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warwick avatar image

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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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.