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 Post subject: Powering the grid from your car
PostPosted: Sat Apr 16, 2016 5:36 am 
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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

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 Post subject: Re: Powering the grid from your car
PostPosted: Sat Apr 16, 2016 6:35 am 
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Joined: Thu Dec 27, 2012 10:55 pm
Posts: 605
n3ckf wrote:
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

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Last edited by fromport on Sat Apr 16, 2016 6:42 pm, edited 1 time in total.

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 Post subject: Re: Powering the grid from your car
PostPosted: Sat Apr 16, 2016 8:44 am 
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Joined: Wed Nov 14, 2012 9:50 pm
Posts: 4030
Location: San Diego
We can and will build some type of interface between the CHAdeMO inlet on your RAV4 EV and a DC to AC inverter.


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 Post subject: Re: Powering the grid from your car
PostPosted: Sat Apr 16, 2016 4:55 pm 
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Joined: Tue Jan 08, 2013 6:09 pm
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TonyWilliams wrote:
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. ;)


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 Post subject: Re: Powering the grid from your car
PostPosted: Sun Apr 17, 2016 10:47 pm 
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Location: Los Altos, CA
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.

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 Post subject: Re: Powering the grid from your car
PostPosted: Mon Apr 18, 2016 5:20 am 
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500 VDC inverter:

http://www.solaredge.com/files/pdfs/pro ... asheet.pdf


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 Post subject: Re: Powering the grid from your car
PostPosted: Mon Apr 18, 2016 7:13 am 
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Joined: Sun May 12, 2013 6:00 am
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Location: San Diego, CA
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.


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 Post subject: Re: Powering the grid from your car
PostPosted: Mon Apr 18, 2016 3:14 pm 
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Location: San Diego Co
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).

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 Post subject: Re: Powering the grid from your car
PostPosted: Mon Apr 18, 2016 8:11 pm 
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Location: Los Altos, CA
TonyWilliams wrote:
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.

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 Post subject: Re: Powering the grid from your car
PostPosted: Mon Apr 18, 2016 11:46 pm 
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Joined: Sun May 12, 2013 6:00 am
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Location: San Diego, CA
dstjohn99 wrote:
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 .


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