Need a lesson in Electricity 101

[prius2pony]

I have ordered an Extended Range Premium. I recently had solar panels installed on the roof. It is typical in these summer months for me to use 25-30 kWh, but to generate 40-50 kWh. I'm a retired, low-milage guy most of the time, and anticipate that at a 270 mile range, I'll only need to recharge once every 2-3 weeks. Can anyone explain to me how many kWh I will use to charge my Extended Range Premium from near-empty to the 80% capacity?
Also- Is the answer the same regardless of Whether I do so from a Level 1 Charger (120v/12amp for 95 hours), a Level 2 charger (240v/32amp 14 hours), or a Level 2 Ford Connected Charge Station (240v/48amp for 10 hours)* These stats are from the brochure for an "Ext Range RWD"- would these charge times be different because my car is AWD?
Lastly, Do I need to drain the battery pretty low before recharging, or can I "top it off" more frequently?

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[timbop]

The ER battery is 88kwh of usable capacity, so 80% is 70 kilowatt hours. However, you should never drain to 0%; 10% is a safe minimum charge level. So, assuming you charge at 10% to 80%, that would be 61.6kwh. It doesn't matter if you charge with a level 2 240V charger, or a 120 volt level 1 charger - it will always take that same 61.6kwh. The only difference is how long it takes to charge, with 120 volt being slower. Since it always the same 61.6 kwh and you pay by the kwh, the price will always be the same.

You can think of it like filling a pitcher with water. It holds the same amount, no matter how fast or slow you have the spigot turned on.

 

[prius2pony]

The ER battery is 88kwh of usable capacity, so 80% is 70 kilowatt hours. However, you should never drain to 0%; 10% is a safe minimum charge level. So, assuming you charge at 10% to 80%, that would be 61.6kwh. It doesn't matter if you charge with a level 2 240V charger, or a 120 volt level 1 charger - it will always take that same 61.6kwh. The only difference is how long it takes to charge, with 120 volt being slower. Since it always the same 61.6 kwh and you pay by the kwh, the price will always be the same.

You can think of it like filling a pitcher with water. It holds the same amount, no matter how fast or slow you have the spigot turned on.

So, since on a fairly sunny day, my panels are over-producing my consumption to the tune of about 4kW through 8 hours, I could do 32kwh of charging on one day, and 32kWh on the next day, and I'd be getting all of my power from my cells, not relying on the pulling from the grid. Am I right? (I'll try to upload a screenshot of my panel data.)

 

[JamieGeek]

That sounds about right but you have to keep in mind that it isn't 1 for 1. e.g. putting 10kWh into the car doesn't equal 10kWh into the battery--some of it is lost as heat. Thus you'll have to put more into the car to get that 10kWh into the battery--its usually above 80% efficient however.

 

[Kamuelaflyer]

I plan on charging my MME once our solar system has had a chance to start recharging the batteries from the post-sunset use and finish up for the day with enough time to allow it to top off the batteries. Most likely that means roughly 10 am till about 2 pm out here. Or I could shift and do 2 pm on easily. That should be in the general vicinity of 30 kwh of recharge per day for me. (rough math)

 

[timbop]

So, since on a fairly sunny day, my panels are over-producing my consumption to the tune of about 4kW through 8 hours, I could do 32kwh of charging on one day, and 32kWh on the next day, and I'd be getting all of my power from my cells, not relying on the pulling from the grid. Am I right? (I'll try to upload a screenshot of my panel data.)

Ah, I see where you're going. If you're concerned about only putting your solar energy in the car, then that is a bit of a different story. To be "sure", you'd have to program the car to only charge during your solar panel window, and you'd probably need to ensure you only draw 16-24 amps at most (240v x 16A = 3.8kw) to keep under what your panels produce throughout the day. In the winter your panels will be producing a lot less per day, so you'd probably have to tweak it some more.

Since you aren't planning to drive that much, you could do a two-pronged approach. You could have an electrician put in a 40amp 240v line that you would only use with the included portable charger in situations when you need a faster charge and don't mind going over your panel's production. Then, for daily use put the 120v plug on that portable charger and leave the car plugged in with the charging times set to match your solar panels' output - it won't hurt the car to leave it plugged in all the time as long as you set the max charge to 80% or lower.

 

[abr]

Ah, I see where you're going. If you're concerned about only putting your solar energy in the car, then that is a bit of a different story. To be "sure", you'd have to program the car to only charge during your solar panel window, and you'd probably need to ensure you only draw 16-24 amps at most (240v x 16A = 3.8kw) to keep under what your panels produce throughout the day. In the winter your panels will be producing a lot less per day, so you'd probably have to tweak it some more.

Since you aren't planning to drive that much, you could do a two-pronged approach. You could have an electrician put in a 40amp 240v line that you would only use with the included portable charger in situations when you need a faster charge and don't mind going over your panel's production. Then, for daily use put the 120v plug on that portable charger and leave the car plugged in with the charging times set to match your solar panels' output - it won't hurt the car to leave it plugged in all the time as long as you set the max charge to 80% or lower.

But if you are concerned about $$, and you have a TOU rate plan (best for solar panels), it is better to collect solar electricity during the day and put it back into the grid (highest rate) and use it (charge the MME) at night when the rates are lowest. Even if you use more electricity than you use, you are $$ ahead.

 

[timbop]

But if you are concerned about $$, and you have a TOU rate plan (best for solar panels), it is better to collect solar electricity during the day and put it back into the grid (highest rate) and use it (charge the MME) at night when the rates are lowest. Even if you use more electricity than you use, you are $$ ahead.

I don't believe that will be the case. With net billing, they typically combine the production with the draw over a 24hr period so at best it would be a wash. Also, the wholesale rate they buy the power from you is less than that TOU billing.

Nonetheless, it seemed like he was concerned about using what he generates.

 

[abr]

I don't believe that will be the case. With net billing, they typically combine the production with the draw over a 24hr period so at best it would be a wash. Also, the wholesale rate they buy the power from you is less than that TOU billing.

Nonetheless, it seemed like he was concerned about using what he generates.

Not the way I am billed. I create at higher rate and use at a lower rate. While they don't send me a check, I do carry forward any credit balance. I can actually use more electricity than I create overall and still pay nothing because of the difference in billing rates.

 

[Marcel]

So, since on a fairly sunny day, my panels are over-producing my consumption to the tune of about 4kW through 8 hours, I could do 32kwh of charging on one day, and 32kWh on the next day, and I'd be getting all of my power from my cells, not relying on the pulling from the grid. Am I right? (I'll try to upload a screenshot of my panel data.)

The Ideal charger for Solar to car
Zappi charger

 

[EVer]

Lastly, Do I need to drain the battery pretty low before recharging, or can I "top it off" more frequently?

Note that keeping the batteries at a high state of charge (SOC) is stressful for them. You can top it off whenever you want, but it's better for them to maintain an average SOC around 50%.

 

[timbop]

Note that keeping the batteries at a high state of charge (SOC) is stressful for them. You can top it off whenever you want, but it's better for them to maintain an average SOC around 50%.

Yup, that is true -I didn't think about that. Since he is essentially keeping it in storage, maybe generally set the SOC to 50% instead of the 80% I mentioned, but then charge up to 80% if you are going on a longer journey.

 

[ChasingCoral]

So, clearly you have a decision regarding when you want to charge: direct use of your solar or cheapest energy. Just plan to plug in whenever you get home and use the programming to have the Mach E charge itself at the time you want.

 

[FredT]

I don't believe that will be the case. With net billing, they typically combine the production with the draw over a 24hr period so at best it would be a wash. Also, the wholesale rate they buy the power from you is less than that TOU billing.

Nonetheless, it seemed like he was concerned about using what he generates.

In California the utility credits us at retail, so the best strategy is to sell at peak time and charge off-peak.

 

[timbop]

In California the utility credits us at retail, so the best strategy is to sell at peak time and charge off-peak.

Lucky you. Here in NJ we still have a way to go, although things are getting better.

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