Excess solar for EV charging - how to automate?

[PConlin]

AFTER the house batteries are fully charged I want to send EXCESS solar production to our Tesla. We are zero export grid tied so once batteries are full any excess solar power not used by the house is wasted. Sending the excess to the cars makes charging them truly “free”. I see some discussion in these forums about using excess solar for domestic hot water (which I’d like to do too someday, as a 2nd priority after the cars are charged) but I don't see a solution to control/automate this process but maybe I missed it and someone can send me a link.

Emporia says their EV charger, when combined with their Vue energy monitoring, can charge off of excess solar but I can’t find the technical details to know if this will do exactly what I want. Prowse mentioned this feature in his L2 charge comparison video but didn’t go into detail and it sounded like he didn’t test it. Has anyone here use this Emporia excess solar charging feature?

This is another form of “Smart Load” or “Smart Panels”. Sol-Ark and EG4 have a smart load feature that I am still trying to understand. Sol-Ark will soon sell a Smart Panel load shedding system and other companies already make them. This is the future of this industry but I think these features/products are all either on or off because most circuits are fixed loads and/or need a minimum current to properly function. I want to keep the car plugged in but only charge it with the excess solar, which is going to rise and fall with sun/clouds and with house loads. The car can easily handle varying charge current. A relay/contactor on the EV charger circuit would be crude all or nothing 50A or 0A.

What I want is to control the current going to the EV so only the excess solar power is consumed by the car(s) and no grid power is consumed.

Tesla is adding this feature to their ecosystem but we are more DIY here, or at least AIY (Assemble It Yourself).

 

[DIYrich]

This is another form of “Smart Load” or “Smart Panels”. Sol-Ark and EG4 have a smart load feature that I am still trying to understand.

You would hook up the charger to the Gen Input of the Sol-Ark.
In the "Smart Load" tab, you select "Use Gen Input as Load Output".
Then set "Smart Load On Batt" to 95%. When the batteries hit 95%, the connection is energized, and your charger will start receiving power.
You also need to set "Smart Load Off Bat" at something lower than "Smart Load On Batt". At that level, the connection will turn off.
There is also a "solar watts" setting. When "On Grid", the connection will turn on if solar production exceeds the wattage. That is helpful if excess wattage exceeds the charge speed of the batteries, and you prefer not to export to the grid the excess.

The problem you have is limiting power to the charger. You can't say: "I have 1kW of excess, charge at that rate".

Automatic Solar Powered Car Charger Overflow Dump

I put together a very small MPP HV/LV2424 2400 Watt inverter, on 1300 watts of panels, which powers most 120v devices in house all day/night (fans/refrig/lights/computers) and often found my 4.3kwh lithiums filling up with my average 500 watt home load on sunny days. This simple script turns...

diysolarforum.com

 

[Rusty959]

I'll start by saying I don't have a perfect answer for you, but I've always viewed the Emporia as being able to do exactly what you're describing. The communication between "wall connector" and the EV is definitely capable of real time adjustment of current drawn so that when say you have 2000 watts of excess, it pulls 2000 watts.

Since I've already got the Vue setup, I've considered adding the EV charger, just haven't pulled the trigger yet.

The Sol Ark or EG4 are not able to control output on the smart load port, it's only on or off, which with the massive amount of power an EV can pull means it isn't all that useful for this purpose. In most cases you'd have to just manually turn the charge current way down on the EV and have rough numbers set on the inverter that won't actually correspond to the use elsewhere in the house, true excess. So it's not worthless, but definitely not optimal.

If you wanted a cheap solution, the Emporia Vue can also do smart "excess" control with the smart plugs, which is a bit easier on the wallet than the EV charger, besides being useful for other purposes.

 

[Hedges]

I don't think EV chargers have CT to vary charging for the purpose of implementing zero-export.
But home batteries do.
So just let your EV charge at either level 1 or level 2 rates, and have your home battery charge with whatever surplus would otherwise export.
You might use a timer to switch EV between level 1 and level 2 according to approximate PV production curve.

What you ask for is reasonable, but software is more expensive, more difficult, less reliable than hardware. It should be available as a product eventually. In the mean time, implement the opposite priority charging using available products.

 

[Ampster]

Emporia says their EV charger, when combined with their Vue energy monitoring, can charge off of excess solar but I can’t find the technical details to know if this will do exactly what I want. Prowse mentioned this feature in his L2 charge comparison video but didn’t go into detail and it sounded like he didn’t test it. Has anyone here use this Emporia excess solar charging feature?

I use the Emporia excess solar charging feature. It works pretty well even though the Emporia doesn't know how to take into consideration the charging load of my SolArk and the DC solar attached to the SolArk. I have the CTs that measure solar on my AC coupled micros that go into the gen port of the SolArk. It seems to work pretty well. The hardest part was figuring out that the Emporia needs some set up and then it needs to be in Pause mode so that the excess Solar algorithm can pick the correct charging rate.

 

[Ampster]

I don't think EV chargers have CT to vary charging for the purpose of implementing zero-export.

That is correct. The term EV charger in some of the above posts is actually referring to the EVSE which in the case of the Emporia, is able to use the CT in the other part of the Emporia Vue system. Then it does the calculation and sends the correct signal to the onboard charger to set the charging rate of the onboard charger.

 

[timselectric]

When I get that part of my system set up.
It will be a simple charge/no charge, based on the SOC of my system batteries.
Once my system batteries are above 90%, the charger will be active. And at 70% it will be deactivated.
All excess production will be handled this way. And sent to various loads.

 

[PConlin]

Thanks for all the responses so far.

It is good to hear the Emporia “excess solar” mode works on their charger together with their Vue energy monitor. Really smart strategy on their part to build a system this way. However, I don’t think it will work for our situation. As I understand it so far, the Vue uses current sensors on the mains so their “excess solar” mode is essentially doing zero metering. It ramps the charger down and up trying to get the outbound power towards zero. Cool. But.

Unfortunately our Sol-Ark is going to be doing the same thing as the Emporia system because we need to operate it in zero meter mode as we can’t export power to the grid, so it would be decreasing output power to the house regardless of excess solar. This means the Vue is never going to see negative power (export) so it won’t ramp up the EV charger, so the car always gets nothing. At least this is how I understand the Emporia solution.

The Sol-Ark 15k and EG2 18KWPV have a “smart load” function (replacing the auto generator mode, as mentioned above by Ampster & Rusty959). This is binary on-off based on programmable thresholds on PV and battery SOC, so it won’t work to provide variable power the EV charger. So what about this idea? What if I connected these smart load terminals to a water heater element in a pre-heat tank AND to the EV charger. Let the Emporia Vue measure current for just the water heater. The Emporia algorithm would then regulate the EV charger trying to consume the “extra” power going to the water. The Central controller would regulate the smart load on or off when there is excess solar so when the sun goes down the EV charger would not pull from battery. When the car is full or unplugged the charger would direct all the excess solar into the water. Neat. The only glitch would be when the water tank hits its high temp limit shutting off it’s heater element. When this current went to zero I think Emporia would ramp the EV charger down to zero thinking there was no excess solar. I would have to use a larger tank or come up with another energy sink like sending the water to a hot tub in the summer or to a water-to-air radiator in the winter but that would be a good thing. And I would need a “car priority” transfer switch to power the EV charger from mains when the car needs charging when there is no excess solar.

Another crazy idea would be to power charger from mains and use an IotaWatt to measure PV and battery, and some custom software to command the appropriate charge current on an OpenEVSE charger. This custom software could then also charge the car when the PV goes to zero indicating it is night time and there will be no excess solar coming before the car needs to be full by morning for tomorrow's commute. If we ever get TOD or surge pricing here we could incorporate timing and power limiting into this special software to optimize for lowest cost. I know also nothing about IotaWatt or OpenEVSE programming, other than they are both open source, so I’m just guessing this is possible at this point.

 

[pollenface]

There's a bit of discussion about this on the MG EV forum, using a photo-sensing relay to trigger the signal wires in a granny charger.

 

[OffGridForGood]

I went 'low tech' and set a simple relay on a "geeni" operated with my I-phone.
If it is sunny out, and the Solar Assistant is reporting ESS SOC above 80% then I click "ON" on my phone app, and the relay closes sending power to the EV charger, as long as I have internet access I can manually switch on the charger no matter where I am.
That said, one sunny day I came home thinking the EV will be nearly fully charged, only to see my spouse forgot to plug it in....doh!

 

[45North]

KISS
First, I would take a look at the overnight rate from your power company - mine just announced a super-low rate of $0.02 /kwh. I assume you wouldn't jump through too many hoops to save 2 cents!
All you would need to take advantage of that would be a simple timer switch, or some EVs already have them built-in.

 

[PConlin]

KISS
First, I would take a look at the overnight rate from your power company - mine just announced a super-low rate of $0.02 /kwh. I assume you wouldn't jump through too many hoops to save 2 cents!
All you would need to take advantage of that would be a simple timer switch, or some EVs already have them built-in.

Simple would be no solar and no batteries. We have flat rate constant pricing. At $0.02 you don't need solar, just batteries.

 

[OffGridForGood]

KISS
First, I would take a look at the overnight rate from your power company - mine just announced a super-low rate of $0.02 /kwh. I assume you wouldn't jump through too many hoops to save 2 cents!
All you would need to take advantage of that would be a simple timer switch, or some EVs already have them built-in.

Yes, me too, were in Ontario and have that 3rd option rate available. The down side is the on-peak moves up to higher rate of 24 cents/kWh.
I am considering if it will be best to stay on the current rates, since we rely on Hydro-One during November and December (crappy solar time for us) or to take advantage of the new 'ultra low rate' 11:00 Pm to 7:00Am every night, and just add more ESS to be sure we are 'good' during that super high rate period 4:00Pm to 9:00Pm weekdays. I already use timers to ensure the ESS doesn't charge using peak rate power, (my Elect HWT hasn't run during peak rates in five years - see Home Depot HWT timer controller intermac 30).
The trick may be to run EV chargers and recharge ESS every night during Nov -Jan on timers set to 11:00 Pm as a normal rule, and then add to my system to ensure I have sufficient ESS and inverter capacity to run the shop and the house at the same time from the battery bank. As we are set today I don't normally power the clothes dryer and Electric stove with the Solar ESS, but these could need to run simulaneously 4:00Pm to 9m on a weekday, and the shop normally runs unil 5:00Pm pulling an additional load on the system all at once.
I calculate my cost for using the ESS is about the same rate of 2.4cents per kWh as the ultra low overnight rate, so definitely a win to use the utility during those hours, or charge the ESS to ensure we shift the loads to all be carried by ESS during peak and mid-peak TOU.
As you say, with a good sized battery bank and inverter, no PV would be a good option for many people too, we just have too many power outages around here to go that route, my business is next door and needs to operate or I am in trouble.

 

[jasonhc73]

I use the Emporia Vue and Charger. It works exactly as expected.

You set the EVSE to excess solar.

When the Vue detects more than 1200 watts going out to the grid, the Vue signals the EVSE to turn on and charge the car. Every 240 watts more after that is another amp more to the EVSE.

You attach two CTs on the line side of the meter and then plug in the EVSE to a 14-50 or hard wire it. It works with any EV with a J plug, I use it on my tesla model 3 with a J-Tesla adapter.

 

[Shimmy]

The reliable options are to run something like Emporia or using Home Assistant and the Tesla API or an OpenEVSE. Personally I like having more control than just if load is under X and PV is over Y then start charging; I want to make sure I will be able to put in at least 1kWh per session.

 

[PConlin]

I use the Emporia Vue and Charger. It works exactly as expected.

You set the EVSE to excess solar.

When the Vue detects more than 1200 watts going out to the grid, the Vue signals the EVSE to turn on and charge the car. Every 240 watts more after that is another amp more to the EVSE.

You attach two CTs on the line side of the meter and then plug in the EVSE to a 14-50 or hard wire it. It works with any EV with a J plug, I use it on my tesla model 3 with a J-Tesla adapter.

Glad it works. But you have net metering. We don't have the ability to send power to the grid so we are operating in zero-meter mode. So the Vue will NEVER see negative (export) power so it won't ramp up the charger. Hence my proposed plan--above--to have a second smart loads breaker panel and have the Vue monitor that.

 

[Ampster]

Unfortunately our Sol-Ark is going to be doing the same thing as the Emporia system because we need to operate it in zero meter mode as we can’t export power to the grid, so it would be decreasing output power to the house regardless of excess solar.

I guess it depends on where your loads are. If your EVSE is wired to the SolArk then it might work without the Emporia EVSE but I don't think you can change the charging rate automatically. Have you thought about external CTs so the EVSE could be powered before the SolArk curtails export?

 

[zanydroid]

Another approach is to use one of the ModBus based EVSE that can have multiple EVSE hanging off one bus along with a power meter (Wallbox is the listed option for US, there are AliExpress options too). Power sharing and peak shaving.

And then implement a custom controller to masquerade as the meter or leader EVSE.

 

[PConlin]

I guess it depends on where your loads are. If your EVSE is wired to the SolArk then it might work without the Emporia EVSE but I don't think you can change the charging rate automatically. Have you thought about external CTs so the EVSE could be powered before the SolArk curtails export?

Remember, original goal is to send all excess solar power to the car without sending battery or grid power to the car. The point is to use the car to capture more free sun energy than we have house battery capacity. All while the SolArk keeps us from exporting any power to the grid.

Where are you suggesting the "external CTs" would go?

 

[zanydroid]

I don't think EV chargers have CT to vary charging for the purpose of implementing zero-export.

The class of EVSE I mentioned are set up to interface with CT via a RS485 power meter that digitizes the CT measurements