Direct solar to Charge Leaf

I am curious about electric vehicle and actually almost bought a leaf but decided on a Hyundai accent for the same price. Close by no cigar...

Anyways, now I am interested in getting my own solar panel system. This whole solar idea brings to mind that solar panels provide DC power. The leaf accepts DC power having a big battery essentially. Normally if you want an "off the grid" or "hybrid" solar panel system to power your house you would need a bunch of batteries to store the power.

Here is my idea, why couldn't we just use the leaf as the battery supply?
Here is the diagram to help understand:


So instead of having this battery bank thing, just use the leaf as a battery bank? I bet the battery in the leaf is superior to many batteries you can find since a lot of research has been done to make long lasting batteries.

Another idea is wouldn't this provide more efficiencies for charging the leaf? Because the leaf would be getting DC power, it would charge faster than AC?

The last thing is another efficiency gain in a solar panel to leaf charging setup. Instead of having to waste energy converting the DC from the solar panels to AC for the house and then back to DC for charging the leaf (converting is a waste of energy because its not 100% efficient), wouldn't it be much more efficient to just somehow plug the solar panel directly into the leaf?

Does anybody know any plug that can be wired to DC power? I know that there already is that super fast charging at the nissan dealerships that provide 30 minutes charges that are DC, so I guess it is possible. Maybe just wiring that plug to a solar grid instead? :? I know that it probably won't be as fast as charing in 30 minutes but it also depends on the number of solar panels.

My idea is I think it would be cool if you had 2 options with the solar grid, you could either plug directly into the solar panels through some specialized outlet/plug or just use the house's public power grid's AC power (in night situations). Also say that you are driving your leaf during the day and want your solar panels to be powering your house/public power grid. It would be nice to just have a switch that instead of powering your leaf, just sends the electricity back to your home like it would be in a normal on the grid solar panel home setup. Kind of like this

Tell me what you guys think

in Japan they have a system they called "Leaf-to-home" doing something like what you've outlined. I'm not sure on the details as I've never looked into it.

Yup, its been talked about for a long time. Both in regard to solar but also vehicle to grid type demand leveling. While there have been pilot programs and studies, I'm not aware of any serious moves in this direction in the US. Perhaps Tesla's Power Wall being the closest thing so far. But without buy in and support from utilities it will be difficult. For example, I believe my grid tie interconnect agreement with my local utility specifically restricts anything being connected to the DC side. And without support from the utility meter even demand leveling on the AC side can be challenging.

If you wanted to try it, I think the key missing piece would be the dc:dc converter / charge controller. There are inverters with the capability to charge batteries built in, but not anything that would be appropriate for charging something like a Leaf battery to my knowledge. You'd also have to look at what you'd really gain by skipping the conversion to AC. As I recall the efficiency of the big grid tie inverters is on the order of 97% or better. You might be able to cook up some combination of existing equipment that could load the solar panels efficiently (MPPT), convert the dc voltage to the proper level, and manage battery charging, but it would be complicated and could easily end up being no more efficient.

Bear in mind that most all efficient dc:dc converters operate by converting to AC and back to DC at the new voltage. So going through the 120/240V AC conversion and back is maybe not as big a deal as it seems like. There's really no way to feed solar dc directly into a battery efficiently. That's basically the purpose of the MPPT controller. It loads the solar to produce the voltage/current output that maximizes output power. And that optimal point will vary considerably with weather, time of day, temperature, etc. Even if you were able to design your solar array such that the output voltage range under all conditions covered the range needed for the battery charging, under most conditions it would not be efficiently loaded. This would likely result in a much more significant hit to efficiency than a dc:dc converter, or the conversion through AC line voltage and back.

Rob

Rob's discussion is very much on-point with the current state of solar PV panel charging (DC/DC) of high voltage EV batteries. A number of clever individuals (on this forum and others) use the Leaf's battery modules for solar PV charging, however (seems) most have used nominal 48 volt DC designs (re-configuring the modules). Nominal 48 VDC is a common solar MPPT charge controller design. The recent advances in these charge controllers have been in the PV panel voltage - with panel voltages allowable in the 600+ VDC range - with very good efficiencies. There has been one (higher battery) voltage charge controller commercially offered - the Midnite Classic 250KS that will charge 120 VDC battery banks. It was discontinued due to low volume (and "technical" problems according to Midnite), but has recently been offered with warrantee by Midnite. I bought one for my 120 VDC inverter (240 VAC output) for my level II Leaf charging system. Currrently installing the panel system. Although this solar PV/CC/inverter system is quite efficient, the Leaf's charger is not!

Electric MotoWerks makes several high voltage (DC input - up to 800 VDC) charge controllers that are suitable for the Leaf's battery voltages (in situ) and , but do not have MPP tracking capabilities (yet), so are not suitable for PV panel use.

https://emotorwerks.com/index.php/store-juicebox-ev-charging-stations/75-quickcharge-25000-hv-a-25kw-pfc-charger-for-higher-voltage-batteries/related_product-112

Honda, Tesla and Nissan appear to be integrating with solar PV, but appear to be grid-tied designs for energy shifting/smoothing of the (highly erratic) solar power.

Seems the high battery voltage MPPT CC is the "missing" link for non-grid tied solar charging. I'm very interested if anyone has more information on this.

Here's a thread on the PV-direct-to-LEAF topic.

On the topic of using BEVs as batteries, I have proposed the idea of BEV net metering to allow electric vehicle owners to use their batteries to provide storage for grid-connected PV, even if the car is away from home during the daytime.