Solar panels to EV charging

4798 Views 57 Replies 9 Participants Last post by electro wrks, 4 mo ago

Allan56

Discussion Starter · Feb 4, 2022

I'm looking to charge a 144 volt Lifepo equipped EV with solar panels, DC to DC. I've been reading old posts related to this but nothing directly about how to do it.
Recently, I read that a Zivan NG3 will run on 100 to 200 volts DC and have an email in to the Zivan dealer to confirm that, no answer yet. That would seem like a great solution.
Has anybody done solar to EV charging or feel willing to share some ideas?
Thanks Allan

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Electric Land Cruiser

· #13 · Feb 5, 2022

Sorry these guys are giving you a hard time without substance.

I have not found an example of solar to EV charging that does not use batteries as an intermediary between the panels and the EV battery. In this case your friend's experience with solar off-grid systems he should be able to build a battery back-up, if he doesn't already have one. Then he can plug in a normal EV charger/EVSE into his normal 240VAC off-grid system and charge like normal.

The most efficient is using microinverters on each panel into a 240VAC circuit powered by batteries and a pure sine inverter.

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Electric Land Cruiser

· #16 · Feb 5, 2022 (Edited)

AC microinverters are the new hotness in PV. They convert to 240VAC right at the panel on each individual panel. Better efficiency than hooking them into a DC circuit. Also with DC the panels are wired in series which causes a the whole string to go down when one panel is covered by shade.

Solar DC to charging an EV you have to convert the voltage multiple times and if you are using a normal EVSE then you need AC power anyway. If you are charging with batteries in the loop then you will most likely have a 48v system that's going to need either a step up for custom DC chademo or you're using an AC inverter, again making microinverters the best choice.

e. With the batteries producing the AC sine wave through an inverter; the microinverters sense that power and automatically produce slightly higher voltage. In this case when the solar is producing enough power to charge the car, the batteries will just be floating the inverter and the majority of power will go to the EV directly from the solar panels. I.e. the most efficient solar charging setup.

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Electric Land Cruiser

· #18 · Feb 5, 2022

cricketo said:
I would propose that you're a bit confused. So first of all, microinverters have been around for a decade. They have their place, but also they have their drawbacks. The main thing is that conversion efficiency is affected by the voltage differences. So like when 300VDC gets converted to 240VAC, efficiency is a lot higher than when 30VDC gets converted to 240VAC. For that reason microinverters are only installed in case you're describing - when partial shading is likely to cause more issues than reduced inverter efficiency.

If you're using onboard charger that takes AC input to charge the vehicle, then it's a different story irrelevant to the original question. I will just add that you're making some conflicting statements regarding hybrid systems with both battery and solar inverters coupled via AC path.

The battery powered inverter is only needed in order to produce a 60hz sine wave to activate the microinverters. If you have another idea on how to charge an EV at home on solar other than "AC input EVSE" then please describe it!

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Electric Land Cruiser

· #20 · Feb 5, 2022

cricketo said:
I already did describe it. You charge the EV battery the same way you'd charge the battery of a stationary system - using an MPPT charge controller. For factory EVs that may be a bit complicated due to higher voltage and no easy way to get into the DC path, but theoretically possible. In the OPs case though the voltage is much lower, from which I concluded it's a DIY project so it's definitely doable.

Didn't think so

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Electric Land Cruiser

· #22 · Feb 5, 2022

cricketo said:
Didn't think what ? That I explained the end-to-end solution ? I didn't, because that wasn't the question, and my name ain't Brian

You didn't. You said it would be complicated with no easy path, "but theoretically possible."

So you described a theoretical possibility. No solution. I offered a solution that actually works

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Electric Land Cruiser

· #24 · Feb 5, 2022

cricketo said:
If you want to be pedantic, you haven't offered anything. You basically described how people do charge EVs while being off-grid and solar-powered. You murkied the water by bringing the topic of micro-inverters, which are irrelevant. If you're charging from AC, you're charging from AC. Whether AC is a product of solar, wind, hydro or diesel is not important.

Now if the question is how to charge a factory street-legal EV from PVs directly via DC, we can talk about that. That wasn't the original question (factory street-legal EV part) though based on the voltage and chemistry the OP mentioned. So assuming that is your question, the answer is the following...

First we would require a charge controller that can operate in the desired output voltage range. Charge controller will also dictate the open circuit voltage of the PV array to achieve such output. Say for a 96s configuration we'd need to be putting out 403.2v or so, charge controller needs to be able to output that, and will likely require something like 500VDC OCV on the PV side. Then we need to hook up the output to the high voltage path of the EV. That's the same place where on-board charger is connected, and the same place where CCS or ChaDemo DC paths would terminate if present. For a moment we assume that EV doesn't have those. Finally we need to activate the DC path by telling the BMS that we're charging. That would probably involve some kind of CAN messaging specific to the particular vehicle.

Now if the vehicle is in fact equipped with a CCS or CHAdeMO adapter, then we can also exploit that. Would need to implement the wiring and the negotiation protocol - there are already projects showing that, especially CHAdeMO.

Then what happens the next day when it's overcast and the panels aren't putting out 500 volts anymore? No charging that day?

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Electric Land Cruiser

· #26 · Feb 5, 2022

cricketo said:
Correct. Output will be fluctuating from max to none both with the time and also with cloud cover. It may be impractical in some cases, but that's again not the question.

Sounds like a bad system if you can only charge in perfect conditions. I like mine better.

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Electric Land Cruiser

· #28 · Feb 5, 2022

cricketo said:
You should use whatever works best for you. But you also should remember even a system with an additional battery to balance out the supply-demand is not bullet proof if your system is under-producing. So for example, I have a 6kW solar array (actual system I have, not a hypothetical one). On a cloudy winter day (basically 5 months out of the year in PNW) it will put out 100-200W of output. That is way below the threshold to drive even the Level1 charger, which needs something like 1.2kW from AC. So effectively one would need to charge up the stationary battery for a few days in order to charge the EV for a few hours. With DC coupling those 100-200W could trickle into the EV's battery without much trouble though, and without additional losses which will amount to decent 25% or so in your system.

Smart microinverters to the rescue! Using production and consumption monitoring you can throttle the output to the EVSE to match what solar is producing and no more.

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Electric Land Cruiser

· #36 · Feb 6, 2022

cricketo said:
6A at 240VAC is roughly 1400W. So if the array is putting out a couple of hundred watts, no matter how smart your inverters are, you can't satisfy that demand. So you end up shedding the load, charging your stationary bank until it reaches minimum capacity, then firing back the inverter output to begin charging. Besides inefficiency in multiple conversions this obviously adds charge/discharge cycles to the stationary battery.

Bottom line - ELC was arguing that such approach is "better", and I can only agree that it's probably better in a sense that it's more straightforward for an average Joe to implement. Otherwise it requires more components, operates at lower efficiency. One example where "my approach" is better, and is basically the only game in town, is camping. I hope I don't need to elaborate what I mean...

Yes, exactly. When the solar panels aren't generating enough power to meaningfully charge the car, then they charge the battery bank storing the energy for future use. And as stated the lowest charge power for the J1772 is 1440 watts at 240VAC but at 120VAC then it's 720 watts. Easy to hit those numbers nearly every day with a 2-3kw array. Versus your idea which can only charge on perfect weather days and gets knocked out by a single passing cloud. Your idea is not more efficient; the panels produce power every single day, some days more than others. The point of solar is to capture that energy and use it.

The features I'm talking about are all native to the components and the price of microinverters vs. an MPPT large enough is at best a wash but most likely the microinverters will be cheaper. The software already exists to switch between charging the EV and charging batteries and throttle output to match what solar is generating.

In the end you agree that mine is better begrudgingly. Your system still doesn't work for camping because now you need to have your absolutely massive array become mobile and oh yeah it still needs a perfect weather day to work.

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