Griddy & Powerwall, HPWC etc

[pete8314]

Posting this in the local forum as I know Griddy (referral link, you'll get $25 added to your account if you signup) is fairly widely used in north Texas. For those that know nothing about it, it allows you to buy power at wholesale rates, which means if you keep an eye on things and have a little flexibility in the house, you can save quite a bit of money.

Obviously, charging the cars is one of the main consumers, and normally something that can be scheduled with a degree of flexibility (as opposed to AC). There's times when the cost of power goes negative, which is great, but more often then not at some point in the week I can charge at well below 1c per kw/h.

Griddy has basic IFTTT integration, and there's an API that can pull the real-time price, but what I'd really like to do is:

• Only allow charging when power cost is below a defined threshold
• Stop charging if power cost exceeds a defined threshold
• Same logic for Powerwall, fill it up on cheap power, so it can expend it's power during peak hours

Has anybody managed to do this?

 

[ScottStout]

Hey peter. I’m interested in this approach. I have solar but no batteries. Wondering if (assuming this automation could work) could the battery price be justified based on the savings (by looking at historical price fluctuations). I could probably set up the logic assuming the correct apis exist to start/stop charging on the Tesla side. I’ve been working with Microsoft Flow which is similar to IFTTT.

 

[Chris TX]

Hey Pete,
In order for IFTTT to be able to act upon the Griddy price changes, there needs to be an IFTTT enabled app that uses Tesla's API for Powerwall control. There are several 3rd party apps for controlling/monitoring the cars, but I haven't seen one yet that can control or monitor the Powerwalls. I considered Griddy for a while, since I've got two PWs coming this quarter (fingers crossed!) but came to the conclusion that Green Mountain Energy's free power from 8-6 is plenty to fill up the batteries in the PWs and two electric vehicles. My house isn't optimal for solar, so storing cheap/free wind energy at night might as well be the same effect on my power bill.

 

[mociaf9]

I considered Griddy for a while, since I've got two PWs coming this quarter (fingers crossed!) but came to the conclusion that Green Mountain Energy's free power from 8-6 is plenty to fill up the batteries in the PWs and two electric vehicles. My house isn't optimal for solar, so storing cheap/free wind energy at night might as well be the same effect on my power bill.

Just beware that charging the PWs from the grid will mean that they aren't eligible for the 30% federal tax credit (ITC), which requires that they only be charged from "on-site" renewable generation. I.e. For a residential install, you can only charge them from your home's solar (or, if you have a one, a wind turbine) to remain eligible.

 

[Missile Toad]

@Chris TX , how many hours does it take to fill up each PW? Do they need all 10 hours? I've been tracking wind generation as a proportion to the TX grid demand (or load). If you want to soak up the highest concentration of wind (and minimize CO2 impacts), I've found that more often than not, peak wind appears between midnight and 4AM -- even more so in the Spring, when winds are strongest in Texas. If I were to guess, during seasons with moderate temperatures, your batteries will rarely deplete -- but rather still have 20% or more charge at the end of the day.

 

[OrbiterTI4]

Came here to echo the Green Mountain free energy from 2000 to 0600 plan. I have dual ACs, so I still wouldn't be covered by a two Powerwall situation, but curious how that setup plays out for you.

 

[Chris TX]

Considering my Powerwall2s are

Just beware that charging the PWs from the grid will mean that they aren't eligible for the 30% federal tax credit (ITC), which requires that they only be charged from "on-site" renewable generation. I.e. For a residential install, you can only charge them from your home's solar (or, if you have a one, a wind turbine) to remain eligible.

My two Powerwalls aren't costing me anything, so hooray!

 

[pete8314]

I missed all these replies, Microsoft seems convinced the TMC notifications are spam.

I did look at the GM plan, but Griddy still seems to be the best option for us. For April, we used 3028kwh. 1900 of those were grid, at an 'all-in' price of 6.1c (3.2c for the power, the rest is transmission charges). the rest were solar/battery. Mostly I'm able to manage the basic power flow by only charging the cars at night, or when the price goes negative, which happens every now and then, but I'd much prefer that everything was a bit smarter. The real-time price can (and does) spike at 130c per kw/h, but normally just for a few minutes until a gas power station cranks up, but if you're sucking down power to charge a couple of cars at that time, it get's pricey! Ideally if the price exceeds X, then shut down the air, pool and car charging, and switch over the solar & battery. But if the price gets super-cheap, charge the cars, boost the pool pump and fill up the battery!

 

[ryanm77]

I'm working on getting this working now. I'm a software developer, so I think that between the Griddy API, SmartThings, and the Tesla API, I should be be able to control at least my ACs and charging of my car based on current prices. I'll keep you posted on what I come up with.

 

[pete8314]

That's cool. I have basic logic between Griddy and AC via IFTTT. But it's just that, basic. It'll turn up the temperature if the price spikes, but it can't be made smart enough to only do that if the AC is currently cooling, nor can it reset all the settings once the spike is over. But, the Tesla car and PW implementation would be more useful, if it gets to the point where the car is just plugged in all the time it's in the garage, and just draws power when the price drops below a setpoint.

 

[Missile Toad]

@ryanm77 welcome!. I'm up in Kingwood. I've built a price-sensitive automatic charging program that has been charging my two cars, automatically. This program activates charging when prices (reported by Ercot.com) descend below a user-selected price. I'm also tying in to the Tesla API. Most of the finer points are well-polished off at this point. I'm currently working on an IoT feedback mechanism to report three things:

1. Connection state (wouldn't want to miss big winds and low prices, by not being connected);
2. State of Charge;
3. Which charging source (I have garage options to get 16kW or 1.8kW).

These details are particularly important in the morning, if my 'set price' never got triggered overnight.
Here is my UI, which shows a small graph of projected wind generation over the next 7 days. The percentages indicate the amount of wind penetration on the Texas grid (wind-generation / load).
.

Give me a call/text if you want to discuss this project 281-889-1842.
Robert Rolnik AKA Missile Toad

 

[ryanm77]

Very cool. Sounds like we have slightly different use cases. I really like your solution though. I was actually able to accomplish everything I wanted to do using SmartThings, webCoRE, and IFTTT. I had to add two new SmartApps in SmartThings (one for Griddy and one for the Tesla). WIth those in place, I just had to set up webCoRE and create a piston that does what I'm looking for. So far, it has this functionality:

• If Griddy wholesale price exceeds 5 ¢/kWh
  
  • If Tesla is charging, stop
  • Set Nest thermostats to 82 (using IFTTT Webhooks)
    • I may tweak this a bit using presence data from Nest or my phone and need a way to set the thermostats back down to a cooler temp once the price drops back down to something reasonable.
  • Notify me that price has spiked
• If Griddy wholesale price drops below 1 ¢/kWh
  • If Tesla charge state is less than 90% charged, begin charging
  • Notify me that power is cheap so I can do laundry or whatever too

Other than tweaking the conditions in which some of the actions are taken, I think my next little project is going to be setting up control for the pool pump. Right now, it runs 8 hours a day on a schedule and it's during the hottest part of the day. I'm thinking I'll turn the pump off if prices spike just so I'm minimizing my power draw as much as possible during those times.

 

[ryanm77]

That's cool. I have basic logic between Griddy and AC via IFTTT. But it's just that, basic. It'll turn up the temperature if the price spikes, but it can't be made smart enough to only do that if the AC is currently cooling, nor can it reset all the settings once the spike is over. But, the Tesla car and PW implementation would be more useful, if it gets to the point where the car is just plugged in all the time it's in the garage, and just draws power when the price drops below a setpoint.

I've basically implemented exactly what you described. Check out my post above. If you want to go the same route, feel free to hit me up if you could use any help.

 

[Missile Toad]

I've basically implemented exactly what you described. Check out my post above. If you want to go the same route, feel free to hit me up if you could use any help.

@ryanm77 so I'm looking at SmartThings.. Are you energizing and de-energizing a SmartThings outlet based on the IFTTT logic?

I'm commanding the car, via My server > Tesla-server > ISP > house wifi (usually) > car to make the transitions from 'not-charging' -> 'charging' -> 'not-charging'.

Also, I find 1 ¢/kWh a bit too aggressive. It only gets to that level about 0.5% of the time, and even with a 16kW charger, wouldn't be enough to fuel my driving habit. I'm having better luck setting the threshold to 1.7 ¢/kWh, which, statistically, seems to allow an hour and a half charging, nightly, (on average) here in Houston.

... however, wind-generation forecasts are expecting about 18 GW generation from the panhandle tonight (near record levels), so tonight, 1 ¢/kWh is about right.

 

[ryanm77]

@ryanm77 so I'm looking at SmartThings.. Are you energizing and de-energizing a SmartThings outlet based on the IFTTT logic?

I'm commanding the car, via My server > Tesla-server > ISP > house wifi (usually) > car to make the transitions from 'not-charging' -> 'charging' -> 'not-charging'.

Actually no. The Tesla SmartApp that I linked to above uses the Tesla API directly, so it can control the car without the need for an outlet in the middle and without the need for me to host a server for integration. It's a pretty slick set up. When prices spike, SmartThings sends a command to the Tesla API and it stops charging.

 

[Missile Toad]

OK, I'm digesting the code now. I'll read over the next night or two. Only part that gets me a little nervous shows up in the first 50 lines:

To use Tesla, SmartThings encrypts and securely stores your Tesla credentials.
​

I'm also checking out trentfoley/SmartThingsPublic

More details emerge... SmartThings

Smartapps are written in smartthings’ own variation of groovy and run in the smartthings cloud.​

 

[ryanm77]

OK, I'm digesting the code now. I'll read over the next night or two. Only part that gets me a little nervous shows up in the first 50 lines:

To use Tesla, SmartThings encrypts and securely stores your Tesla credentials.
​

I'm also checking out trentfoley/SmartThingsPublic

Yeah, the way the SmartApp is coded currently requires your creds. You could fairly easily alter it to use an API token though. There's a really simple method for generating one in this thread. Just scroll down to @HankLloydRigh

 

[ryanm77]

Yeah, the way the SmartApp is coded currently requires your creds. You could fairly easily alter it to use an API token though. There's a really simple method for generating one in this thread. Just scroll down to @HankLloydRigh

Accidentally clicked "Post" there. Anyway, just scroll down to @HankLloydRight 's comment on how to generate a token.