question

MondeoMan avatar image

Self Consumption without ESS

Hi,

Electrical engineer here, heavily DIY oriented, trying to understand "the Victron ecosystem".

I want to build a Backup and Self Consumption power supply system for some of my house loads.

ESS "Optimize for Self Consumption" would be almost perfect for me, but unfortunately ESS is completely out of the question due to grid regulations.

Grid outages happen about 5 times per year.

I am considering a Multiplus II 48V / 3 kVA inverter, 10 kWh Winston LiFePo4 (16 x 200 Ah cells) and a two-signal BMS. I could afford to go for 4 x Pylontech US2000 boxes if it's worth the extra cost...

I also have room for 10 - 12 PV panels (250 - 300 Wp each) and a SmartSolar charger.

Requirements:

1. When the grid becomes available (on initial power-up of the system or right after a grid outage ends), charge the batteries from the grid up to a nice, crisp, 100%. After this initial grid-supported charging, DO NOT USE GRID TO CHARGE batteries, until after the next grid outage.

2. After this initial charging, only PV power should charge the batteries.

3. During normal operation, when battery SOC drops below 50%, stop discharging and switch loads to grid.

4. When PV power becomes available and battery SOC rises above, say, 60%, switch loads from grid to battery and PV.

5. If grid is down, support the loads from the battery down to, say, 5% SOC.


Can these requirements be met with Victron Equipment? What additional hardware do I need? Is a CCGX really needed? Are there any Assistants that can make the inverter behave like above?


Additional requirement (6). About half of the grid outages happen during the winter. Heavy snow + aerial power lines do not go well together. It also takes the most time to be fixed, due to bad weather. So...I also need to connect a backup generator into this picture. Would go nice with requirement 1, I should be able to fully charge the batteries during the day and run on battery power during the night. :)


Many thanks in advance!


Multiplus-IIAssistants
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3 Answers
Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi @MondeoMan

this part is possible to realize with just a Multi (or Quattro), but the problem is SOC measurement as the MPPT charges the battery and the Multi needs to know this. thus a GX device is needed. (when using a battery type where SOC corresponds with voltage, you can do without).

  • When grid is unavailable, switch loads to battery.
  • When SOC drops below 50% AND grid is available, switch loads to grid but do not charge battery from grid.
  • When SOC rises above 60% (due to PV), switch loads to battery.

With the above requirements, you basically just use the inverter part of the Multi.

connecting to grid is best done with the 'generator start-stop' assistant, you can set multiple options for connecting the grid (SOC, low voltage, high power use):

https://www.victronenergy.com/live/assistants:ignore_ac_input_using_the_generator_assistant

for disabling charging, you can use a combination of assistants, I've made an example here:

you'll have to connect the temp-sense input +/- with the NO side of the K2 relay for this to work,


Please note that getting the SOC calculations right is the key to getting this system to work as expected, this may need some tweaking. the settings below would be a good starting point:

A full charge once a week or something might be needed to re-synchronize the SOC.


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Thank you!

Just to clarify: If I get a BMV and a CCGX, the Assistants (running inside the inverter), would work based on the SOC reported by the BMV to CCGX?

Hi @MondeoMan

That is correct, if you set the BMV as battery monitor in the GX device (this normally is automatically selected) (and have enabled battery monitor in the inverter), the BMV values will be used in the inverter.

MondeoMan avatar image
MondeoMan answered ·

ESS is out of the question because it is not legal to connect such an inverter to the grid, even with "limited" feedback.

I'm not worried about adding external logic, I design and build all sorts of electrical automation cabinets for my daily job. Mostly relay-based, timers, counters, etc. I do admit I'm a bit old school and I'm not very comfortable with things that I can't touch and can't directly measure and poke...I mean software / firmware / bluetooth / bigmouth / etc. I still design my projects drawing ladder logic with a pen & paper...

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What Country ? (I'm guessing UK)

Sorry but I just don't want to go through the hassle of obtaining the legally required permits to connect it on-grid with ESS. I'm just sick and tired of dealing with the corrupted and arrogant energy authorities.


So, can anyone please advise how could I obtain the following behavior with Victron Equipment?

  • When grid is unavailable, switch loads to battery.
  • When SOC drops below 50% AND grid is available, switch loads to grid but do not charge battery from grid.
  • When SOC rises above 60% (due to PV), switch loads to battery.


Thank you all!

Murray van Graan avatar image
Murray van Graan answered ·

Why do you say ESS is out of the question? I’m asking because it is possible to prevent feeding back to the grid. As an alternative you could use an assistant to control the ac input in an island system, but it’s going to be hard to get it to recharge fully after grid outages only. For this you’ll need external logic controlling the system.

Consider a Quattro unit when using a generator, as it has 2 AC inputs and each one can be configured separately. If using a Quattro, you’ll need an external anti islanding relay.

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