Charging Model S from excess solar

[andrewrogers]

I've dug around a little and can't find anyone other discussion of this, wanting to know if anyone has looked into charging the model S from excess solar PV?

What I had in mind was a system that could recognise when the PV system was producing more power than was being used by the home and then tip any excess into the Tesla. Cloudy days would get very little charge, sunny days lots of charge.

Systems like Solar-Log (Homepage) or the SMA Sunny Home Manager look like they could do the routing. Can the HPWC be given varying amounts of current to work with?

My memory was that Tesla recommend leaving the car plugged into the charge whenever possible (even if charging is onlye scheduled to occur at night). I assume this avoids wasting finite battery charging cycles from idle power consumption, cooling etc. If in the above setup an actuator was being used to kill power to the HPWC I assume this is not so good for the car?

Has any tried to work through any of these issues?

 

[paulp]

You can do this with a zennio automation system. It determines when excess solar is available, then activates whatever is pre-programmed to use the excess power, and in a hierachy. Obviously the car has to be plugged in during the day for this to occur, unless you have battery storage.
Your car went two months without charge on the journey to australia. One or two days wont hurt it - the tesla battery warranty should answer your concerns.
Also worth noting that my car charges faster under solar, the voltage is cleaner, more consistant, and higher.

 

[360C]

My system uses SMA Sunny Home manager. See my posts in the running costs of Model S thread.

 

[miimura]

SmartEVSE has been used in this way. See this thread: Smart EVSE (Open Source)

 

[andrewrogers]

Very helpful, thank you kindly all, Smart EVSE or Zennio sound like they will do the job.

To clarify what I'm hoping to achieve - all little more background:

- The car is often at home during the day
- My typical distance travelled is 20-30kms per day so plenty of tolerance for only partly charging each day
- I'm on time of use power so using solar is good but using grid power during the day ($0.2 / $0.4 per kWh) quickly removes the benefit (vs $0.11 kWh at night)
- I can only get a $0.05 / kWh FiT
- I have my own monitoring of grid consumption in place via the solar inverter
- I don't have any batteries for the house
- I'm wanting to use power represented by the the purple are of this graph to charge the car. Blue is existing solar self consumption. Grey line is grid consumption.

 

[gcgp]

I made something that did this.
I used an arduino and had it monitor the voltage of my battery bank (my house is partially off grid) and it switched on a relay to start charging my Volt when the battery bank was full.

 

[paulp]

Very helpful, thank you kindly all, Smart EVSE or Zennio sound like they will do the job.

To clarify what I'm hoping to achieve - all little more background:

- The car is often at home during the day
- My typical distance travelled is 20-30kms per day so plenty of tolerance for only partly charging each day
- I'm on time of use power so using solar is good but using grid power during the day ($0.2 / $0.4 per kWh) quickly removes the benefit (vs $0.11 kWh at night)
- I can only get a $0.05 / kWh FiT
- I have my own monitoring of grid consumption in place via the solar inverter
- I don't have any batteries for the house
- I'm wanting to use power represented by the the purple are of this graph to charge the car. Blue is existing solar self consumption. Grey line is grid consumption.

You wont be needing many solar panels for 30km per day, so your purple area should provide plenty. Of course you could always self manage using the phone app and your panel app, but that would get tiring after a while.

 

[TesAus]

You wont be needing many solar panels for 30km per day, so your purple area should provide plenty. Of course you could always self manage using the phone app and your panel app, but that would get tiring after a while.

If you only want to top up a small amount each day and car is around for most of the day then just set the charge rate really low so that it will take most of the day and your chances of exceeding the capacity of the solar is minimised?

 

[paulp]

If you only want to top up a small amount each day and car is around for most of the day then just set the charge rate really low so that it will take most of the day and your chances of exceeding the capacity of the solar is minimised?

Good point!

 

[bradjc]

Hoping to do the same. Does the Telsa app let you change the charge rate remotely? I could tweak it during the day when the sun comes out. I can't access the app to play around until my MS arrives. :/

 

[paulp]

Hoping to do the same. Does the Telsa app let you change the charge rate remotely? I could tweak it during the day when the sun comes out. I can't access the app to play around until my MS arrives. :/

You can only start or stop charge, or change the charge limit (eg 85% charge)
From the car you can set the amperage ant it tells you remaining time, so maybe tweak the amperage so the remaining time is until just before sunset.

 

[NovoCasGreeny]

Surely there is a smart switch/software system that will only feed charge to the car when it is available, ie. in excess of the consumption at the property?

 

[paulp]

Surely there is a smart switch/software system that will only feed charge to the car when it is available, ie. in excess of the consumption at the property?

Yep, a zennio management system does that. It monitors solar and consumption, and if solar exceeds consumption, it turns things on in a pre-programmed order.

 

[gizmonty]

The biggest problem with this is that there is no way of setting the charge rate of the car via the API. Like you my car is home during the day (maybe 3 days/week) and I would love to have a system in place that recognises that I have 8 Amps of excess solar currently so please feed that into my car.

What I do instead is have my car set to charge at 10-15A depending on the season (I have a 5 kW solar system) and have a start time of around 8am set. I have to remember to manually stop the charging when the sun is heading down. If I head out during the day I plug it back in when I'm home. If it's within a few hours of the programmed start time it will start charging but I have to check if it's later in the day.

It's all a bit of a hassle, but I do manage to achieve the majority of my charging from solar for most of the year. I drive about 200km/week.

If Tesla released an API that let me set charging rates then I would hack something together to do what you describe, but being forced to choose a charge rate and stick with it, I just don't think the gain would be worth the extra effort over what I'm already doing.

 

[paulp]

Yes its not a precise outcome

 

[Didaho]

Old thread - but I found it so:
Cool little project that adds a Raspberry Pi to the HWPC (v2) to control the feed rate.

 

[srwx]

I did a micropython version that lets me change the charge rate via MQTT which in turn is managed by my self written home automation which by default dumps all excess solar into the car. Basically the sam as the RaspberryPi solution but with fewer complications (like failing SD cards and having to manage a OS).

 

[Hungry Mile]

Yep, a zennio management system does that. It monitors solar and consumption, and if solar exceeds consumption, it turns things on in a pre-programmed order.

Cool little project that adds a Raspberry Pi to the HWPC (v2) to control the feed rate.

I did a micropython version that lets me change the charge rate via MQTT

Wow. Have you guys heard of the Zappi? Then again, it's over $1000, so maybe you've all "nup"!
I must know more...

 

[srwx]

Wow. Have you guys heard of the Zappi? Then again, it's over $1000, so maybe you've all "nup"!
I must know more...

For me I already had a perfectly good HPWC and I enjoy reverse engineering things, so it was mostly me prioritising fun over cash. It also means I can do more specific implementations that suit how I want it to charge my car, e.g. I have a command I can run on my server where I simply set a SOC I want to achieve and the time I want to achieve it and my automation works out the correct charge rate to do that - thus charging my car and perfectly pre-conditioning prior to departing

 

[paulp]

Wow. Have you guys heard of the Zappi? Then again, it's over $1000, so maybe you've all "nup"!
I must know more...

From what I can tell from their website, its using ct clamps to determine the direction of energy flow and then activating the charger. Thats exactly what my zennio whole of house system does. Mind you this time of year when I’m pumping over 20kw out to the grid I fairly much just run everything to save giving up my power cheaply. Waiting for approval for my 3 powerwalls.