Experimenting with an "Off Grid" Solar Charging Setup. Need Some Help.

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I purchased an inexpensive 100 Watt 12V Solar kit. Can only produce about half a kwh per day at most. I bought a 105 amp hour Flooded Lead Acid deep discharge marine battery from a local battery store, and a 3,000 Watt 12V Pure Sine Wave Inverter from Amazon https://www.amazon.com/gp/product/B0792LW2H7/ref=ppx_yo_dt_b_asin_title_o02_s00?ie=UTF8&psc=1.

I have a Model S and a Fiat 500e. Each has a dedicated 50 amp circuit I charge with normally.

Why am I doing this? In part for fun, to see if I can get it to work. Also, in the event of a prolonged power outage I’d have a way to charge my cars at least a little. Solar panels and batteries aren’t super expensive. So if I can get it to work, it’s pretty easy to add batteries or panels to the setup.

Goal: If I can get it to work, I can expand my battery setup to maybe 400ah. A single 100 watt panel might take a week or so to charge those batteries. Then I can trickle charge about 3 or 4 kwh into one of my EVs. The real value of the setup is it's a source of emergency power for the cars and household items.

Live in Houston. Those of you in California might not understand, but loss of power for several days if not weeks is a real possibility with hurricanes and such. We have a gas car too, but if there’s widespread power outages you might not be able to get gas.

I’m hoping someone out there has some experience with a similar setup. Searching this forum and the internet didn’t yield me a lot of info with regard to EVs. I found a post somewhere about a guy in Australia who charges his Mitsubishi iMiev off grid. And someone who posted a review on Amazon (for a power inverter) who has an off grid setup at home and charges a Chevy Volt.

Where I am now: The basic solar setup is pretty simple, but I’m pretty sure my problem is either with the Inverter or the Battery Setup. For now I just have the lone 12v 105 ah Flooded battery. Trickle charging would pull about 1.4 kw from the battery. It’s certainly not efficient to pull that much from a 105ah battery but I thought it could work. 1400 kw is only half of the Inverter capacity of 3,000 (6,000 surge). The Inverter powers on fine and shows an output over 120v and shows that the Battery Voltage is above 13. When I plugin my Tesla Mobile Connector (From a 2015 Tesla. I also have a 2017 Mobile Connector which I haven’t tried.) I get 4 flashing red lights. So perhaps some kind of grounding issue. When I plug in the EVSE that came with my Fiat the first 3 lights turn Green and the 4th light turns red. I didn’t proceed to plug either into the vehicles. Also, the Model S let's me set the Charging Amps as low as 5, so in theory I can charge it without stressing the Inverter or Batteries too much.

My Next Steps: The Inverter has 2 AC outlets and a Terminal Box for “Higher Power” appliances. It’s possible the AC outlet doesn’t supply enough Amps, so it might help if I hookup an external AC outlet to the Terminal Box on the Inverter. I’ll try that over the next few days. Also, it’s likely that a 105ah battery just can’t supply enough voltage, and the EVSEs can test for that and flash red. So I can also procure more batteries and see if the EVSEs like that better.

Now it’s possible that EVSEs just don’t like this source of power. Maybe it would also work better if I used a 24 Volt Battery/Inverter setup so the Inverter doesn’t have to draw so many Amps? Does the Inverter need to be Grounded a certain way? Is there a certain type of Inverter that EVSEs like? Maybe there is some kind of cheap Chinese made EVSE that is less picky about power source I can use just for emergencies but not on a regular basis? Does someone know if there is a certain battery bank size I need to make the setup work? My plan was to stick with Sealed Lead Acid batteries going forward. Lithium Iron Phosphate is a bit too expensive.

But there has to be a way. Many people have battery backup systems like Tesla Powerwall that should work. The power doesn’t have to be tied to the Grid. Any insights would be appreciated. If there is any interest I’ll keep you posted on my progress, or lack thereof. Thanks!

 

[tjkessler]

What are you doing for ground on the inverter? EV's are generally particular about having ground don't like if neutral is not effectively ground. There are several internet videos where people run into the same problem with generators. The typical workaround (which could be dangerous) is to install a "goof" plug that ties neutral and ground together.

 

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I just ran a 12 gauge copper wire from the bottom connection of the Inverter and stuck the other end into the Earth. I really didn't know what else to do.

 

[ewoodrick]

Let's do some basic math.
Let's sat that you do have a LOT of sun and can get 10 hours of 100 watts. That's 1kW per day. Over a week, that's 7 kW. A model S is going to use about 300 watts per mile. That then gives you 23 miles.

Now your 105 ah 12V battery will hold 12 kW theoretical in very specific use cases. I do hold that it's not a 105 CCA, which isn't that big. But, that puts the battery being able to provide 42 miles MAX. Reality will be a LOT less.

So, you're going to charge on a standard 5-15, which is 12A @120V. That's 1440 watts. Which at 12V is 120 amps!!! Aside from that fact that they are really big wires, I'm pretty sure that the battery's rating isn't at that output (more like 5A). Prolonged 12A @120V draw, in a perfect world will discharge the battery less than an hour.

In other words, if you leave the battery charging, then you may be able to get a charge of about 20 miles (I said 42 MAX). It will then take a week and a half to charge the battery back up again (make sure you have a solar regulator in place) to get another 20 miles.

Your car has the equivalent of a 6,000 ah @12V battery in it. It's massively paralleled, so it can provide high currents.

By the way, before you try plugging the car into it, try testing with a 1500 watt portable space heater. See how long it runs. Then see how long it takes to charge the battery back up.

 

[ericonline]

So, you're going to charge on a standard 5-15, which is 12A @120V. That's 1440 watts. Which at 12V is 120 amps!!! Aside from that fact that they are really big wires, I'm pretty sure that the battery's rating isn't at that output (more like 5A). Prolonged 12A @120V draw, in a perfect world will discharge the battery less than an hour.

Yeah, it would be 120 Amps. It is high, but it's a short distance between the battery bank and the Inverter. Maybe 2 feet or so. My plan was to just buy a 4/0 gauge Cable from Home Depot, as well as set the Tesla to fewer than 12 Amps. Also switching to a 24V Battery would cut the Amps in half.

The 105ah Battery holds a lot less than 12kwh. I think it's 105ah*12v =1.26kwh.

I have a 1500 watt space heater. I'll try it out tomorrow and see what happens.

 

[ewoodrick]

1.26 kWh is 4 miles. I have to think to myself is it worth it.

 

[ericonline]

1.26 kWh is 4 miles. I have to think to myself is it worth it.

That is just 1 battery. If I can get this going I can buy 4 200ah batteries and connect them in parallel. That's enough for about 9 kwh. I could drive 40 miles in my Fiat.

What are you doing for ground on the inverter? EV's are generally particular about having ground don't like if neutral is not effectively ground. There are several internet videos where people run into the same problem with generators. The typical workaround (which could be dangerous) is to install a "goof" plug that ties neutral and ground together.

So I just watched a video of a guy charging his BMW i3 with a Yeti 3000 - big Lithium Battery/Inverter combo that costs $3k. He plugs in his BMW EVSE and gets the Red Ground Fault error. He says the Yeti outlet ground opening is empty so he proceeds to use what he calls a "Ground Fault Bypass Box" that connects the ground and neutral. I'm not doing that.

So I shine a flashlight in my Inverter AC outlet and looks like the opening for the Ground is just empty plastic. So this must be a common feature of many Inverters and Generators. But my Inverter has a separate Terminal Panel with 3 outputs - Hot, Neutral, and Ground. So I could hook that up to a GFCI Outlet and maybe that will satisfy the EVSE error codes? Safe?

 

[glhs272]

So yes, in principal this can work. I am doing a similar thing to charge my Tesla. However, I have a significantly larger scale system. I use 6 Tesla battery modules running in parallel at 24 volts. This would amount to about 30kwh in nameplate capacity. However, in reality I get much less. You have to take into consideration inverter losses, charging losses, and etc. I also don't fully charge the modules or fully discharge them to improve their longevity and reduce risk of overcharging them. Reality is I can get about ~40 rated miles into my car out of a fully charged stationary battery. Considering my battery bank is massively more capacity than your single 100ah setup, don't expect much out of it. I also have several 1000 watts in nameplate solar power to charge the stationary battery.

Really you will struggle to get much practical charging from your system as is. Even overcoming the car's vampire drain will probably be impossible. But if you can scale up your system, either with significantly more batteries or with significantly more solar power or both you can get this idea to work.

In my case I don't heat my batteries in the winter. This means I must shut it down to prevent damaging the batteries. So I switch back to lead acid batteries in winter. Basically, this means I can only charge while the sun is shining. The lead acid batteries are just a buffer to get the inverter going and deal with short term shading. Even with 4 200 ah batteries I can only get about 4 miles out of those alone. The other annoyance is the inverter shuts down if the voltage gets too low and won't auto-recover. So I am building a custom EVSE to monitor battery voltage and stop the charging when it gets to low, then re-engage when the voltage goes up past a set amount. Doing this with an OpenEVSE unit.

 

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I attached a GFCI outlet to the inverter. My receptacle tester shows it has "Open Ground". Apparently this inverter like many generators has a Floating Neutral. Some people use some type of Neutral Ground Bonding Plug. I'm not sure that is safe. I might just find an inverter that has the Neutral and Ground Bonded. Then I guess an EVSE would work?

I also plugged a 1500 watt space heater into the inverter. It worked ok for a little while. As I turned it up the voltage started to drop and after a 30 seconds or so the inverter shut off.

 

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Ordering Samlex 24v PST-2000 Inverter.

According to the manual "Bonding of AC Output Neutral to Chassis Ground The Neutral slots of the NEMA5-20R GFCI Duplex Receptacles (5, Fig 6.1) are internally bonded to the metal chassis of the inverter." So with any luck this inverter will work with the EVSEs right out of the box with no modification or external grounding plugs.

Samlex 24v 2000 Watt Pure Sine Wave Power Inverter PST-2000-24

 

[ericonline]

Update: Just wanted to provide an update to this project in case anyone comes across this thread and is curious how I proceeded.


I returned all the original equipment and went with a 24v inverter/battery bank setup. This decreases the amount of amps that needs to flow between the battery and inverter. The Samlex PST-2000-24 inverter worked with both the Tesla UMC and the Fiat EVSE without and need for a bonding plug or any other modifications. BTW Samlex tech support was very helpful when I called them to ask some questions about their products with regard to this project.


I installed a pair of 24v 120w solar panels on my front fence and wired them in parallel. I used a Victron MPPT 100/30 charge controller. I wound up buying 4 12v 100ah sealed lead acid batteries and wired them in series/parallel to get a 24v 200ah battery bank. If my math is right this gives me a battery bank that can hold 4.8kwh, and I think roughly half of that is usable.


I was concerned that the battery bank wouldn’t support the draw of the inverter when charging the Tesla/Fiat at 12 amps, but so far it seems to work ok. I haven’t let it charge for more than an hour straight. The inverter fan cycles on and off during that time. Roughly it takes about a week for the panels to charge up the battery bank with 2-3 kwh. I have the panels positioned sub-optimally, mounted vertically and with some shading. This gets me about 8 miles of charge in the Tesla and probably a little more than that if I charge the Fiat. My plan/hope is to upgrade the battery bank with lithium batteries if they become more economical. Upgrading solar panels is easy if I ever want to do that.


PLEASE NOTE: I am not an electrician. You should always hire or consult a licensed electrician before you do anything ever. I did my best to follow, meet, or exceed local laws and NEC regulations at every step. I got a permit from my city and provided them with a detailed diagram of the installation. I installed the largest gauge wire practical at every step, outdoor rated conduit, a weather proof junction box to connect the panels, multiple fuses, etc. This entire thread is for entertainment purposes only and should not be used for an instruction guide for anything.

 

[Scott1620]

Nice setup, I have a 100 w off grid 12v system that I am tinkering with as well (also a 9.9kw grid tied system). Not for charging the car though, for other small loads. I actually monitor my system voltage using an ESP8266 dev board, some custom device handler code, and smart things app/hub. Planning on setting it so if I hit a certain voltage it will switch off the inverter and notify me. You don't want to let your voltage get too low or it will kill the batteries...

 

[miimura]

Nice setup, I have a 100 w off grid 12v system that I am tinkering with as well (also a 9.9kw grid tied system). Not for charging the car though, for other small loads. I actually monitor my system voltage using an ESP8266 dev board, some custom device handler code, and smart things app/hub. Planning on setting it so if I hit a certain voltage it will switch off the inverter and notify me. You don't want to let your voltage get too low or it will kill the batteries...

The inverter should have a low voltage cutoff so that it won't kill the batteries.

 

[azmikejan]

We are completely off-grid and charge our 2014 S85 totally off the panels/ batteries. We have 10 35kwh lithium batteries and 12.2kw of panels. We charge at 24Amps most of the time getting about 18 mph. It is a bit bigger setup, but we would be glad to answer any questions, if we can be of help.