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john-gordon avatar image
john-gordon asked

ESS with Multiplus and MPPT RS - Design sanity check

Hello community. This design is ESS for a house, 230 V 50 Hz, Ireland. Initially, starting with 5.6 kWp of solar PV but will scale to about 20 kWp (AC and DC - PV). I have two quick questions I'm also wondering about, and if there is anything about this diagram you think looks funny, please let me know!

1. Are the DC disconnects between the MII and MPPT to the Distributor recommended/necessary? (Or just a nice-to-have?)

2. Do we get away with bolting directly to the Shunt, as shown? I know it's not preferred, but is it functionally incorrect? It will happen to look a lot nicer to go in from the side in this case.


Many thanks in advance!house-1-wiring-diagram.png

Multiplus-IIESSmppt rs
house-1-wiring-diagram.png (576.7 KiB)
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2 Answers
cargol66 avatar image
cargol66 answered ·

Hi John,

Best wishes for 2023.

PV isolators are useful and both polarity should be disconnected, but only once. No need two isolators.

PV fuses are required when more than two PV strings are connected in parallel. So here as you have only one string per tracker fuses are useless.

Beware to check VOC at minimum temperature to be lower than 450 V.

yes DC isolator are mandatory on positive wire, at least for the battery connection. Not sure you have to disconnect minus polarity (3 isolator saved!) Always disconnect without DC current, when you have to isolate a device prior to maintenance.

your battery fuse seem litlle bit low, may be 200 A will be better and will be warmless.

battery usable capacity will be about 5 kWh. Beware of your house consumption. 5 kWh is few.

As your 2nd question, not sure to understand it...

Regards.

Bruno.

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shaneyake avatar image
shaneyake answered ·

I would agree with @Cargol66 on most things except:

I would still have fuses on each PV string incase the mppt has a failure, I know in most cases it would be fine but not completely useless in a dead short.

I actually wouldn't have any fuse on the battery as the BMS and circuit breaker are enough as you have fuses down stream that would blow in a Dead short conditions that the BMS may not be able to handle.

1. We don't normally install any disconnects on the battery side. If there is a emergency shutting PV and battery off is normally the way to go. You can then remove fuses if a piece of equipment needs to be isolated but I am not sure about your local rules/laws.

2. Yes, this is fine, just have a way to cover up the terminals but again check your local rules/laws.

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