Optimizing Home Charging for Solar

[g2hmb]

We have a solar array at home that generates an average of 6-9kw at peak (depending on weather, season, etc) We also have tesla powerwall with 3x batteries. We have an order (since last Feb) for a MME premier.

My question is how do you optimize charging so it keeps pace with the solar generation without pulling too much from the grid? At this time we are net zero on our PGE utility bills.

Thanks for your insights!
--Gary

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[timbop]

You can certainly schedule your charging in the car (or in a smart charger) to correspond with daytime charging so you're using sunshine, although to keep the drain below your production you'll probably need to adjust the charging current. The car can't adjust the current, so you'd need an EVSE (charger) whose power level you can adjust. The included Ford mobile charger doesn't have that, but clippercreek, grizzl-e, etc should all have the ability to set the current to 24 or 32 amps which should keep you below your production.

 

[bruceski88]

We have a solar array at home that generates an average of 6-9kw at peak (depending on weather, season, etc) We also have tesla powerwall with 3x batteries. We have an order (since last Feb) for a MME premier.

My question is how do you optimize charging so it keeps pace with the solar generation without pulling too much from the grid? At this time we are net zero on our PGE utility bills.

Thanks for your insights!
--Gary

 

[MachEMaster]

Set the vehicle’s charge schedule for 12-6am drawing off the Tesla Powerwalls, and then charge up the Powerwalls from Solar PV during the day.

 

[bruceski88]

You should have net metering. It only matters if you have a Time of Use plan that charges less for electricity at certain times of the day. Just charge when electricity rates are cheapest. I have solar and refused to got on one of those plans since we only use electricity from the grid when it would be expensive. We set the car not to charge between 5-10pm out of courtesy when the grid is short. Right now there is controversy about when is a good time to charge so we do it any other time.

 

[timbop]

Set the vehicle’s charge schedule for 12-6am drawing off the Tesla Powerwalls, and then charge up the Powerwalls from Solar PV during the day.

DOH! Or that .

However, OP you'll want to make sure you charge frequently (ie keep it topped off) to make sure you don't need to put 50 or 60kwh into it at once, which could exceed your production for a day.

 

[@kWhpony]

Below is a pic of my current solar production today in suburban Phoenix on a clear day. System peak production when activated in July was just over 11 kwh. Notice on the graph that I plugged in early this morning to charge and you can see what the impact is on consumption. I have a Grizzl-e Classic set at 40A. By adjusting what I'm drawing, I could fall within the production curve but probably wouldn't be able to fully charge when starting at a low SOC. The session below delivered 47% over 4:47 hours with estimated 142 miles.

 

[Blackpony]

I have solar as well and we have net metering so on a monthly basis we bank 60% of what we produced and didn't use. I have assumed that this means if I use electricity at whatever time to charge my MME as long as my total use that month including the charge for my MME is less than my production it will be free to me. In later months with less sunshine, I will be looking to my banked production.

As an aside, we have put in a geothermal system for heating and cooling which is why I added more solar. I have removed my oil burner and I am about carbon free. I should a good idea in the coming year if this is so.

 

[MachEMaster]

Below is a pic of my current solar production today in suburban Phoenix on a clear day. System peak production when activated in July was just over 11 kwh. Notice on the graph that I plugged in early this morning to charge and you can see what the impact is on consumption. I have a Grizzl-e Classic set at 40A. By adjusting what I'm drawing, I could fall within the production curve but probably wouldn't be able to fully charge when starting at a low SOC. The session below delivered 47% over 4:47 hours with estimated 142 miles.

I would charge every night off the Powerwalls, to 90% from 12-6am. Then you won’t get a 13,000 watt spike just as the Sun is coming up. Your graph will thank you.

 

[g2hmb]

You can certainly schedule your charging in the car (or in a smart charger) to correspond with daytime charging so you're using sunshine, although to keep the drain below your production you'll probably need to adjust the charging current. The car can't adjust the current, so you'd need an EVSE (charger) whose power level you can adjust. The included Ford mobile charger doesn't have that, but clippercreek, grizzl-e, etc should all have the ability to set the current to 24 or 32 amps which should keep you below your production.

I appreciate the tips, I'll check out those chargers

 

[markboris]

We have a solar array at home that generates an average of 6-9kw at peak (depending on weather, season, etc) We also have tesla powerwall with 3x batteries. We have an order (since last Feb) for a Mach-E premier.

My question is how do you optimize charging so it keeps pace with the solar generation without pulling too much from the grid? At this time we are net zero on our PGE utility bills.

Thanks for your insights!
--Gary

Hi Gary, we have similar systems (Solar with 3 Tesla PowerWalls) except my peak during the hours of roughly 11:00am-2:00pm is 11.4kW. During the month of June, I produce as much as 100kW daily but now that we have less daylight, I'm at around 85kW and in the winter will be 70kW daily and this is of course if it's sunny.

I generally keep my ChargePoint HomeFlex charger set to the 40 amp setting so that it will deliver 7.8kW while charging the Mach-E. That way when I charge during the day, there is plenty of solar between the hours of around 10:00am to 3:00pm to charge the car, run the house AC and pretty much anything else. 5 hours is more than enough to top off the car or I can do that two days in a row to charge it fully if it was very low. If I need to charge in a hurry, I set the ChargePoint charger to the 60 amp setting (it is hardwired to a 60 amp breaker) then it delivers 11.2kW.

If I need the car charged to 100% in one day and the solar did not charge the car up fully, then I'll use the PowerWalls at night to finish charging. They output 12kW each as I have them set to stop discharging at a 10% level. That is only 36kW and not enough to fully charge a Mach-E if it has a low SOC. I prefer to charge during the day using solar as PG&E here in CA hardly gives you any credit for your surplus solar so I'd rather use as much as I can.

I am on a Time of Use plan and my peak rates are Mon-Fri 5pm-8pm. My PowerWalls run the house exclusively during those peak hours and mostly any other time when there is no solar. I have a net zero on my PG&E bill. Unfortunately at true up time, they don't pay you for any excess power you have provided them nor do they roll it over to the next year (it would be nice if they did).

My typical daily power broken down:

 

[g2hmb]

Hi Gary, we have similar systems (Solar with 3 Tesla PowerWalls) except my peak during the hours of roughly 11:00am-2:00pm is 11.4kW. During the month of June, I produce as much as 100kW daily but now that we have less daylight, I'm at around 85kW and in the winter will be 70kW daily and this is of course if it's sunny.

I generally keep my ChargePoint HomeFlex charger set to the 40 amp setting so that it will consume 7.8kW while charging the Mach-E. That way when I charge during the day, there is plenty of solar between the hours of around 10:00am to 3:00pm to charge the car, run the house AC and pretty much anything else. 5 hours is more than enough to top off the car or I can do that two days in a row to charge it fully if it was very low. If I need to charge in a hurry, I set the ChargePoint charger to the 60 amp setting (it is hardwired to a 60 amp breaker) and it uses 11.2kW.

If I need the car charged fully in one day and the solar did not charge the car up fully, then I'll use the PowerWalls at night to finish charging. They output 12kW each as I have them set to stop discharging at a 10% level. That is only 36kW and not enough to fully charge a Mach-E if it has a low SOC. I prefer to charge during the day using solar as PG&E here in CA hardly gives you any credit for your surplus solar so I'd rather use as much as I can.

I am on a Time of Use plan and my peak rates are Mon-Fri 5pm-8pm. My PowerWalls run the house elusively during those peak times and mostly any other time when there is no solar. I have a net zero on my PG&E bill. Unfortunately at true up time, they don't pay you for any excess power you have provided them nor do they roll it over to the next year (it would be nice if they did).

My typical daily power usage broken down:

Thanks Mark, really great insights using a similar setup!

 

[woody]

We have a similar system (2-9kWh, 20 - 60kWh/day).
We have 2 EVs.
We alternate the EVs charging directly from the solar array via the critical load panel. No programming - simply plug in manually.
We only have a 30kWh battery backup which we only use as a "back up". Not enough for EV charging. (should have 3-4X as much in order to run system year round [winter being the reason])
Only rarely use EVSE, mostly in winter if we do.
Cannot use all of the production most of the year (7+ months).
95%+ of EV energy directly from solar.
Xcel gives virtually no credit here as well (5mils/kWh, but only on 80% of what we send them, etc.).
When it comes to all electric year round (we are 100% electric)we need to double our solar array (~20kW), increase battery capacity as aforementioned, and have a bi-directional EV [80+kWh]).
That said, we currently produce more electricity than we use.
W/O winter, we would be perfect right now.
(since Vacaville's average low/year round is only >39F, you should not have to expend that much on heating?)

 

[hayhayday]

I have the emporia evse plus the emporia connect which reads the pg&e meter and adjusts itself every few seconds. I find that the peak demand setting set to 0.01kw works better than self consumption setting as it tries to zero each 15 min interval which coincides with the metering interval used by pg&e to calculate non bypassable charges. Previously just set charger to 21A\~5kw on my 9kw array and ended up fairly close.

 

[ChuckA]

Set the vehicle’s charge schedule for 12-6am drawing off the Tesla Powerwalls, and then charge up the Powerwalls from Solar PV during the day.

I agree. In CT our off-peak is 8pm - 12 noon. Our MME is usually done charging at 2 am since I’m only going from SOC 45% to 90%.

Whatever kWh you put into the Powerwalls during the day, you’ll draw from at night.

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