Im planning my own home PV system. Ive got a relatively big gable roof, but sadly not really optimally faced. One side is relatively free of obstacles, both on the roof and nearby, but its facing 60° north-east, the other side is therefore facing 240° south-west but has a lot of obstacles, both on the roof (chimneys, windows, vents) and nearby (a few trees and a neighboring building), theres always some shade going across it throughout the day. So im looking into options on how to use the roof optimally. Currently im thinking about using microinverters on the SW side, and using string inverters on the NE side. I would like to maximize winter production, so im fine with overpaneling or just not producing as much as the panel area could in the summer.
To the actual question: Im having a hard time finding a sweet spot for the RS 450/100. Theres always some hurdle. You got to keep the battery voltage in mind, since theres the Vbatx8 limit, you got to keep the 4kW per tracker limit in mind, while its also limited to 5.8kW in total, you got to keep the Isc of a string under 20A, so you cant just parallel two for most panels, and the string has to hit 120VDC in order to start the tracking.
Meanwhile the 250/100 can charge with the same max 5.8kW, has a 70A Isc limit, Vbat+5V to start tracking and is not bound to a battery voltage factor as the upper limit, just the 250V (245V) max. That is so much easier to work with, to find valid combinations of panel numbers and string configs. I feel like maxing winter production with a 250/100 is just add a string or two more in parallel and bobs your uncle, done. No?
Yes the RS is completely different internally, and it provides actual isolation towards the PV side, and it can handle higher voltage strings which lowers the cable losses, but im just having a hard time justifying that. Im surely not the only one. Have you been in that situation? How did you solve it?
I’d go with this panel type paired with a Tigo optimiser. That setup also gives you the option of array-level shutdown for safety. The 450/100 is limited to 16A, making this panel a great fit. Since it’s a half-cut panel, you’re effectively running two strings in parallel, which helps with shading. Plus, the 450/100 has a shading algorithm (unlike the 250/100). If you’re planning to overpanel an MPPT, I’d pick the isolated 450/100. The cost of a Tigo optimiser vs running heavy high-current cables is probably about the same. I can start my 450/100 with 4x48V Voc panels, no problem.
You should be able to add 20 of these panels, 10 per tracker, the 450/100 can take a massive 7200 W.
I run both. I started with the 450/100 then added the 250/100 later.
Its best to think of the 450/100 as two 450/50s due to the per tracker 4kW limits. And then the 450/200 it can be around three 450/70s, versus 4 450/50s.
The main thing with the 250/100 is that obviously youll need multiple parallel strings to max it out. I use staubli branch connectors and inline mc4 fuses for 5s4p, it can approach 40A so wire appropriately:
Downside is you lose the battery isolation of the rs450 line. But my understanding is the more recent 250/100s have a user resettable relay in case there’s a pv to battery short.
That 18A limit is just the limit of the reverse polarity protection. The manual in fact specifies you can overpanel beyond that with caution.
In January this year with very overcast conditions I connected 10s2p to each of the two trackers on my 450/100 for 15kWp. Worked fine. But with that amount of ovepanelling when the sun comes out from behind the clouds the 450/100 really ramps up its fans to a maximum I wasn’t aware of during non overpanelled edge effect conditions. So to capture that intermittent sunshine I added sufficient scc capacity to cover that, and avoid excessive fan noise.
Some of us choose to not use the RS, apart from it’s bumpy past, when building a system with multiple orientations, and factoring in the probability of a failure, It is just better to use dedicated MPPT’s. Failures in panels are rare. Failures with the gear and the related connectivity is more common. While more expensive, having one MPPT derate, or being able to isolate a single charger due to a fault, is a better approach imo.
I could easily reduce my own 4 charger footprint, (the joys of a Tuscan roof) to one RS. But I would never do it.
And never use optimisers, they aren’t supported for a reason.
I don’t know why you all don’t like the RS series, I work with it exclusively. I prefer the 450/100 model, it’s got a really nice balance of price, quality, and efficiency. I rarely use the 450/200 in my projects, not a fan of putting all my eggs in one basket. By the way, just received the latest revision for a big installation.
