Off Grid Home AC or DC Coupled? Help me decide.

[brucet9]

You are full of crap and do not know WTF you are talking about. You should have done a little research before you opened your smart mouth.

Example from this article Chevy Volt only allows customers to 65% of capacity. They only allow customers to charge up to 87% SOC and call the tow truck at 22%

Nissan Leaf uses the same kind of battery as the Chevy Volt a NMC chemistry. For extended range on a Leaf, Nissan limits SOC to 90%. First Low Voltage First Warning happens at 18% SOC, Second Warning at 10%, Turtle Mode at around 6%, call tow truck at 3%. It is well known Leaf only allows 83% of its capacity to be used.

As I said both Chevy Volt and Nissan Leaf use NMC batteries. NMC has a very distinguished discharge Slope that accurately determine the Battery SOC. Nissan uses a 96S NMC battery and terminates charge at 384 volts or 4.0 vpc. Full charge on NMC and Leaf's battery is 4.2 vpc and if you do a little math is easy to figure out 96 x 4.2 = 403.2 volts. Read and weap.

Shall I go on about how Tesla limits charge or have you had enough?

Is it possible for us to conduct a civil discussion?

I said nothing about discharging 100% of battery capacity. I only answered your incorrect assertion that no EVs can be charged to 100%.

Volt is not a large battery EV. It is a hybrid.

Quote from 2017 Chevy Bolt EV owners manual, "When using a 240-volt charging station, it will take approximately 9.5 hours to charge the vehicle with the 32 amp setting, allowing approximately 40 km (25 mi) for every hour of charging. 25 miles x 9.5 = 237.5miles, the claimed range of Chevy Bolt, so it is clearly charging to 100% SOC.

Quote from 2017 Nissan Leaf owners manual, "It takes approximately 5.5 to 9.5 hours (depending on the charger) in order to charge the Li-ion battery from discharged (low battery charge warning light illuminated) to 100% charged." Presumably, they will enable the new longer range version to charge to 100% SOC as well.

I drive a Tesla Model S. Tesla does not limit the charge. I regularly charge at home to 90% SOC and Tesla specifically tells owners that charging to 100% SOC is best done just before a road trip and further suggesting that it is best not to leave it at 100% for too long.

Perhaps you meant to say that there is some reserve battery capacity that the manufacturer does not enable users to see. The fact that Tesla suggests not charging to 100% SOC very often and not to leave it at 100% SOC for very long, suggests that, for non-software-limited batteries at least, we really do charge to 100% SOC. Since all of the BEVs, when fast DC charging, automatically taper the charge rate as the battery nears full SOC, I presume that the others are not holding back a capacity buffer either.

[Mike90250]

Again you seem not to understand that some people can't make that life style change as easy as others. Even if it means they save on their electric bill. If you are not in their shoes you really can't understand their limited options.

The fridge is the common household power hog, and it currently (except for a couple high $$ models) has no timer or load shed function. And what is the value of defrosted and refrozen ice cream to save 5 cents in electricity?

[SunEagle]

I think you underestimate people. But to each their own.

I agree we both have different opinions concerning what people will do or not do.

What I have been exposed to at places around the US and even on this forum is that people will find a way to cheat the system or find an illegal way to get electrical power that they do not have to pay for.

Putting a price penalty using TOU rates will only drive those people harder to find a way around the system. In the end the Grid will still have a high usage at times it can't support the demand and it will be people like you and me that will suffer because of a few that won't follow the rules.

It is sad but quality of people's action seem to be taken a nose dive into the gutters.

[jflorey2]

Again you seem not to understand that some people can't make that life style change as easy as others. Even if it means they save on their electric bill. If you are not in their shoes you really can't understand their limited options.

I think you underestimate people. But to each their own.

[Sunking]

All of the large battery EVs enable charging to 100% of rated charge..

You xxxxxxxxxx do not know WTF you are talking about. You should have done a little research before you opened your smart mouth.

Example from this article Chevy Volt only allows customers to 65% of capacity. They only allow customers to charge up to 87% SOC and call the tow truck at 22%

Nissan Leaf uses the same kind of battery as the Chevy Volt a NMC chemistry. For extended range on a Leaf, Nissan limits SOC to 90%. First Low Voltage First Warning happens at 18% SOC, Second Warning at 10%, Turtle Mode at around 6%, call tow truck at 3%. It is well known Leaf only allows 83% of its capacity to be used.

As I said both Chevy Volt and Nissan Leaf use NMC batteries. NMC has a very distinguished discharge Slope that accurately determine the Battery SOC. Nissan uses a 96S NMC battery and terminates charge at 384 volts or 4.0 vpc. Full charge on NMC and Leaf's battery is 4.2 vpc and if you do a little math is easy to figure out 96 x 4.2 = 403.2 volts. Read and weap.

Shall I go on about how Tesla limits charge or have you had enough?

[SunEagle]

Exactly. But it will mean a lot to lower income people. Thus, if they can save money by using more power late at night and less power during the day, they will do so to save money. They will want that lower pricing.

Again you seem not to understand that some people can't make that life style change as easy as others. Even if it means they save on their electric bill. If you are not in their shoes you really can't understand their limited options.

[jflorey2]

Higher pricing and lower availability is something a customer that is not living paycheck to paycheck can do. The people on fixed incomes will be the ones to suffer while those the are in the higher tax brackets will continue to waste power because they can afford to and really don't care about the rest. TOU and penalties will mean nothing to them.

Exactly. But it will mean a lot to lower income people. Thus, if they can save money by using more power late at night and less power during the day, they will do so to save money. They will want that lower pricing.

[SunEagle]

Yep, or more likely reduce charge rates. J1772 EVSE charging systems (i.e. 99% of the EV chargers out there) have a pilot signal that tells the vehicle how much it can draw. You can throttle from 6 to 30 amps via the pilot signal.

Yes, and that will have the side effect of smoothing the demand curve considerably. It would take true real time pricing for that to be effective - but several utilities (including mine) are now offering that on a trial basis.

Higher pricing and lower availability is something a customer that is not living paycheck to paycheck can do. The people on fixed incomes will be the ones to suffer while those the are in the higher tax brackets will continue to waste power because they can afford to and really don't care about the rest. TOU and penalties will mean nothing to them.

There needs to be a carrot and stick process where those that can change their habits by reducing or using at low peak times get rewarded and those that abuse the usage get penalized.

But there is still a % of people that will have a hard time to reduce their usage because it is already low so how do you keep them from getting hurt or provide them with incentives to reduce even more?

Remember there are some POCO's that actually reduce their charge rate if you use more than a certain amount of power. While in places like CA you are penalized for too much usage. Why is that? IMO it due to the political climate and how they have demanded changes in the power distribution of their state.

[jflorey2]

One problem the POCO's are worried about is if the % of plug in EV's continue to increase there is a chance too many trying to charge at the same time could overload some of the grid feeder systems. They may need to introduce some type of demand shedding system to disconnect some chargers for periods of time to level out the demand. That will require more than just smart meters but automatic disconnecting systems at the home placed on specific high loads.

Yep, or more likely reduce charge rates. J1772 EVSE charging systems (i.e. 99% of the EV chargers out there) have a pilot signal that tells the vehicle how much it can draw. You can throttle from 6 to 30 amps via the pilot signal.

If EV's ever become (more) common, it may well be that the current super off peak times, that now probably have some correlation with EV charging times, will become peak rate times, or at least shift from super off peak. Supply and demand.

Yes, and that will have the side effect of smoothing the demand curve considerably. It would take true real time pricing for that to be effective - but several utilities (including mine) are now offering that on a trial basis.

[J.P.M.]

One problem the POCO's are worried about is if the % of plug in EV's continue to increase there is a chance too many trying to charge at the same time could overload some of the grid feeder systems. They may need to introduce some type of demand shedding system to disconnect some chargers for periods of time to level out the demand. That will require more than just smart meters but automatic disconnecting systems at the home placed on specific high loads.

I have something like that now where my POCO can turn off my pool pump or AC system if they need to lower the demand. I also had one of those on my water heater until I replaced it with a solar thermal water heating system.

Another tool POCOs may be able to use, either now, or in the future, is to shift T.O.U. times and rates as a demand leveling tool as they now claim as the source of T.O.U. rate time adjustments. Nothing says T.O.U. rates/times have to be only about PV impacts.

If EV's ever become (more) common, it may well be that the current super off peak times, that now probably have some correlation with EV charging times, will become peak rate times, or at least shift from super off peak. Supply and demand.

[SunEagle]

Agreed. Of the BEV/PHEV owners at my company (260 the last time we polled them) 78% had level 2 chargers. Generally the people who had only level 1 (or no) chargers were the PHEV crowd.

One problem the POCO's are worried about is if the % of plug in EV's continue to increase there is a chance too many trying to charge at the same time could overload some of the grid feeder systems. They may need to introduce some type of demand shedding system to disconnect some chargers for periods of time to level out the demand. That will require more than just smart meters but automatic disconnecting systems at the home placed on specific high loads.

I have something like that now where my POCO can turn off my pool pump or AC system if they need to lower the demand. I also had one of those on my water heater until I replaced it with a solar thermal water heating system.

[jflorey2]

Small battery hybrids may charge at 120V AC, but longer range BEVs charge L2 at home at 240V and more than 6kW.

Agreed. Of the BEV/PHEV owners at my company (260 the last time we polled them) 78% had level 2 chargers. Generally the people who had only level 1 (or no) chargers were the PHEV crowd.

[brucet9]

That is complete nonsense. EV's charge rate is less than an Off-Grid Solar Battery System at Level 1 rates using 120 VAC. Slightly less than or equal to Off-Grid at Level 2 208-240 VAC. Only at level 3 and 4 do they charge as fast or faster than Off-Grid. Verry few ever use it in the USA because of the expense and large amount of power required. 95% of EV customers in the USA use Level 1 Charge Stations at their home. L1 charge rate varies depending on which EV battery size you have.

At no time will any commercial EV BMS ever allow the customer to fully charge the battery. Under normal operating conditions where no Balance is required is a straight forward CC/CV charger, and the BMS will turn off the charger when current tapers to a set value determined by the manufacturer.

So much out-dated information!

There is no way that 95% of EV customers in USA charge at Level 1 at home anymore since battery sizes and driving ranges of real EVs have gotten bigger.

Small battery hybrids may charge at 120V AC, but longer range BEVs charge L2 at home at 240V and more than 6kW. 7,500 Chevy Bolt EVs can charge at 240V, 7.6kW. Teslas (more than 130,000 in the US) charge at 240V 9.6kW or 17.2kW. Nissan Leafs (about 100,000 in US) charge at 240V 6.6kW. BMW i3 (28,000 in US) at 240V 7.4kW. Every BEV coming out in the future will be at least 6.6kW charge rate, most of them considerably higher.

All of the large battery EVs enable charging to 100% of rated charge.

I haven't seen any home storage battery rated for more than 5kw and none with storage capacity above 13kWh; enough for only about 45 miles per day.

[jflorey2]

For standard off-grid systems where the battery will be operating at less than half their rated charge and discharge rates I think the only communication that is necessary is a signal from the BMS to the charger and loads to say STOP which could be as simple as a relay or solid state switch.

I would also note that Midnite has a remotely operated DC circuit breaker that can open the circuit when a cell goes under or over voltage. Since pretty much all battery installations have a main breaker, this doesn't require any new switching in the DC circuit (the highest current circuit in the system.)

[raenrfm]

Hey sunking I appreciate your input but I wonder how that's going to help me decide on the design of my off grid home? I don't have an EV note do I plan on getting one. I want to know people's experiences with AC vs DC coupled systems as I'm wrestling with the pros and cons of each.