The Future of EV Home Charging and the Grid

[nwdiver]

So what will something really large like the Rivian truck do? It has a 180 kWh battery. Basically like charging two Tesla's at once.

More like charging one Tesla for twice as long if you drove that far that day.

The high amp onboard chargers appear to be falling out of favor. Even Tesla has nerfed the onboard charger in the new S/X to 48A, not sure if the 72A charger is still available 'off-menu' or not. Makes sense, you generally don't need a charge rate >30A much less ~72A at home and public L2 rarely supports >32A. If you're lucky enough to find a Destination charger that supports the higher rate sometimes the grid can't. I'd be surprised if the onboard charger in the Rivian is >48A.

 

[Feathermerchan]

Good point. Less effect on the grid too. But it may interfere with those who have a TOU schedule if it takes too long to charge.

 

[gnuarm]

So I guess another issue is that when the local grid is overloaded the Tesla on board chargers will not charge at full rate. Not only will the local grid need upgrading, the charging won't work as well while waiting for the upgrades.

What will the other brands of EVs do when the grid voltage sags?

 

[StealthP3D]

More like charging one Tesla for twice as long if you drove that far that day.

The high amp onboard chargers appear to be falling out of favor. Even Tesla has nerfed the onboard charger in the new S/X to 48A, not sure if the 72A charger is still available 'off-menu' or not. Makes sense, you generally don't need a charge rate >30A much less ~72A at home and public L2 rarely supports >32A. If you're lucky enough to find a Destination charger that supports the higher rate sometimes the grid can't. I'd be surprised if the onboard charger in the Rivian is >48A.

That's a good point. I do think the move for EV's to go to ultra-fast, high amperage on-board chargers was an over-reaction to criticisms from ICE interests that EV's can't "refuel" fast enough. But now common sense is returning and people realize that while ultra fast DC supercharging is very valuable on a road trip, for everyday charging it really doesn't matter if it's speedy or not. And a high amperage on-board charger is not necessary for high-speed Supercharging. At home we can just let the electrons trickle in overnight at rates less than that used by hot tubs, electric ranges and air conditioners.

You've laid the case out very well that EV's are simply one more incremental consideration in the continual evolution of the grid, not an impending disaster about to bite us. And that this is a net positive for utility profits and future electrical rates.

 

[nwdiver]

So I guess another issue is that when the local grid is overloaded the Tesla on board chargers will not charge at full rate. Not only will the local grid need upgrading, the charging won't work as well while waiting for the upgrades.

What will the other brands of EVs do when the grid voltage sags?

Because the charging won't work as well means the grid likely WON'T 'need' upgrading. EVs are dynamic. They won't take the load unless there's load to be taken. If you're super irritated that once every 2 months you can only get ~32A instead of your usual 72A you can pay to have your local service upgraded. OR... just accept that once every 2 months you only get 32A instead of 72A... not the end of the world and the utility would likely agree no upgrade is 'needed'. A friend of mine is in a similar position. Crazy terrible connection. On a good day my car will limit charging to 60A. Utility has been out twice and said everything is fine.

You've laid the case out very well that EV's are simply one more incremental consideration in the continual evolution of the grid, not an impending disaster about to bite us. And that this is a net positive for utility profits and future electrical rates.

I read 'The Grid' a few years ago. It's a history/explanation of the electric grid written by an anthropologist so it's easy to understand from a lay perspective.

The history of the grid is demand chasing supply. It wasn't hard to figure out that generating electricity 24 hours/day wasn't much more expensive than generating it 4 hours/day. So companies like GE and Westinghouse needed to find a way to sell power outside the time that people wanted electric lights. It's not a coincidence that early electric appliances were made my early electric companies.

Far from being an expensive challenge. Due to their dynamic nature and the potential to act as super super cheap peaking power EVs may be the best thing to ever happen to the grid. The flatter the demand curve the happier the grid is. EVs have more potential to flatten the demand curve than anything else we've ever seen.

 

[Feathermerchan]

I am more concerned with our ability to build generation capacity to meet transportation demand. Generation is far more expensive.

I have learned though that our cars get cleaner and cleaner as the grid gets more green generation.

 

[nwdiver]

I am more concerned with our ability to build generation capacity to meet transportation demand. Generation is far more expensive.

I have learned though that our cars get cleaner and cleaner as the grid gets more green generation.

The only problem most utilities are having with generation is they have too much.

 

[gnuarm]

The transformer next to you house owned by the utility is called a distribution transformer.
The transformer in a substation is called a substation transformer.

Are there any transformers between the one feeding your house, the distribution transformer, and the substation transformers? What voltage is fed to the distribution transformer?

 

[nwdiver]

Are there any transformers between the one feeding your house, the distribution transformer, and the substation transformers? What voltage is fed to the distribution transformer?

Not usually. Electric distribution generally follows the same progression. Transmission (>100kv) => Distribution (>5kv) => Service (240/208/480)

 

[gnuarm]

Because the charging won't work as well means the grid likely WON'T 'need' upgrading. EVs are dynamic. They won't take the load unless there's load to be taken. If you're super irritated that once every 2 months you can only get ~32A instead of your usual 72A you can pay to have your local service upgraded. OR... just accept that once every 2 months you only get 32A instead of 72A... not the end of the world and the utility would likely agree no upgrade is 'needed'. A friend of mine is in a similar position. Crazy terrible connection. On a good day my car will limit charging to 60A. Utility has been out twice and said everything is fine.

According to you, not only will I not be able to get full power from the line, but with a >30% voltage drop, my neighbor's appliances won't work right either. Should they pay for having their hot tub on at the same time I am charging?

I read 'The Grid' a few years ago. It's a history/explanation of the electric grid written by an anthropologist so it's easy to understand from a lay perspective.

The history of the grid is demand chasing supply. It wasn't hard to figure out that generating electricity 24 hours/day wasn't much more expensive than generating it 4 hours/day. So companies like GE and Westinghouse needed to find a way to sell power outside the time that people wanted electric lights. It's not a coincidence that early electric appliances were made my early electric companies.

Far from being an expensive challenge. Due to their dynamic nature and the potential to act as super super cheap peaking power EVs may be the best thing to ever happen to the grid. The flatter the demand curve the happier the grid is. EVs have more potential to flatten the demand curve than anything else we've ever seen.

There is no question that EVs can help even the demand side of things. What is not so clear is how they will impact the distribution issue. The fact that you are talking about the heavy loads (which don't require 70 amp draws from any one car, many houses will have two or three cars) dropping voltage by 30% shows exactly the problem. The distribution closest to the homes will be affected in this way. The next level of distribution can also be affected when that also reaches capacity.

The issue is that distribution has been designed for the expected loads seen to date. The power company doesn't have any way of knowing what your loads will be or how much they may grow in the future. What is clear is that the utilities have not planned for EVs which have not even been on the horizon until the last few years. EV charging can easily make residential loads increase by 50% or even 100%. Since this is beyond the growth any planning would be accounting for it is likely that over the next 10 years significant growth in residential distribution will be needed... IF nothing is done to set methods of controlling WHEN EV charging happens.

I don't want to leave it up to the utilities to control when my EV will be charging.

 

[gnuarm]

I am more concerned with our ability to build generation capacity to meet transportation demand. Generation is far more expensive.

I have learned though that our cars get cleaner and cleaner as the grid gets more green generation.

As others have said, it is likely that EVs will help with properly utilizing the renewable resources that are starting to become a significant portion of our generation. If we have charging available at work, solar energy which is not well matched to the peak load curve, can be fully utilized to charge EVs. Wind power, which is a larger portion of our total generating capacity, provides more power at night, again not well matching the demand curve and so can charge EVs at night.

Much like the distribution issue, generation won't be a problem if we find ways to encourage charging at off peak times. TOU billing will help with that, but not if users don't know about it. TOU is not a panacea since a user has to then pay peak rates for all uses other than EV which can be easily scheduled. The way my TOU billing worked, before I modified my usage, my bill was higher than on the standard plan. Most people won't want to modify their usage at all other than the EV charging. So I'm not sure TOU will be popular at all really. Do you want to pay five times the normal rate to cook dinner or to heat hot water or even heat your home?

 

[nwdiver]

According to you, not only will I not be able to get full power from the line, but with a >30% voltage drop, my neighbor's appliances won't work right either. Should they pay for having their hot tub on at the same time I am charging?

I said no such thing. 1) It's a 30v not 30% drop. 2) Everything in your house should work fine at 210v, my friends house regularly dips to 205v and the only thing that notices is his Model 3.

There's a bit of a paradigm shift when thinking about utility infrastructure compared to what we're used to around the house. If you have a 16A appliance you install a 20A breaker and you expect the breaker to trip at ~20A. You install NEC recommended wire size for 16A. Things are much more flexible in the utility world. As @Feathermerchan said previously a 25kVA transformer isn't really a 25kVA transformer like a 20A breaker is a 20A breaker. You can pull >40kVA depending on conditions. The only definite limitation is the fuse... which seems like the transformer would probably die before the fuse goes unless there's a fault. Maybe @Feathermerchan can answer that question. My guess would be that it's likely a 10A fuse so if primary voltage is ~7kV that 25kVA transformer could 'support' ~70kVA.

So the grid doesn't really stop working because someone started charging their EV. It just gets a little less efficient. Utilities are routinely monitoring this and upgrading systems as needed.

So I'm not sure TOU will be popular at all really. Do you want to pay five times the normal rate to cook dinner or to heat hot water or even heat your home?

That's the misconception. Electricity ALREADY costs ~5x more during peak hours (often even more). It's just being spread across the rest of the day. So the REAL question is should people that modify their behavior or invest in storage to reduce use when electricity is expensive be subsidizing people that don't? That's the accurate way to frame that.

It's like asking, 'Should everything in the grocery store cost $5 including lobster or just charge $20 for the lobster and $3 for pasta.'

 

[gnuarm]

I said no such thing. 1) It's a 30v not 30% drop. 2) Everything in your house should work fine at 210v, my friends house regularly dips to 205v and the only thing that notices is his Model 3.

My bad. I was thinking 30 volts off 120 which is about 30%. Even so, at 210/105 volts many appliances are drawing more current to get the same power so exacerbating the problem. Focusing only on what the Tesla equipment does paints a rather inaccurate picture.

There's a bit of a paradigm shift when thinking about utility infrastructure compared to what we're used to around the house. If you have a 16A appliance you install a 20A breaker and you expect the breaker to trip at ~20A. You install NEC recommended wire size for 16A. Things are much more flexible in the utility world. As @Feathermerchan said previously a 25kVA transformer isn't really a 25kVA transformer like a 20A breaker is a 20A breaker. You can pull >40kVA depending on conditions. The only definite limitation is the fuse... which seems like the transformer would probably die before the fuse goes unless there's a fault. Maybe @Feathermerchan can answer that question. My guess would be that it's likely a 10A fuse so if primary voltage is ~7kV that 25kVA transformer could 'support' ~70kVA.

You seem to be focusing on the equipment rating vs. the distribution design. If the system was sized for an expected peak load of X kW and adding EV charging raises that to X+Y on a regular basis, I'm pretty sure the power company is going to do something about that. "Doing something" can be as simple as instituting a program to schedule charging... or it can be as expensive as replacing transformers on a widespread basis. Someone suggested I should pay for the problems created by charging my EV on top of my neighbor's hot tub and heat pump, etc. That's the sort of thinking I want to head off lest we end up with an EV tax from the utility. We already have a special EV tax in many states.

So the grid doesn't really stop working because someone started charging their EV. It just gets a little less efficient. Utilities are routinely monitoring this and upgrading systems as needed.

Why do you keep focusing on the grid not working? Is that all you can understand??? I've never once said anything about the grid not "working".

That's the misconception. Electricity ALREADY costs ~5x more during peak hours (often even more). It's just being spread across the rest of the day. So the REAL question is should people that modify their behavior or invest in storage to reduce use when electricity is expensive be subsidizing people that don't? That's the accurate way to frame that.

There's no misconception. People pay the same rate no matter what time. That's the reality they live in. You can talk about storage or whatever... but that's not the issue. That is about generation... AGAIN!

It's like asking, 'Should everything in the grocery store cost $5 including lobster or just charge $20 for the lobster and $3 for pasta.'

Lol! Ok, whatever. I still want to remain on topic of the thread and talk about distribution where costs are set by maximum capacity needed, even if only used once a fortnight.

 

[SageBrush]

That's the misconception. Electricity ALREADY costs ~5x more during peak hours (often even more). It's just being spread across the rest of the day. So the REAL question is should people that modify their behavior or invest in storage to reduce use when electricity is expensive be subsidizing people that don't? That's the accurate way to frame that.

I know the flip side of your coin (and you do too): the payback on a home PV system without storage has little no financial incentive. One of our local utilities wants to put everyone on a TOU scheme that will cost 4 cents a kWh off-peak and 18 cents a kWh on-peak. As you can probably guess, on-peak is off-PV.

I entirely agree with you that a 24 hour homogenized rate is inefficient but be careful what you wish for.

 

[SageBrush]

Far from being an expensive challenge. Due to their dynamic nature and the potential to act as super super cheap peaking power EVs may be the best thing to ever happen to the grid. The flatter the demand curve the happier the grid is. EVs have more potential to flatten the demand curve than anything else we've ever seen.

As in V2G ?

Yeah... NOT

 

[nwdiver]

Lol! Ok, whatever. I still want to remain on topic of the thread and talk about distribution where costs are set by maximum capacity needed, even if only used once a fortnight.

That is distribution. The increased cost is largely due to distribution not generation. The utilities can aggregate the timeframes and allocate costs according to distribution. In a rate case they divide up the rate classes and the rates are determined by the load profiles of each rate class. It would be like charging people based on age group at the grocery store instead of by purchase because millennials love off-season avocados more than senior citizens. Shifting to charging by what you ACTUALLY buy isn't telling you what to eat it's just charging you according to the ACTUAL cost of what you're buying. TOU didn't exist because you can't change TOU with a regular meter.

You seem to be focusing on the equipment rating vs. the distribution design. If the system was sized for an expected peak load of X kW and adding EV charging raises that to X+Y on a regular basis, I'm pretty sure the power company is going to do something about that.

My point is the the peak load is STILL ~2x what you're able to pull and your car will likely take action before the utility thinks it's cost effective to upgrade. If your car keeps slowing the charge rate to 32A because your 25kVA transformer that can actually push 60kVA is pushing 30kVA as far as the utility is concerned there no problem. If you want to pay for an upgrade so you can charge at 72A whenever, where-ever. That's on your dime.

 

[nwdiver]

As in V2G ?

Yeah... NOT

No. Demand Response. If you have 2000 EVs collectively charging at 2kW each that's 4MW of peaking power available by telling those cars to stop charging. 4MW of lowered demand is the same as 4MW of increased supply.

 

[Feathermerchan]

When we were an integrated utility (Generation -> meter) we designed rates to cover our costs with a little return for investors.
We designed a TOU rate for residential customers that was revenue neutral. That means that if we put every residential customer on that rate, we would receive the same annual revenue. If customers changed their usage habits so their bills went down, our costs would also decrease. It was not popular because people were afraid that they would pay more and there was not enough perceived value (incentive) to get them to change their usage habits. Until utilities get really expensive AND customers realize that they can save a lot of money (like with cell phones where many now bring their own phone to the plan instead of getting a 'free' phone every 2 years) I don't think things will change.I think deregulation has made it more difficult to support TOU because the costs are separated into generation and transmission/distribution.

 

[SageBrush]

Lol! Ok, whatever. I still want to remain on topic of the thread and talk about distribution where costs are set by maximum capacity needed, even if only used once a fortnight.

I think you are talking about recouping equipment acquisition and O&M costs. It is hard to be fair outside of a dedicated circuit such as placed for a large power consumer because the participants on a typical residential circuit are heterogenous in their peak loads, both in duration and amount. I'm inclined as a consumer to accept demand charges that exceed the local median once the homogenized per kWh rate is reformed to only cover generation and median per household transmission costs.

 

[SageBrush]

No. Demand Response. If you have 2000 EVs collectively charging at 2kW each that's 4MW of peaking power available by telling those cars to stop charging. 4MW of lowered demand is the same as 4MW of increased supply.

First you have to increase capacity and transmission facilities to accommodate them.