Question on pv array size vs mppt

I am putting a solar system on my TT. I have purchased 4 of Rich Solar 200w panels (from amazon) and 1 Victron SmartSolar 100/50 mppt charge controller. I know the charge controller is slightly undersized for this, but my rational was:

1) I doubt I'll get full power from the panels most of the time anyhow
2) When I have partial shade or otherwise imperfect sun I will appreciate getting more power (vs 3 panels say)
3) I understand the Victron will simply limit the input to 700w (from the docs)

I like the form factor of the 100/50 controller for my installation vs. the 150/60 or whatever the 'right' sized controller is. Its simply a lot larger.

My question is, am I asking for trouble if the PV regularly produces more power than the MPPT is rated for (again, the victron docs state it will limit the input power of the PV, but I'm not sure this is a good long term practice). Will the unit run hotter or or fail faster if it is regularly running at the limit? I don't really mind throwing away some power during mid-day as these will more than charge my batteries, but are there other negative consequences ?

I just got the panels today, tested them and they were producing 45v @4.6 amps - mostly full sun. This was with no load but simply calculating those two values would be 207w each... I was expecting they would come in under 200. (BTW: The amazon page claims these are 24v * 9.8a, which the clearly are not, but I'm okay with it).

Bob

Hello!.

MPPT can work with some overwattage, how much it depens on the product, but i heard figures about 120 - 150%.... maybe someone can correct me if im wrong or add specific data for your model. If the unit works most of the time at 100%, ill probably run a little hotter compared with another that haves some overhead, and maybe last less.... but nevertheless being Victron it shouldn't be a problem on the long run.

- Its usual practice to oversize the PV array for cloudy days and have more available power during the initial / final hours of the day. The controllers just clip the excess power, wich is wasted, but better for overall production.
- Panels can overproduce in cold days with good sun, their ratings are usually at 25c.

Just watch the VOC and make your calculations for your absolute coldest day, it should never exceed the specs of your charger.

mrdavvv said:

Hello!.

MPPT can work with some overwattage, how much it depens on the product, but i heard figures about 120 - 150%.... maybe someone can correct me if im wrong or add specific data for your model. If the unit works most of the time at 100%, ill probably run a little hotter compared with another with another that haves some overhead, and maybe last less.... but nevertheless being Victron it shouldn't be a problem on the long run.

- Its usual practice to oversize the PV array for cloudy days and have more available power during the initial / final hours of the day. The controllers just clip the excess power, wich is wasted, but better for overall production.
- Panels can overproduce in cold days with good sun, their ratings are usually at 25c.

Just watch the VOC and make your calculations for your absolute coldest day, it should never exceed the specs of your charger.

Click to expand...

Thanks, I plan to put these in parallel so no worries on the voltage (nor the amperage) but the overall power may occasionally be higher than the mppt is rated for (700). Sounds like this will be fine, if not optimal.

I just wish I knew these were going to be 45v & 4.6A when I ordered them, I could have gone with a smaller wire size than 6awg from the combiner box. Oh well I have it now so use it.

A good MPPT controller will simply current limit if it ever hits the amp limit on either its PV input or load (battery) output. Victron, like other quality manufacturers, also specify a max permissible current available on the PV input, the max PV short circuit current. For a 100/50 this is 60 amps. This is likely more about controlling the situation if something goes terribly wrong in the controller rather than protecting the controller in regular operation.

Cheapie controllers may not current limit at all, or may have poor algos that allow them to exceed the absolute rating on their switching transistors, letting the magic smoke out.