solar advice needed please

[baileyboy]

i have a victron 75/15 solar controller
and the standard 100watt panel on roof
what size of panel can i add to this setup without changing the controller
thanks

 

[scallywag15]

i have a victron 75/15 solar controller
and the standard 100watt panel on roof
what size of panel can i add to this setup without changing the controller
thanks

i have same setup..i think probably another 100.

 

[lorger]

I have the same controller with 180 watt panel if that helps.

 

[mitzimad]

220 wats is the limit

 

[PlacidoD]

This is at the extreme edge of my knowledge from reading (and the answers you have above may be all you need to know for now) but I think I am right in saying that if e.g. you had 300 watt of solar panels much of the time they would produce less than 220 watts output (angle of sun and cloud etc) and when producing 300 watts the additional 80 watts would just go to waste rather than do any harm. If I am wrong someone please do correct me!!

I have two solar controllers - one came with the van and handles the 200 watts that I have on the roof. Off Grid added a 2nd controller for me when a fitting 300 Ah LiFePo4 battery and inverter. The 2nd controller handles a freestanding 160 watt EcoFlow panel with a roving cable. The idea is to face East overnight, mount the panel on the windscreen and harvest early morning sun while breakfasting and showering etc. and/or follow the sun round moving the panel during the day if I am remaining with the van. The 2nd controller has some spare capacity. So should I manage to squeeze a final 100 watts onto the roof real estate. I can feed it via that 2nd controller.

 

[baileyboy]

thanks for the replys guys

 

[TheMobileWanderer]

...and when producing 300 watts the additional 80 watts would just go to waste rather than do any harm. If I am wrong someone please do correct me!!

Some people have their system set up such that when the batteries are full, the excess goes to power something like a water heater.

 

[CAB96]

You also need to match the panel output voltage to the original panel so as not to waste any solar.

Victron apparently have a useful solar calculator, presumably on their website?

 

[pat100]

Connecting them in series keeps the amps that they pass the same as for a single panel so you don’t need to update the wiring if it’s a bit skinny. The controller needs to handle about 50V with them in series.

 

[herald_400rl]

MPPT Calculator - Victron Energy

MPPT Calculator - Victron Energy

www.victronenergy.com

You need to make sure input voltage limits aren't exceeded.

 

[Lenny HB]

Best to wire the panels in parallel on a Motorhome roof and it makes wiring very easy.

The 75/15 max is 220 watts but you can go a bit above that as you will rarely see max output from the panels.

Idealy the output voltage under load should match on both panels I like to keep them within ½v for good efficiency.

 

[Steve Stallion]

i have same setup..i think probably another 100.

I have 180 watts rigid panels on the roof wired in series giving about 40 volts. This goes into my 75/15 Victron controller. I’ve had 150 watts or thereabouts and 12.5 amps. I would say you should be ok to add a 100 watt panel. Be aware though that in bright sunlight especially when cooler you could get 200 watts which would be about the limit of the controller.

 

[baileyboy]

it sounds like i should have bought a larger controller

 

[TheMobileWanderer]

it sounds like i should have bought a larger controller

Well, google AI provided this.
(I know; in my experience, it's the worst for hallucination).

Controller Limits

• • Voltage limit (75V): The controller accepts up to 75 volts on its input from the solar panels (open-circuit voltage, or Voc), which is well above the typical ~20V to 25V of a single 100W panel.
  • Amperage limit (15A): The controller can output up to 15 amps to your battery. A 100W panel on a 12V system only produces around 5.5 to 6 amps, which is safely below the 15A maximum limit.

Performance Notes

• • Oversized capacity: A 75/15 controller can handle up to 220W of solar panels on a 12V battery system (or 440W on a 24V system).
  • Room to expand: Because a 100W panel uses less than half of the controller's capacity, you can easily add a second 100W panel later without needing to buy a new controller.

hth

 

[Jon Stuart]

Some people have their system set up such that when the batteries are full, the excess goes to power something like a water heater.

Offgrid Power Solutions do a lovely solar dump to the fridge when your battery is fully charged.

 

[autorouter]

Ideally if you are adding a second panel, get one that is the same as the existing one. Then wire it in parallel, to the controller. Connect panels positive to positive, then to the controller positive. Then connect panels negative to negative, then to the controller negative.

If you do that, the voltages and amps values will match, and the two panels will both give out their maximum power.

If you can't get an identical panel, you have to look at the panel specs to make sure they match. 100W panels are all much the same, so they would very likely match OK. The important figure is the voltage at maximum power, Vmp. If the Vmp of both panels is about the same, within a volt or so, then that's fine.

If you can't get at the label on the back of the existing panel to see the spec list, you could count the number of cells on the front of the panel. The voltage depends mostly on the number of cells, so if both panels have the same number of cells then they will probably match OK.

Most 100W solar panels are 36 cells, arranged as 4 x 9.