Limiting current draw with Solar PV?

[SnaxMuppet]

I have a 2.4kWp solar PV grid-tied array. I am considering getting a plug-in electric vehicle (EV). The car has its own built-in charger drawing 2400W from a normal 13A socket (10A / 240V).

The problem is this... I want to charge the car using just power generated from the PV and rather than get involved in anything complicated (or expensive like EMMA) the best way to do that is to limit the power taken by the cars charger to some value under the max power from the PV. The power that is generally available, and is normally exported to the grid, is about 1500W. So, if I can find a device to limit the power of the onboard charger to say, 1500W then when it is sunny it will not need to import from the grid at all.

Is there such a device? A device that can limit the power drawn by an appliance, such as the car charger or anything else for that matter?

Should this be possible it would mean that I could charge the car totally on free and CO2-free electricity.

Any advice would be appreciated.

PS I ought to say that I am a complete beginner with electrics or electronics so I am not up to building things myself BUT I might be willing if there was someone willing/able to build something for me - or even better would be if I could find a device that offers this functionality that I could buy.

[rogeriko]

I am sure the charger is full of electronics and if the correct voltage and current is not available it will shut down. What you have to measure is the charger voltage and current going INTO the vehicle maybe you can reconfigure your panels to be the same voltage/current then you can just plug your car directly into the panels, no mains necessary. This would be a huge step forward and something some electronics manufacturer should come up with for all those people that have installed panels on their roof.

[Baz]

If the charger is built in it will be a special design for the car. It will certainly be possible to limit the power but in this noddy world they probably won't give you any option because they will be more intent on having it fully charged as quickly as possible to prevent people going off with it part charged and then whinging about the short range. What you need to do is get hold of the car public relations people (who will have the technical understanding of a dead frog) and persuade them how essential for their 'eco' credentials it is to charge it off solar. Don't bother to mention things like current limit which will be quite beyond them. Once they have grasped the basic mantra 'solar charger good' you can engage the engieering part of the organisation to make it work. It is no good going to the engineers first as marketing will just stomp on their ideas.

[billi]

can one not get just a light sensor that senses intensity of the sun  and than start a relay to switch on the charger of the car  or again    a small off grid system hooked up in combi with the  gridconnection and charge   from the off grid battery inverter then when ever needed ?

Billi


Roger

maybe you can reconfigure your panels to be the same voltage/current then you can just plug your car directly into the panels, no mains necessary.

sound good but guess one would loose FIT payments 

[SnaxMuppet]

Billi, the problem isn't when to charge. I can do that manually. The problem is that the charger takes 10A and my solar can only supply 6A meaning I end up buying 4A from the grid all the time which I want to avoid. If I can charge at 6A then yes, it takes longer, but I don't buy from the grid at all and it is then free... I don't want to change my solar PV system in any way. I am very happy with my grid-tied PV system as it is. All I want to do is limit the current drawn by the charger to 6A. Thanks anyway

The problem is not really connected to what I am doing really because I might want to limit other devices to just 6A if this were possible.

I have already contacted the manufacturer but not yet got any reply.

[billi]

I somehow understand  sure  and i try to get my off grid silly billi head involved  

so was just thinking to have a little backup system in the garage  with an off grid inverter/ charger   and a battery

where you feed your PV from the GTI /grid trough while sunny  and the off grid inverter boosts  to your 2400 watt   to charge your EV (taking capacity from the extra battery that was charged sometime from your PV before)  , but perhaps then you get  close to the costs  of Emma   , but still you will have a backup in case grid fails and you can as well charge even when not sunny from your   off grid  battery


So basically what i say is boosting the PV power up to match your charger  

What voltage is the cars battery by the way ?  Perhaps there are more silly ideas  

Billi

[billi]

is it this one ?

http://www.nissan.ie/new_vehicles/nissan-leaf/nissan-leaf.aspx

[SnaxMuppet]

Yes, it is a Nissan Leaf.

This isn't a showstopper for us if we can't limit charge to 6A but it sure would be good.

Billi, you ideas are Not silly. I really appreciate you offering to help. Thanks

[Outtasight]

I couldn't find any specific details about the Voltage used but the LEAF battery pack is composed of 48 modules of 4 lithium manganate LiPo cells.  Presumably all 192 cells are in series to give about 576 to 615 Volts working (and up to 768V at the top of charge cycle).

The main 230V "8 hour" charger that is recommended for the car uses a dedicated 16A spur to be installed in the garage and will be hard wired, not a 13A square pin plug.  They also sell an "emergency 12 hour" charger that draws 10A from a normal 3 pin plug, but is not recommended for continual use as it may overheat the ring main wiring if other appliances are used at the same time. 

Dealers will have a 480V / 500V 125A fast charger (for 30 minute splash and dash emergency charging at a dealership).

It seems that all the chargers must step up the Voltage to the 768V that a typical LiPo cell would need for a 4.0V per cell top off charge.  The modules could be arranged as two parallel strings of 96 cells, but that would make the Voltage a bit low at only 307V.  The RAV4 EV used a 288V NiMH battery pack a bit bigger than the 24kWh LEAF battery, at 27kWh capacity.  But the LEAF has a higher top speed (90mph) compared to the RAV4 EV (78mph).  The LEAF peak battery output is 90kW (which would equate to just short of 300A at 307V).  There might be some complicated charging in sequence going on though.  If the pack is actually all in series then the 768V required will probably be sub-divided into charging by module banks rapidly in turn (say 12 modules at a time at 192V each).  This isn't as whacky as it sounds because the cells have to be monitored and charged / balanced individually.  Plus, it would be possibly cheaper than building a very high power step up inverter from 230V AC to 768V DC (and then still having to manage each cell individually anyway).

If the pack were "only" 307V, that would put it in range of being charged directly by a PV string and a high Voltage DC charge controller (not that one exists for DC Voltages that high, but it could).  You'd still need to somehow interface with the Battery Management System (BMS) to allow the balancing function to work.

It's not something that you can safely bodge together (and will certainly invalidate the battery warranty) and it's doubtful any 3rd party maker will be allowed to make one either anytime soon.  If Nissan are smart, they'll make it an option. 

You could use a clamp on sense coil (like from a common energy meter) on the inverter output and when it was full output, you could trigger a relay to turn the factory charger on.  This isn't going to get around the fact that you're short of solar Amps, even at maximum output, but it would at least optimise your use of generated power.

For other things around the house... The only thing you can easily do is with resistive loads like an immersion heater.  By stepping the AC Voltage down, you can reduce the current consumption.  I have a 3kW off grid inverter and run a 3kW immersion heater, but through a 4kVA tool transformer.  This feeds it only 115V and so runs at about 5.5A (or 630W) instead of 13A (3000W).  Any electronic items just won't work or they'll just adapt to the low voltage and consume the same power that they want to (like laptop power adapters that work on any Voltage from 90V to 240V).

[SnaxMuppet]

Outtasight, Thanks for your comments. This is a new car, I am not going to be changing or tampering with any aspect of it while it is under warranty

Your comment about it being 16A is partially correct. There is a 16A option and it requires a charger to be installed, as you suggest. However, the 10A charger is an acceptable method of regular charging as far as the car is concerned. The only caveat is, as you said, that a continuous 10A draw on a ring main could cause problems with overheating and sparking, particularly at older properties. However, I have had a dedicated 32A circuit just installed with its own RCD in the consumer unit so the issues of overheating etc don't exist in my particular case. Thanks for the warning though because many people will think that the 10A charger can be used on a normal ring main socket, which it can providing everything is in tip-top condition and other loads on the ring are limited. Old wiring or loose connections could cause problems at 10A continuous especially if there are other loads on the ring main.

As for installing relays etc... again, this is a new grid-tied PV system, I won't be making any changes to it without the installation company being involved as they are guaranteeing it.

Interesting suggestions regarding battery configuration but again, it is not a self-build project so theoretical only I am afraid The battery voltage is 400VDC BTW. There is a DC charging port that accepts 400VDC from a fast charger at 50kW. This will charge the car from flat to 80% in just 30 minutes. These fast chargers are not intended for installations in the home.

No, I think I will just have to accept that for now I will have to always import at least some power from the grid when charging the car and hope that Nissan develop a charger with a variable current draw (not likely I know but I live in hope!).

Thanks anyway.