Powering the grid from your car

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n3ckf

Well-known member
Joined
May 13, 2013
Messages
362
Location
Volcano, CA
So. I've been doing a little reading around about what's called "V2G" (vehicle to grid) applications.
There's a ton of research about "how to use electric cars as buffers for the grid", ie. you charge one during low periods, and if the grid needs power, you discharge them into the grid.

So how would you do that?

Well first, you need to bypass the "onboard charger" in the vehicle straight away. The charger will only take A/C and make it into DC (to charge the batteries) but not the reverse.
What's more, you wouldn't want to carry around additional hardware *in the car* if you're hooking it to your house anyway (your house can hold that itself, and its not going anywhere).

So you need a direct connection to the car battery (ie. a "DC" connection).
Enter ChaDEMO. Thats exactly what it is, a direct connection to your battery with a bunch of control logic to control the external charger that pumps amps *in* to your batteries.
(this is what that cool box that QuickChargePower sells for the Rav4EV does).

What's more we want that fancy control stuff in there, because we don't want your car battery to go flat while you're imitating Grand Coulee Dam in your garage.

There's *another* piece of hardware that a lot of people have that works like the reverse of what the DC charger does though, and thats the Grid Tie Interactive Inverter a lot of people have on their solar power systems.
Example here

Thats a 9000watt Grid Tie inverter (its very close to the one on a friend of mine's house), and it takes up to 21amps of DC power at 300-480volts and converts it to 240Volts A/C and synchronizes it with the Grid.

So what happens if you put these 2 items together?

Hook the batteries in your car, to a grid tie inverter which inverts the DC and turns it into A/C?
(I'm a little worried about the fact that your car's batteries can generate a ridiculous amount of current if they want to, unlike the solar panels on your roof. How do you keep them from vaporizing the inverter by sourcing near-infinite current into it?)

The motor can take 115KW out of the batteries (its rated capacity), that's 156HP and 115KW at 386 volts (the nominal voltage) = 297amps (holy arc-welder man!)
(Ludicrous mode in the Model S apparently uses *1500* amps. Gee wow.)

The cool thing about grid-tie inverters is the MPPT ones will actually track the voltage on the input to generate an "efficient" conversion from the solar panels to the grid (think of it as a big switching power supply). So as the batteries in your car "discharge" this looks just like the sun moving on your solar panels, and the inverter will continuously re-adjust (until the voltage goes below the drop-out point which is around 300V for a 240Volt feed.)

So folks who know more about this stuff than i do, tell me why I die if i try turning my car into a generator :)

(a little more researchfound this discussion in the spec sheets for a particular kind of grid interactive inverter. Apparently the MPPT circuit in this inverter type effectively raises the input voltage tracking to limit current to the inverter's max capability. (I dont know how it does that exactly) but that would tend to prevent too much battery current from flowing into it).

Slightly more research produces and engineering app note on a 3K solar inverter system
 
n3ckf said:
Hook the batteries in your car, to a grid tie inverter which inverts the DC and turns it into A/C?
(I'm a little worried about the fact that your car's batteries can generate a ridiculous amount of current if they want to, unlike the solar panels on your roof. How do you keep them from vaporizing the inverter by sourcing near-infinite current into it?)

If you hookup 10x the amount of solar panels to an inverter, the inverter goes slightly above it's maximum power.
eg: 215 watt enphase microinverter on 2 x 250 watt panels will produce about 225 watt AC (did a real life measurement)
So a 9kW sunnyboy would probably be able to produce 110% or close to 10kWatt AC.
Ofcourse, as soon as the electronics get hot, are monitored, the electronics might slow things down because of thermal management.

Problem with solar inverter is that is grid tie only for the 10kW.
Modern sunnyboy inverters have a few _hundred_ watt of non-grid tie output to run a fridge/freezer in case of emergency and the grid is down.
But you could not power your whole home from it.


You need chademo 2.0 protocol to make the DC go bi-directional.
I believe nissan sells units in .JP that with modern leafs can power a home.
Grid tie & off grid when I am not mistaken
 
TonyWilliams said:
We can and will build some type of interface between the CHAdeMO inlet on your RAV4 EV and a DC to AC inverter.

Sign me up for one of these right now. ;)
 
The fundamental difference between inverter systems is how they are regulated. The grid-tied inverter is trying to convert the maximum power available at any given instant from the panels into AC power that will go into the relatively infinite sink that is the grid. An off-grid inverter will use as much DC current from the battery as is needs to maintain the AC voltage and frequency demanded by connected loads. A V2G system that is active with a good grid must rely on a command system to determine how much current flow is desired and in which direction. The strategy is somewhat arbitrary depending on the goals of the command system.

From an individual's perspective, you probably want to minimize the amount that you pay to the utility. In theory, you could come home in the evening when you solar system has already gone to zero output and use your car's remaining battery energy to power your house, basically halting the flow of energy through your utility meter. That will avoid paying high peak power rates that continue until relatively late in the evening (9pm in PG&E's case). At 11pm, the rate is back down to the lowest price, so you can let the grid power the rest of the stuff in your house and you can slowly charge the car back up to full by morning. Of course, you could do this with a stationary battery also and then it wouldn't matter if you were home or not. This kind of system will be much easier to put together when high voltage off-grid inverters are common. Currently, I can't name one that is commercially available. Traditional off-grid inverters are optimized for up to 48VDC nominal since anything over 60VDC requires much more stringent insulation requirements in the building code. I hope that enterprising people will provide vehicle battery interface kits to allow easy integration of EV batteries into off-grid or grid-assisted systems. Basically it would entail an insulated cable system to go from the inverter to the stock battery pack connector so that the inverter system can make use of the HVDC directly from the battery and use the Battery Management System already in the pack. It would be really awesome to just buy a complete battery pack from a totalled EV and hook it up directly to an inverter system.
 
The car already has a DC to DC converter to step down the voltage for the 12 volt battery.
Depending on voltage, you just need find the correct voltage and amperage DC to DC converter needed (48 volt being preferred).
Then connect to a grid interactive inverter such as Schneider Electric SW or Outback Radian series inverters.
I would further then get a Reliance Controls Q series transfer switch, and wire it so that you chose which breakers should be powered by the Inverter.

These inverters are also connected to the grid, so they will automatically switch between power sources, and can be programed for any desired time of use.

Key here is that, if you do lose power, your inverter with your car's power pack will still be able to power your house vs. solar inverters that need the grid, or a sophisticated islanding setup (which these inverters offer as well) to be able to provide power during an outage .
You also get a generator input on the transfer switch, so if all fails, you can fire up the old gas generator ....

Hybrid inverters have come a long way, and with proper setup, you do not have to be giving anything back to the power company and being charged for it ... You use the grid only as a freebie generator to supplement power only when needed.
 
You definitely want an inverter tailored to islanding operation, as well as battery management and grid tie. Something like the Sunny Island http://www.sma-america.com/products/battery-inverters.html is what I have considered. I think the DC-DC converter idea has merit - are they two way and relatively efficient? Otherwise I have considered stringing 7 Sunny Island inverters together for about 400 volts max, 336 nominal DC voltage and AC output of up to 35kW. But that gets crazy expensive, and 35kW is insane for residential applications.

These inverters are typically designed for this type of battery system http://www.aquionenergy.com/products/energy-storage-battery or a string of deep cycle lead-acid batteries. But unfortunately these inverters are typically only 120 Volt single phase. If I'm going to spend big money for off-grid capability I definitely need 240V and two way power (draw from batteries or charge batteries as appropriate).
 
TonyWilliams said:
500 VDC inverter:

http://www.solaredge.com/files/pdfs/products/inverters/se-single-phase-us-inverter-datasheet.pdf
Tony, I don't see anything on that datasheet that says it can directly handle a battery. Looks to me like a normal SolarEdge inverter to use with their Solar Optimizer system. They are supporting the PowerWall by integrating the logic to command the DC/DC in the PowerWall.
 
dstjohn99 said:
You definitely want an inverter tailored to islanding operation, as well as battery management and grid tie. Something like the Sunny Island http://www.sma-america.com/products/battery-inverters.html is what I have considered. I think the DC-DC converter idea has merit - are they two way and relatively efficient? Otherwise I have considered stringing 7 Sunny Island inverters together for about 400 volts max, 336 nominal DC voltage and AC output of up to 35kW. But that gets crazy expensive, and 35kW is insane for residential applications.

These inverters are typically designed for this type of battery system http://www.aquionenergy.com/products/energy-storage-battery or a string of deep cycle lead-acid batteries. But unfortunately these inverters are typically only 120 Volt single phase. If I'm going to spend big money for off-grid capability I definitely need 240V and two way power (draw from batteries or charge batteries as appropriate).

Both the Conext, and Radian are split phase 240 volt. So, you get full power on each 120 volt phase.
Why would you want an islanding feature as a must ? Have you looked at the complexities involved ? You will have to dump your extra load, or you will blow up everything,. How will you properly manage that ?

For batteries, nothing will compare to Nickel Iron batteries. although they may cost as much or more than lithium, or double the cost of lead acid, you never have to worry about batteries for the next 20 to 40 years ... Some of the original 100 year old Edison batteries are still producing power .. try that with a Tesla Power Wall ... You can go to 0 and back to full charge, over charge, and all you need is to make sure they are toped off, and no battery management needed .
 
miimura said:
TonyWilliams said:
500 VDC inverter:

http://www.solaredge.com/files/pdfs/products/inverters/se-single-phase-us-inverter-datasheet.pdf
Tony, I don't see anything on that datasheet that says it can directly handle a battery. Looks to me like a normal SolarEdge inverter to use with their Solar Optimizer system. They are supporting the PowerWall by integrating the logic to command the DC/DC in the PowerWall.

This is a single phase inverter, which means you will need an autotransformer to convert to split phase. There are a lot of step down transformers that will step down to 120 volts, but you will only be able to power one phase of your breakers.
This is also a Solaredge transformer that will expect to communicate it's optimizers that need to be connected to the solar panels ...

If you want to go with this option, I would just use a string inverter that will give you split phase power, and most can handle 300 to 600 volts of open DC voltage ...
 
The original one i posted was a string inverter (I have a solar system with SolarEdge optizers and a 7KW inverter already).

Yeah you want one that just takes the DC in and converts it to 240V split phase (which is what a lot of grid-tie inverters do).

The issue is dealing with effectively infinite supply (compared to solar panels). This is all about the DC first stage of the inverter and how it works. One could easily make it self-limiting so it would "only" pass X Amps, i just dont know if the inverters do that out of the box. It would seem likely given how some of them say they're safe for "overpowering".
 
rayray said:
The car already has a DC to DC converter to step down the voltage for the 12 volt battery.
Depending on voltage, you just need find the correct voltage and amperage DC to DC converter needed (48 volt being preferred).
Then connect to a grid interactive inverter such as Schneider Electric SW or Outback Radian series inverters.
I would further then get a Reliance Controls Q series transfer switch, and wire it so that you chose which breakers should be powered by the Inverter.

These inverters are also connected to the grid, so they will automatically switch between power sources, and can be programed for any desired time of use.

Key here is that, if you do lose power, your inverter with your car's power pack will still be able to power your house vs. solar inverters that need the grid, or a sophisticated islanding setup (which these inverters offer as well) to be able to provide power during an outage .
You also get a generator input on the transfer switch, so if all fails, you can fire up the old gas generator ....

Hybrid inverters have come a long way, and with proper setup, you do not have to be giving anything back to the power company and being charged for it ... You use the grid only as a freebie generator to supplement power only when needed.

I could be mistaken, but I think the DC-DC is only good for 1.5kW. Throw in the inverter losses from 12V to 48V and 48V to 240VAC conversions, and you have about 1kW available. Enough to keep your refrigerators and lights going in a black-out, but that's about it.
 
rayray said:
dstjohn99 said:
You definitely want an inverter tailored to islanding operation, as well as battery management and grid tie. Something like the Sunny Island http://www.sma-america.com/products/battery-inverters.html is what I have considered. I think the DC-DC converter idea has merit - are they two way and relatively efficient? Otherwise I have considered stringing 7 Sunny Island inverters together for about 400 volts max, 336 nominal DC voltage and AC output of up to 35kW. But that gets crazy expensive, and 35kW is insane for residential applications.

These inverters are typically designed for this type of battery system http://www.aquionenergy.com/products/energy-storage-battery or a string of deep cycle lead-acid batteries. But unfortunately these inverters are typically only 120 Volt single phase. If I'm going to spend big money for off-grid capability I definitely need 240V and two way power (draw from batteries or charge batteries as appropriate).

Both the Conext, and Radian are split phase 240 volt. So, you get full power on each 120 volt phase.
Why would you want an islanding feature as a must ? Have you looked at the complexities involved ? You will have to dump your extra load, or you will blow up everything,. How will you properly manage that ?

For me, the primary reason to bring batteries to the party is to provide residential power during a grid outage. Unless you have an inverter that is capable of operating without the grid, then any investment made to use battery power is useless when the grid is down. An inverter already tailored to batteries as a power source can limit the power draw to match the load, and when including solar panels the excess power goes to charge the battery or is discharged to the grid. They also manage the excess solar power when the batteries are fully charged and there is no grid connection, though I am not familiar with the method.
 
SMA Sunny Island, Schneider Xantrex Conext, and Outback Radian are all designed to be Off-Grid and Grid Interactive in different modes. They can all work with and without the grid and they all have generator auto-start at least optionally. In addition, the Conext and Radian have completely independent solar charge controllers. When the batteries reach the full setpoint, the MPPT function just retards the solar production so that the batteries are not overcharged. The Sunny Island adjusts the frequency of the AC output and the SunnyBoy inverters that are connected will also retard their output so the batteries are not overcharged.

These are the established market leaders in off-grid systems. However, they all use 48VDC nominal battery battery banks. If you use big battery banks you also have to have big bus bars to distribute the DC current to the connected inverters. These inverters can also be run in parallel to build large systems.

In case you didn't know, the Schneider XW was used for the Solar City Tesla battery pilot program before the PowerWall was announced. you can see Schnieder's white paper here.

What we really need is a version of those inverters that can take 200-500VDC battery packs. Rumor has it that at least Outback is working on it.
 
actually i was thinking of a different application, which is time-shifting my solar.

So my solar array generates peak about 5.5KW (A/C) and will generate up to about 40KWH (on the best sunny day in early June which is my "best" time). My array points at 157degrees True so my peak day isnt June 21st (as you'd expect) but a little earlier in the year.

Anyway, if i could use the car to accept the charge early in the day and then give it back starting at say 3PM (when the actual solar power is dropping off pretty fast), then i could "move" my peak power from noon-1PM to 4-5PM. Which will be really handy when they change the rates to reflect the "Duck Curve" (google it).

This is the same thing the Powerwall was designed to do. (except its limited to 10KW). If i had my car here and plugged in, i could essentially 'buffer' a bunch of power in it to spread out my solar peak.

(yes using it to power the house when power is down is interesting too, but i have a 17KW generator and 200 gallons of propane (which runs the house for around 5-6 *days*), so i dont really need that. I could never run the house for more than a few days on 42KWH of stored power.
 
I am also interested in the "time-shift" application, but my car is rarely home during peak production. I would need to pick up a couple of used Nissan Leaf's for batteries, or maybe a wrecked Rav4 EV or Tesla. I am willing to do this but the interconnection will need to be fully functional.

I also have a generator and ample propane, but the batteries also provide the potential to "throw the switch" and go completely off grid permanently as the utility companies get more and more hostile towards PEV systems and point of use generation. In $/kWh used EV batteries are pretty attractive, and you can drive them around if needed. Maybe even using one of the unlimited charging plans with a monthly access fee and Chademo fast charging - Go out to lunch/dinner/work and pick up enough energy to power your home for a day or two.

One drawback on the generators is they are grossly inefficient because they run mostly unloaded so the fuel / kWh is not very good on average. I almost wish I had two smaller generators. A generator is only an intermittent short-term use for me, such as a brief power outage. I would hate to run on generator for several days or more, though I have done that during a couple of prolonged So Cal grid outages.
 
the longest time i've run my generator is 59 hours. That was when a large fire burned down the main line connecting Amador County to the grid. PG&E eventually brought in their own generators (10MW worth) and ran the county on them until they could repair the line a week later.
 
Actually, a system built with an Outback Radian and about 40kWh of junkyard EV batteries would be a really nice setup for you guys. I have thought about this a lot. This is my planned architecture.

Grid_Assisted_Diagram.jpg


What this gives you is a whole subpanel of loads that are basically on a huge Uninterruptible Power Supply. The only reason for the transfer switch is to make it more serviceable in case there is any trouble with the inverter, you just cut the subpanel back over to the main panel feed. The Radian has two grid inputs. One is grid interactive and one is a simple input only. The grid interactive input can synchronize to the grid and feed battery energy into the grid. This would require special permission from the utility. Normally, the second input is used for generators. However, if you wanted to ensure that there is no feed-in from the battery to the grid, you could use that input since it's just a battery charger and put the generator on the one that is capable of grid interactive.

Some of you may have noticed that the solar is on the main panel. When the grid goes down, this solar will also go down. I have Enphase microinverters that are already installed at this location, so that's the main reason why it's there. However, this is actually better for grid arbitrage because it's already authorized to feed into the grid. You could also connect a separate array of solar panels to the battery with MPPT charge controllers. The output of those panels would always be available, even when the grid was down.

The Outback Radian has a new mode called GridZero. With solar directly charging the battery bank, the inverter will try to satisfy all loads from the battery first but not feed anything back to the grid. However, it is a grid interactive strategy and it can use the grid to blend in power if the inverter or battery would be overloaded by the demand. It also uses the grid to ensure that the battery never goes below the low battery limit. This is by far the easiest and most automatic mode to use.

The mode that I was planning to use requires the use of the Mate3 control panel and its optional USB interface. Using that interface, you can change the inverter's parameters on the fly. What this means is that even without any solar panels directly charging the batteries, you can command the on-board battery charger to do things at different times of the day. The most simple strategy would be to let the inverter power all the household loads in MiniGrid mode with the battery charger turned off during Part-Peak and Peak hours, then charge the battery as slowly as possible to recover back to a nominally full state by the end of the Off-Peak period. The solar would then feed the grid and earn you NEM credits in a maximal way. Alternatively, you could use less grid energy off peak and only charge the batteries from the grid to a minimum set point, then self-consume as much of the solar as you can during Part-Peak until the batteries are full or the Peak period begins. You could do this by monitoring the current at the meter and adjusting the charging current to achieve a net energy of zero for small periods of time like 1-5 minutes.
 
I like it, except I want / need a parallel solar system that can make this system "perpetual" power.

Also, I see no reason that an autotransfer switch can't separate the grid tied panels from the grid. We just need a simple method that regulates load. We could have one switch per solar panel that we could manipulate based on load.
 
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