for the additional info. I am really confused as you will see, but moving right along---

Before starting you had a load of say 33 watts. WAG battery at 12.5v, so load was 2.6 amps.The shunt also reads amps, and that is about right.

Now you enabled solar and got 923 watts at the shunt. Battery voltage spiked from now being charged so WAG 13.5v? So 923/13.5 = 68.3 amps of which 2.6 was load.The shunt will go negative with the amps, and it will calculate how long the batteries will last at the present rate of discharge.

I am not clear whether you should add the -33 load to the 923 or if the 33 is part of the 923 the way that is displayed. the negative 33 is the draw with no solar output. As solar comes on line, it climbs to zero and turns positive, So the negative reading needs to be added to the positive to get the output from the solar. Need help there. The 33 was at 12.5 batt, but the 923 was at 13.5? If that even matters--not sure!The victron showed 923 watts, and 67.79 amps @13.61 volts

I am lost on what shows as total controllers' output and what shows at the shunt. Normally, the shunt shows what the battery is getting, not what the loads are getting. Part of what to do with that 33 watts.

The 714w is output from the Victron controller? so is part load, but with two solar sets, how much of the 33 is in the 714 and how much Jamboni? (If that matters)That is an interesting question that I had not thought of.... I guess both systems probably contribute to erasing the negative,,, but it is such a trivial amount,,, I don't think it matters much.

As you see I am not clear on what you have there! Seems like it cranks out the amps though. You must be pleased it all worked out.

Yes I am pretty happy with it, and already looking towards adding the additional string of 3x 120 watt panels to the victron, for a total system of 1380 watts... Then I am done. Just gotta replenish some funds first.

[BFL13]

Thanks for the additional info. I am really confused as you will see, but moving right along---

Before starting you had a load of say 33 watts. WAG battery at 12.5v, so load was 2.6 amps.

Now you enabled solar and got 923 watts at the shunt. Battery voltage spiked from now being charged so WAG 13.5v? So 923/13.5 = 68.3 amps of which 2.6 was load.

I am not clear whether you should add the -33 load to the 923 or if the 33 is part of the 923 the way that is displayed. Need help there. The 33 was at 12.5 batt, but the 923 was at 13.5? If that even matters--not sure!

I am lost on what shows as total controllers' output and what shows at the shunt. Normally, the shunt shows what the battery is getting, not what the loads are getting. Part of what to do with that 33 watts.

The 714w is output from the Victron controller? so is part load, but with two solar sets, how much of the 33 is in the 714 and how much Jamboni? (If that matters)

As you see I am not clear on what you have there! Seems like it cranks out the amps though. You must be pleased it all worked out.

[Huntindog]

BFL13 wrote:
The solar controller usually has a display showing output amps and battery voltage. Some also have input info.

Is this one of those smart shunt, bluetooth deals? If from the shunt then that would be amps to the battery after any loads are taken care of, but I don't know how those work exactly. Might help to explain the set-up and a link to the Victron where you are getting the readings so we are talking the same language.

It takes about two minutes or so for the panels to heat right up when first put in the sun. Could your Pmax reading have been when they were first exposed to the sun?

I doubt that 99% efficiency for 24-12. Perhaps for 12-12 or 24-24. Are there efficiency curves for your controller? Ones I have seen show lower efficiency -mid 90s- the bigger the voltage diff between in and out for the buck converter in the controller.

I have the 250/100 ve can model, I also have the smart bluetooth shunt.https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-250-70-up...

Both the shunt and the controller transmit data to my phone. You may remember that I also have the factory Jaboni system. So the shunt shows what is being supplied by both systems, and the victron controller app shows what is happening with the Victron/AIMS 120 watt panels only.
When I got the 714 watt reading, the total of both systems read 923 watts, and it was negative 31-35 before enabling the solar. That means that the total solar system was putting out over 950 watts.... The total of both systems panels is 1020 watts. They are all flat mounted, It was around noon and I am in Phoenix AZ, so it was hot already before the panels were enabled... (I have a breaker box with breakers for both systems.

[BFL13]

The solar controller usually has a display showing output amps and battery voltage. Some also have input info.

Is this one of those smart shunt, bluetooth deals? If from the shunt then that would be amps to the battery after any loads are taken care of, but I don't know how those work exactly. Might help to explain the set-up and a link to the Victron where you are getting the readings so we are talking the same language.

It takes about two minutes or so for the panels to heat right up when first put in the sun. Could your Pmax reading have been when they were first exposed to the sun?

I doubt that 99% efficiency for 24-12. Perhaps for 12-12 or 24-24. Are there efficiency curves for your controller? Ones I have seen show lower efficiency -mid 90s- the bigger the voltage diff between in and out for the buck converter in the controller.

[Huntindog]

BFL13 wrote:
Those Victron terms don't mean anything to me, such as Pmax. Please use volts and amps and where you measured those.

The easiest measurement is output watts, where the controller will have a reading of battery voltage and the solar amps output (not to be confused with amps to the battery!!!) Multiply those to get your output watts.

Pick a number for your controller's efficiency--say 97% --then now you have your approx input watts. Compare that with your panel watts rating.

If you do that with the panel aimed at high sun your input watts should be less than panel rating by about 10% for panel heating and another 2% or whatever for wiring loss.

If panels flat, then you can get a rough idea of the loss there from your latitude and the day of the year.

P max is the panels maximum watts that the controller saw. The efficency is over 99%, according to the specs.

I have no way to measure the solar amp output.

[BFL13]

He was thinking panel amps output instead of controller output. He did not see that he was doing 24 panel to 12 battery.

[StirCrazy]

cliffy49 wrote:

StirCrazy wrote:
I would run them in series on a MPPT controler if you can. the beausty of the MPPT is the conversion to a lower "charging voltage and that nothing is lost except for the efficency. also running in series means higher voltage lower amprage which lets you run a smaller wire with less line loss than you would get with a lower voltage, but higher amprage, on the same wire size. of course like PT and others have mentioned you have to be aware of the effects of shading so you have to place your panels a little smarter. another side benifit of running in series is the morning and evening charging will start sooner and finish laiter and you will get a higher amprage during that time than you would in parralel as you have a higher voltage hiting the controler.

the panels you referenced you could easy run two in series on that, but if it was for myself I would go with at least a 40 amp MPPT
controler.

Steve

You are at least the second person to say that I should use a 40 MPPT controller. To be honest, I can not understand why a 40 and not a 20. At the bery best, this panel is only going to be putting out a little over 8 amps if wired in series and 17 if wired in parallel.

Can you please explaiin to me what I am missing in all of this. I apologize for the questions but my solar knowledge is zero and I am trying to learn.

because if you decide to get more panels you dont have to buy a whole new controler. once you are set up it is cheep as heck to add more panels, expensive to throw away a controler to buy a bigger one. and if you go a bit bigger at the time of purchase it is only a little more. then if you decide to add panels later all you have to do is splice them in.

Steve

[BFL13]

Those Victron terms don't mean anything to me, such as Pmax. Please use volts and amps and where you measured those.

The easiest measurement is output watts, where the controller will have a reading of battery voltage and the solar amps output (not to be confused with amps to the battery!!!) Multiply those to get your output watts.

Pick a number for your controller's efficiency--say 97% --then now you have your approx input watts. Compare that with your panel watts rating.

If you do that with the panel aimed at high sun your input watts should be less than panel rating by about 10% for panel heating and another 2% or whatever for wiring loss.

If panels flat, then you can get a rough idea of the loss there from your latitude and the day of the year.