TOU w/ PV battery charging strategy

[ASword]

I haven't found a thread yet which discusses this situation. I'm interesting in installing a hybrid inverter and a set of batteries (with about 1 day of capacity), to add to my existing AC coupled grid-tied PV and my standby generator (winter outages are common). Our utility has started offering TOU billing, where we pay less for power from about midnight to around dawn, and more for 4pm - 9pm. If I'm storing energy its clear that I would ideally capture excess PV to the battery, and then use it during the peak rate time. But I also want to ensure that I have enough in the battery to get through the peak rate time... which is also our peak rate time. The best time to charge from the grid is during the low rate period, but solar is cheaper than the lower rate so it seems that ideally we would predict how much solar is expected and charge from the grid enough so that the solar would fill the batteries. Prediction is hard, however, and most inverters don't have sophisticated external controls (and certainly no internal predictive logic). Plus this varies greatly seasonally -- in the winter solar is about zero, and in the height of summer solar exceeds household consumption (and gets sold back to the grid, albeit at a mediocre price).

What strategies are people using in this sort of situation?

 

[BipedalPrimate]

In the Victron universe, there is DESS (Dynamic Energy Storage System) which takes battery size, solar forecast, grid charges by time of day, consumption forecast and sell to grid price to determine an optimal charging strategy.

Not sure if it includes generator capability.

 

[ASword]

I think I’ve collected enough seasonal and historical data now that I could train a reasonable predictive model for this. Just need enough programmatic control over the inverter, which actually seems to be the bigger problem.

 

[BipedalPrimate]

which actually seems to be the bigger problem.

Again in the Victron universe, you can use Node-Red with Victron created nodes to read/write control signals to the inverter.

 

[ASword]

Is there a Victron equivalent to the EG4 18kPV / FlexBoss / GridBoss, or Sol-Ark AIO, or Midnite Solar AIO, etc?

 

[jgh]

I'm using Home Assistant, pulling data from Solcast and controlling my Solis using self-developed HA automation via mqtt/ethernet/rs485.

 

[ASword]

Excellent— very much what I want to do with my own self-developed HA. I don’t think the solis inverter can do what I need, but I’ll go back and check. Do they have a published interface, has somebody done the reverse engineering in HA, or did you do the heavy lifting yourself? Is it modbus or LAN?

 

[BipedalPrimate]

Is there a Victron equivalent to the EG4 18kPV / FlexBoss / GridBoss, or Sol-Ark AIO, or Midnite Solar AIO, etc?

Not for the North America market.

 

[jgh]

Excellent— very much what I want to do with my own self-developed HA. I don’t think the solis inverter can do what I need, but I’ll go back and check. Do they have a published interface, has somebody done the reverse engineering in HA, or did you do the heavy lifting yourself? Is it modbus or LAN?

It's modbus/tcp as far as HA is concerned. There's an HA integration (that's their term; think "loadable module") which does the heavy-lifting to present named entities for the registers. I have an external ethernet/rs485 converter; the hardware port on the Solis is rs485.

You lose the wifi dongle that reports to the Chinese website-access, because that also uses the 485 port.
Unless you add another external gadget to multi-master rs-485 (the Solis is a 485 slave).