Ampster
Renewable Energy Hobbyist
The Modeules he is talking about are not LiFePO4 and are just modules of 74P6S without a BMS so putting them in series and using a 12S BMS is simple.
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Seeking Advice from the Pros
- Thread starter Colton
- Start date
Colton
New Member
Ideally Reno, but I can travel to get the panels if needed. (Just cost-benefit of paying a little more to have them local or shipped to me)
Ampster
Renewable Energy Hobbyist
It is an issue because you need a separate BMS for each series group. The reason is that each module has 74 cells in parallel and there is no way to separate the Modules. He also needs a BMS for 12S and one that can handle the different voltage of that chemistry.
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400bird
Solar Wizard
There are plenty of BMS options, Overkill resells and rebrands a halfway decent BMS and this kit includes a breakout board/adapter for the Tesla modules. You might call them to discuss options on putting two in series.
Tesla BMS kit – Plug-and-Play Retrofit Kit – Overkill Solar
overkillsolar.com
Ok, I don't have any experience sourcing panels out there. Search for a CED Greentec, they are nation wide. They won't hold your hand, but they should be able to provide a price list for the panels they have in stock.
I was thinking these were distinct batteries that just needed a BMS to finish them off.
400bird
Solar Wizard
Not 14s
I'm pretty sure each Tesla pack is 6s, hence the need for an inverter with lower voltage range than the standard 48v battery range.
Ampster
Renewable Energy Hobbyist
You are correct. Those modules are 74P6S. I corrected my post.
Colton
New Member
Ampster
Renewable Energy Hobbyist
I am a big fan of the Orion JR2 BMS because it uses a Hall Effect current sensor and a contactor. It's heritage is EV conversions so there are options for that environment that make it more complicated than the typical BMS which came out of the e bike and golf cart sector.
Colton
New Member
Reno
Ampster
Renewable Energy Hobbyist
They are modules of 74P6S and access to the groups of 74P cells is not easy.
So graduate level DIY? Given the chemistry and how you describe it, that would be outside my comfort zone and I've been known to really dig into things.
Ampster
Renewable Energy Hobbyist
Just not run of the mill DIY. One of the biggest mistakes I have seen is not understanding that with that chemistry and configuration the voltages are not like many other Lithium packs. The cells peak voltage is 4.15 which means for six cell groups that is maximum of 24.9 volts per module or 49.8 volts max per battery. Low voltage of 3.5 volts per cell means 42 volts for LVD and some inverters do not go that low.
JK14
New Member
One problem with your panels is there is a lack of data on the info sheet on Amazon. The first Amazon reviewer points this out as well and suggests it is intentional to hide the true power of the panel.
Monocrystalline panels have a rather consistent 17-19 watts per sq/ft and Renogy's flex panels are 16.1 W/SqFt. I get your calculation of 16 Vmp divided into 250W = 15.6A but that would mean ~40 W/SqFt for these small panels and would be impossible at std test conditions. Guessing an Imp of 6-7A would mean 16-18 W/SqFt and total watts per panel of 96-112.
Like @MisterSandals said - the Voc range also does not make sense. It should be one number tested at std conditions. My guess is that 19.2V is the "real" one at STC and 36V is a made up number imagining really cold conditions which in theory could calculate to 250W with a current of 7A. Maybe they include it to reduce lawsuits?
But now I have made 2 guesses about the actual panel stats and that makes planning really hard. If Voc is actually 19.2, you can put 6 in series = 115V *1.25 for lower temps/higher irradiance = 144V and you should be OK for the charge controller max of 160V. But if Voc is 36, 6 in series will damage the SCC.
Same problem with actual amps, is it 6 or 15? Not knowing the real numbers makes it hard to plan wiring and fusing.
Monocrystalline panels have a rather consistent 17-19 watts per sq/ft and Renogy's flex panels are 16.1 W/SqFt. I get your calculation of 16 Vmp divided into 250W = 15.6A but that would mean ~40 W/SqFt for these small panels and would be impossible at std test conditions. Guessing an Imp of 6-7A would mean 16-18 W/SqFt and total watts per panel of 96-112.
Like @MisterSandals said - the Voc range also does not make sense. It should be one number tested at std conditions. My guess is that 19.2V is the "real" one at STC and 36V is a made up number imagining really cold conditions which in theory could calculate to 250W with a current of 7A. Maybe they include it to reduce lawsuits?
But now I have made 2 guesses about the actual panel stats and that makes planning really hard. If Voc is actually 19.2, you can put 6 in series = 115V *1.25 for lower temps/higher irradiance = 144V and you should be OK for the charge controller max of 160V. But if Voc is 36, 6 in series will damage the SCC.
Same problem with actual amps, is it 6 or 15? Not knowing the real numbers makes it hard to plan wiring and fusing.
Colton
New Member
Thanks JK14.
Would it be worth testing these panels and trying to figure out the “average” volts/amps or is that too risky and I should buy some like in the last Amazon link I sent?
Would it be worth testing these panels and trying to figure out the “average” volts/amps or is that too risky and I should buy some like in the last Amazon link I sent?
MisterSandals
Participation Medalist
The average is meaningless when it comes to making sure your array does not exceed the voltage limits of your SCC (which usually results in releasing the magic smoke).
Same for amps; you need to wire and fuse for the highest expected amps (or wire for the lower of highest expected and fuse rating).
I did a quick search and Reno has nowhere near the number of panels available on craigslist as it does in Sacramento.
That whole Stockton, Tracy and Livermore area is quite prolific with solar installations and extra panels.
Are your rigid panel concerns mostly about weight? My thought is that if you are trying to stay cool with solar in Tracy, you will always be wanting more solar. So if it were me, i would try to find panels that maximized space on top with the biggest and fewest panels possible. Having a bit for carryout is a good idea too, especially if you park in the shade.
Colton
New Member
Yeah biggest concern is weight. I’ve already initiated the return on these panels I have.
Looking at some locally to replace them. I agree with what you said about maximizing space, just a game of finding panels with dimensions that will fit my space right.
I’m considering these 400w Tesla panels from Santan…just concerned about freight times.
Looking at some locally to replace them. I agree with what you said about maximizing space, just a game of finding panels with dimensions that will fit my space right.
I’m considering these 400w Tesla panels from Santan…just concerned about freight times.
Hedges
I See Electromagnetic Fields!
- Joined
- Mar 28, 2020
- Messages
- 21,021
Weight varies. Make a table of panel models and score by W/lb. metric.
Measure your roof, and figure out what size panels would tile it most effectively.
Trailer in the shade is good to stay cooler, but panels need to be in sun as Sandals said. Portable panels may be the best way to go. Then you need to worry about them growing wings or legs.
Measure your roof, and figure out what size panels would tile it most effectively.
Trailer in the shade is good to stay cooler, but panels need to be in sun as Sandals said. Portable panels may be the best way to go. Then you need to worry about them growing wings or legs.
MisterSandals
Participation Medalist
<deleted rehash of what Hedges just wrote>
Either way, run the panel specs by us here for a sanity check.
Do you have an SCC in mind? I think you will need a reliable/quality SCC to survive a summer in the valley. Your SCC selection may affect your panels options, and vice versa.
Colton
New Member
I put links to all my equipment in the first post, including the SCC. Does that or anything else look insufficient assuming I find a decent solar panel replacement?
