Portable Solar Charging Thought Experiment

[GZDongles]

I tried posting this in the technical forum, but I thought I might get some responses here instead!

I know this seems to be a controversial topic here for some reason, but I'm interested in exploring how it might be possible to use foldable portable solar panels to charge the car. I know there are a lot of reasons that this may be a bad (and certainly a cost and time inefficient) method of charging, but I just want to focus on how I might go about this in theory if I wanted to try.

The (hypothetical) scenario I have in mind is that I'm doing some long term car camping out west in a Model 3 LR AWD. I may be doing long day hikes in an area with pretty much constant sun, and may be sleeping in a campground with no available power at night either in the car or in a tent relatively close by.

I know it would be relatively easy (but not cheap) to fit about 1-1.5 kW DC worth of foldable solar panels into the trunk while still having plenty of room for camping and other gear. This is an example of a folding panel in the right size/power range (assuming two to three of them). I'm sure there may be better ones out there, but it's just for example. At 1.5 kW, you could theoretically charge at 3-5 mph, depending on charging losses. With the summer sun, that could be 30+ miles per day and 60+ over a two day hiking trip.

So, even though it's not really a very practical option, I'm interested in how I might pull this off.

1. What type of inverter would you use?
2. Would the most efficient/simple route be solar panel -> inverter -> 120V outlet -> mobile connector?
3. Will the car handle potential sudden variations in amperage without stopping charging?
4. Will the car be able to automatically start charging again if the power cuts out (due to passing clouds, etc.) and comes back?
5. Are there any other technical roadblocks I'm missing?

Thanks for your input! Again, I know this isn't a practical (or cost effective) method to charge a car on this sort of trip, but it's an interesting thought exercise!

 

[Tessaract]

I tried posting this in the technical forum, but I thought I might get some responses here instead!

So, even though it's not really a very practical option, I'm interested in how I might pull this off.

1. What type of inverter would you use?
2. Would the most efficient/simple route be solar panel -> inverter -> 120V outlet -> mobile connector?
3. Will the car handle potential sudden variations in amperage without stopping charging?
4. Will the car be able to automatically start charging again if the power cuts out (due to passing clouds, etc.) and comes back?
5. Are there any other technical roadblocks I'm missing?

Interesting questions.
If you had the option of designing your own, the most efficient arrangement would be a solar panel > 400VDC> Tesla connector (a "panelvertor"?). That way you would bypass the onboard charger and its efficiency loss entirely. A critical bit of design would involve the communications protocol between your HVDC "panelvertor" and the car. But once you have that worked out, I speculate that you would also be able to avoid the car "barfing" on constantly changing charging current, because bypassing the charger and associate logic might also bypass the "safety protocols" associated with normal AC charging.

Now that I've checked out the folding solar panel, it occurs to me that rewiring the 10 panels in series instead of in parallel would already provide ~400V. Just a thought...

 

[Sophias_dad]

1) Not sure, but don't be surprised if it requires some tweaks. I have a Prowatt 2000 pure sine inverter I tried as an experiment. It worked fine right up until the car tried to start charging, and then the GFCI in it tripped. I assume the car is testing for a good ground/neutral. I'm sure I could make it work, but haven't tried yet.

2) yes. The most efficient route is really (enormous rack of solar panels putting out hundreds of volts DC-> supercharger_imitator-> car), but your idea is simplest.

3) If the inverter is smart and shuts itself off sharply when input voltage decreases, then reactivates when the DC comes back, the car should be fine.

4) See 3. Try it with your UMC. There's a random delay built in so that the entire neighborhood of Tesla's doesn't ask for power instantly(at least with the HPWC, I assume the UMC is the same.

 

[Sophias_dad]

I should note that really cheap inverters should probably be avoided. I don't know if the UMC would take kindly to a non-sine waveform, and I also had the unfortunate experience of trying an inverter that SAID it was good to 750 watts but would completely shut down if you asked for more than 150 or so. Happily, I was only trying to run a fish tank filter/heater/aerator, but that was about all it could do.

 

[Watts_Up]

This is an example of a folding panel in the right size/power range (assuming two to three of them).

Just for fun and to learn about solar technology, I would be interested building such system.

I don't want to get a full solar panel installation in my home right now. This system would be use on a separate circuit,
controlled by a timer, to run some appliances, such as a refrigerator, during the ToU peak hours which are from 4 pm until 9 pm.
The electricity cost is around $0.50 per kWh during the summer and $0.30 in winter, and the off peak is around $010 per kWh.

I like the folding panel solution, but I cannot find the cost of this 500 W panel using the link to EnergyWave.net that you provided.

- Do you have any idea of the price of such item?

- Is there a big difference of price when comparing with a rigid panel?

- Would such panel work if put inside, like behind a large window in a veranda?
(So I would not need to remove it in case of high windy)

 

[GZDongles]

Interesting questions.
If you had the option of designing your own, the most efficient arrangement would be a solar panel > 400VDC> Tesla connector (a "panelvertor"?). That way you would bypass the onboard charger and its efficiency loss entirely. A critical bit of design would involve the communications protocol between your HVDC "panelvertor" and the car. But once you have that worked out, I speculate that you would also be able to avoid the car "barfing" on constantly changing charging current, because bypassing the charger and associate logic might also bypass the "safety protocols" associated with normal AC charging.

Now that I've checked out the folding solar panel, it occurs to me that rewiring the 10 panels in series instead of in parallel would already provide ~400V. Just a thought...

That's a really interesting idea. I'm probably not in a position to do anything to the DCFC system that could potentially void a warranty, but I'd be interested to know if there are any specs published anywhere about the DC charging communication protocols. It may be a bit roundabout, but possibly the CHAdeMO specs are public so I could use an adapter. I guess I would still need a DC-DC variable voltage converter as well since the solar output voltage would vary with the amount of sunshine. I would expect that there are solar specific converters that could handle that, since it must be a common problem with portable solar systems.

 

[GZDongles]

Just for fun and to learn about solar technology, I would be interested building such system.

I don't want to get a full solar panel installation in my home right now. This system would be use on a separate circuit,
controlled by a timer, to run some appliances, such as a refrigerator, during the ToU peak hours which are from 4 pm until 9 pm.
The electricity cost is around $0.50 per kWh during the summer and $0.30 in winter, and the off peak is around $010 per kWh.

I like the folding panel solution, but I cannot find the cost of this 500 W panel using the link to EnergyWave.net that you provided.

- Do you have any idea of the price of such item?

- Is there a big difference of price when comparing with a rigid panel?

- Would such panel work if put inside, like behind a large window in a veranda?
(So I would not need to remove it in case of high windy)

Those are good questions. I'm not sure of the cost, but I would expect somewhere from $1.5-4 / Watt. I have a home solar system that was close to $4/watt including installation, permitting, and all the associated hardware with good quality SunPower panels. I would expect a folding DC output panel to be cheaper on a $/watt basis.

I think the effectiveness behind glass would depend on the type of glass but most importantly the orientation of the window. Panels need to be positioned at a certain angle and orientation to be most effective. The most efficient position changes by both time of day and season, but of course for normal roof mounted panels you are usually compromising on efficiency in favor of aesthetics so the panels can be flat-mounted to the roof.

 

[Tessaract]

That's a really interesting idea. I'm probably not in a position to do anything to the DCFC system that could potentially void a warranty, but I'd be interested to know if there are any specs published anywhere about the DC charging communication protocols. It may be a bit roundabout, but possibly the CHAdeMO specs are public so I could use an adapter. I guess I would still need a DC-DC variable voltage converter as well since the solar output voltage would vary with the amount of sunshine. I would expect that there are solar specific converters that could handle that, since it must be a common problem with portable solar systems.

The ChaDeMo spec could be one way to go. I haven't done an internet search, but there may be info available, and perhaps even on the Tesla connector protocol.
I agree that a circuit would need to regulate the output voltage of the solar panels to ensure that maximum charging can take place for all solar conditions. However, if the panels were wired in series, then the different between the panel loaded output voltage (as low as 360V) and the battery charge voltage (~420v?) would be relatively small, likely less than 15%, and a small boost convertor could handle this. Inefficiency of the boost convertor would also be applied only to the voltage boost percentage, rather than the full charging power.

 

[user212_nr]

Thanks for your input! Again, I know this isn't a practical (or cost effective) method to charge a car on this sort of trip, but it's an interesting thought exercise!

https://www.solaredge.com/sites/default/files/ev_charging_inverter_brochure_nam.pdf

It only costs $2,795.00.

You could also use the solar panels to charge a few batteries and then use an inverter. You'd need either to have a means of preventing it from getting over-discharged or to charge the car separately when you know the batteries are ready. Scheduled charging could work with some guesswork.

Chadmo is protocol that requires you to program your own embedded computer in order to use it. It is not a simple mechanical/electrical "adapter" that you can hot-wire to your voltage outputs.

 

[Watts_Up]

https://www.solaredge.com/sites/default/files/ev_charging_inverter_brochure_nam.pdf

It only costs $2,795.00.

You could also use the solar panels to charge a few batteries and then use an inverter. You'd need either to have a means of preventing it from getting over-discharged or to charge the car separately when you know the batteries are ready. Scheduled charging could work with some guesswork.

Chadmo is protocol that requires you to program your own embedded computer in order to use it. It is not a simple mechanical/electrical "adapter" that you can hot-wire to your voltage outputs.

When you look at the PowerWall, you are only allowed to charge it using solar panels.

Note: In case of bad weather and risk of power outage, then the electrical power companies
sends you an alert and allows you to charge your PowerWall using the gird, and only in that case.

I wonder if it is because the electrical power companies don't want you get electricity at reduce rate
during off peak hours and sell then back the electricity during peak hours?

When you have an EV and charge its battery during off peak hours.
If you are at home during peak hours, and if your car battery is still charged enough,
it would be great then to be able to use your car battery for your home usage

This would be both economical for you, and save the grid from additional load during peak hours.

 

[drj3]

1) Not sure, but don't be surprised if it requires some tweaks. I have a Prowatt 2000 pure sine inverter I tried as an experiment. It worked fine right up until the car tried to start charging, and then the GFCI in it tripped. I assume the car is testing for a good ground/neutral. I'm sure I could make it work, but haven't tried yet.

I have about 900 watts of panels that I installed on a shed with a 3000 watt pure sine inverter and a small bank of batteries. I have the system grounded to earth with a deep grounding rod and have used the system to run a pool pump, sprinkler timer and various power tools (and a crock pot to cook dinner yesterday when the power was out for 6 hours). I tried charging the Tesla with it a few days ago, but got an error on the screen saying that it was unable to charge because of improper grounding. Does anyone know if this is an issue with the way the inverter has the neutral and ground set up and if there is a way to correct it? I've seen some posts about issues with the ground when using gas generators to charge. Do inverters have the same issue?

 

[joetomasone]

I have about 900 watts of panels that I installed on a shed with a 3000 watt pure sine inverter and a small bank of batteries. I have the system grounded to earth with a deep grounding rod and have used the system to run a pool pump, sprinkler timer and various power tools (and a crock pot to cook dinner yesterday when the power was out for 6 hours). I tried charging the Tesla with it a few days ago, but got an error on the screen saying that it was unable to charge because of improper grounding. Does anyone know if this is an issue with the way the inverter has the neutral and ground set up and if there is a way to correct it? I've seen some posts about issues with the ground when using gas generators to charge. Do inverters have the same issue?

Yep, neutral and ground must be bonded. Same issue when charging from a generator.

And I have to point out that a small ~3500w generator would be a much better charging solution than tens of thousands of dollars worth of these panels. Interesting thought exercise to be sure, but highly impractical.

 

[Tessaract]

Yep, neutral and ground must be bonded. Same issue when charging from a generator.

That may be true from an electrical code perspective, but doesn't explain the Tesla error message. The Tesla HPWC is not connected to neutral, only ground.

So my question would be: drj3, are you using the HPWC or the Mobile Connector?

 

[drj3]

I was using the mobile connector.

 

[Tessaract]

I was using the mobile connector.

That explains why that error message was even possible. The mobile connector can sense neutral-ground problems because it is actually connected to both. The HPWC cannot, because it doesn't connect to neutral.

 

[Vaillant]

I’ve thought about something similar. You could use those high power suction cups to hold the panels to the roof of the car (the same kind some ski racks use). Potentially they could even be lockable.

I think there would be a market for this, even at something like $2k. It would make camping in a S3XY vehicle a lot easier, that’s for sure.

Something like this:
Classic Ski Rack

 

[Vaillant]

Here’s someone who is attempting to pull something together to charge his Nissan Leaf. He has different reasons....severe battery degradation has destroyed his range, but, regardless of why, he managed to pick up 17 miles while sitting out in the parking lot:

 

[Sophias_dad]

I'm not quite calling BS on the youtube guy, but it would be so very easy to fake. We don't know whether those batteries in the trunk were low enough to not be able to run the inverter when the day started. Rough estimate is that he added 4kwh to the car.

From some of his other videos, I see there are 250 watts of panels on his roof, and estimate another 60 on the hood. that's 310w maximum, at noon. Assume 12 hours of that, and he gets 3.7kwh, which lines up well enough to call it 4kwh.

In reality, at 6pm, those roof inverters are putting out a whopping 66 watts, per

(time 23:36), so you really gotta reduce the true capacity of the system for a 12 hour charge session. I'm sure I could spend a half hour and get some correct value for the constant, but lets suppose its 60% overall for the day's light. Now those panels are producing 2.2kwh/12h. The extra power had to come from somewhere, and that's likely the pre-charged 200 lbs of batteries in the trunk. This is all assuming 100% energy conversion efficiency.

He apparently spent ~$2000 on the parts for the system, and for that he gets a car with no trunk, a system which he needs to re-ice(literally) every day, and he still can't get home if its cloudy on a particular day. (Actually, he can, but only because of the bank of batteries he added in the trunk!)

Actually, reading the very first comments on the video, those batteries in the trunk will supply 2.88kwh when fully charged. Were it me, I'd just put the batteries in the trunk, and skip all the solar. Apparently he's not really in it for the youtube views(or its not working out, anyway!), so I commend him on the project.

 

[Vaillant]

I think a key item here is not the specific numbers, but the ability to charge with a portable, ungrounded setup.

The quantity of panels and the number of batteries are all variables that can be optimized, as needed.