[astroteuthis]

My daily commute is really short, and, as a result, I use only around 1.2 kWh of power maximum a day from the high voltage battery on my Volt. The power in the area I live comes from coal plants, and I've been looking for a way to reduce the emissions footprint of my volt (regardless of increased cost per mile). Rooftop solar isn't an option for me, as I currently live in an apartment.

As it stands, I believe I can make a 400 W rated solar charging system that can be stored inside the Volt and deployed on top of it when parked. This would allow me to collect power while at work during the day.

The system would consist of the following:
4x 100W rated semi-flexible solar panels
1x P30L PWM solar panel regulator
2x 100Ah 12V deep cycle batteries (in parallel)
1x 2000W 12V DC to AC inverter

Total system cost is around the $1000 mark, though that can vary a bit depending on the specific equipment used.

On a normal day, the system should get around 1 kW into the deep cycle batteries, accounting for some losses.
The batteries would be discharged about halfway through the DC to AC inverter to power the portable EVSE that came with the Volt running at the 8A setting. A 2000W inverter should be able to handle the ~960W load the EVSE takes.
At a 50% depth of discharge, the deep cycle batteries shouldn't be too damaged. I figure that even with the losses from the EVSE and inverter, this should still handle at least 75% of my Volt's daily power needs.

The batteries don't add much to the cost, and they allow for the use of many fewer solar panels than would be required to run the Volt's charger directly.

There are two potential issues that are keeping me from immediately proceeding with this plan:
1. The EVSE that comes with the Volt is fairly picky about what it's plugged in to, and most inverters use modified sine waves, not pure sine waves. Pure sine wave inverters are more expensive.
2. The manual highly stresses the need for proper grounding when charging. It is possible that a temporary grounding solution for the inverters might not be good enough.

My questions, particularly with anyone who has an off-grid solar charging system for their Volt, are as follows:
1. Has anyone used a modified sine wave inverter with their Volt charger, and, if so, do you have recommendations?
2. How hard would it be to ground a portable inverter to make it suitable for charging a Volt?
3. Are there any other potential issues with the system that you can think of (besides the economic aspects)?

EDIT: Corrected instance where I said 400 kW when I meant 400 W, thanks for catching that.
EDIT: I do NOT need an amount of solar panels with output sufficient to run the EVSE on its own. Using a battery system to buffer the input from a smaller set of solar panels over a longer period of time is the whole point. You're not going to fit a 1 kW+ solar array on the top of a Volt (not without space-grade solar cells in any case).

 

[rob]

The minimum charging current it'll accept is somewhere around 5A, so you'll want around 600W of panels and an inverter rated for the same. And then an EVSE you can set that low. The OpenEVSE is the only one I know of. And the inverter will trip-off anytime a cloud comes by and the batteries get pulled down too far, so it needs to be one which will auto-restart.

The EVSE which comes with the car only does 8A or 12A, so you'd need at least 900W of panels to use it on the 8A setting.

Turn off your "charging interrupted" messages...

Grounding - you're in a parking lot. Not usually a lot of options for proper grounding there, as they generally frown on people driving rods through the asphalt. Tying everything to the vehicle ground is probably the best you can hope for.

Don't forget to allow for venting of the 12V batteries. Power unlocking a car full of hydrogen could be very, very bad...

So, there are a few challenges to overcome.

 

[firehawk72]

My daily commute is really short, and, as a result, I use only around 1.2 kWh of power maximum a day from the high voltage battery on my Volt. The power in the area I live comes from coal plants, and I've been looking for a way to reduce the emissions footprint of my volt (regardless of increased cost per mile). Rooftop solar isn't an option for me, as I currently live in an apartment.

As it stands, I believe I can make a 400 kW rated solar charging system that can be stored inside the Volt and deployed on top of it when parked. This would allow me to collect power while at work during the day.

The system would consist of the following:
4x 100W rated semi-flexible solar panels
1x P30L PWM solar panel regulator
2x 100Ah 12V deep cycle batteries (in parallel)
1x 2000W 12V DC to AC inverter

Total system cost is around the $1000 mark, though that can vary a bit depending on the specific equipment used.

On a normal day, the system should get around 1 kW into the deep cycle batteries, accounting for some losses.
The batteries would be discharged about halfway through the DC to AC inverter to power the portable EVSE that came with the Volt running at the 8A setting. A 2000W inverter should be able to handle the ~960W load the EVSE takes.
At a 50% depth of discharge, the deep cycle batteries shouldn't be too damaged. I figure that even with the losses from the EVSE and inverter, this should still handle at least 75% of my Volt's daily power needs.

The batteries don't add much to the cost, and they allow for the use of many fewer solar panels than would be required to run the Volt's charger directly.

There are two potential issues that are keeping me from immediately proceeding with this plan:
1. The EVSE that comes with the Volt is fairly picky about what it's plugged in to, and most inverters use modified sine waves, not pure sine waves. Pure sine wave inverters are more expensive.
2. The manual highly stresses the need for proper grounding when charging. It is possible that a temporary grounding solution for the inverters might not be good enough.

My questions, particularly with anyone who has an off-grid solar charging system for their Volt, are as follows:
1. Has anyone used a modified sine wave inverter with their Volt charger, and, if so, do you have recommendations?
2. How hard would it be to ground a portable inverter to make it suitable for charging a Volt?
3. Are there any other potential issues with the system that you can think of (besides the economic aspects)?

I have done solar. I did my own solar install. It is grid tied and I produce a lot of electricity. My advice (which you will not want to hear or probably take) is to use that 1k and pay down some debt, invest it if you don't have any debt, put it in a savings account, go on vacation, or simply keep it, anything but what you are considering.

 

[edk-austin]

I've actually done what the OP requests. I won't recommend anything, as what I do is often to prove a concept, not necessarily the feasibility of a successful product.

The Volts OBCM needs a minimum of 6A to operate. A custom EVSE (which I built), signals 6A to the Volt. The source (battery +panels) must be able to provide the full amount continuously, or the OBCM shuts off. At 720W + inverter conversion losses, you will soon completely deplete the batteries. The Inverter will turn off, release the load (car), and the panels will quickly get the voltage up on the batteries to the point that the inverter will operate, but the batteries do Not have a full charge, so the cycle quickly deteriorates, and your batteries will wear out.

To make it work, you need a energy in/out tracker that looks at energy out of the batteries, and energy in from solar. And makes sure the input energy fully replenishes the battery so as to not progressively wear it down. Even a periodic 50% discharge will wear out lead acid. I also built an energy monitor, with current/voltage sensors and an custom micro-controller to enable and disable the inverter output. If I have 200W of solar, and 800W of power draw (which was one of my tests), I need to cycle the inverter on and off and a <=25% duty cycle to maintain the battery. Which the microcontroller does.

To note, the car does horn chirp on charge start. And cycling on and off like this Does cause a chirp on every cycle. Annoying.

You do need an inverter that allows connecting neutral to ground. Safety dictates that you don't want to accidentally float the neutral, or allow the car chassis to float to a shock hazard.

Volt itself doesn't care about MSW or sine wave AC. Oddly enough the 2014 EVSE Does test for sine wave, and will fault on MSW (although someone told me I need to double check that). But with my custom EVSE, it doesn't care and tells the car only 6A is available, which reduces the battery load. I've ALSO found that Volt doesn't even care if it's straight DC input. Yes, I've skipped the AC inverters output stage and charged my Volt (briefly) from 120V DC.

So given that we can use DC directly, I may yet experiment with more direct DC input, on the J1772. No time to do that lately. The other step of course is direct HV charge of the traction battery. But really, while it could be done, solar panels operate most efficiently at a specific V(mpp), and the HV battery must be limited to a max cell voltage, so you really need a good lithium charger anyways. And you already have one in the J1772 to HV battery OBCM, which on gen 1 is about 85-90% efficient (gen 2 is better).

I might add too, that you can dispense with the separate 12V batteries. Volt Does have one of those. So, provided you can work the correct DC isolation from the J1772 plug (inverter has isolated output), you Can use the Volt 12V battery as the buffer. And I've done that too, although I cut the charge period to about a third of my separate battery approach. (my Volt 12V battery is already kind of worn from a previous dead battery issue, which had nothing to do with me! Really!)

I gave a demo once with a 100W panel and the Volt 12V battery. Charge cycle lasted about 30 seconds. Inverter turned off, cloud came by, and 10 minutes later the audience lost interest, as the panel Still had not replenished the battery.

Only recommended if you're ok with an expensive hobby.

 

[srmarti]

That's a 400 watt system the OP is describing, not 400 kw. Probably just a typo. My experience is that daily solar production can vary greatly. On my home grid-tied system, I can get over 50kWh on a good day. On a bad day near zero. I think before I hauled all that stuff to set up in the parking lot and pack it back up after to MAYBE get the back 1 kWh used getting to work, I'd walk. That way I'd reduce the carbon footprint and get some exercise.

Maybe build some sort of temporary carport with a solar roof at the residence?

 

[Mister Dave]

The power in the area I live comes from coal plants......

Mississippi is 85% natgas fired, and only 12.2% coal fired.

https://www.eia.gov/state/?sid=MS

At best I can find 4 coal fired plants in the entire state.

 

[edk-austin]

Actually, re-reading your plan, you carry around 2.4KW of energy in the lead acid batteries and just discharge half of that back into Volt. So you don't need the energy cycle controller that I made. The problem with this is that the AHr ratings of batteries is generally spec'd at the 1/20 C rate. So a 100AHr battery discharging at ~600W each, is discharging at the 0.5C rate, and had MUCH less capacity at that rate, compared to it's spec. An AGM lead acid may have only 60% of it's capacity at 1C discharge load, compared to 1/20C discharge load.

So maybe use 4x 100AHr batteries? That's becoming quite an unwieldy load in the back!

 

[Cord]

small portable wind system would be lighter.

Just add wind ;-0

and ( DC fuser ? ) posted about this 5 + years ago ( charging his Volt with his off grid solar )

 

[Ohms Law]

You really need to think about this. You use no more than 2kWh per day and the car has at a bare min 10.3kWh. Why exactly are you considering putting $1000 toward something like this. Most power suppliers have real-time pricing nowadays and where I'm at I pay on average .014/kWh off peak. I can buy a lot of electricity at for $1000 at .014/kWh. A few times this month, for several hours I was about -.1067 (yes that's a negative where they were actually giving me nearly free power).

If you were talking about lots of miles or you were gonna put solar to your house, I'd feel differently in my suggestion, but less than 2kWh day.... if you are that much of a purist, a Bolt woulda been a better bet.

 

[Mcgsp]

you could always haul this around.

 

[astroteuthis]

The minimum charging current it'll accept is somewhere around 5A, so you'll want around 600W of panels and an inverter rated for the same.

The purpose of the battery buffer is to reduce the required amount of panels, because direct charging from solar requires too many for easy transport.

Grounding - you're in a parking lot. Not usually a lot of options for proper grounding there, as they generally frown on people driving rods through the asphalt. Tying everything to the vehicle ground is probably the best you can hope for.

I was considering only transferring power from the lead acid batteries to the car (using the inverter) when parked at home where I can reliably ground it. The reason the solar panels travel with the car is because I don't have a place to leave them outside at home (unless they let me use a parking spot...).

Don't forget to allow for venting of the 12V batteries. Power unlocking a car full of hydrogen could be very, very bad...

That's a good point, and I was concerned about them getting too hot anyway, so I was considering leaving the 12V batteries outside the car under a ventilated mylar shade (lots of infrared heating in a parking lot). Possibly with some sort of lock connecting them to the car.

 

[astroteuthis]

I'm aware of the general statistics for my state, but the particular city I'm in is connected to TVA's grid. The section of their grid that supplies my town is predominantly handled by a coal plant, with auxiliary gas generator turbines for peak power demand matching. The last place I lived here was further south and almost 100% natural gas, like you said.

 

[astroteuthis]

small portable wind system would be lighter.

Just add wind ;-0

There was a crazy guy a while back who thought he could make a perpetual motion car by putting a wind turbine on an electric car... totally not understanding that the conservation of energy applies...

 

[astroteuthis]

That's a 400 watt system the OP is describing, not 400 kw. Probably just a typo.

Thank you for pointing that typo out, you were correct, it's a 400 watt (maximum) system. I have edited the original post to reflect that.

I think before I hauled all that stuff to set up in the parking lot and pack it back up after to MAYBE get the back 1 kWh used getting to work, I'd walk. That way I'd reduce the carbon footprint and get some exercise.

That's a fair point, but I kind of wanted a little side project for the summer like this, and I honestly really don't walking around in the summer here for more than a mile or so. It regularly gets over 100 in the summer, and I prefer not to be soaking wet when I get to the lab.

Maybe build some sort of temporary carport with a solar roof at the residence?

A college of mine just suggested that today, and I think it's a pretty good idea, but I'm worried about keeping it stable in high winds. Wouldn't want it flying away or damaging cars. Maybe I can borrow some of the massive lead weights lying around the lab.

 

[astroteuthis]

you could always haul this around.

With a setup like that I could probably power most of my apartment, but my neighbors would kill me XD.

 

[Mister Dave]

I'm aware of the general statistics for my state, but the particular city I'm in is connected to TVA's grid. The section of their grid that supplies my town is predominantly handled by a coal plant, with auxiliary gas generator turbines for peak power demand matching. The last place I lived here was further south and almost 100% natural gas, like you said.

Ouch. Do you know who owns TVA? Here's a clue:

I'll guess you're near either Starkville or Memphis.

 

[astroteuthis]

To note, the car does horn chirp on charge start. And cycling on and off like this Does cause a chirp on every cycle. Annoying.

It's pretty easy to disable that on the gen 2's.

Volt itself doesn't care about MSW or sine wave AC. Oddly enough the 2014 EVSE Does test for sine wave, and will fault on MSW (although someone told me I need to double check that). But with my custom EVSE, it doesn't care and tells the car only 6A is available, which reduces the battery load.

Interesting. Don't the 2017's come with the same EVSE as the 2014's? If so, I guess I'd definitely need to buy a third party one to use with a MSW inverter, though it might be cheaper just to bite the bullet on a pure sine wave inverter and keep using the stock EVSE...

 

[astroteuthis]

Ouch. Do you know who owns TVA?
I'll guess you're near either Starkville or Memphis.

First guess was right. Yeah, I know some people don't approve of TVA and think the government overreached, but it was instrumental in bringing this area of the country up to the technological level the more populated areas had been enjoying for some time already. I also have had fewer issues with them than when I got my power from Entergy at the last place I lived.

I wish my part of the TVA grid was supplied by one of their nuclear plants. I wouldn't probably bother with a solar project if that were the case. I'd probably just find some other silly project to work on.

 

[astroteuthis]

Actually, re-reading your plan, you carry around 2.4KW of energy in the lead acid batteries and just discharge half of that back into Volt. So you don't need the energy cycle controller that I made.

Thanks for taking the time to re-read. Yeah, the big buffer batteries were my way of getting around needing a controller like yours since I'm not that great with electrical engineering, though your solution is definitely better in the long run.

The problem with this is that the AHr ratings of batteries is generally spec'd at the 1/20 C rate. So a 100AHr battery discharging at ~600W each, is discharging at the 0.5C rate, and had MUCH less capacity at that rate, compared to it's spec. An AGM lead acid may have only 60% of it's capacity at 1C discharge load, compared to 1/20C discharge load.

I was afraid that running them at that level might reduce the capacity, but now I can see I underestimated how much it would.

So maybe use 4x 100AHr batteries? That's becoming quite an unwieldy load in the back!

The original plan was for a stationary system with more like 600W max solar output, but I wasn't sure they'd let me leave it in the parking lot. I had 4 batteries in that plan. That does seem like a lot to put in the car, about 120 lb. I guess it's only about as much as a passenger though. The solar panels themselves weigh hardly anything.

I'd be interested to read more about your past projects.

I may try to strike a deal with apartment complex owner to let me install a few solar panels or reexamine the temporary carport or trailer ideas (assuming they let me use an extra spot like the boat people).

 

[Mister Dave]

I know some people don't approve of TVA and think the government overreached, but it was instrumental in bringing this area of the country up to the technological level the more populated areas had been enjoying for some time already.

Yes, that's true. What stinks is how TVA has been exploiting its special status as a federal corporation to sidestep federal regulation. Instead of reforming TVA, Barry proposed "privatizing" it in 2013.