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diy solar

DIY 11kW Bifacial, Rooftop Tiltable, Solis 15kW3ph Hybrid, 28kW LiFePO4

ichiban

New Member
Joined
Jun 14, 2023
Messages
15
Location
Thailand
This is my 1st post here. I am totally new to Solar and attempt to DIY my home solar system :

Now is about 80-90% completed, baby step at a time. It took me a really a long time to do this.

Pls recommend the most appropriate way to go for my DIY solar ESS batteries connection. Most of the parts are on hand while some are on the way.

The design is by myself and have people help to assemble the whole set-ups.

Here, I try to provide parts, sketches, design, pictures, specs info used in this project. So the gurus can clearly see & help answer according to my needs. I also try to upsize the parts re cables, terminal lugs, bus-rods, etc. to minimize current bottleneck & future problems. Most of these parts are from my old stock or bought cheaply for DIY sake. Since DC batteries matter to the m
W and hundred of amps magnitudes, so it needs specific expertise where basic AC electricity familiarity are not all applicable here.

The whole 18PVs will be laid in one big plane all the way on the roof & the extended structure (with H-beam).

Since my roof is -30 slope but the sun perpendicular angles (my PVs) are between -35 to +20 deg, so I will manually adjust the panels accordingly. I arrange 3 PVs in a group, total 6 groups, so there will be 6 adjustment monthly. Adjustment is by cordless wrench, 20-sec per group. Not difficult. I even design/DIY a power stair for this purpose, again, liftable by cordless wrench upto 3.5m height. I bought a cheap stair of 1-m high & mod it with cheap bike parts & construction tie-rod. So, it is a 1-person operating equipment with small footprint when not in use. This liftable stair is not done yet but soon. It will be used for both adjusting the angle of the PVs monthly and clean the PVs as well. Actually, adjusting the PVs' angle do not require any stair, the adjusting mechanic can be accessed with 1 person standing on the ground and can be finished in 5-10 minutes for the whole 18 PVs. But cleaning PVs require power washer & some rubbing at certain spots, so stair is needed for spotless result.
 

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This is on my carport roof in Bangkok. 18PVs * 630w ~11kW, Bi-facial Jinko N-type. I made it tiltable by means of feed screws & push-rod. Most of the structures are HDG / SS304 and etc. for longevity & low maintenance for the year-round hot & very humid weather. If not, repainting/repairing will be needed every few years.
 
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Parts on hands (mostly) :

  1. Car-port roof-top 18PVs * 635-W Jinko, Bi-facial, N-type (18pcs * 635wh ~ 11.43 kwh, roof painted white), monthly adjust solar tracking (tiltable)
  2. Inverter : Solis-S6-EH3P15K02-NV-YD-L 15kW, 3-ph, Hybrid On/Off grid, lo-volt batt
  3. Batt : Pre-assy, rack style, LiFePO4 from Luyuan, Seplos V3 BMS (2-amp active balance) in each batt box. 2-pc * 51.2V / 280Ah ea. Will connect them in parallel to get 51.2V / 560Ah (Tot ~28kWh). These 2 batts should be par with home usage for the next few years. In case EV is coming in the future, more batteries can be added.
 

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4. Batt rack, industrial 4-storey heavy gauge steel, powder coated, 400-kg/storey : Totally enclosed with T3-mm PC sheet (on all sides) & aluminum frames for doors. Vent fans or not is TBD (good idea to have to prevent condensation & heat dissipation). The 4-storey are for 4 batts, one on each, and I have only 2 batts now for the 2 bottom shelves. This batt rack will be in my carport, only roof cover with PVs on the top, no walls. We do not have cold weather but lots of rain, so this is a typical parking space for us.
 

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5. Bus-rods : Plan to use bus-rods or diagonal style connections OR both (hybrid). For bus rods on hand : 2 pcs (+ & -) * L1.25-m * Æ16-mm (Æ5/8") solid round copper bus rods (~195sq.mm. / ~450-500A in free air), with T25-micron nickel-plated (anti-corrosion). Connections : 95 sq.mm. batt cables will be mounted on copper bus-rods by using SS304 (or steel) hose clamps, securely and evenly wrapping around each L5-cm (or longer) tinned copper opening strand along circumference. The contact area (between batt cables & bus-rod) = Pi * Æ16mm * L50mm = 2,500+ sq.mm which is much bigger (>4-5x) than any terminal lugs of same cable size. The quality of joints depend heavily on how well I can evenly wrap/distribute these - but not difficult at all. There will be no drilling into these copper bus-rods, so all the full Æ16-mm copper rod is for electrons to wander happily. These bus-rods will be securely mounted using insulated stand-offs (bekelite ?) to the steel frame. I've been using this strand wrapping method in my e-bike spot-welding probes without any problems for years, capable of 2000-A burst (from super-cap bank). No soldering at any joints ensures the lowest ohmic connections, as good as it gets. This should be quite a robust set-up given the cost & DIY works put into it.
 

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6. DC MCCB : the cheap TOMZN-250/2300 (rating 250A / max 1000V / Ic 35kA/50kA ) DC MCCB should be arriving next week (mid Jan 2025). Still looking for CHINT 350A, DC MCCB which is much more costly but not in time for the Chinese New Year 2025, since most stores in China start to close for the long holiday for about a month. So I need to proceed with this TOMZN-250/2300 (230A) for now. Plus this TOMZN 250-A breaker can take minutes to trip at its 250A current limit according to their datasheet (250A * 51Vdc = 12.75kW, this should cover whole house usage (2025.01) - but may not include future EV(s) charging. Should be OK with that. Future upgrades might be ChinT 350-A MCCB & 350-400A fuse in series before feeding to the Solis inverter. Asking the seller, they cannot provide me wiring diagram for this TOMZN DC MCCB. I do not know why such simple info is hard to find, even on TOMZN own website. So, is it polarized ? What should be the correct way to connect it ?
 

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7. Batt cables : I have an old 10-m left over of CV 95sq.mm. (90 deg C) cable with quite high strand counts and in good shape, should be good enough for the whole house. BUT EV charging might need another separate circuit (with extra batts).
 

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Pls comment on everything/anything. Especially the battery connections, diagonal / busbar / hybrid and etc. Since above design is my own and I am still a noob & ready to learn. Appreciate every constructive comment.

PS : there are a lot of detail for this project since I designed the whole thing from scratch. Bought only those avail in the market (PVs, Inverter, Rack, batt, etc) and DIY quite a lot of parts. I can post detail of parts if people are interested. I expect to learn from here and share some of my experiences.
 
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You had an interesting idea on using hose clamps to hold the wire to the bar (rod), but I do think that you will have problems in the future with that connection. This questions addresses it in detail, but it seems that you need to provide enough pressure on a electrical connection so air/oxygen doesn't enter it and oxydize the surface contact. A hose clamp is not able to provide that pressure.
I also believe that bus bars are flat to provide more surface area between the wire and the bar when using the flat connector.
The lesson here is that we should rely on tested and tried solutions.
 
You had an interesting idea on using hose clamps to hold the wire to the bar (rod), but I do think that you will have problems in the future with that connection. This questions addresses it in detail, but it seems that you need to provide enough pressure on a electrical connection so air/oxygen doesn't enter it and oxydize the surface contact. A hose clamp is not able to provide that pressure.
I also believe that bus bars are flat to provide more surface area between the wire and the bar when using the flat connector.
The lesson here is that we should rely on tested and tried solutions.

Thanks for your comment, caki.

The copper rod is nickel plated (I order the shop to dip it 1 hour where they normally dip only 15-20 minutes for T=10micron, so mine should be 25-30 micron thick, I guess). Plus my 95-sq.mm. cable is pre-tinned, so should not have problem with different-metal connection corrosion for a long while (decades). I believe that this 25-micron nickel-plate thickness should be heavy-duty grade, compare to those avail in the market. I have not physically checked plating thickness (microns) but just trust the shop - been using them for decades. Ensuring every parts to specs is superb, but will be quite exhaustive.

Your ref of "Can I use hose clamp to ground a wire to EMT ?" is very interesting - I never knew thought of that. EMT is e-galvanized or zinc plated ? Bare copper wire will react with that easily & corrode quickly. Plus the clamp type to use is important.

Normally, 3/4"-1" hose clamps can provide very tight connection. It even squeezes water hose to shear-off if driven too tight. Think about your garden hose with these clamps to the water tap, how often do you have to re-tighten it ? Every year, every 2-3 years ? Mine is longer than that, and if it is SS304, you probably forget about it for years. Remember that garden hose moves all the time, while our copper bus-rod connections never move. I can even put a drop of medium thread locker at the hose clamps threads too - but do I really need that ? I normally use at least 1 clamp per an inch of copper strand. So, minimum of 2 clamps per 1 connection should be very tight. The screw threads & steel belt slots design of this clamp make it very difficult to back off by itself with its high mechanical advantage. One will strip it before loosening it. I never tested clamping pressure of this clamp before, but judging by its applications that can hold pressurized hose virtually a long time. I believe it will hold reliably for our applications. This is a DIY project and some new tricks will be used all the time. I truly do not wish any hot-spots in my battery rack whatsoever. Too scary. And for sure that we need good electrical connections from reasonably good mechanical tightness.

If this hose clamp & bus-rod, both round (& should have evenly distributed clamping force along circumference), will be used in area with strict codes & regulations, you better check and comply. My area is not applicable LoL. Sad but true. But I always build my things robust in the first place, since I am too lazy to fix it later.

I still cannot find Tin VS Nickel galvanic corrosion effect if in contact for long term. Not likely that it is severe, anyone ?

I really like this kind of discussion, everyone can learn something. Thanks again for your insightful comment, caki.
 
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Forgot to mention that I also ordered fiberglass insulator for the bus-rod... 600 deg C. Need to figure a way to easily install & remove it off from the rod. These are not shrink tubes.
 

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Let me rephrase the main question, may be I made it too complicated :

How do I connect the 2 batteries to balance/share load equally ? Without being too costly / too complicate.

Hope this is very clear.
 
Is this the way to go ?

When I need to add more batt, just connect within the "diagonal" and on the bus-rods ?

As long as the total current drawn not exceeding the capacity of the Cu bus-rods ?

In this case, the very end of each bus-rod where each 95 sq.mm. cable connected and feed to DC MCCB, will handle the highest current ?

So this connection is to ensure a good load/current balance among the batteries ?

I can find out when everything connected and measure each batt's current drawn, will report back.
 

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The gurus here pls point me the technicals behind this diagonal connections how it helps to balance batteries loads. Or point me to some threads that discuss about this in details. I am really interested and can explain to some enthusiasts around me. Thanks in advance.
 
I came across another type of hose clamps, shown. Should be tighter & much stronger from its structure. There are other types to choose from to serve our purposes. I need to finalize and test which to use.
 

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Found myself a dielectric gel for electrical connections protection. It is Super Lube 82003 Anti-corrosion gel at ~ USD15 a 85-g tube. This is not the best product but fairly priced and should works well. It is to coat only at outer surface of high current carrying paths, after the connections are done, to have long term protection against corrosion. This gel is non-conductive and cannot be applied between conductors connections since it will cause high resistance spot. "ONLY AT" outer of metal parts and not in between. Don't expect any problem for another 5 yrs.

Some people use regular petroleum grease for this purpose on their car battery, it works OK. But I found it quite messy to work with, especially when you have to do some maintenance and forgot that the grease is there. This Super Lube gel is way better. Make sure you get the right one since there are similar Super Lube products but that is mainly for lubrication purpose.
 

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