Eco mode" with smart load from solar inverter + scheduling on a zero export solar system?
M
Michael Oosting
started a topic
5 days ago
I've been trying to figure out if the OpenEVSE could be integrated with the solar system I'm installing in the way I'm envisioning in an automated way, because it seems like the "eco mode" was not set up for this kind of installation.
Let me explain why this would be complicated, bear with me because it's a lot. Government grants for solar systems here in Ontario, Canada can for some reason only be used for zero export load displacement systems instead of a conventional net metering system that exports excess solar power to the grid. I would not be allowed to export to the grid at all, even though the inverter would be directly connected to the grid. Ie, while my house and inverter would be connected to the grid, the solar inverter is configured to prevent export to the grid under any circumstances using a CT to the meter and instead store excess solar power in batteries to be used at night and just cut off the panels from the grid if the batteries get full. However, unlike in many other jurisdictions which force you onto tiered billing with home solar, I am allowed to stay on a time-of-use billing system with this setup with my utility and take advantage of their ultra-low overnight rate.
The OpenEVSE's "eco mode" intended to be used with solar installations, and really any EVSE I've found with solar integration, seems to be designed to use a CT to detect when there would be export to the grid in a classic net-metered solar system and enable EV charging whenever this happens. In OpenEVSE's case it seems this is done via an Emonpi which enables the EVSE through MQTT or HTTP Post. This would not work at all for my installation as grid export would always be prevented by the CT connected to the inverter itself. So I need some way to activate the EVSE based on the solar battery charge level, instead of based on a CT detecting grid export.
Theoretically, the inverter itself provides a solution to this problem. The inverter I would be installing is a Luxpower LXP-LB-US 10K, a 10kW hybrid split phase inverter. It has a feature it calls a "smart load" output right on the inverter which will go live at up to 240V 41.6 amps (10kW) whenever the batteries reach a configured state of charge (say 100%) and some configured amount of photovoltaic watts are detected (say, something low like 100W) and then stay on and drain the solar batteries until whenever the batteries drop to a certain threshold (say 50%). This is designed, at least according to the manual (which I've linked a screenshot of to show the smart load configuration), to be connected to something like a second hot water heater so you could store excess solar power in some form other than the batteries connected to the inverter. But there's no reason it couldn't be used for an EVSE. In theory I could just wire an EVSE set to 40 amps directly to this smart load output, and bam, I get an EVSE that will only turn on when there is excess solar power beyond what I can store.
There's three problems with that approach though. The first is that this would cut all power to the EVSE at all whenever the smart load is off, which is not exactly how they're designed to be run and would require it to boot up whenever there's excess solar power. The second is that this would draw all power used to charge the car from the solar batteries instead of the grid, wasting battery life cycles and causing losses from DC>AC conversion for no good reason. And the third is that since I am still able to use time-of-use billing, I would also want the EVSE to charge the vehicle during off-peak power from 11pm-7am. So what I want is this. I want the EVSE to begin charging under either of these two circumstances:
1) The smart load output of the solar inverter is live (or some other method of detecting when the batteries are full), either by drawing power from the panel or from the smart load itself 2) It is between 11pm and 7am, only drawing power from the panel and not the batteries
Does anyone have any ideas as to how this could be done? As someone who knows way more about electrical circuits than about home automation, I've come up with a few ideas to do this in actual hardware, but none seem practical or cost-effective. For example:
1) Use an automatic transfer switch and a timer to switch between the smart load output during the day and a circuit directly on the panel connected to the grid during the night 2) Use the smart load to power a relay that connects the EVSE to the grid 3) Use a CT to detect current on the smart load connected to some small secondary load, like a light, and enable a main panel connected OpenEVSE in eco mode with that CT instead of putting the CT on the power main out of the house.
It's too bad that the OpenEVSE doesn't just have a direct "smart load" input that could interface with this feature, as it's not exclusive to this brand of solar inverter. Lots of hybrid solar inverters on the market have the exact same feature and it would make this way easier. But absent that if anyone has any good ideas as to how I could do this, I'd appreciate it.
Michael Oosting
I've been trying to figure out if the OpenEVSE could be integrated with the solar system I'm installing in the way I'm envisioning in an automated way, because it seems like the "eco mode" was not set up for this kind of installation.
Let me explain why this would be complicated, bear with me because it's a lot. Government grants for solar systems here in Ontario, Canada can for some reason only be used for zero export load displacement systems instead of a conventional net metering system that exports excess solar power to the grid. I would not be allowed to export to the grid at all, even though the inverter would be directly connected to the grid. Ie, while my house and inverter would be connected to the grid, the solar inverter is configured to prevent export to the grid under any circumstances using a CT to the meter and instead store excess solar power in batteries to be used at night and just cut off the panels from the grid if the batteries get full. However, unlike in many other jurisdictions which force you onto tiered billing with home solar, I am allowed to stay on a time-of-use billing system with this setup with my utility and take advantage of their ultra-low overnight rate.
The OpenEVSE's "eco mode" intended to be used with solar installations, and really any EVSE I've found with solar integration, seems to be designed to use a CT to detect when there would be export to the grid in a classic net-metered solar system and enable EV charging whenever this happens. In OpenEVSE's case it seems this is done via an Emonpi which enables the EVSE through MQTT or HTTP Post. This would not work at all for my installation as grid export would always be prevented by the CT connected to the inverter itself. So I need some way to activate the EVSE based on the solar battery charge level, instead of based on a CT detecting grid export.
Theoretically, the inverter itself provides a solution to this problem. The inverter I would be installing is a Luxpower LXP-LB-US 10K, a 10kW hybrid split phase inverter. It has a feature it calls a "smart load" output right on the inverter which will go live at up to 240V 41.6 amps (10kW) whenever the batteries reach a configured state of charge (say 100%) and some configured amount of photovoltaic watts are detected (say, something low like 100W) and then stay on and drain the solar batteries until whenever the batteries drop to a certain threshold (say 50%). This is designed, at least according to the manual (which I've linked a screenshot of to show the smart load configuration), to be connected to something like a second hot water heater so you could store excess solar power in some form other than the batteries connected to the inverter. But there's no reason it couldn't be used for an EVSE. In theory I could just wire an EVSE set to 40 amps directly to this smart load output, and bam, I get an EVSE that will only turn on when there is excess solar power beyond what I can store.
There's three problems with that approach though. The first is that this would cut all power to the EVSE at all whenever the smart load is off, which is not exactly how they're designed to be run and would require it to boot up whenever there's excess solar power. The second is that this would draw all power used to charge the car from the solar batteries instead of the grid, wasting battery life cycles and causing losses from DC>AC conversion for no good reason. And the third is that since I am still able to use time-of-use billing, I would also want the EVSE to charge the vehicle during off-peak power from 11pm-7am. So what I want is this. I want the EVSE to begin charging under either of these two circumstances:
1) The smart load output of the solar inverter is live (or some other method of detecting when the batteries are full), either by drawing power from the panel or from the smart load itself
2) It is between 11pm and 7am, only drawing power from the panel and not the batteries
Does anyone have any ideas as to how this could be done? As someone who knows way more about electrical circuits than about home automation, I've come up with a few ideas to do this in actual hardware, but none seem practical or cost-effective. For example:
1) Use an automatic transfer switch and a timer to switch between the smart load output during the day and a circuit directly on the panel connected to the grid during the night
2) Use the smart load to power a relay that connects the EVSE to the grid
3) Use a CT to detect current on the smart load connected to some small secondary load, like a light, and enable a main panel connected OpenEVSE in eco mode with that CT instead of putting the CT on the power main out of the house.
It's too bad that the OpenEVSE doesn't just have a direct "smart load" input that could interface with this feature, as it's not exclusive to this brand of solar inverter. Lots of hybrid solar inverters on the market have the exact same feature and it would make this way easier. But absent that if anyone has any good ideas as to how I could do this, I'd appreciate it.