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Solar power, can it be done DIY?


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9 minutes ago, Sophon said:

I am also not clear on what cable sizes I need for a 5 kW system, one of the sellers of inverters on Lazada quoted 4 sq.mm. but is that enough for a sustained energy flow of up to 5 kW? FWIW the finished cables that Global sell does seem to be mostly 4 sq.mm.

Inverter cable. Output 5kW divided by 220v = 23A

So you need cable that can take 23A (4mm can take 25A-32A)

 

PV cable. Strings will be under 500V max 10A.

Normal 2.5mm twin insulated cable is rated 16-23A @ 500V

You just need a few MC4 connectors (10bht each).

 

Battery cable. 48V x 100A = 5kW.

I use 4 strands of 4mm connected in parallel giving me a 120A connection.

 

My local store sells single 4mm cable at 10bht/m.

No need to buy special expensive 'solar' cables.

 

Edited by BritManToo
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Yup ^^^. 

Do get the correct crimp tool for the MC-4 connectors, if you're doing more than a few you really can't just squidge them up with the pliers.

 

We did invest in "solar" cables, purely because they are supposedly UV stable and more resistant to attack from the local wildlife. But the regular stuff works just fine. 

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1 hour ago, BritManToo said:

Inverter cable. Output 5kW divided by 220v = 23A

So you need cable that can take 23A (4mm can take 25A-32A)

 

PV cable. Strings will be under 500V max 10A.

Normal 2.5mm twin insulated cable is rated 16-23A @ 500V

You just need a few MC4 connectors (10bht each).

 

Battery cable. 48V x 100A = 5kW.

I use 4 strands of 4mm connected in parallel giving me a 120A connection.

 

My local store sells single 4mm cable at 10bht/m.

No need to buy special expensive 'solar' cables.

 

Thank for the info, that will come in handy. 

Quote

Battery cable. 48V x 100A = 5kW.

I use 4 strands of 4mm connected in parallel giving me a 120A connection.

I have some 16 sq.mm. cable left over from the house construction, so I guess I could use that.

 

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A couple of general questions, not directly solar related.

 

I used a Schneider consumer unit when building the house, so I am not familiar with DIN boxes. Would a "double decker| box such as this one make connecting everything easier? In my head it seems like it would.

image.png.f590c45b9d8a411eb00705890274958d.png

 

The above box (unlike my Schneider) doesn't come with an earth bus bar. So would you buy and mount a normal bus bar such as these?:

image.png.6ba601de2aab3a708eb340e7f23c1f8a.png

 

Or would you use something like this, that can be easily mounted on the DIN rail?

image.png.52b0b81a0c005566ecd7f00b2f2ccd89.png

 

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1 hour ago, Crossy said:

Yup ^^^. 

Do get the correct crimp tool for the MC-4 connectors, if you're doing more than a few you really can't just squidge them up with the pliers.

 

We did invest in "solar" cables, purely because they are supposedly UV stable and more resistant to attack from the local wildlife. But the regular stuff works just fine. 

Will do.

 

What kind of cable size will I need for connecting the AC and DC surge suppressors?

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3 minutes ago, Sophon said:

Will do.

What kind of cable size will I need for connecting the AC and DC surge suppressors?

 

We have 10mm2 to connect the suppressors to ground, and 6mm2 on the other side, it's only short lengths so that's big enough.

 

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1 hour ago, BritManToo said:

Inverter cable. Output 5kW divided by 220v = 23A

So you need cable that can take 23A (4mm can take 25A-32A)

 

PV cable. Strings will be under 500V max 10A.

Normal 2.5mm twin insulated cable is rated 16-23A @ 500V

You just need a few MC4 connectors (10bht each).

 

Battery cable. 48V x 100A = 5kW.

I use 4 strands of 4mm connected in parallel giving me a 120A connection.

 

My local store sells single 4mm cable at 10bht/m.

No need to buy special expensive 'solar' cables.

 

But am I right to say that this doesn't take into consideration Energy Loss over longer runs?

 

I believe the OP is also talking about a RUN of 50m!

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39 minutes ago, MJCM said:

But am I right to say that this doesn't take into consideration Energy Loss over longer runs?

 

I believe the OP is also talking about a RUN of 50m!

All the solar equipment (panels, battery, inverter) will be very close together, the 50 m run is AC from the inverter to the house and we already have buried 16 sq.mm. cable in place for that.

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22 hours ago, Crossy said:

OK, let's take the easy one first.

 

The second unit (with the red handle) is clearly marked + and - on the little diagram, it doesn't seem to be line/load marked. OK for battery.

 

The Tomzn one also has + and - markings but they appear to differ at the top and bottom of the little drawing. Need to investigate just what this means.

With what BritManToo wrote about the battery cables needing to be able to handle 100A, the Taxnele one in the link would be undersized (only goes up to 63A). But I found this other Taxnele DC breaker, that can handle bigger currents:
image.png.64679bf1efb85d8a2ca234b7b0f0937c.png

 

And this one is actually described as a "battery switch". Would you go for the 100A or the 125A version (same price).

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Quote

PV cable. Strings will be under 500V max 10A.

Normal 2.5mm twin insulated cable is rated 16-23A @ 500V

You just need a few MC4 connectors (10bht each).

I'm sure that the above is correct, but can someone help me understand how you arrive at 10A?

 

Taking this panel from Global as an example:
image.png.f5cfba491e3a0758df4f9826f5e9d345.png

image.png.6da15d9fd5b251287e55f683f827654d.png

Wired up in two strings of six panels, I make it a total of 6x38.2V = 229V. As the maximum the inverter will support is 5kW, that would make a theoretical maximum current of 5kW/229V = 21.8A. In reality a bit less than that, as the panels at the rated 340W would only produce about 4.1kW.

 

Where am I going wrong?

Edited by Sophon
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22 minutes ago, Sophon said:

Where am I going wrong?

 

10A is assuming all 12 panels in series (12S). Two sets of 6 series in parallel (6S2P) would be 20A ish. At which point you probably want to go the 4mm2 cable. All our panel strings (9S and 10S) are actually wired in 6mm2 (the biggest that fits in my MC-4 connectors) for minimum volt drop.

 

How you arrange the panels depends upon the inverter MPPT parameters. It is imperative that the Voc (open circuit voltage) of your series panels does not exceed the maximum input voltage of the MPPT, ever! 

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23 minutes ago, Crossy said:

 

10A is assuming all 12 panels in series (12S). Two sets of 6 series in parallel (6S2P) would be 20A ish. At which point you probably want to go the 4mm2 cable. All our panel strings (9S and 10S) are actually wired in 6mm2 (the biggest that fits in my MC-4 connectors) for minimum volt drop.

 

How you arrange the panels depends upon the inverter MPPT parameters. It is imperative that the Voc (open circuit voltage) of your series panels does not exceed the maximum input voltage of the MPPT, ever! 

My inverter (like many) has a maximum input of 18A, so I can only do 1 string.

My panels say max 9A, but I've seen them producing 10A.

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33 minutes ago, Crossy said:

 

10A is assuming all 12 panels in series (12S). Two sets of 6 series in parallel (6S2P) would be 20A ish. At which point you probably want to go the 4mm2 cable. All our panel strings (9S and 10S) are actually wired in 6mm2 (the biggest that fits in my MC-4 connectors) for minimum volt drop.

 

How you arrange the panels depends upon the inverter MPPT parameters. It is imperative that the Voc (open circuit voltage) of your series panels does not exceed the maximum input voltage of the MPPT, ever! 

So in my set-up 4/6 sq.mm. cables. 4 sq.mm. will probably do as the inverter will be located right under the panels, so the longest cable run will be around 6 m. Breaker 25A or 32A?

 

An inverter such as this one from Lazada:
image.png.4dc1278920c7c19a2483cba131bcd53f.png

 

with these specs:
image.png.23d9b85aaf7911e96d9679f7be6b33d4.png

would fit nicely with my approx. 229V input voltage, but it would be right on the limit if I arranged by twelve panels in series (which i am not going to do). 

 

Still a ways to go, but I feel like I am getting a grasp on how this is going to work, and am almost certain that I will end up going for it.

Edited by Sophon
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9 minutes ago, BritManToo said:

My inverter (like many) has a maximum input of 18A, so I can only do 1 string.

My panels say max 9A, but I've seen them producing 10A.

OK, so in addition to the PV input voltage having to be in the inverters MPPT range, the current also has to be below the inverters maximum input. Where do you see what that limit is, In the specs for the inverter I linked to above I can see no mention of this?
0a88a57de8e25b5c54202c3245cd8e36.jpg_2200x2200q80.jpg_.webp

 

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11 minutes ago, Sophon said:

Breaker 25A or 32A?

 

25A for a 6S2P arrangement.

Don't forget DC surge arrestors on the panel input and AC arrestors on the mains input (put both close to the inverter).

 

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2 minutes ago, Sophon said:

OK, so in addition to the PV input voltage having to be in the inverters MPPT range, the current also has to be below the inverters maximum input. Where do you see what that limit is, In the specs for the inverter I linked to above I can see no mention of this?

 

The inverter will limit the input current so if you are a bit over panelled it won't kill anything. It's in input voltage that kills.

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9 minutes ago, Crossy said:

 

The inverter will limit the input current so if you are a bit over panelled it won't kill anything. It's in input voltage that kills.

Thanks, that's a relief. The Jinyuan panels from Global are rated at 8.94A so two strings should just sneak in under the limit anyway, if the inverter has a maximum input current of 18A. I still can't see this stat mentioned anywhere though.

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You should keep the string voltage as high as possible without going over the limits.

 

I think what you are suggesting is just fine and you have headroom for a few more panels.

 

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6 hours ago, Crossy said:

You should keep the string voltage as high as possible without going over the limits.

 

I think what you are suggesting is just fine and you have headroom for a few more panels.

 

From what I understand, if panels are connected in series and one panel is underperforming (partially shaded, lower quality, slightly faulty) then every panel in the string will as a result be similarly underperforming. That would be one reason why it could make sense to split your panels into strings, even if your inverter can support more in series.

 

But I could have misunderstood the above.

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15 minutes ago, Sophon said:

From what I understand, if panels are connected in series and one panel is underperforming (partially shaded, lower quality, slightly faulty) then every panel in the string will as a result be similarly underperforming. That would be one reason why it could make sense to split your panels into strings, even if your inverter can support more in series.

 

But I could have misunderstood the above.

Not true.

Modern standard panels are divided into 3 vertical strips (24 cells per strip), if any part of a strip is in shadow, a bypass diode switches it out. If all 3 strips are in shadow the complete panel is electrically bypassed. This diagram only shows panels with 1 bypass diode, but anything made in the last 10 years will have 3.

 

 

Bypass-Diode-Diagram-Shaded.jpg

Edited by BritManToo
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4 minutes ago, MJCM said:

 

Yeah, they go under the panel, you need one per panel ???? Although I understand that you only need to put them on panels that get shaded ???? 

 

If you have space it's cheaper to add more panels.

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