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Discussion Starter · #1 ·
Hi,

I'm an older guy with lots of electronics experience, some solar experience and 2 electric cars. I'm looking for help solving the following global environmental problem, starting with our own little problem:

> 1) I want to charge our Nissan Leaf and Tesla model 3 ONLY from the sun, and
> 2) I want to do this as efficiently as possible.
Sounds simple, and done-that-already, but it's not, unless I'm just wrong, it's not really got a solution yet.

Now in theory, and as simple as possible, this means the following setup:

1) Some solar panels,
2) One DC-DC converter*,
3) A battery charge controller to throttle up and down the converter, and
4) A car run by a traction battery.

Notes:

  • Here the converter needs to be the maximum power point type to most efficiently use the solar panels.
  • Also to help minimize losses that every converter or inverter stage has, between the solar panels and the battery it would be best to have just one DC-to-DC converter. In practice, however, directly tapping and charging the high voltage DC traction battery is not very smart with an expensive car that is under warranty.

So moving to a more practical solution, I'm thinking of using the existing J1772 car charging ports (with the J1772 adapter to the Model 3), but to have my solar system smart enough to tell the cars how much solar power is available at any given moment so the car can track the solar production. This makes it so that when a cloud cuts the output of the panels, the car just takes what is available at that moment. And it means the car charges at the rate that we have sun that day, and no more. Yes, this adds one additional layer of inverter inefficiency, because now you first have a DC to AC converter from the solar array, and it then feeds an AC to DC converter and battery controller inside the car. But it also means not directly tapping into the high voltage DC of these car batteries, and also hopefully being able to use more off the shelf components.

Sounds simple. It's not. So far I've not found an off the shelf solution to this.

Here's are the ideas I have so far to accomplish this, DIY style:

* I already have purchased the J1772 specs, and can see that the pulse width can be programmed to tell the cars that can use that input how much current you want a J1772 car to draw. The trick is getting this available current from an off-grid solar array and then passing it to this J1772 interface.

* I have also found the design of a J1772 interface that could be modified here: Arduino EV J1772 Charging Station .

What I'm still looking for is a good off-grid solar inverter that will tell me how much current is available, and then some way to have the Arduino read this information to convey that to the car via the J1772 controller.

So I guess my question is: has anyone else done this, or if not, how might you go about this, or is there an off the shelf solution somewhere. I haven't yet built the solar array, but am hoping to do that this summer (2021).

I've already seen these:


AT A MINIMUM, if I decide to be grid tied instead, I would like to be able to set the J1772 output current from information coming from our current solar output in amps, so as to NOT draw power from the grid to charge the cars if at all possible. The idea is that once we have enough sun then, and only then can we drive.

Thank you.

-- Howard
 

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Just do not go direct from the solar production to the EV.

Put in a staging battery many times bigger (kWh capacity) than your EV pack.

Then you are still collecting energy while the car's being driven.

And you can recharge quickly rather than always taking days and days

buffer when weather is bad etc.

You better have a whole lotta panels if you want to drive more than a few hours per week, especially in winter. Might with the storage bank, cost ballpark same as a new Tesla.

But at least my way you are a bit less at mercy of the weather as to the timing of your ability to drive.
 

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Discussion Starter · #3 ·
Thanks, and doesn't solve the better coupling between solar production and car usage that I'm seeking.

Also your suggestion adds unnecessary significant cost for unnecessary batteries and their maintenance, and with any extra cost comes extra environmental impact by it's very nature to manufacture these extra components.

The basic idea is to accomplish the car charging as simply as possible, not to make it any more complicated or expensive than necessary.

Also for us, a few more panels is not a significant issue as we have space for quite a few. I admit that how many solar panels I put in to get this done will be a guess at first. I plan to start a little low, and add panels as needed to get it to work for us without too much overkill.

Also in Hawaii we don't worry about cold weather.

And I'm retired, so we don't need to drive every day. We can wait until a car has the juice available. We're learning to slow down and try to work with what the earth offers, not to try to overpower her.
I know that what I'm seeking is non-standard for the industry, but I've installed solar before, and have grid tied solar on one house now, and we've thought about this long and hard, and we just want a simple system to directly charge the car battery.

Furthermore, this means we don't have to sell our excess energy back to the utility at only 1/3 of the cost of energy that we get out of the grid, (i.e. we pay $0.31 to buy a kwh, but can only sell at only 0.$10 per kwh). So for us this also makes financial sense. It maximizes the capital cost of our solar panels by using our own energy. (Someday I might add a switch once the cars are full to help power the house or a battery to the house, but that is a future seperate thing, and secondary in my opinion, as we don't really use that much juice for the house now.)

So, thanks for your quick response, but I'll keep seeking an answer to this question, because that's what I really want and need.


Just do not go direct from the solar production to the EV.

Put in a staging battery many times bigger (kWh capacity) than your EV pack.

Then you are still collecting energy while the car's being driven.

And you can recharge quickly rather than always taking days and days

buffer when weather is bad etc.

You better have a whole lotta panels if you want to drive more than a few hours per week, especially in winter. Might with the storage bank, cost ballpark same as a new Tesla.

But at least my way you are a bit less at mercy of the weather as to the timing of your ability to drive.
 

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OK, but you could be talking many days even with 10 grand in panels.

Have a backup ICE vehicle for emergencies

or even retired people get invited to dinners or whatever right?

My suggestion has nothing to do with the grid, I lived off it for decades homesteading in the bush would not have wanted any utilities from outside even if that were possible.

Just like having tanks so you have water when you need it.
 

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Discussion Starter · #5 ·
Thanks John, yes first, we do keep an old ice vehicle around for things the ev's won't do, like camping on rough roads.

Also, as for how many days needed to charge, how much we drive each week will determine how many panels are needed. But week to week, our needs are remarkably consistent so I can work this out in time.

And btw, we still have the old way of charging the cars if necessary just by plugging them in to the grid.

I'm trying to build a system to move us mostly off of this grid based charging to save money and to get us off the carbon as most grid is still produced from carbon.
 

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It is going to be hard to compete with the efficiency of the grid. My advice is to get a grid tie system; and size it according to how much power you normally use, including your electric car. If you want to feel good about only charging your car with solar, then switch your charging time to the middle of sunny days. You would have to do that anyway with your proposal, so it should not be a problem, right?

Trying to squeeze out every last penny is just going to drive your wife crazy, anyway, so I suggest you look at the bigger picture: Namely, a solar system is an investment that will pay itself off in probably 5-7 years in your climate, and will easily last for 20 or more. So, make the grid be your battery. Someone already built it; the energy is invested, so you might as well get some return on all that infrastructure. You might think getting paid 10 cents sounds like a rip-off, but you are paying yourself 31 cents each time you put a kwh in your car battery (when the sun is shining). Those two cars, if you can charge them both during sunny spells, and then make the range last through cloudy times, will I think really help reap the most return out of a grid-tie system.

After half a decade, you will be getting your power for free, and any that you dont use will help to make the grid that much greener for everyone else.
 

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Discussion Starter · #7 ·
Thank you OR-Carl.

Actually, we already charge the Leaf from a grid tied solar, but after doing that for awhile we're not happy with it, and think it could be improved for our needs.

Also please take a good look at this chart and you will see that most grid electricity still comes from carbon, so we want to get away from that mode of thinking:


We mostly use the 12A - 120V level 1 charger, but also have a 32A level 2 220V charger that we sometimes use in a pinch. It's a pain to feel we have to plug and unplug the level 1 charger as the sun comes and goes during the day, just to get a reasonable electric bill. I know we can do a better job of this.

But at 60 I'm a little past my prime to engineer this myself. So I'm searching for the best off-the-shelf components that can be put together in a more creative way to more efficiently charge our car.



It is going to be hard to compete with the efficiency of the grid. My advice is to get a grid tie system; and size it according to how much power you normally use, including your electric car. If you want to feel good about only charging your car with solar, then switch your charging time to the middle of sunny days. You would have to do that anyway with your proposal, so it should not be a problem, right?

Trying to squeeze out every last penny is just going to drive your wife crazy, anyway, so I suggest you look at the bigger picture: Namely, a solar system is an investment that will pay itself off in probably 5-7 years in your climate, and will easily last for 20 or more. So, make the grid be your battery. Someone already built it; the energy is invested, so you might as well get some return on all that infrastructure. You might think getting paid 10 cents sounds like a rip-off, but you are paying yourself 31 cents each time you put a kwh in your car battery (when the sun is shining). Those two cars, if you can charge them both during sunny spells, and then make the range last through cloudy times, will I think really help reap the most return out of a grid-tie system.

After half a decade, you will be getting your power for free, and any that you dont use will help to make the grid that much greener for everyone else.
 

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Hi Howard.

I see a few options for you.
I have Tesla solar on my house. The inverter displays how many Amps the array is producing. Tesla also provides an API where you can find out if you are producing excess electricity. I don't have a Tesla car, but I wouldn't be surprised at all if you can set the car to charge only when your Tesla array is producing excess power.

The other DIY option would involve a solar array coupled with a home-brew DC/DC converter. You'd have to explore some of the latest chips which figure out how much current you can draw from the solar array. I suspecting you might be able to use a Leaf Inverter as a base for that if your solar array can produce a high enough voltage. My arrays produce in the 400-500 volt range, so could
go directly to the car (through a DC/DC converter which kept the voltage and current within range. Would be a fairly involved project. Quite a bit of learning and safety involved.. ;)
Have fun and let us know what you are going to do.

Bill
 

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I have been using this with the solar controller , The designs are available online. It monitors current flow and direction to change control pilot to bring import power to 0. Only thing to note is min of 6a as per j1772 spec. Not some much on an issue on 110v or iff you have a large enough array.
 

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I think no matter how you go about it, relying on renewable power requires one of two things: A way to buffer the variable output (a battery, or a grid tie) or a lifestyle change to the point where you only use the resource when it is available.

If you want the system to be hands-off - then I think you are going to find you need to buffer it. You are trying to keep the system as lean as possible, but you still need to size it for the worst case scenario (whatever that is in Hawaii), and you will inevitably have a surplus at other times. You could go completely off grid (jump on in, the water is fine :)) but if you (or the wife) are accustomed to all the niceties of a grid-tie then you will need a lot of batteries, which defeats your goal of reducing your carbon footprint. My household uses 1 or 2 kwh of electricity a day, so my battery bank is tiny. I do burn 20lbs of propane a month for hot water and a couple cords of firewood, because we do not live in a tropical paradise.

But, I think the probably remains, a well designed off grid system has to be sized for the worst case. With an off grid system that creates "waste" (really it simply delays the eroei) - with grid tie, the waste is more like opportunity cost, but at least the power gets put to use.

Here is a thought, though, What about setting up a relay that controls the AC to the EVSE. Get a tiny solar panel as your sensor, and use that to open and close the relay. It might need some simple circuit to control it, but I suspect you could devise something pretty easily. I guess the only unknown for me is if the car will resume charging on its own if the EVSE is unplugged and reconnected. (I know how you can find out, though :))
 

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Discussion Starter · #11 ·
I have been using this with the solar controller , The designs are available online. It monitors current flow and direction to change control pilot to bring import power to 0. Only thing to note is min of 6a as per j1772 spec. Not some much on an issue on 110v or iff you have a large enough array.
Interesting. Close to what I'm looking for but solves different problems. It can run in max or smart mode. In smart mode it is used for load balancing with up to 4 parallel units. It's not really what I'm looking for, but it's interesting. Also I noticed that it's in 'evaluation' only, as they are not ready for production yet. Thank you for this idea. https://www.stegen.com/pub/SmartEVSEv2.2_install_2.17.pdf
 

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Discussion Starter · #13 ·
What about setting up a relay that controls the AC to the EVSE. Get a tiny solar panel as your sensor, and use that to open and close the relay. It might need some simple circuit to control it, but I suspect you could devise something pretty easily. I guess the only unknown for me is if the car will resume charging on its own if the EVSE is unplugged and reconnected.
On your 2nd point, I can't be sure, but both of our 2 EVs will resume charging on their own if the ESVE is unplugged and reconnected.

On your 1st point, that is very roughly in the direction that I'm headed, but allowing only on or off doesn't work very well, and here is why: Say for example that we're sometimes getting 100% out of our solar array, and other times we're getting 50% out of it. Then turning charging fully off when we're only producing 50% doesn't make any sense, nor does charging at only 50% when we're getting 100% of sun. Instead what makes sense is to tell the car to charge at 50% of the rate, when we have 50% sun, and at 100% rate when we have 100% sun.
 

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That would be nice, but I have been unable to confirm that it can do this.
I googled that thing and it looks like it could be done with an API (software, computer and programming), or a different charger (Zappi?, I don't know what car's are compatible with this)

I looking into the API a little further. If you had a powerwall, you could get the state of the battery reserve. With that information, you could decide to charge the
car or not. Then you could monitor the powerwall status, and every minute make the decision to keep charging or stop. Obviously, this involves some type of powerwall
(I think you can make your own, which would get you much closer to doing the same with your car(s).
 
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