Solar panels to EV charging

4840 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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cricketo

· #2 · Feb 4, 2022

you should look at something like Midnite Solar charge controllers. DC-DC from PVs is a bad solution.

cricketo

· #4 · Feb 4, 2022

You may have heard the term MPPT, here is an article with a better explanation than I can provide

Maximum power point tracking - Wikipedia

cricketo

· #15 · Feb 5, 2022

I don't know how this conversation got derailed, but there is no need for AC to be involved with charging batteries from PVs. Solar inverters all do the same thing as the solar charge controllers, plus the inverting stage. Merely having a string of PVs at the proper OCV and a charge controller that can take that OCV and regulate to the required battery voltage should be sufficient.

cricketo

· #17 · Feb 5, 2022

Electric Land Cruiser said:
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.

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.

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cricketo

· #19 · Feb 5, 2022

Electric Land Cruiser said:
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!

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.

cricketo

· #21 · Feb 5, 2022

Electric Land Cruiser said:
Didn't think so

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

cricketo

· #23 · Feb 5, 2022

Electric Land Cruiser said:
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

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.

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cricketo

· #25 · Feb 5, 2022

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

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.

cricketo

· #27 · Feb 5, 2022

Electric Land Cruiser said:
Sounds like a bad system if you can only charge in perfect conditions. I like mine better.

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.

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cricketo

· #29 · Feb 6, 2022

Electric Land Cruiser said:
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.

You're side-tracking again, but I am curious nonetheless - what's the minimum charging current for J1772 ?

cricketo

· #31 · Feb 6, 2022

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...

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cricketo

· #34 · Feb 6, 2022

remy_martian said:
One thing you are casually ignoring.

The solar system you propose, with a 144VDC car as an integral part of it will fail county electrical inspection..."high voltage" is anything over 48V, iirc.

That didn't make any sense to me, can you elaborate ? What exactly would be against the electrical code, assuming one had a desire to be up to code and get an inspection ?

cricketo

· #39 · Feb 6, 2022

Electric Land Cruiser said:
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.

Holy cow, after all of this back and forth you're still "confused." I rest my case.

cricketo

· #44 · Feb 6, 2022

remy_martian said:
@cricketo - you can cowboy all you want but what you are suggesting makes the EV an integral part of the stationary offgrid system.

Being over 48V, that means it becomes part of the installation inspection and has to meet code. A plugin EV is not subject to inspection that stops at the electrical socket because it's an appliance and not part of the system.

I really fail to see the logic you're applying. If it's not hard-wired, then it's not an integral part. Would a vehicle integrated via CHAdeMO be an integral part too ?

cricketo

· #45 · Feb 6, 2022

Electric Land Cruiser said:
Ad hominem signals your defeat.

I didn't say your claims are wrong because you're dumb. I said I can't seem to get my point across to you, and there is no benefit for me to keep trying. The fact you're misusing "ad hominem" signals something else.

cricketo

· #49 · Feb 6, 2022

remy_martian said:
I already addressed that.

A dedicated DC charger, like your Chademo offboard charger, is an approved device that's hardwired and its installation has to be signed off. A 50 amp AC socket is an approved device. An EVSE is an approved device. A Tesla wall box is an approved device. All set a limit on what current the car can ask for and are aware of the circuit limits to which they are wired.

I didn't readily find any NEC requirements supporting that description. Like NEC doesn't call out CHAdeMO by name. NEC also doesn't significantly limit PV voltages (used to be 600VDC max, now I think 1000VDC is max). Please share if you've seen them.

A storage battery for an offgrid system is integral to that system by design. That needs approvals, PE signoffs, etc. The fact you put wheels on it changes nothing if your offgrid power system doesn't work without it. You can't extend the system without approvals unless there's a demarcation device there.

And off-grid system doesn't require a battery. There are solar inverters that will operate with variable output and without a battery. If you absolutely must, you can have the system approved with one of those. Then hook up to DC path after the fact

And if you say you can disconnect it -- that means of connection and disconnection has to be signed off because of the voltages involved.

And that's usually the thing - NEC doesn't normally prescribe / regulate system design or intent. NEC is concerned with individual design components and certain safety features. Meeting those requirements should be possible in any configuration. Like having a high voltage DC outlet for ANY number of reasons should be permissible if the outlet, wiring, fusing, disconnects are all up to sniff.

Finally, NEC applies only to permanently installed systems, whether rooftop or freestanding. So one can mount the stuff on a non-permanent structure like a trailer.

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cricketo

· #52 · Feb 7, 2022

A small citation regarding high voltage batteries :

Electrochemical energy storage systems

Part III of Article 706 applies to energy storage systems that comprise sealed and non-sealed cells, batteries, or system modules that comprise multiple sealed cells or batteries that are not components within a listed product. An informational note at the introduction of Article 706 Part III states that an energy storage component, such as batteries, that is integrated into a larger piece of listed equipment, such as an uninterruptible power supply (UPS), is an example of components within a listed product.

For dwelling units, an ESS cannot exceed 100 volts between conductors or to ground. An exception dictates that where live parts are not accessible during routine ESS maintenance, voltage exceeding 100 volts is permitted at the dwelling unit energy storage system. This information can be found at 706.30(A).

When addressing the disconnection of series battery circuits subject to field servicing, where the circuits exceed 240 volts nominal between conductors or to ground, provisions must be made to disconnect the series-connected strings into segments not exceeding 240 volts nominal for maintenance by qualified persons. Non-load break-bolted or plug-in disconnects are permitted.

iaeimagazine.org

Energy storage systems–NEC Article 706

iaeimagazine.org

iaeimagazine.org

cricketo

· #54 · Feb 7, 2022

remy_martian said:
That's a nice reference - thanks.

However, it does not apply to the pickup truck being used as an offgrid storage element:

"The scope of Article 706 informs Code users that this information applies to all permanently installed energy storage systems."

As global sales of electric vehicles seem to be exponentially growing the committee that wrote NFPA 855 thought it would be important to include requirements for houses that will use their electric vehicles as energy storage systems. There are really only two main requirements. First, any electric vehicle used to power a dwelling while parked needs to comply with the manufacturer’s instructions and NFPA 70, National Electrical Code®. Second, the use of a vehicle to power a home can’t exceed 30 days.

Either way, since this is just mental juggling for most people, I'm done looking into it. My last suggestion stands - make it non-permanent (setup everything on a metal stand that's not anchored to the ground), and you're free to do whatever.

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