My future 1st solar

Announcement - Help us fight the BOTS! Please report all spam including stuff in your inbox!

Overmind

Member
Joined
Jan 16, 2019
Messages
434
I will do a solar system at my folks country place and I'm currently on the research phase.

Desired rating is 2.5-5KWh.

I long-ago established that I will go with LiFePo4 cells of 100Ah, I have a good supplier for such "bricks".
16S of them will make 48V-equivalent. So far so good, this one is settled.

Now I'm trying to figure out what panel and inverter combo to use.
I have a local supplier of panels that are 36V @ 310W.
Another one can give me 5KW MPPT inverter (model HYB5032MN) that supports 40-145 VCC from the solar panel side and the 48V, 117A battery input.

1. It it fine to put like 3x36 V panels in series (please ignore the HV safety issues, let's talk just about the tech part) to power up this 5KW inverter ?
If a panel is shadowed how much will this affect overall charging ? What happens on the current side ?
Is there a better way of connecting ? Should I rather go more parallel ?

2. One more thing I'd like to have is a BMS to control max charge voltage (to set it at 55, 56V whatever I want/need).
Any recommendations for a good BMS maybe with possibility to control settings via smartphone ?
Will such a BMS work good with the MPPT inverter ?

3. Is there anything else needed (excluding the connectivity part) except the panels, batteries, MPPT inverter and maybe a good BMS ?

Thank you.
 

Oberfail

New member
Joined
Jun 22, 2021
Messages
25
1. Yes, if one gets shaded, the whole string will loose its power, Voltage might stay high, but ampers will go down significantly. You probably need a higher Solar Voltage than your battery voltage, so putting 3 in series is the best option there.

2. Go on Aliexpress and search for DALY Smart BMS, they seem to work well with a good useable phone app for settings and such.

3. Set the voltage limits on your MPPT inverter and use the BMS's settings only as a last resort for voltage and ampere limits.
Maybe get 4 solar panels, so you can do a 2s2p configuration with them or better 6 solar panels for a 3s2p config.
 

Korishan

Moderator
Joined
Jan 7, 2017
Messages
6,522
If a panel is shadowed how much will this affect overall charging ?
Shading hampers a panels power output drastically. Some panels can handle it better than others, just depends on how they are wired up in the panel. Each little square is a cell. If a cell gets shaded, it usually becomes a "sink" and draws power from the others. Think of that cell as immediately going Self Discharge during shading.
Some panels have a lot of diodes inside the panels to help with this, but this drives up the cost of the panels. I'm not sure what they call these types of panels.
This is why it is good to have more than one 1 panel in parallel as each panel definitely has blocking diodes to keep a single panel from bringing the rest down.

Will such a BMS work good with the MPPT inverter ?
Kind of depends on the MPPT and the BMS. If they don't talk to each other, then you might have issues. You'd have to check with your MPPT to make sure it can handle sudden disconnects.
Normally, you set your charger, in this case the MPPT, to the correct full voltage. The BMS only is used as a backup in case the voltage jumps to high over the limit.
I do know that Batrium BMS does communicate via CANBUS with a load of different types of chargers/inverters. But they are a bit pricey, imho. However, you are buying also the support and developed system.

Is there a better way of connecting ? Should I rather go more parallel ?
If you can go at least 2p, that would be better than a single string. This doesn't necessarily mean that every pair of panels are connected in parallel, though it does help. You could have 2 strings of 3s1p connected in parallel at the ends before going into the charge controller. Or you could have 3s2p. The latter configuration will give you the best yields of these two methods.
The third method would be to have 2 strings, and 2 charge controllers. Each controller is responsible for its own string of panels. The output to multiple controllers into a single battery bank can then be paralleled to the battery. This gives the best use of power tracking as no panel shaded effects the other string at all.
 

OffGridInTheCity

Active member
Joined
Dec 15, 2018
Messages
1,708
I will do a solar system at my folks country place and I'm currently on the research phase.

Desired rating is 2.5-5KWh.

I long-ago established that I will go with LiFePo4 cells of 100Ah, I have a good supplier for such "bricks".
16S of them will make 48V-equivalent. So far so good, this one is settled.

Now I'm trying to figure out what panel and inverter combo to use.
I have a local supplier of panels that are 36V @ 310W.
Another one can give me 5KW MPPT inverter (model HYB5032MN) that supports 40-145 VCC from the solar panel side and the 48V, 117A battery input.
2.5kw / 310w panels = 8.06 panels
5kw / 310w panels = 16.13 panels.

1. It it fine to put like 3x36 V panels in series (please ignore the HV safety issues, let's talk just about the tech part) to power up this 5KW inverter ?
Yes.
If a panel is shadowed how much will this affect overall charging ? What happens on the current side ?
Any shading - even a 4" x 4" patch or a 1" band of shadow along an edge on 1 panel in the series will effectively pull that series to 'nothing'.

For example, my arrays on roof and ground array in the back yard are shaded 'a bit' thru the AM due to next door neighbor's house and my own house roof-line on the back-yard until 10am in winter time (low sun). This gives me 10% loss for the day?... but its just the nature of panels.. unless they track the sun with no clouds or heat or 'anything' you will never get 100%. Its more about what is OK for you. In my case - I'm cool with it and just planned in a couple of extra panels.

Is there a better way of connecting ? Should I rather go more parallel ?
As @Oberfail pointed out...
I'd shoot for 3s (3 in series) so the voltage is appropriately higher than the battery bank for good MPPT -> Battery charging - this may be more efficient but you can perhaps find the published efficiency curve (e.g. pv power in, charging power out by voltage) for your MPPT and answer this without guessing. 2s (72v) will pull down a bit for MPPT - say to 65v - and that might be too low for optimal 48v battery bank charging where the top voltage is around 58v. 3s (108v) will likely pull down to 90v for MPPT - plenty of head-room above 58v max battery voltage.

3s3p = 9 panels * 310w = 2.8kw PV array.
3s5p = 15panels * 310w = 4.6kw PV array.
(etc....)

@Korishan an makes an excellent point about shading... if you have tricky shading then perhaps 2s could work, but if not, then 3s should work with no issues.

Battery bank: If you're doing off-grid.....
I would suggest (just generally) that you'll need a 3 * PV ratio for 100% consumption of PV power. There are many factors but based on my own experience its a 3 * PV ration for 80% DOD range. So 2.8kw of PV = 2.8kw * 3 = 8.4kw battery. 4.6kw * 3 = 13.8kw battery.

100ah @ 48v = 5.2kw... smaller that you'll likely need in the long run. I don't say this to be discouraging... and you can get started with 100a * 16s, just to alert you to perhaps leave room in your physical setup for a larger battery bank down the road.

2. One more thing I'd like to have is a BMS to control max charge voltage (to set it at 55, 56V whatever I want/need).
Any recommendations for a good BMS maybe with possibility to control settings via smartphone ?
Will such a BMS work good with the MPPT inverter ?
As mentioned above - the BMS is not typically the right component to control min/max charging. Any decent Charge controller will let you set this. I'm Batrium... USB and WiFi access... Windows... its very expensive but its a good way to go if you plan to expand. I started with 14 packs (of 260ah each) and now have 84 but continue to use the same central unit... I just keep adding longmons.

I also use Chargery, and this would work for 16s @ 100ah each and I love them - but as I've posted several times, they are cheaper! and prone to burning up on any misstep of hookup. The main thing about Chargery is it has its own 'view screen' and doesn't need a phone.
You may want bluetooth/phone - so maybe DALY or something.

3. Is there anything else needed (excluding the connectivity part) except the panels, batteries, MPPT inverter and maybe a good BMS ?

Thank you.
Electrical boxes, conduit, circuit breakers / boxes, wiring, lightning arrestors, ATSs (perhaps), .... much 'hookup' hardware and tools. I used Ironridge railing on the roof and Universal Strut + 2" pipe on the ground mount.
 
Last edited:

italianuser

Member
Joined
Feb 25, 2020
Messages
340
2.5kw / 310w panels = 8.06 panels
5kw / 310w panels = 16.13 panels.
Yes, exactly how I calculated mine. For a 14s20p 44Ah @51.8V battery I should be able to fully charge the battery during sunny time of the day with 6x 280W panels. So I'd need at least 12 panels for an 88Ah battery, if you have important shading problems you could consider adding more panels.
 

Overmind

Member
Joined
Jan 16, 2019
Messages
434
Thank you all for the feedback.
I'll start gathering what's needed and keep this up to date.
Will probably start with 6 panels and 100Ah@48V and go from there later on.

Regarding the S/P connectivity between panels I assume there are some sort of junction boxes, right ?
 

OffGridInTheCity

Active member
Joined
Dec 15, 2018
Messages
1,708
Regarding the S/P connectivity between panels I assume there are some sort of junction boxes, right ?
Its common to 'combine' the serial strings at a 'combiner box' near the PV array outside. The box typically has 1 fuse or circuit breaker per string and then hooked to a common busbar (combined) in the box so that you have a + and - and ground to run to your charge controller. Note - the combiner box is a termination point for grounding the array as well.

Some combiner boxes (Midnite Solar is an example) have an external handle for 'quick disconnect' for fireman to turn off the circuit breakers.

Its also an OK place to connect your lightning arrestor.

I know it sounds like a lot... and its $$... ($200-$300) and some may just twist the wires together- but it really does make sense and is code is many places. If you decide to go combiner box etc - I can offer some specific links.
 

Overmind

Member
Joined
Jan 16, 2019
Messages
434
Sure, any info is useful for me at this point.

And if I got this right, hybrid inverters would 1st drain power from solar and at increased consumption from battery, then from grid. Is that correct ? I never tested one in practice.
 
Last edited:

OffGridInTheCity

Active member
Joined
Dec 15, 2018
Messages
1,708
Sure, any info is useful for me at this point.
An array of panels is often organized into S and P like a battery. In my case, I have 24 panels on my roof and I've organized them into 2 sets of 3s4p. Each individual 3s (3 in series) goes to a combiner box. I had to have 2 combiner boxes because I have 8 sets in series and the largest Midnite combiner only holds 6 circuit breakers. So each box has 4 circuit breakers. Here's some pics....
The overall roof array of 24 panels....
1631544903845.png


One of the combiner boxes - 4 strings (120v @ 9a) each combined into 1 pair of wires with 120v @ 36a going to charge controller #1. The 2nd combiner box does the same thing and goes to charge controller #2.
A key useful diagnostic is with individual breakers - I can turn on/off each 3s string and confirm its working.
1631545340748.png


The above are Midnite Solar style boxes and breakers and external handle (optional). There are other options but I went with Midnite because they are UL (per code) and I have Midnite Classic charge controllers. Not pushing Midnite - just sharing they are a good choice.

Generic Box with 6 slots - https://www.amazon.com/MidNite-Solar-MNPV6-Combiner-Box/dp/B00PV5Y0WS
One with Quick Disconnect handle - https://www.altestore.com/store/enc...ite-solar-mnpv6-disconnectcombiner-box-p9714/
15a Breakers - https://www.amazon.com/MidNite-Sola.../B007IAAGPE/ref=pd_bxgy_1/140-0687880-1929332
Lightening Arrestor - https://www.amazon.com/Midnite-Sola.../B00SGGWAZ8/ref=pd_bxgy_2/140-0687880-1929332

And if I got this right, hybrid inverters would 1st drain power from solar and at increased consumption from battery, then from grid. Is that correct ? I never tested one in practice.
I'm off-grid, will defer to the hybrid experts on this board :) If you're doing micro-inverters (e.g. AC right at the panel) then the above does not apply.
 
Last edited:
Top