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Warwick Bruce Chapman avatar image
Warwick Bruce Chapman asked

Thinking Exercise: Using Batteries & Solar to Reduce Utility Consumption

I have been asked a quizzer by someone looking to install a Victron Energy Storage System.

Here in South Africa, the mindset is very much about resilience to power failures, either as a result of local grid failure or "Load Shedding" by the national generating entity.

However, this person is an immigrant from Germany and they want a solution that optimises for reducing their expenditure on the utility even if that is at the expense of resilience to grid failure.

My thinking has always been: "Batteries are there to provide backup in the event of grid failure. Therefore you want them to be fully charged so they can keep things running as long as possible, ideally until the grid returns".

However, this person wants to make use of battery power during high demand periods in the day and charge them during low demand periods. They then want the batteries to supply power in the evening, again to reduce usage of the grid. I think there is some sense to this but I'm just feeling it with my fingertips.

To provide power in the evenings, by the end of the day, we will want the batteries fully charged. So, one might say that before 14h00 each day, the batteries can be used to supplement supply but only to 70% SoC. Below 70% or after 14h00, batteries must charge back to 100% before being used to supply again.

One might equally say that in the morning, the batteries must get back to 100% before they are used to supplement supply. That might only happen at 10h00. Thus, the batteries would be supplementing supply between 10h00 and 14h00 in that example.

Is something like this configuration possible with a Multiplus II 48/3000, Lithium Batteries and MPPTs?

ESS
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Phil Gavin avatar image
Phil Gavin answered ·

Warwick,

(Caveat: I use LA batteries).

I do a sort of flavour of this using scheduled charging.

At least, multiple schedules with a "Min SOC" setting is what I'd start messing with for your particular application.

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nigelfxs avatar image
nigelfxs answered ·

Hi Warwick

I have a system similar to what you describe and it works very well to reduce the overall energy consumption from the grid and also provides backup in case of grid failure/load-shedding.

One slight difference from your description - is that solar power is normally first used to supply the AC loads and then charge the battery when excess power is available. [Edit] You can also schedule battery charging from the grid if the battery state of charge (SOC) is below a programmable level.

There are many different settings in ESS that can change how this works, so can be quite confusing to try and get an overview of what is possible.

Note that South African regulations make it very difficult or financially impractical to push any excess power back to the Grid (I am in Cape Town). I strongly recommend checking the requirements of your local electricity authority/municipality since there are very strict rules and procedures to follow before you can install a solar system.

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Warwick Bruce Chapman avatar image Warwick Bruce Chapman commented ·

Thanks Nigel. We're not looking at feedback in this system, just reducing consumption by using solar for base loads and battery for spikes so that only what those two cannot handle comes from the grid.

Strict in Cape Town and maybe a few other municipalities there. Not sure the rest of the country is on the ball.

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rotevery avatar image
rotevery answered ·

Not sure how to do this on my Quattro/RS 450/100/Cerbo GX/LFP Batteries system. On my Sorotec VM II inverter system there's a PAL setting that makes the Solar and Grid to share the load and share the battery charging burden during the day. This achieves exactly what you want. Not sure if there is such a simple way to achieve this in Victron systems.

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mondeoman avatar image
mondeoman answered ·

Just use ESS and set the Minimum SOC to a high enough value, e.g. 50% or 70%, depending on the available total battery capacity.

You do not gain anything if you discharge your battery before 14:00 to avoid consumption from the grid, but then a minute later you charge the battery from the grid.

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rotevery avatar image rotevery commented ·

I think the intent is this: Discharge the battery (not below 70% SoC) before 1400 hours irrespective of grid availability/unavailability if and only if solar generation is not enough to carry the load (high demand periods) because there's time / chance to recharge the battery to 100% from solar generation only before 1400 hours (between say 1000 and 1400 hours). Charging power source is solar only up until 1400 hours. Load supply source priority is solar with battery sharing the load when necessary and battery taking over all the load whenever solar goes to zero provided battery is above 70% SoC. If battery goes below 70% SoC, then the grid takes over the load but does not charge the battery. If and only if both solar and grid are unavailable, then battery would carry all the load and the system would allow the battery to discharge below 70% SoC until the low battery cut-off voltage is reached.

Below 70% SoC and after 1400 hours, getting the battery to 100% SoC / keeping the battery at 100% SoC becomes the highest priority with charging source priority being solar but with ready support and/or simultaneous supply of charging power from the grid as well. Grid would share or take over all of the battery charging power supply burden. Load supply source priority is solar with grid sharing the load when necessary and grid taking over all the load whenever solar goes to zero.

Complex requirement. The question is, is it doable? Can this be programmed? I think it's possible but maybe the functionality is not yet available.

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ponzoa avatar image ponzoa rotevery commented ·
Sounds complex but is very reasonable for a Victron sistem.


Dimension, select and install a Multiplus or Quottro as required.

Dimension batteries so that the 70% or other value can carry them through a load shedding or black out scenario and supply enough nominal power to the inverters.

Dimension the solar array(s) with MPPTs so that this array can carry the required load of the house and a surplus for charging the batteries.

In the GX (Cerbo);

switch off allow export to grid (unless you're allowed to export)

Set scheduled charge in ESS using a night tarrif and set max SoC from grid here. Note, this will happen always as per programmed until you reach the required SoC set.

Set minimum SoC unless grid fails to the required settings. Optimize without battery life. Once consumption reduces this SoC, cosumption will come from solar and/or grid until the SoC min. limit is exceeded.

The system will supply all house loads on AC1 out always and AC2 out when grid is available, from solar. If there is not enough solar, the power will be extracted from the batteires down to min.SoC.

It really is a very efficent system and saves a lot on power bills apart from protecting from shedding/black outs. If you get decent batteries and install it properly, you won't have any issues. You can always add more solar and MPPTS, or batteries in the future if consumption habits change. If you're not sure to dimension it apropriately, you can always go to your minimums and when you see you need more, add on. If you take this approach, rememnber that the Multi II 8/10 & 15KVA can not be connected in parallel so if you need 10kVA and think you may need to grow, set up 2 x Multi II 5KVA in parallel and leave space in the install for a third.

Good luck.

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