MPPT sizing confusion: 2x200W on 100/30?

[rillweed]

Hi all

I have been trying to determine which size victron mppt to get for my system. I am getting 2xRich Solar mega 200W panels. Voc = 24.3V, Isc = 10.2A

Wiring these panels in series, both the faroutride calculator and the explorist.life calculator suggest that I can get away with a 100/30 MPPT. At first glance this seems wrong since 400W/12V=33A, but after some more reading it is because 12V batteries charge at ~14 volts. My epoch 460Ah suggests 13.8-13.9 max charge voltage and 13.4-13.5 float voltage. So, 400W/13.4=29.9A. Is this enough headroom to still use the 100/30 or is there anything else that I am missing?

 

[Suijkerbuijk]

Personal.
I will go for one model higher .
Just so that i have head room if i go for more solarpanels in the future.

Than again its correct 400watt : 14.6v (bulk charge) =27.6A -20% (you never have the max solarwatts)= 22a.

So you can even go for a 100/20 model .

 

[chrisski]

If this is a system used intermittently, it’s fine. If it’s used a lot recommended the 50 amp.

Also, if these are angled into the sun, likely to see close to 400 watts when poured at the sun. I move my ground mount three times a day. This is more important to change to the 50 amp model if used a lot.

If these are flat on a roof like an RV with partial shading through some of the day, I expect to see only 200 watts total or about 15 amps and then a 20 amp controller would be fine.

IME, bit of an art. If you buy the 50 amp version and you find your falling short on amperage production, this lets you add one or two more to increase output.

 

[rillweed]

these panels are going on my van (flat mount). i definitely don't have room for another 200W panel. best case i can fit a wide 100W and two 50W (next to fan) panels but I don't see that being worth the effort right now (you never know for the future though).

 

[rillweed]

does more head room just allow the charger to run more efficiently (less heat)?

 

[Suijkerbuijk]

does more head room just allow the charger to run more efficiently (less heat)?

Yes it have more cooling ribs on the back and its bigger unit.
I have 100/50 model my self .


For the rest you can all Victron mppt combine from all series.
So long its smartsolar model (bluetooth model)
A bluesolar model do not have bluetooth .
So always go for the smartsolar model.

If you do not use a shunt or a victron gx unit.

Go for a battery smart sensor from Victron
This unit connect you on the battery.
If you use more that one battery in parallel or in series.
Set this unit on the busbar that connect all battery together.


This unit tell the mppt controle from Victron .
The real battery volt and the real temperatuur by the battery
This way the mppt wil more efficient and if the battery are to cold it shut down the charge.

 

[GXMnow]

It is very unlikely the panels will ever hit the STC rated power in the real world. My DC array is a total of 2,000 watts of panels. I am using a Victron 150/35 in a 48 volt system. In a full year of operation, it has only hit clipping once. It was a very sunny and cool day, I saw the trend graph flat top at 35 amps for about 20 minutes at solar noon. The battery voltage was at 52 volts x 35 amps = 1,820 watts. You can safely over panel all the Victron units up to the output current rating on the input. I am not even close to that with just 22 amps on the input side.

That being said, it also does not hurt you, other than costing a bit more, to use a larger controller. The unit will run cooler and it may even have a bit less internal resistance. The standby power is so small, I don't think it increases losses with a larger unit. With only 400 watts of panels laying flat, you probably want to be sure you never clip and waste any of the power you can grab. Going up to the 50 amp would give you a ton of headroom. When stopped at a site, you could add another pair of the 200 watt panels on a ground mount and aim them at the sun. That would clip at a bit over 600 watts. If you parallel panels, keep in mind you want the VMP voltages to be very close.

In hindsight, I wish I had gone with the 150-45 over the 150-35 as I am looking at adding a few more panels. But they may end up at a different angle, so a separate MPPT will be better, but more expensive.

 

[rillweed]

ok so sounds like i should be fine with 100/30 BUT if I ever want to add more panels then i'm probably out of luck in series.

 

[chrisski]

ok so sounds like i should be fine with 100/30 BUT if I ever want to add more panels then i'm probably out of luck in series.

I use three Victron MPPTs for my RV. If you decide to add a ground mount, you can just add a second MPPT for the battery. After using it a while you’ll figure out what is right for you.

Yes there is less heat generated on the ones that aren’t maxed out. On my 24 VDC battery, I do max one 100/30 out with 900 watts of panels and I see it produce over 800 watts.

 

[penra]

these panels are going on my van (flat mount). i definitely don't have room for another 200W panel. best case i can fit a wide 100W and two 50W (next to fan) panels but I don't see that being worth the effort right now (you never know for the future though).

Consider portables also for a van, moving them for best collection.

 

[Weekend van]

I remember watching a solar radiation output chart once. On a partly cloudy day there were some pretty impressive spikes. I forget the name of it, but clouds can act as a lens and at the perimeter of the shadow there are spikes in solar energy.
I'll also state that on a clear summer day I have seen over 1100 w/m2 in the same data. That is 10% above STC that the panels are rated at. STC gives a good apples to apples comparison between panels. But that isn't the peak environmental conditions that can exist.

Personally not a fan of running anything electrical at 100% intentionally. There is always things that are overlooked where the simple math failed to take into account the small variables.

 

[sunshine_eggo]

I remember watching a solar radiation output chart once. On a partly cloudy day there were some pretty impressive spikes. I forget the name of it, but clouds can act as a lens and at the perimeter of the shadow there are spikes in solar energy.

Cloud Edge Effect. A prismatic effect at the cloud edge focuses a higher concentration of solar energy. It's typically very short lived. In cold conditions it can seem like longer as the period panels are covered, their temperature drops, and they put out even more power when re-energized.

I'll also state that on a clear summer day I have seen over 1100 w/m2 in the same data. That is 10% above STC that the panels are rated at. STC gives a good apples to apples comparison between panels. But that isn't the peak environmental conditions that can exist.

Yep. I've seen ~3700W out of a 2970W array up around Show Low... 6500', so thinner air and colder conditions. One time it was high enough to trip a marginally sized breaker between the array and the MPPT.

Personally not a fan of running anything electrical at 100% intentionally. There is always things that are overlooked where the simple math failed to take into account the small variables.

Given that the very nature of operation of a MPPT, I have zero concern about 100%.

It's going to be at 0% when it's dark. It's only going to be at/near 100% for a moment during the middle of the day, and even if there is more available than 100%, it's still output limited. Unless MASSIVELY over-paneled, it's unlikely to have more than a 25-30% duty cycle over a 24 hour period.

 

[mikefitz]

been trying to determine which size victron mppt to get for my system. I am getting 2xRich Solar mega 200W panels

Most of the bulk charge period for a 12v lithium battery occurs around 13.6 volts. Only as the battery nears full, will the voltage rise to absorbtion volt, and at this point the current raken by the battery falls. With horizontal mounted panels you won't get full power and the heating effect will reduce power further. You loose about 3% for every 10 degC above 25 deg C. It's not uncommon to lose 10%.
The 100/30 and 100/50 are identical, same size case , same weight. The cost of the 100/50 is 50 % Increase over the 100/30.
Unless you wish to add more panels there is no advantage in using the 100/50. If at some time you add panels , perhaps portable ground mounted, using an additional controller is the best option.