Delaying/Limiting Powerwall Charging Until Midday Peak Solar Production

[xrg458]

Situation:

• I’m in Western Australia and our energy provider restricts our inverter output to 5kW (this is TOTAL output of the inverter including home and grid export - yes crapola).
• I’m planning a large solar system (circa 13kW of panels) + single Powerwall 3 + EV (not Tesla, most likely VW product) and EV charger (not Tesla, most likely a Zappi).
• Standard charging behaviour is to fully charge PW3 battery and after battery fully charged to use excess solar power to go into EV charger/EV using EV charger CT placed on the side measuring power flowing to the grid.
• Problem with this approach is that PW3 will have charging priority first and will be fully charged by mid/late morning given my oversized solar system for most of the year (sunny climate).
• Issue is that late morning to early afternoon solar generation power curve will reach over 5kw for ~9 months of the year (up to circa 9kW in my setup in summer) and I'll be wasting that excess solar after battery has charged even with full 5kW household (including EV charging) based on the total 5kW inverter output restriction.

Requirement:

• I want to be able to delay/restrict PW3 charging to around these midday peak generation curve hours so I can maximise EV charge rate throughout the solar window - this will ensure one (and maybe even second EV in future) is fully charged by excess solar vast majority of the year.
• I’ll need single PW3 battery fully charged by 3pm to coincide with energy provider’s peak time of use period. During three or so months in winter, standard PW3 Time Based Control should be fine as unlikely to be generating much over 5kW peak solar generation and will need to partially charge PW3 from grid during cheap grid consumption period (9am-3pm).

I’ve investigated Charge HQ however is unable to accommodate this Western Australia specific constraint unfortunately (they can deal with export limitations not total inverter limitation on an oversized system).

I’m leaning towards either the following options:

1. Setting fake PW Time Based Control rate settings to manipulate charging behaviour as has been talked about in some forums.
2. Doing something with Home Assistant (still to research)
3. Doing something with NetZero (still to research)

Inputs appreciated.

 

[jgleigh]

Why can't ChargeHQ do what you need? Set EV as priority over battery and it will charge first.

 

[jjrandorin]

You want more customization than Tesla provides. I think you should be looking at some other system other than a Tesla one.

 

[BGbreeder]

I do not see how @xrg458 can game this much if the inverter output is throttled. I think a little could be done by a fake utility rate would help, but as far as I know nothing short of CT monitors on the inverter and on the EV, with a variable EV charger would likely optimize the inverter output.

 

[xrg458]

True, however their solar excess function isn't based on

Why can't ChargeHQ do what you need? Set EV as priority over battery and it will charge first.

True, however from their site regarding excess solar function, “Excess Solar: only excess solar is used for charging. Excess solar = generation - household consumption”: Using Export Limited Solar for EV Charging

However as my PW3 inverter will be 5kW total (household + grid export combined) AC restricted (local energy provider requirement) + excess DC going into battery charge the formula for excess solar to go into EV charger should be generation *up to 5kW* minus household consumption.

So for example if the home is consuming 2kW and the Powerwall is supplying up to 5kW max then there is a solar excess of 3kW that can be used for solar charging only. Have reached out to Charge HQ to see if this is something they can support.

I've pulled out the crayons to diagrammatically represent what I'm trying to do:

Based on this, how would you meet requirement, in particular how to achieve the functionality represented in green?

i.e. I don't want to charge PW3 battery earlier in the morning as the (single) 13.5kWh battery will be fully charged by mid-late morning and will therefore will waste solar generation above 5kW from midday onwards as can't be "used" by inverter given 5kW total production limit.

The "best" solution is to somehow implement the logic which is "EV charge FIRST (before PW3 battery charging) up to 5kW after first subtracting household load based on solar excess only (not sure if EV smart chargers can be configured this way). PW3 would then dump remaining solar generation above 5kW into DC battery using its standard behaviour.

Notes:
1) Our energy provider limits single phase oversized hybrid inverters to 5kW output TOTAL production capacity (household + grid combined).
2) Blob in blue will be handed by a conventional "smart" EV charger with CT on grid export side (from PW3) of wiring (will read 0-5kW max at any one time given that's max output of inverter).

 

[BGbreeder]

Do you have a sense for how many kWh might be in your "excluded" green peak? (Per day? Per year?)

I would look for a DC loads that you might be able to add; hot water heating elements (inexpensive), a programmable controller for other DC loads, e.g. DC AC unit(s), DC freezer fridge, or even a DC battery by a different vendor... or try to find a vehicle that could respond to some signal to DC charge.

 

[jgleigh]

The "best" solution is to somehow implement the logic which is "EV charge FIRST (before PW3 battery charging) up to 5kW after first subtracting household load based on solar excess only (not sure if EV smart chargers can be configured this way). PW3 would then dump remaining solar generation above 5kW into DC battery using its standard behaviour.

Doesn't ChargeHQ already support this? You can prioritize EV charging over battery charging and set max charging limits. How is the 5kW inverter maximum enforced?

The ChargeHQ guys are in Australia and typically very responsive to inquiries.

 

[Mark Purcell]

Tesla Charge on Solar does this natively. It will prioritise charging EVs and will hold the Powerwall battery at the current State of Charge, until EVs pass the Charge of Solar threshold.

I also do the same thing with Home Assistant, so you have lots of options.