Recommendations for SCC setup using 10x100W panels

[Bryant Tonkin]

Hi there people of the interwebs,

I need some guidance. I'm in the process of building out a camper van and I'm becoming overwhelmed with the electrical system options. My main challenge at this point is deciding on a BMS and SCC options. I was originally planning to go with one or two mppt controllers but, since I'm tempted to go with the SBMS0 as my BMS anyway, I'm wondering if there's any advantage to using dssr20s instead. The cost savings would only be ~$150 but there would also be less to go wrong. Here's what I know. 

1. I'm using 10 x 100W 64 cell panels (https://hqsolarpower.com/content/HQST-100D-SSP-Spec.pdf) because they fit perfectly on my van roof.
2. I've ordered 8 x 280Ah Lifepo4 batteries and I'm probably going with a 24v system voltage
3. Not as relavent for this conversation but worth mentioning- I'm shooting for an inverter between 2k-3k but can't decide if I want it to be part of an invert/charger unit or maybe an all-in-one like the Growatt 3000. 

I'm happy to hear any suggestions but here are the two questions I'm focused on. 

1. What are you thoughts on using the dssr20s vs mppt controllers for my 10 panels? What series/parallel configurations would you suggest?
2. If I go with mppt controllers I need some way to cut charging for low temp or over voltage conditions. It looks like the dss20 isn't quite up to the task for my solar capacity so can anyone recommend a bigger SSR or another option that can be controlled by the SBMS0?

Thanks for your suggestions. 

Bryant

[Demosthien]

Try checking out the posts about my setup for some info that might be of use...

https://groups.google.com/d/msg/electrodacus/tZghzAOf0lY/pUQWgdPYAQAJ

[Dacian Todea]

Bryant,

1. Those are 32 cell panels just made of cut cells so is like two 50W panels in parallel.

If you go for a 24V battery then you can use groups of two of this panels in series that way is equivalent with 64 cells in series tho 60 cell panels will be a much better fit if this panels just work better on your roof then difference is not that large.

3x 100W panels will have larger surface area 1.78m2 vs a single 60 cell panel rated at 300+ Watt that will be around 1.65m2

Also a 300+ Watt 60 cell panel will put around 11A in to the 24V battery while you need about 4x 100W panels to do the same using the DSSR20.

One DSSR20 can handle 6x 100W panels connected as groups of two in series and then 3 groups of those in parallel and I expect that from this 6 panels you will see around 18 to 19A in to the 24V battery while with 2x 60 cell panels you should see around 22A in to battery using the DSSR20

3. For all in one inverter charger you are limited to Victron multiplus 3000VA as the Growatt will not work with Lithium. It can work as an inverter only but you can not use the charger.

You can use as many DSSR20 as you like up to 48 so up to 30kW PV array is possible. 

[Bryant Tonkin]

Thank you both for your input. 

Dacian,

I agree that 300+ Watt panels would be preferred but it seems all of the high watt panels I can find are too large to fit on my van roof without sticking over the edge. 

It's awesome that for about $50 USD I can control all of my solar with two dssr20s and the SBMS0 that I will be purchasing anyway. I'm also thinking about having a tiny water heater in the van and the dssr20 with diversion could work nicely for sending any excess solar into that. 

For what it's worth, my understanding is that the Growatt and MPP units can be programmed with custom voltages to allow the charger to work with Lifepo4 batteries but there's no way to disable the charging in the event of a low temp or over voltage event. Is that was you were referring to as far as not being able to use the charger?

[Dacian Todea]

The 60 cell panels are usually all made with 6" cells mounted as 6x10 or there may be half cut cells so 120 half cells but taking the same area thus those panels are always around 1m wide x 1.65m long.

Assuming 10x 100W panels that are 0.904m x 0.657m are connected as 2x 5 so will take 1.314m with and will be 4.52m long then you should maybe be able to have 3x 60 cell panels that will take just 1m width and 4.95cm in length and the 3 panels should perform similarly with the 10x 100W panels.

The total battery voltage limit is completely useless for Lithium thus why a BMS that reads each cell is needed. So the fact that you can set battery voltage limits will not help in any way protect the LiFePO4.  The BMS is the one that needs to be able to stop the charging from any source and Victron implemented that properly and even have a document explaining how that needs to be setup https://www.victronenergy.com/upload/documents/Manual-Connecting-other-lithium-battery-systems-to-Multis-and-Quattros-EN.pdf

The Growatt is a copy of MPP solar so nothing different and I have the MPPT solar but I use that just as an inverter as I'm fully offgrid that works great as I only need to turn OFF the inverter when any cell is below 2.8V

Below you can see how LiFePO4 voltage varies with state of charge and at both ends the voltage will increase or drop super fast thus there will always be a cell to charge or discharge first thus you can have one all 8 cells close to 100% but one of them just a fraction more charge maybe because of slight internal resistance and or capacity variation thus maybe they will all be around 3.4V and then in a few seconds one of the cells being full will get above 3.55V 

Same at discharge 7 cells may be at 3V almost fully discharged and then one cell will drop very fast but 7x 3V = 21V so if you where to set that as the low limit then one of the cells can be 0V and even if you set 23V that is way to high for a low limit one cell can still be below 2V so still bad just a BMS can properly terminate the charge when any cell is below 2.8V and has nothing to do with total battery voltage.  

[Bryant Tonkin]

Unfortunately, I have a fan and an awning on my van roof that limit the width and length that I can fit without sticking over the edge of the roof. I'm limited to about 60" (1.524m) wide x 80" (2.032m) long at the front, and about 60" wide x 56" long at the back. It just happens that the 100w compact panels I found are 40" x 20" so I can fit two next to the fan and 9 more between the front and back. I'd much prefer to go with larger panels but I just haven't found any that fit as well. 

I see what you're saying about the Growatt/MPP units and the cell voltages. I really wish someone could figure out a way to hack in a remote on/off for the AC-DC charger and the mppt charger of the all-in-one units. The Victron Multiplus and Samlex Evo are both options but I have a hard time spending that much money on an inverter/charger that still needs to be told when to stop charging. 

Thanks for all of your time. 

[Dacian Todea]

Bryant,

Not sure at what panels your refer to as the 100W ones you linked are 25.9" wide so you can not fit 3 of them on 60" only two are possible and likely that can also not fit on each side of the fan.

If you found some narrower panels they may not be 100W. I guess those narrower panels will be made with 3 rows of 6" cells (cut cells) for maybe a total of 33 cells.

The inverter is used in reverse when grid charging is needed so is only one physical device while the MPPT is a separate device and you may find a simple way to hack a remote ON/OFF to that.

[Casey & Gina]

Hi Bryant,

Why are you worried about a little overhang?  I thought like you at first - I was going to use a mix of 4x 60-cell and 4x 36-cell panels to optimize roof space, but am glad I ended up going with 6x 60-cell panels on my trailer roof.  The center two overhang the sides by a few inches (my trailer is a 7'x16') - it really doesn't make any difference - the fenders on the trailer are significantly wider anyways..  Roof vent in the center.  Each panel is 64.57 x 39.06 inches.