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londonflatthing asked

Multi RS Solar 48/6000 setup

Hello everyone.

I'm just setting up my first victron based domestic system in a flat in London. I've made the following "design setup" ... can you critique it?


Since I'll be running "off grid with AC input" - i.e. no feedback to grid possible. I don't need a DNO declaration (as far as I know!).


I decided to mate the high-voltage Maxeon3-400 Panels (5 panel string) with the high voltage Multi RS-Solar 48/6000... hoping to achieve decent efficiency from dawn till dusk... time will tell if it works out.

victron-solar.png

ESSsystem designmppt rsmulti rs
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4 Answers
wkirby avatar image
wkirby answered ·

The DNO must be informed (G98) or an application submitted (G99) if you are going to connect a device which will run in ESS mode, also known as grid interactive mode or grid parallel mode. This mode of operation is capable of feeding in to the AC input source, the inverter can run and interact with the AC input source whilst the input safety relays closed. If the AC input source is the national grid then, again, your DNO must be involved. The DNO needs to know how much generation capacity his or her sub stations are capable of and he or she wants to know that the connected equipment will interact in the manner that they want it to do.

Currently, the Multi RS does not support ESS mode, it is therefore incapable of feeding back energy into the AC input.
The Multi RS can only run in standard inverter / charger mode. This means that when valid AC is present at the input and the input safety relays are then closed, it only acts a consumer of energy from the AC input source for charging batteries or for passing through AC to loads on its output. The inverter cannot run if the input safety relays are closed, it can only run after the input safety relays have opened, thus it is incapable of feeding in. This not only serves to maintain the integrity of the AC input source but also for safety reasons.
Standard mode is used for when grid interactivity is not required or it would not be allowed. For example boats, professional vehicles, recreational vehicles and welfare units, to name a few scenarios off the top of my head. There are countless such installations all over the world.

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johnone avatar image
johnone answered ·

Re informing the DNO, it's best to ask them - explain what you want to do and provide them with your schematic. I've found them to be quick to respond and very helpful. AFAIK (and there isn't consensus on here), the fact that you are connecting a device which, if it failed in some way, could feed back into the grid, you need approval. Maintaining the integrity of the grid is, IMHO, something we should all buy into. One purpose of the approval of the DNO is to ensure you are using devices which have been shown to be able to fail safely. Unfortunately, AFAIK, the Multi RS hasn't been approved for connection to the UK grid. Your DNO will provide the definitive response on all of this.

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johnone avatar image
johnone answered ·

Can this can be kept to the specific context - i.e. it's not a boat or RV, it's a flat in London. And anyone might think their device is safe to use, but it's up to the DNO to decide if any device is safe to connect to their network.

In a house setting it seems to me to be irresponsible to suggest that the DNO don't need to be involved.

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wkirby avatar image wkirby ♦♦ commented ·

The owner of the system will decide how they plan to use it and then take the appropriate action.
If they wish to use the device in grid interactive mode then they MUST ALWAYS involve their DNO. This is because the device will be configured to allow feed in and the DNO will be interested in that. Even if you don't actually feed in because it's a financial loss to do so these days, the fact that the equipment is configured to be able to feed in mens that you must involve your DNO.
Remember, the G98 and G99 forms are used when you wish to feed in electricity, not to consume electricity.

If the device is not configured for or is not capable of operating in grid interactive mode then it only acts as a battery charger with passthrough when the AC input is connected. A battery charger only consumes electricity from the AC source and we do not need to seek permission to consume electricity. If your DNO did not want you to consume electricity then they would not facilitate it.

The short list of scenarios which a mentioned earlier were just a few.
I'll provide a few more scenarios related to dwellings.
A home with a poor or unreliable electricity supply would use an inverter / charger in standard mode as a UPS to maintain a supply within the dwelling. No feed in is allowed.
Perhaps a home owner simply has no incentive to feed in to the grid, so they choose not to. They then opt to use the device in standard mode where feed in is impossible.
A home owner without permission to feed in has a motor home with an inverter / charger installed within. They wish to keep their onboard batteries topped up when parked on their driveway. The device is used in standard mode so that it will be impossible for the system within the motor home to feed back into the house's electrical system.
Please understand that I'm simply trying to help you to identify the difference between the two modes of operation and which one does apply to grid interaction and feed in and which one does not.

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johnone avatar image johnone wkirby ♦♦ commented ·

My understanding is that DNOs are interested in both generation and consumption. For example, EV charging affects load balancing in local sub-stations. A battery and PV system designed to not feed in but to charge up at night for use in the day changes the loads the DNO has to manage. Assume the regs are constantly changing, but seems to be the case that EV charging requires DNO notification. Stands to sense this is also the case with inverter and battery system, even if there's no export, given you're changing consumption patterns. Be interesting to delve deeper, but could be the case that every device you plug in to the grid - in theory - has to in some way be certified. Doubt it's the case, and for good reason, that you can plug in what you like.


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johnone avatar image
johnone answered ·

Aside from the DNO rabbit hole, re matching panels and Multi RS, I'd have thought that losses from inefficiency relate to battery voltage and grid voltage. MPPT solar chargers are very efficient at reducing the PV array voltage down to the battery voltage. Whereas, it's the 50v Dc to 230v AC conversion where the losses are. For example, when charging batteries from the grid (at night, in winter), then using battery power during the day, there are substantial losses in the 'round trip' of 230v AC to 50v DC then 50v DC to 230v AC.


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Hi. Yes I'm aware of the round trip inefficiency, but if charging late at night on economy 7 it still works out ahead.
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Shiv avatar image Shiv commented ·
There's a 200 to 300% cost delta between cheap overnight tariffs.

I haven't worked out the roundtrip losses, but I'd persume they're around 20%. Still works out a lot cheaper.

But obviously will need to factor in the cost of the equipment, etc.

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