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Best Practices for Vehicle Charging with Solar + Powerwall

gigawatt1010

Member
Aug 21, 2016
496
484
Orange County, New York
So now that I'm a proud owner of Tesla's Solar Glass Roof + 3 Powerwalls - I wanted to pick your brains on Vehicle Charging best practices.

I tried plugging in our MX on the HPWC last night and scheduled to have it start charging at 12:15am (net metering). It started drawing 12KW from the 3 Powerwalls that were 100% charged from the solar we got that day and after about 5 minutes, it started pulling from the grid and drained the PWs to 65%.

Is this a good practice? How are you guys charging your EVs in conjunction with Solar and PWs?
 

getakey

Active Member
Jan 28, 2020
1,320
429
95762
I don't understand why the EV would pull any power from the PWs after midnight. What is your PW setting and how is your PEak time set in the app?
 
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arnolddeleon

Supporting Member
Jul 21, 2012
839
909
SF Bay Area
What utility rate are you on?

Did you receive any incentives with your batteries? (e.g. SGIP)

What are your goals? Save money? Use your own solar? How important is having a big backup reserve?

Those are some of the inputs needed to come up with a "good practice"
 

gigawatt1010

Member
Aug 21, 2016
496
484
Orange County, New York
I don't understand why the EV would pull any power from the PWs after midnight. What is your PW setting and how is your PEak time set in the app?
Hi, I don’t understand it either. Here’s a screenshot of my settings. I haven’t stumbled on where you set the peak time yet.

BC7ECCED-2DFF-4FC7-B98A-785F216D65FF.png
 

getakey

Active Member
Jan 28, 2020
1,320
429
95762
Self powered is the reason it pulled from the PWs.
If you chose Advanced, you can set your Peak rate period. And if you use Cost Saving mode, it will never charge EV from your PWs if your EV is set to charge during Off Peak
 

gigawatt1010

Member
Aug 21, 2016
496
484
Orange County, New York
What utility rate are you on?

Did you receive any incentives with your batteries? (e.g. SGIP)

What are your goals? Save money? Use your own solar? How important is having a big backup reserve?

Those are some of the inputs needed to come up with a "good practice"

Tesla made me complete forms for the incentives.

Obviously, saving money is always preferred, but not a big fan of penny-wise dollar foolish.

I think my ideal scenario is charge the car(s) at off-peak rates and not draw from the batteries as I'd much rather use those to power everything else. Although based on what I've seen so far, when the sun goes down and PWs kick in to power the house starting at 100% SOC, I only use about 20-25% power from them before the sun is out again the next day and starts charging them back up to 100%.

Just curious to hear what more seasoned solar + PWs users have been doing.
 

getakey

Active Member
Jan 28, 2020
1,320
429
95762
I run Cost-Savings mode and Charge EV off peak. In the winter, I set my reserve fairly high (70 to 75%) due to less sun hours to recharge. I'd rather be ready for an outage with high SOC. In summer, I lower reserve to 33%. I have 3 PWs and I can make it through the night on 1 PW in case of outage.
 

miimura

Well-Known Member
Aug 21, 2013
6,362
6,065
Los Altos, CA
I use Advanced - Balanced Mode. My solar is small, so I don't have any extra stored energy to charge cars from the Powerwalls. I use all the Powerwall energy to avoid Part-Peak and Peak consumption from the grid. The cars charge overnight from the grid.
 

jjrandorin

Moderator, Model 3, Tesla Energy Forums
Nov 28, 2018
9,583
10,793
Riverside Co. CA
Tesla made me complete forms for the incentives.

Obviously, saving money is always preferred, but not a big fan of penny-wise dollar foolish.

I think my ideal scenario is charge the car(s) at off-peak rates and not draw from the batteries as I'd much rather use those to power everything else. Although based on what I've seen so far, when the sun goes down and PWs kick in to power the house starting at 100% SOC, I only use about 20-25% power from them before the sun is out again the next day and starts charging them back up to 100%.

Just curious to hear what more seasoned solar + PWs users have been doing.

In self powered mode the powerwalls will discharge into the car. Self powered mode basically uses the powerwalls to power "everything" when there is not enough solar to do so.

I just set my reserve to something I am comfortable with for the season and how much solar I expect, and let the car drain the powerwall down to that.

I also have my car set to charge at like 3:30am in the morning, One of the other modes is more appropriate if you dont want the car to use powerwall power but i dont mind putting powerwall power in my car as long as I have enough power to last till the solar starts powering my home again in the morning.

Definitely a YMMV thing though.
 

Electrph

Member
Aug 29, 2019
426
280
Central California
Very much a YMMV ...I run self powered w/ 30% reserve
My work schedule / normal short commute allow me on my lunch to charge my model 3 at max connector speed during time when my solar production is at max and keep it at my desired battery % ... ideal for me since powerwalls recover to 100% well before dusk .. if I need to unexpectedly drive further next day I would allow car to drain powerwalls down to my reserve after 9pm and dip into lowest tou grid charges ... again it’s what works for you economy vs convenience
 
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Ampster

Active Member
Oct 5, 2012
1,780
477
Kenwood, California
My solar is small, so I don't have any extra stored energy to charge cars from the Powerwalls. I use all the Powerwall energy to avoid Part-Peak and Peak consumption from the grid. The cars charge overnight from the grid.
That is an important point. There are no simple answers without analysis. A lot depends on the solar that one has on their roof, the rate plan that they are on, and most importantly the consumption patterns that they have.
Some of those factors may be known or only assumptions. For example, I am in contract for a new home. The roof can support 8 kW of solar but the orientation is such that I might only be able to get 9 or 10 kWh per year. PG&E may limit that and only allow me 3 or 4 kW based on the square footage of the house. I have to replace the 100 Amp Zinsco panel because it is dangerous so I am committed to a panel change out. Should I replace the panel with a two meter panel so I can use EV B rate?

I am not asking for an answer because I think I know the concept and seveal workarounds depending on how PG&E responds to my reguest for GT solar. . If I can put 8 kW of solar then one meter might make sense since I can use solar production to offset the off peak charging of the EVs on current NEM 2.0 even at the EV2-A rates. If I get limited on solar production to a 4 kW array, installing a two meter main panel might make sense because the EV-B rate is .03 better on EV-B than EV2-A rates. I estimate that I will charge about 3000 kWhs per year off peak.
Another factor that make my situation unique. I do not have a Powerwall but I do have a hybrid inverter and 42 kWh of batteries and I can get a building permit to install enough solar panels to power the home most of the time using self consumption. I do not have to ask PG&E permission to do that, So the house load does not figure into the above analysis.
The bottom line is that either PG&E gives me permission to install 8 kW of GT solar or I go with 4 kW of GT solar and add another 6 kWh behind the meter with batteries and charge my Teslas with a separate meter off peak at EV-B rates
 

garrett5688

Member
Oct 7, 2017
579
1,019
DFW
If you chose Advanced, you can set your Peak rate period. And if you use Cost Saving mode, it will never charge EV from your PWs if your EV is set to charge during Off Peak
This is not entirely true. Even on advanced cost savings, off peak, the gateway will use stored energy to “make room” for future solar production. It’s totally ridiculous but it’s in the description and works that way. Drives me crazy.
 

getakey

Active Member
Jan 28, 2020
1,320
429
95762
This is not entirely true. Even on advanced cost savings, off peak, the gateway will use stored energy to “make room” for future solar production. It’s totally ridiculous but it’s in the description and works that way. Drives me crazy.
Are you sure? I've never seen mine discharge during off peak. I have seen it discharge during Shoulder. However, I changed my settings to eliminate Shoulder. My PWs only discharge during Peak
 

arnolddeleon

Supporting Member
Jul 21, 2012
839
909
SF Bay Area
Tesla made me complete forms for the incentives.

Obviously, saving money is always preferred, but not a big fan of penny-wise dollar foolish.

I think my ideal scenario is charge the car(s) at off-peak rates and not draw from the batteries as I'd much rather use those to power everything else. Although based on what I've seen so far, when the sun goes down and PWs kick in to power the house starting at 100% SOC, I only use about 20-25% power from them before the sun is out again the next day and starts charging them back up to 100%.

Just curious to hear what more seasoned solar + PWs users have been doing.
Do you happen to know if you have discharge requirements. For example because my first two Powerwalls are on SGIP I need to discharge a minimum amount per year (easily achieved for me with my usage).

I started off running advanced/cost saving mode. I then switched to advanced/balanced mode to trigger more self consumption. The downside of self consumption is the roundtrip loses through the batteries. The downside of using the grid storage are the non-bypassable charges. I also ran export limitations (long side story) which pushed me towards more self consumption.

With my previous solar and 2 batteries I was not riding through enough hours to my liking during the time of year when we were running air conditioning. At end of the day I decide I wanted more self consumption during the night hours for a variety of reasons. So I added more solar and battery. I now have 3 Powerwalls and about 17 kW of solar (effectively less but another long side story).

Right now with mild weather I'm charging cars during the day to avoid the round trip through the Powerwalls. This is easy to right now since I'm working from home. My reserved set at 20% but I'm currently not reaching that. It appears that I will have enough solar to fill the batteries before peak once some summer rates hit, likely before part peak during low air conditioning days.

I've seen the system discharge to offset car charging during some of the times and other times it didn't. I suspect this Tesla trying to forecast how much energy it will have left.

Knobs to turn:

Reserve (what is the minimum you want for a power outage)

Advanced Time Base Controls

Price Schedule (you don't have to follow your tariff exactly). Currently I'm still in winter schedule but I've put in peak and part peak hours to bias which hours the system will self consume if it thinks it doesn't have enough energy in the batteries before solar charging begins (I'm choosing to support the grid as much as possible from to 4 pm to midnight) I noticed when I didn't have enough solar/batteries it tried to start self consumption as late as possible to minimize the time it was a low state of charge. For example it would stop discharging at 9:00 pm and resume discharging at 3:00 am. At the moment it's pretty moot because I'm in the period of excess battery and solar.

My recommended settings for you based on your goals:
Time based control/balanced (this will encourage self consumption to the system).
Lower your reserve to the what you are comfortable with
Set your car to delayed charging/departure schedule. This will make it charge at around 3 to 5 am (assuming you have a departure time of around 7 am.

Note: If your system is new you might need to give Tesla time to get data for the behavior to stabililze. When you a change a setting or usage patterns you may need to let the system "settle" or "learn". I don't think anyone has official documentation on the exact details but observed behavior is Tesla is trying to be "clever" by predicting consumption and production. It appears to factor in historical data and things like weather forecasts.
 
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FreePower

New Member
May 5, 2021
1
2
UK
So now that I'm a proud owner of Tesla's Solar Glass Roof + 3 Powerwalls - I wanted to pick your brains on Vehicle Charging best practices.

I tried plugging in our MX on the HPWC last night and scheduled to have it start charging at 12:15am (net metering). It started drawing 12KW from the 3 Powerwalls that were 100% charged from the solar we got that day and after about 5 minutes, it started pulling from the grid and drained the PWs to 65%.

Is this a good practice? How are you guys charging your EVs in conjunction with Solar and PWs?
I only charge the car during the day when solar is being produced. In the winter, I charge at low cost rate electricity through the night for both car and to fill up the powerwalls to drain through the daytime.

Winter the powerwalls are set to Advanced ‘cost saving’. Most of the rest of the year they are set to Self Powered.
This system has worked for me for 2 years. I’ve 15kwh of solar PV and 3 PW’s
 

jboy210

Supporting Member
Dec 2, 2016
5,194
3,232
Northern California
So now that I'm a proud owner of Tesla's Solar Glass Roof + 3 Powerwalls - I wanted to pick your brains on Vehicle Charging best practices.

I tried plugging in our MX on the HPWC last night and scheduled to have it start charging at 12:15am (net metering). It started drawing 12KW from the 3 Powerwalls that were 100% charged from the solar we got that day and after about 5 minutes, it started pulling from the grid and drained the PWs to 65%.

Is this a good practice? How are you guys charging your EVs in conjunction with Solar and PWs?
Since we permanently work from home, I charge our EVs mid-day when most of the power comes from solar. If I do that twice a week (once per car) we only use about 12-15 kW to fill each car. And that still leaves plenty of solar power to refill the Powerwalls before the 4 PM peak.
 
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gigawatt1010

Member
Aug 21, 2016
496
484
Orange County, New York
Great suggestions and practices guys!

My wife and I have long commutes so it's important that we charge to 80% on a daily basis. I have about 80-100 miles of daily commute on my 60D MS (yes, 60kWh). I always charge that to 100% since it's technically a 75kWh, software reduced to 60. 5 years, 120k miles later, I still get about 210ish miles. My wife has about a 70 mile daily commute so she gets by with about 50% charge on a daily basis. Both cars have FUSC and we also have access to 2 Superchargers (one of them a V3) along our daily routes. I have an HWPC at the office too.

Thanks to your suggestions, I am learning how to use the app and tailor it to my usage. I am starting to get familiar with how my utility company charges me, whereas prior to all this, I just know I pay them roughly $200ish per month and I really never bothered to get all geeky with it.

Definitely an exciting learning experience.
 

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