My Panels specification Amps ??

Paulp · Member

My Panels specification Amps ??

Mike Harding · Guru

I am just about to buy two very similar panels for use with a Victron 100/30 controller.

I suggest you rewire the panels to be in series rather than parallel, your controller is quite capable of handling the 90V the panel will produce and you will be able to use lighter wire (or have less voltage drop with heavier wire).

Your are correct: in parallel 36.74V at 5.17A (x 2 = 10.34A) under standard test conditions. In reality you will rarely see the full output power from them, as a rule of thumb I knock off 20% from the panel rating so I'd rate your two panels at about 150W each in decent (need a hat) sun. Whether they are suitable for your use depends entirely upon how much power you use per day in your van. I have calculated that 360W will be sufficient to run a domestic inverter fridge/freezer in my caravan in Victoria for most of the year, July/August will need support from a generator.

Edit:

Keep in mind your MPPT controller will turn that panel energy into, roughly, 12V at 30A in perfect conditions.

-- Edited by Mike Harding on Sunday 8th of August 2021 07:59:10 AM

Whenarewethere · Guru

As said above.

I have the Victron 100/20, it's a great bit of kit. Wire the panels in series. You will only get maximum power when the sun is square on to the panels & on a summer day. You could tilt the caravan square to the sun during the day & rotate it a bit every hour!

If the sun is only up at 20° there is not much power. Sketch it out on the back of an envelope the percentage width compared to the sun square on, to see the reality of fixed horizontal solar panels, & when they are clean.

Also not to forget that a tiny little shadow on one panel can bring down the whole setup. Either a tree or self shadowing.

Brenda and Alan · Guru

Mike wiring those panels in series would require the services of a qualified electrician and hence expensive. Best to wire in parallel and the very small loss in cabling would be negligible. I think from memory 75V is the max allowed before "experts" are required.

Alan

Aus-Kiwi · Guru

Wired completely in parallel has twice the wire . Yes very little VD !! I would just fit more panels if you can anyway !! Sometimes we get all carried away in theory etc . Easier to test panels also .

Mike Harding · Guru

Brenda and Alan wrote:
Mike wiring those panels in series would require the services of a qualified electrician and hence expensive. Best to wire in parallel and the very small loss in cabling would be negligible. I think from memory 75V is the max allowed before "experts" are required.

Extra Low Voltage is up to 50V AC and 120V for ripple free DC.

Wikipedia

Firewize

Peter_n_Margaret · Guru

Paulp wrote:
I have 2 of these (House) panels in parallel with a Victron 100/20 am I correct in saying although
they 36 V they will only produce aprox 10.3amps in perfect conditions and if that is the case then are these not ideal on the Caravan ??

Their Maximum Power Point rating is 10.3A at 36V. That is 30A at 12V. That is what the MPPT controller does. Your controller may be a bit small at 20A, but they are fine for van use with the right controller.

Cheers,

Peter

kgarnett · Senior Member

Total Watts under ideal conditions = 2x190 = 380W.
380W @ 36.74V = 10.34A and 380W @ 13V = 29.2A

You must use an MPPT solar controller for these panels series or parallel because the panel voltage is too high for use with a PWM controller for a 12V battery.

Ken

-- Edited by kgarnett on Sunday 8th of August 2021 06:04:46 PM

Are We Lost · Guru

I would wire in parallel.

Technically, in perfect conditions, wiring in serial is a better solution, but as Whenarewethere noted, a small shadow on just one panel will kill much of the output. If they are in parallel, and one panel starts to get shaded, the other in full sun will still be performing well. So often there are trees around, so overall, parallel will give better performance.

Paulp · Member

Peter_n_Margaret wrote:
Paulp wrote:
I have 2 of these (House) panels in parallel with a Victron 100/20 am I correct in saying although
they 36 V they will only produce aprox 10.3amps in perfect conditions and if that is the case then are these not ideal on the Caravan ??
Their Maximum Power Point rating is 10.3A at 36V. That is 30A at 12V. That is what the MPPT controller does. Your controller may be a bit small at 20A, but they are fine for van use with the right controller.
Cheers,
Peter

Peter trying to get my head around all of this so this means that i am not restricted what panel spec says 10.3 amps for the 2 Panels

But its the controller that can get 20amps under Ideal voltage ?

Paul

Peter_n_Margaret · Guru

The panels are rated at a nominal 190W. That is their theoretical output under test conditions. That is what they will each deliver to the controller.
The MPPT (Maximum Power Point) controller will convert that input power (Watts) to a voltage that is suitable for charging the batteries. The amps supplied to the batteries will vary according to that voltage. Amps X Volts = Watts. The Watts stays the same. The Watts is the real measure of the panels output.

The controller does the magic conversion using whatever it is given.
BUT the controller can only charge the battery at a maximum 20A, even if there was more power available. That is a limitation of the controller you have.
Hope that helps?
Cheers,
Peter

Jaahn · Guru

kgarnett wrote:
Total Watts under ideal conditions = 2x190 = 380W.
380W @ 36.74V = 10.34A and 380W @ 13V = 29.2A

You must use an MPPT solar controller for these panels series or parallel because the panel voltage is too high for use with a PWM controller for a 12V battery.

Ken-- Edited by kgarnett on Sunday 8th of August 2021 06:04:46 PM
________________________________________________________________________________________________________________________

Hi Paul smile

A MPPT regulator will take the high voltage solar output 36.7V and low amps 10.3A and 'convert' that into the lower battery voltage required which is between 12-14.4 volts and while doing that conversion, step up the amps to between 26-31 amps. Now these are theory numbers and you will get less power flat on a caravan roof. But your 20A Victron is a bit small and will limit the current to 20A to protect itself.

In my opinion forget the series connection, just wire in parallel with heavy wires.

Jaahn

PS I never believe that running anything at its max power rating is good practice and will give a long life. EG running a regulator that is self protecting itself on a regular basis. People may have more faith in it than myself but in my career i always allowed a bit extra and that has been good for me over the years. aww

-- Edited by Jaahn on Monday 9th of August 2021 07:06:15 AM

Whenarewethere · Guru

As the the battery gets charged the MPPT adjusts the voltage to have maximum amps. As voltage goes up amps come down. When the battery reaches absorption & float things change.

But the 100/20 will not output more than 20 amps. 20 amps is it.

Let's say the sun is up at 45° so you will only have about 71% efficiency on a perfect day. So 380 watts x 0.71 = 270 watts.

Your battery is a bit flat & the MPPT is outputting 13 volts, so it will be provide 20.7 amps. Less a little bit for inefficiencies & more wastage if you haven't calculated wire resistance correctly. So a whisker over the 20 amp limit. In theory 0.7 amp in the bin.

With the sun higher than 45°, let's say 60°, the panels will produce more wattage, 380 watts x 0.86 = 326 watts, so /13 volts = 25 amps but the MPPT will reach its 20 amp limit. So 5 amps in the bin.

As the battery gets charged at around 14.4 volts at 326 watts, 60° sun, there would be 22.6 amps, so 2.6 amps in the bin because of the MPPT 20 amp limit.

Whenarewethere · Guru

Jaahn wrote:
PS I never believe that running anything at its max power rating is good practice and will give a long life. EG running a regulator that is self protecting itself on a regular basis. People may have more faith in it than myself but in my career i always allowed a bit extra and that has been good for me over the years.

I originally bought the Victron 75/10 as the nominal PV power was 145 watts & my panels were 120 watts. So within the recommended limit.

My 6 x 20 watt panels' output amps is most of the time up to 7.8 amps (3.9 amps in series) but I noticed a reasonable amount of the time the MPPT output was at its 10 amps maximum.

Like Jaahn, I do not like things running near their limit. Also not good with high ambient temperatures. Additionally I was interest how much power I was missing out on.

So I bought a Victron 100/20 & found on a perfect day & cool panels I was getting up to 137 watts but usually around 125 - 127 watts.

But at 137 watts & a battery in bulk it was sucking up every last amp. Occasionally up to 11.3 amps. But usually at 125 watts the MPPT output is about 9.8 amps in bulk.

The manual for the 100/20 charging a 12 volt battery states a Nominal PV power of 290 watts. 24 volt battery 580 watts. Whether a 12v or 24v battery the MPPT output is 20 amps maximum.

So at 380 watts charging a 12 volt battery it's a lot over the capacity of the 100/20 under perfect conditions. If I increased my 120 watts to 380 watts I could get up to 35.7 amps & probably cook the controller as it only has a 20 amp output.

If you are in Tasmania you will be ok, but in Northern Australia in the middle of the day in theory based off my setup figure you could have a pretty big overload. Probably good to switch off one panel or get a larger controller so you don't have to think. In the meantime use the Victron app & keep an eye on amps under various conditions.

Paulp · Member

I went purposely went to buy Victron 100/30 but solar shop (North Brisbane) in my area said the Victron 100/20 is sufficient that will not cause a issue

I told them all specs as above

Paul

Whenarewethere · Guru

Paulp wrote:

I went purposely went to buy Victron 100/30 but solar shop (North Brisbane) in my area said the Victron 100/20 is sufficient that will not cause a issue

I told them all specs as above

Paul

I am sure they know what they are talking about.

Here is a bit of information on my setup:

https://thegreynomads.activeboard.com/t65231112/custom-6x20-watts-solar-setup-with-mppt/