question

spencerd avatar image
spencerd asked

Daily forecast and delivery

I have a 4kw system with Pylontech batteries, Cerbo GX, Multiplus II 5000 and MPPT RS.

It's been running for about two months and works great giving me zero usage from the grid, but it's summer here and I wouldn't have expected anything else. I.e. the available solar combined with the batteries is greater than my kWh needs.

I'm planning ahead for both my EV arriving and also winter, i.e. my kWh needs will be greater than my available solar.

I've enabled node-red and have an idea in my head but I'm on a very steep learning curve with node-red and I was hoping that someone else had already done what I was planning and I could just use it :)

The idea is as follows, hopefully it's fairly generic and can be used by others:-

I have a known household load which is fairly regular by hour.

I have a forecasted solar energy in kWh broken down by hour from the node-red solar-forecast flow. This uses weather estimates and my location to estimate the kWh per hour for the rest of today.

By taking the forecast energy for the rest of today, less the household load for the rest of the day I get the potentially available solar for the rest of the day. If I add to that the kWh available in the batteries I get the total available for the rest of the day.

I would then like to use this available kWh based on some rules. Each hour I would re-estimate the rest of the day.

All of this would of course need to be fully automatic using e.g. node-red

My two main loads today are a 3kw immersion heater (water heater) and an EV. As the EV may try and take a kW close to the maximum of my Multiplus, I would like to have this on a timer of some sort, e.g. a maximum of 30 minutes at peak load before a 5 minute cool down. The two loads are connected to SonOff 25amp PWR3 boxes, these in turn are enabled/disabled by SonOff MiniR2 switches which connect to the two Cerbo relays.

The rules may be:-

If EV is connected and available kWh is > amount needed to run immersion heater until the tank is hot, then use the available kWh to send to the EV.


I'm hoping I'm reinventing a well made wheel here and someone can point me in the direction of some pre-made flows :)

Node-RED
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3 Answers
hominidae avatar image
hominidae answered ·

@SpencerD "If EV is connected and available kWh is > amount needed to run immersion heater until the tank is hot, then use the available kWh to send to the EV."

...just note, that one cannot send available kWh to an EV. Charging an EV is different.

On AC, an EV only will start charging when al least 6Amps per (connected) phase is made/signaled to be allowed. One can adjust the signal of "allowed Amps" during charging when using an intelligent wallbox, hence steering the load that is charged by the EV. However, the EV will only use a load up to the Power, based on the allowed Amps, but its BMS could decide to charge at a lower rate.

When using the standard 1-phase, portable AC charger (brick) that comes with it, one is limited to max 12A and these things are non intelligent. At best, one can limit the Amp setting every time after it gets plugged into the AC socket.

Based on your use case, best use an intelligent wallbox, that knows about your victron setup (PV, battery, grid status & control) as well as your additional appliances, like your heater and that can prioritize the actual power available. Note: actual power, not energy from forecast).

If not all of that is available in your wallbox, at least go for a wallbox that can be externally controlled - look into EVCC - and then use node-red to add extras, like you intend.




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spencerd avatar image
spencerd answered ·

I would prefer an intelligent charger, it would be neater too. My reason for not getting one at the moment is that the ones supported by the UK power companies with good rates, don’t seem to support solar too well. The victron one is excellent on solar but doesn’t work with the power companies I’d like to use. I hope in time, I’ll be able to change my temporary blue plug solution to a proper smart charger that supports solar and the rates I’d like.

I was under the impression that my new car (Tesla) allows me to specify a charge rate in amps via the AC charger. But as I haven’t tried to use it yet I’m not sure if or how this works in practise.

I think what you’re saying is that you don’t push kWh to a load, the load needs to demand the kWh. If that’s a good summary then yes I am aware of that.

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hominidae avatar image
hominidae answered ·

....again, I recommend to look into EVCC, as linked above. It supports a lot of charging solutions/wallboxes and victron setup as well.

Even a simple Shelly or tasmotized plug (like a sonoff) can be used....

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