[RE-wrenches] Direct PV-EV charging: possible?

[Randy Brooks]

Allan,

As a EV enthusiast, and RE Wrench, I've also thought of, and fielded questions about, direct PV charging an EV. 

- The first issue that usually causes me to not pursue this is getting the most power production from the PV array each day.  If the EV is not there, the PV array output is not being used.  But it sounds like your customer will have the array grid tied when the EV is not present, so PV output is maximized, and he/she wants to be able to switch to direct EV charging when the EV is present.

- So the next issue is having an array wired that could both power a grid tie inverter, and charge a 300 vDC EV battery pack.  If the grid tie inverter is a 600v string inverter, and the battery pack charge controller is a high voltage string charge controller like the Xantrex 600v PV charge controller, then the array could be wired to satisfy both uses.

- The next issue is if the Xantrex 600v PV charge controller be set high enough to control charge to a 300v battery pack.  Maybe Xantrex could custom make one that could do this, and be adjusted for various battery types.

- If the charge controller can be found, then a manual transfer switch could be used to shift array output from the grid tie inverter to the car PV charge controller, and back, as desired.

How's that sound?  :)

Randy Brooks
Brooks Solar, Inc.
Solar Power for People
140 Columbia View
Chelan, WA  98816
509-682-9646
Randy at BrooksSolar.com
www.BrooksSolar.com

On Aug 23, 2012, at 6:50 AM, Allan Sindelar wrote:

> Wrenches,
> We have a customer who has built several EVs, and wants to eventually develop a business around them here. A few years ago we installed a GT system on his home. He has now moved and wants to install a system on his new home as well. This time, he'd like to develop a means by which to charge his EV directly from his array, avoiding the inefficiencies of inverting to the grid and then running a grid-based charger. 
> 
> I know of no way to do this, but then, I'm a veggiehead (drive an old Mercedes on waste fryer oil), not an EV aficionado. I suspect that there are folks out there trying to do this, as it's a logical objective. Can anyone suggest products, links, or websites for this customer to explore?
> 
> Here are his notes about this effort:
> ...this is essentially the idea. to use the EV as rolling battery backup to dual-purpose the investment in battery. The second plus is avoiding loss from two inversions dc-ac-dc, the third being relatively high-amp charge without buying another charger! and dual purposing the inverter to avoid cost of high-amp inverter only used for emergencies for a backup. 
> 
> The tech details of EV battery packs that are going to make this a challenge is the high voltage. The DIY pack running DC are going to be 120, 144, 156vDC nominal most commonly. Guys running AC motors and OEMs might run much higher.... closer to 300v. 
> 
> The charge controller or voltage limit switch needs to be user settable and fairly accurate (+/- 1 volt). The DIY people usually use a 'finish' voltage of 3.65volts / cell being 'done'. So for a 120v nominal system I would want to set the DC charge to come up to 139v and either shut down right then, or if it COULD just hold at 139v until amps drop or a specified time, that would be even better. 
> 
> I am planning to do a grid-tie system at my new house, and yes, the intent is to 'stub-in' capability to both quick-charge the pack direct from the DC side of PV if possible, AND use the car pack as night-time/emergency backup just to show its possible.... 
> 
> My little car has 12kWhr on board, one I'm working on right now will have 20kWhr onboard.
> Thank you in advance for any assistance.
> Allan
> -- 
> Allan Sindelar
> Allan at positiveenergysolar.com
> NABCEP Certified Photovoltaic Installer
> NABCEP Certified Technical Sales Professional
> New Mexico EE98J Journeyman Electrician
> Founder and Chief Technology Officer
> Positive Energy, Inc.
> 3209 Richards Lane (note new address)
> Santa Fe, New Mexico 87507
> 505 424-1112
> www.positiveenergysolar.com
> 
> 
> 
> 
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