Optimising EV charging from PV surplus

Q&A and troubleshooting EVCS
,
1

Hello All!

I Hope you can help me find a solution for the following problem :slight_smile: !!

Optimising EV charging from PV surplus in zero-feed-in ESS setup

System :

  • 5 kWp PV array (SSW orientation, 45° tilt)

  • Victron:

    • MultiPlus II 5 kVA

    • MPPT 250/100

    • Cerbo GX

    • ET340

    • Lynx Distributor

  • 3× Pylontech US5000

  • Location: Corrèze, France

Goal :

Optimise EV charging using excess solar production .

We work from home and our VW e-Up! is usually parked outside during daytime, so charging directly from solar makes perfect sens e.

At the moment we charge using the standard portable charger at around 8 A (~1800 W). Charging is scheduled during off-peak hours (22:00–06:00) and limited to 80% S OC.

With 5 kWp of PV, we expect significant surplus production during summer once the batteries are fully char ged.

Because exporting power to the grid in France is administratively complicated, most systems here are configured for zero fee d-in.

The pr oblem:

An EV charger typically only starts charg ing at:

  • 8 A with a basic charger;

  • around 6 A (~1300 W) with a smart charger.

However, with zero feed-in enabled, the MPPT output continuously adjusts to match actual co nsumption.

As a result, the system never creates a visible surplus of 1300 W, so the charger ne ver starts.

It becomes a chicken-and- egg problem:

  • no charging load → no extra P V production;

  • no surplus → no c harging start.

Possible solutions

  1. Control charging within Victron ESS

I understand there may be a way to manage this directly inside the Victron ecosystem, possibly using some sort of periodic charging test or dynamic control logic.

I would appreciate explanations from users already doing th is successfully.

  1. Allow limited grid export

Probably the cleanest te chnical solution:

  • allow ~1000–1300 W export;

  • start charging once export thr eshold is reached.

Unfortunately this creates contractual and regulatory compl ications in France.

  1. Create a t emporary “dump load”

a. Thermal dump load

Examples:

  • boiler

  • electric heater

  • resistive load

But in summer, when PV surplus is highest, additional heating is usually unnecessary.

b. Small inverter heat pump

For example:

  • a reversible pool heat pump connected to the 800 L floor-heating buffer tank;

  • creating “cold storage” during surplus production.

Interesting idea, bu t with practical challenges:

  • condensation

  • insulation

  • noise

  • plumbing complexity

  • limited seasonal usefulness

Question

How are others solving EV charging in a Victron ESS sys tem with strict zero feed-in?

Particularly interested in:

  • Victron EVCS experiences;

  • ESS configuration tips;

  • elegant charging strategies;

  • real-world examples.

2

get a wallbox and look for the EVCC-Project?

I am really happy with it

3

thanks for the reply.

I had a look, but it seems the wallbox starts charging from a determined minimum setpoint op PV surplus.

But HOW does it know the PV surplus when I am on 0-injetion on the net?

This is the essence op my problem…

Anyone??

4

are you forced by government to zero-feed in?

It is really difficult then

Did you think about some rules in NodeRED to load the car when SOC of Batteries is over lets say 70%
You could see then what the car takes, what goes to battery and regulate accordingly

But be aware that car like yours needs minimum 5-6 Anmpere, doesn´t accept less

For the beginning you could also use the existing charger, add something like a shelly, also controlled by rules

5

Hi @YANNIC ,

please have a look at our Victron EV Charging Station. You can connect it also single-phase, so that charging starts at ~1.300 W, as you mentioned. As it’s a true Victron product, it is very well integrated into our ecosystem and also works great in off-grid and zero feed-in systems. When grid feed-in is limited, it can unthrottle the MPPTs to make use of all the PV surplus available.

And if you want even more and are not afraid of testing beta features, you can have a look at our GX Opportunity Loads Beta feature published today. With that, the GX device can orchestrate not only battery and EV charging, but also dump loads whenever there is enough surplus available.

6

Hi!

Yes, I was thinking about the Victron EV Charging Station, to lower the charging current.

I did hear about the possibility within Victron to ‘test’ possible available PV surplus. You speak about unthrottle the MPPT’s…

What does that mean?, how does it function?, and is it a solution worth while (efficiency wise) and is it an option when I am a true 0-injection (10Wmax / 30minutes) ?

7

You probably need to check details on that, that is not a statement that makes sence (would be either Wh / time or W as a maximum Peak, but then a time constraint doesn’t fit in)

And whatever it is 10Wh or 10W, that’s not a feasible number for any ESS, when targeting a 0 setpoint.

(For example, a good meters precission around 0 currents will be just +/- 0.25A. Per Phase)

8

Hi @YANNIC,

in simple terms, the EV charger increases its charging rate until more consumption would cause continuous battery discharge, as the MPPT’s cannot deliver more power.

Efficiency-wise, charging on low current usually means higher losses in the EV’s onboard charger. But in your case, where otherwise the PV is throttled down si that potential surplus could not be used at all, I would argue this is the most efficient thing you can do :wink:

If you don’t use the ESS assistant in your MultiPlus-II, it will ensure that there is no back-feed into the grid. If you are using the ESS assistant, there is an option in the GX device to not allow DC-coupled PV feed-in. However, as @dognose mentions, there are always tolerances involved.

Do you currently use the ESS assistant and how does the system behave if you start charging with 10A with your mobile charger?

9

evcc does take into account all surplus, including what goes into your battery. You can also configure up to which ESS battery SOC the battery has priority, when that SOC is reached and the battery is still being charged, that power is seen as “surplus” and (if it is enough, above 6A) sent to the car.

I guess as long as you set that “priority SOC” to below 100%, everything should work as expected; you can still fully charge your ESS batteries after the car is full (or has reached the maximum SOC you set in evcc).

Maybe have a look at their demo system to explore all the features (scheduled charging, support for dynamic power tariffs etc) and decide if you want to stay in the Victron world or spend the additional effort to learn and run another system.

10

My system isn’t installed yet, so I don’t have much experience with its behavior, nor the Victron ecosystem…

What I understood is that in France injection is tolerated with systems under 3kW, (I have 5kW ready to be installed). With systems above 3kW injection is not allowed, but there is a tolerance (meter precision) of 10Watts per 30 minutes…
I was thinking of declaring 3kW (installing 5kW) but they will come and verify the whole system, so that would mean adding panels later on. But since there is a castle 500 meters further, it is a possibility they will deny solar panels anyhow… I feel it is my right to produce my proper energy, and even more considering the energy and cyber mess in the whole world. No one will be able to see my panels…

11

Turns out this is actually feasible – I’m running a -10W setpoint, and I use the grid operator’s meter as my meter for it, which only publishes the data every 5 seconds, and still every hour I do get an export reading of 0,01kWh on that meter. Sure there will be fluctuations in instantaneous readings, but in the end this is what gets metered, and in my configuration it works out (probably due to the way the meter does it’s averaging).

12

thanks dognose, your post gives me confidence it will be possible. Now i just need to find a solution getting those panels on the roof without it being refused :worried: