Surge Protection Devices

[Ursi]

Another newbie question: I have 12x 255W panels in series on my roof feeding into an Voltronic Infini 3+ inverter some 10 meters away.

1) Should I get Type I or Type 2 or a combination Type 1+2 DC SPD?
2) Should I install it on the roof close to the panels or inside close to the Inverter?
3) Any product recommendations? -  I am looking at a Cirprotec PSC3-12,5/600PV but it is VERY expensive.

Your advice will be much appreciated!

[Green Bum]

Hey Ursi, thanks for your question with the same inverter and 12x 260 panels I am also dealing with my shopping list. Best answer I can help you with at the moment: move to CPT much cheaper, I can speak from experience! I am not intending to use any surge protection. (we only get wind surges)but maybe I am wrong?

What does the rest of your shopping list look like and how many baths do you intend heating with your setup?

 

[Janma]

Hi Ursi,

I have a setup simular to yours. 13x 255W panels on the roof all in Series. Voc of the string at just below 500V. I also considered building my own  combiner box that include three things (all rated at over 500V).

1. DC Isolator (dual pole)

2. DC SPD

3. Fuse holder with fuse

The DC stuff rated at 500+ Volts are not that easy to source. You can't just walk into any shop and find it. There are places you can find them though. When you find them they are a LOT more expensive than the AC breaker etc. Since, I have mostly Microcare devices already I just closed my eyes and bought their combiner box that include all of the above. There are other solar shops that also supply combiner boxes that include all of the above.

From what I could gather (someone my correct me here) is that most combiner boxes only feature Type 2 SPD. The Type 1 is very expensive and mostly help with direct strikes (Is this correct?) Even so, if you have a direct strike you will most likely still loose a lot of equipment  (the type 1 SPD as well) not to mention roof tiles/bricks etc. That is why I have insurance.  You can protect your house against direct lightning strikes but you need to know exactly what your are doing and spend a lot of money in the process. Before I started the solar journey my house (as most in my area) did not have, and still do not have any type of direct lightning protection. I considered putting it in place but that would just inflate the cost of going solar. So in the end I just have a type 2 SPD on the DC side and a type 2 SPD on the AC side in the main DB. That should protect my investment against induced voltages of overhead lightning strikes or strikes that are close to my house.

I'm also interested to see what the other people on the forum has to say about it.

 

[DeepBass9]

So why not use 2 strings and run at 250V? What charge controller do you have? My MPPT has a max of about 100V so I use my 300W panels in strings of 3.

[Janma]

1 hour ago, DeepBass9 said:

So why not use 2 strings and run at 250V? What charge controller do you have? My MPPT has a max of about 100V so I use my 300W panels in strings of 3.

Hi DeepBase9,

It depends on the type of system that you have and what it does with the power it gets from the panels. If it converts it to 220-240V AC directly it typically needs voltages quite high, typically these type of systems require Voc of the string in the order of 500 - 550 Volts. If the system converts the power from the panels to say 48V DC it typically require the Voc of the string much lower (in the order of 100V). There are exceptions. The key is to stay within the specs of the device you use.

The larger the difference between the input voltage from the solar panels and the output voltage to the batteries/grid the more losses/complexity in the conversion process. I'm sure others on the system can give you more details about it. My system is Grid Tied so it converts to 240V AC that is why the Voc of the string is much higher than say a typical MPPT charge controller that charges a 48 Volt battery bank.

 

 

 

[DeepBass9]

OK, this is for a grid tie system?

[Ursi]

Hi Janma,

Thank you for your comprehensive answer!

One observation though: The MicroCare Single String Box only has a single-pole SPD in it. I would imagine one should ideally have an SPD and Fuse on each of the positive and negative wires coming from the roof. 

[Ursi]

Hi Green Bum

Thanks for your relocation suggestion, but I like my panels at a 25° degree inclination ;-)

My configuration is:

1) Voltronic Infini 3+ Inverter

2) 12x Renesola 255W Panels

3) 24x Shoto GFM 300Ah batteries

4) Victron BMV 702 Battery Monitor

5) An Arduino MEGA 2560 based OpenEnergyMonitor and Victron/Voltronic Serial Gateway (In Progress)

[Janma]

46 minutes ago, Ursi said:

Hi Janma,

Thank you for your comprehensive answer!

One observation though: The MicroCare Single String Box only has a single-pole SPD in it. I would imagine one should ideally have an SPD and Fuse on each of the positive and negative wires coming from the roof. 

@Ursi About the fuse, you only really need one on the string. The reason is that the + and - wires of the string will always carry the same amount of current (Amps). Think of it as a closed loop that start of at the panels, goes through the combiner box to the inverter and then back to the combiner box, back into the panels. The current that originate in the panels always goes back into the panels. A fuse will blow (stop current flowing) if the current through it gets too high. When this happens the current will stop flowing on both the positive and negative wires. If you have two fuses, one on the positive and one on the negative wires, one of the two will blow first and stop the current from flowing through the other.

Regarding the SPD, It is a very good question. You had me thinking for a long time. I am no expert with this but here's what I think. (Someone please correct me if I am wrong)

A single pole SPD has two terminals. The one attaches directly to earth, the other attaches to a "live" wire that you want to protect from surges. If the voltage differential between the "live" terminal and earth reaches a certain value then it will "arch through" and allow the surge potential to dissipate to ground via the SPD (rather than your inverter or other expensive equipment).

If one of the wires (negative or positive) is grounded INSIDE the inverter then the voltage potential on that wire will always be the same as ground (0V). The voltage on the other wire will fluctuate. I suspect, that if this is the case then you would only require a single pole SPD. If on the other had you have a floating DC circuit were neither the positive or the negative wires are bonded to earth (inside the inverter/charge controller) then you would require a dual pole SPD.

NOTE: Don't ever ground your DC negative or positive wire unless the inverter/charge controller manufacturer explicitly state that you have to!

[Green Bum]

Hi ursi, have you made progress regarding fuses for your system ie. the battery bank and PV panels?  ACDC quoted 1.2K for the battery bank fuse (48V 160 ah) and R280 for the PV panel (3100w, 6.8 A, 450V)

Cheers,

Godfried

[viper_za]

7 minutes ago, Green Bum said:

Hi ursi, have you made progress regarding fuses for your system ie. the battery bank and PV panels?  ACDC quoted 1.2K for the battery bank fuse (48V 160 ah) and R280 for the PV panel (3100w, 6.8 A, 450V)

Cheers,

Godfried

Have a look here at Rubicon for fuses.

I paid around R25 for PV fuses might have been even less rated to a 1000v DC

https://solar.rubiconsa.com/category/34-solar-fuses

also fuse holders

https://solar.rubiconsa.com/category/35-solar-fuse-holders

 

The fuse they recommend for the battery bank 48v 160A is a little big (7680W) I will cry if my batts do that.

Also the fuse for PV seems to have a low Amp rating I'm sure your panels are rated more than 6.8A.
Fuses should be rated at 125% of the current to avoid nuisance blowing

[Green Bum]

thanks VIPER

[Green Bum]

Hi VIPER again thanks for your input but could you please do me one more favor, and give me the exact product code nr's you would recommend.

1. Battery fuse and holder

2. PV fuses and holder

[Ursi]

On ‎5‎/‎12‎/‎2016 at 8:16 PM, Green Bum said:

Hi ursi, have you made progress regarding fuses for your system ie. the battery bank and PV panels?  ACDC quoted 1.2K for the battery bank fuse (48V 160 ah) and R280 for the PV panel (3100w, 6.8 A, 450V)

Cheers,

Godfried

Hi Godfried, I paid R147.00 each for 2x 10A/1000V Solar fuses at ACDC and 2x R76.00 for the holders.

 

I chose to use a DC rated 100A C/B for the 48V battery bank - No fuse.

 

I do hope the 10A fuses will not blow too easily - 10A is the maximum recommended fuse size for my DC  surge protection device.