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Off-grid charging

Discussion in 'Rivian' started by Desert Guy, May 5, 2019.

  1. Desert Guy

    Desert Guy Rookie

    May 5, 2019
    6
    Most of the discussion about charging Rivian and other evs focus on how fast you can charge. I have the opposite challenge: a remote off-grid cabin with enough solar panel capacity to charge the vehicle during a week of hiking, but nowhere near enough inverter capacity to power the 11 kw onboard charger.

    Does anyone know if the R1T will support Level 1 charging or Level 2 charging at less than 11kw?

    For my needs Level 1 charging would be best, but I could live with Level 2 if I can configure the onboard charger to draw no more than 7 or 8 kw.

    Any info is appreciated.
     
  2. DucRider

    DucRider Rookie

    May 8, 2019
    7
    The configuration is actually signaled as amperage (not kW) and should be done on the EVSE end. There are some EVSE's on the market that are adjustable (Open EVSE is one).
    The charger (in the vehicle) doesn't care what voltage/amperage is provided (within some limits). There is absolutely no need to provide the maximum that the charger can take. So charging at either 120 or 240 are equally acceptable. It is very likely (almost certain) that the Rivian will come with a cord that will plug in to any 120V outlet and might be perfect for your needs. It will most likely be 12 A @ 120 V or 1.44 kW.

    https://en.wikipedia.org/wiki/SAE_J1772
     
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  3. Desert Guy

    Desert Guy Rookie

    May 5, 2019
    6
    Thanks for the reply. I've been hoping / assuming there will be a 120 V option and that would work just fine for me. I can also deal with a 240 V connection, just not one that's going to try to pull 11 kW. I have no desire to install a full-blown EVSE - I just want to wire up a plug and let the Rivian electronics regulate the charging process.

    I plan to see the Rivian team in Flagstaff, AZ next weekend and will talk to them about remote system charging options. The Overland expo is the perfect place for that convo.
     
  4. Ray Graham

    Ray Graham Rookie

    May 4, 2019
    3
    Hey Desert Guy, I would love to go there but just had a hip replacement. I sure would appreciate it if you would ask them about the rear view mirror. Is it camera based or traditional? I have a bed top tent that will block the view out the rear window while stowed. I would be very greatful!
     
  5. Desert Guy

    Desert Guy Rookie

    May 5, 2019
    6
    Hey Ray - hope the hip replacement goes well. I'll ask about the mirror and post the answer.

    If anyone else has questions post 'em here and I'll try to get answers. Same goes for pics you may want of particular structures on the truck.
     
  6. scramboleer

    scramboleer Rookie

    Apr 30, 2019
    3
    Yes, the Rivian will have a 120V cordset (AC Level 1) as well as support 240V EVSE (AC Level 2) via the J1772 inlet port.
     
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  7. Desert Guy

    Desert Guy Rookie

    May 5, 2019
    6
    The rear view mirror is a mirror, not camera-based. In talking with one of the Rivian peeps at the show it sounded like they might be thinking about a camera-based option, but for now nothing.
     
  8. Desert Guy

    Desert Guy Rookie

    May 5, 2019
    6
    Here's how the R1T could integrate nicely with an off-grid solar cabin:

    1) Install a residential charging system with Time of Day capability set to charge only while the panels are generating more power than the charger needs. That way you charge from the panels, not from the batteries. Select / configure a charger to stay comfortably below the output power of the solar array and of course within the capability of the cabin's inverter(s). A 16 A ChargePoint Home Wi-Fi Connected would deliver about 19 kWh of charge during a 5 solar-hour day.

    2) (Optional if you spend long periods at the cabin). When the solar array is not producing, charge the cabin batteries using 120 VAC from the R1T sockets in the bed of the truck. Rivian engineers confirmed they're rated at 15 A (each) continuous duty. An 18 A / 48 VDC charger could pull about 10 kWh / day from the Rivian. That would come close to doubling the expected life of my cabin's 40 kWh AGM bank by decreasing the depth of daily discharge from about 50% to about 25%. A simple digital timer can control the time of day to draw power from the Rivian.
     
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  9. EyeOnEVs

    EyeOnEVs Rookie

    Mar 5, 2019
    30
    I'm not off-gridder or have solar panels, but it would seem option 2 would be good in a pinch but not so much in the long term. If, as you say, this option can double the life of your cabin's battery bank, would it not then be also decreasing the life of the Rivian EAV batteries due to the increase charge/discharge cycling? If so, the next obvious question would be, which battery bank cost more to replace - the cabin's or the EAV's? Now I don't know how many batteries make up your cabin's battery bank but taking a wild guess here that it would be probably cheaper to replace them over the EAVs ... but I could be totally off base here.
     
  10. DucRider

    DucRider Rookie

    May 8, 2019
    7
    10 kWh out of 105 - 180 kWh (depending on Rivian configuration) is a much smaller percentage than pulling from the 40 kWh cabin batteries. And Li Ion batteries in the Rivian are much more forgiving of cycling than the AGM batteries. The Rivian will basically shrug at the the 10 kWh draw (essentially like driving for 30 - 35 miles a day)
     
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  11. Desert Guy

    Desert Guy Rookie

    May 5, 2019
    6
    Exactly right. Li Ion batteries have much higher cycle life than Lead Acid / AGM batteries. But they're also much more expensive.

    As an off-gridder, it would cost me about $1 k per kWh of Li-Ion capacity. Meaning the value of the batteries in 180 kWh R1T is about twice the expected cost of the vehicle! https://www.wholesalesolar.com/1898866/discover-battery/battery-banks/discover-battery-520ah-48vdc-w-xanbus-26-400-wh-4-lithium-battery-bank

    OTOH, AGM batts costs about $220 per kWh nameplate capacity. Or $440 per kWh available at 50% DOD / $880 per kWH @ 25% DOD.
     
  12. Ray Graham

    Ray Graham Rookie

    May 4, 2019
    3
    Desert Guy, Thanks very much for asking. I’m sure you had a lot on your plate! Wish I could have gone! I was hoping for the camera mirror, but if I can drive Level 3 autonomously, I won’t be as worried about looking out my rear view mirror and my view being blocked by the rail mounted tent. As an aside, I did some back of the envelope calculations and measurements, and the Yakima Skyrise 3 will fit on the Rivian crossbars. Stowed, it will fit over the bed with 8-10” to spare on each side, while overhanging the tailgate about 2 inches. Open, it should unfold properly, but still unsure how the rainfly will fit (next to the cab) until I get one. Ray
     
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  13. EyeOnEVs

    EyeOnEVs Rookie

    Mar 5, 2019
    30
    FWIW, I recall seeing on the R1T (from videos) controls on top of each side of the bed. Toward the back are controls for the lift-gate. Up front I believe for the gear tunnel doors. This may be a non-factor because you'll still have access due to the height of the tent above the bed sides or perhaps there are controls in other locations I'm unaware that can be used, e.g. from within the cabin. None the less, just thought I would throw that out there in case it makes a difference.
     
  14. Domenick

    Domenick Administrator
    Staff Member

    Aug 10, 2017
    2,069
    You could buy a salvage Nissan LEAF for its 24 kWh (or 30 kWh) battery pack for a lot less money. $1,000/kWh is way more than anyone should be paying for lithium batteries in 2019.
     
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  15. Ray Graham

    Ray Graham Rookie

    May 4, 2019
    3
    You are right about button placement, but the width of the tent gives a good 8-10 inches of room left and right. The buttons will all be easily accessible. Thanks for thinking of it though!
     
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  16. ajdelange

    ajdelange Rookie

    Mar 22, 2019
    7
    I think we can assume that the Rivian charging system us going to be at least as sophisticated as the Tesla's meaning that we should be able to set the charging rate and time in the car. The R1T is going to have something like 400 mi range with a 185 kWh battery implying 462 W/mi which seems highish but sticking with it that means that charging at a 1 kW rate will add about 1000/462 = 2.16 mi per hour of charging at that rate. It seems you have a pretty substantial solar setup. Given that you have battery capacity of 40 kWh with average insolation of 5 kWh/m^2/da and that systems are generally designed to be able to charge the battery bank in a single sunny day I'm guessing that your panels are rated around 8 kW which sort of aligns with average electrical consumption for a house in the US and implies about 32 panels and is consistent with your comment in the OP. In any case a strategy for charging the vehicle that minimizes discharge of the batteries is to do the charging when the sun is up and the other electrical loads are low. In the worst (most annoying) case, you sit in the car with your cell phone and monitor consumption and generation riding the car's current draw control to keep production higher than consumption. In a more reasonable approach you set the timer in the car to start charging at a predetermined rate after the sun is well up and minimize the use of dishwashers, clothes dryers etc. on the mornings you are charging.

    What you do will change with season's of course. Where I live in Northern Virginia, as an example, June days begin with sunshine and it's cool so air conditioners are not running and, of course, lights are off and the TV's aren't on. In the afternoon the house has heated up and the air conditioners come on about the time clouds start to roll in. Thus I charge the car in the morning and not in the afternoon or night if I wish to prevent the car from drawing down the "battery" (which in this case is the utility - I'm not off grid and the motivation is to be able to claim that I charge the car exclusively from the sun). For example, if you set the truck to take 4 kW for 3 hours starting at, say 11 AM, would add 3*4*2.16 = 26 miles each day you did that.

    I assume you have some means of monitoring production and consumption. If you don't you will really need something (e.g. an eGauge) to let you do that. The picture below is taken from an eGauge page for a typical June day as described. There is no car charging going on in this picture but to get the idea you can assume that the baseline load of about 1.8 kW is going to a BEV. The green curve is production and the red consumption. When production exceeds consumption the screen is green and in the opposite case, pink. Pink indicates the battery is discharging. The object is to set the BEV charging demand as high as possible without too many pink bits. If you get occasional pink as at just after 8 AM and 9 AM in this example, that's nothing to worry about. The goal is to minimize pink overall in the picture. Note that green in this example goes to charge the infinite capacity battery represented by the utility. In an off grid system it would represent energy going to charge the battery until the battery is full at which time the charge controller would reduce production to match load. With experience you should be able to figure how high you can set the truck's charging rate while keeping pink reasonable. Note also that the time shifting aspect of this approach applies to any load - not just the truck. If you run the clothes dryer when solar production is high it won't discharge the battery.

    Image Unavailable, Please Login

    As for giving most of energy to the truck and using the truck to store it: yes that would spare the AGM's some charge/discharge cycling but think about the efficiency aspect of this. The following conversions would take place (from the panel inverter output):

    1. AC to DC in the vehicle
    2. DC to AC in the vehicle 120V inverter
    3. AC to DC in the AGM battery charger
    4. DC to AC when the energy is used to operate an appliance.

    Assuming that each of those conversions is 85% efficient only 100*0.85^4 = 52.4% of the energy stored in this way would ultimately wind up serving a load.
     
  17. Scott Banko

    Scott Banko Rookie

    Jul 23, 2019
    2
    2) (Optional if you spend long periods at the cabin). When the solar array is not producing, charge the cabin batteries using 120 VAC from the R1T sockets in the bed of the truck. Rivian engineers confirmed they're rated at 15 A (each) continuous duty. An 18 A / 48 VDC charger could pull about 10 kWh / day from the Rivian. That would come close to doubling the expected life of my cabin's 40 kWh AGM bank by decreasing the depth of daily discharge from about 50% to about 25%. A simple digital timer can control the time of day to draw power from the Rivian.[/QUOTE]


    I live in Austin TX and electricity is relatively cheap here. So it does not make financial sense to invest in to a hole house battery like Teslas Powerwall.
    I am researching the practicality of installing a solar system and would like to consider using Rivian (the 180 kWh battery) as a emergency back up power source for my house.

    Any advice as far as how big of solar system I should install?

    In my research I did find a EV solar inverter https://www.solaredge.com/us/products/ev-charger#/
     
  18. DucRider

    DucRider Rookie

    May 8, 2019
    7
    Looking at your current electric bills is a good starting place.
    If you want capacity to charge an electric vehicle, figure 3.5 to 4 miles/kWh. If you drive 1,000 mi/month, that would add about 250 to 300 kWh to the target monthly production.

    Any decent solar company can help you with the sizing calculations based on install location, orientation, etc.

    Using the Rivian as emergency power is an unknown at this point. It has been demonstrated with CHAdeMO (Honda and Nissan come to mind), but not with CCS AFAIK. Rivian may include provisions for this outside of the CCS standards, but if/how that might be implemented would be pure speculation.

    As to the combination Inverter/EVSE, maybe I'm missing something but I don't see the benefit over separate units.
     
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  19. ajdelange

    ajdelange Rookie

    Mar 22, 2019
    7
    The NEC currently expressly forbids backfeed from an EV to the charging supply i.e. EVSE must be equipped with devices to prevent that from happening.
    Having gotten that out of the way we can turn to discussion of how to size a solar system and there are fairly standard ways to do that. The first thing to determine is how much electricity you are currently using and there are various ways to do that. The easiest is to look at the consumption listed on your electric bills. The best way is to install a system like the eGauge which will give you all sorts of statistics over time periods of your choosing and produces pretty pictures like the one in No. 16. You will want something like this when you get solar installed and when you have your EV so that you can keep track of how much juice is going to your EV and how much your panels are producing.

    While you are accumulating data on how much you consume find out how big a system your utility will allow you to install. This varies from place to place but I believe under federal law they must allow up to 10 kW. What they do above that varies but in many places they seem to base system size over 10 kW on some multiple of your maximum demand. How they determine this I don't know. Where I live (VA) they will allow you to install up to 20 kW and bill you according to your peak 30 minute demand. Whatever they do it is designed to discourage you from installing a solar system. The best person to explain the intricacies of the utility's treachery is a reputable installer of solar panels who works in your area. Such an installer will help you with figuring out your demand, whether you have suitable roof orientation etc. and it is probably best to get in touch with one of them as soon as possible. Warning: these guys do tend to be high pressure once they have you on the hook, as it were, and there are a fair number of crooks out there in this business too apparently.

    The main problem here is that your overall and peak demands are going to go up when you start plugging in an R1T. In No. 16 I figured from Rivian's specs that it takes 462 Wh/mi on average to drive the truck. If you do the US average of 12,000 miles in a year that means you will have extra demand of 12000*.462 = 5.5 MWh (equivalent to having six 100 watt lamps on continuously). In Texas an average home uses 14 mWh per year so the RIT will add 39% to your demand. That's pretty appreciable. Adding the new demand to your existing gives your estimated new demand. If average that would get you to 19.8 MWh/yr.The next step is to determine how much of that you want to cover by solar. This depends on how much a panel can produce on average per year in your area and the number of panels you install. It is possible for you to figure all this out yourself but again, an installer is probably the best place to get this info.

    How much you want to cover with solar often depends on more than economics, especially as in your case where the utility is cheap. It's going to take a long time to recover the cost of your installation if the utility sells a kW for a few cents. In such a case the motivation may be "bragging rights" more than anything else e.g. the desire may be simply to say "I charge my truck from solar". If that's where you are the calculus becomes pretty simple. Install an 11 kW system (that's how much the R1T can accept), turn everything else off and only charge when the sun if full out. Or install an 8 kW system, set the truck for 8 kW max charge rate and only charge it when the sun is shining.

    Where you aren't going to mine any money out of the utility (low rates) the main reason for connecting to them is that they serve as your backup battery when the sun is in. Of course, if the utility is out, grid connected systems shut down and you need another source of backup such as a generator. Of course with the Rivian you can plug a small refrigerator into the truck bed outlet.
     
  20. Scott Banko

    Scott Banko Rookie

    Jul 23, 2019
    2
    I guess I did'd post the question properly, so let me try again.

    Teslas Powerwall = 13.5 kWh and that is suppose to last about day

    Rivian is available with 180 kWh battery that's is at least 12 times bigger = so it should last a week in a typical house.

    I have had several solar companies recommend 7 to 8 kW system because if I overproduce electricity I will loose it. In TX its an even exchange, overproduction is lost.

    So as above response suggests I'll install an 11 kW system to charge Rivian and place rest of electricity in the bank for winters / low sun days.

    Has Rivian given us any information as to how that massive 180 kWh battery down the road can be used as Teslas Powerwall and /or vehicle-to-grid unit
     
  21. Poorpilot

    Poorpilot Rookie

    Dec 3, 2018
    46
    Short answer - No

    Long answer - Nope
     
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  22. ajdelange

    ajdelange Rookie

    Mar 22, 2019
    7
    I guess I was not clear in my previous post. You cannot use a vehicle as a backup power source for your house. The NEC prohibits it. If you try to do this you will not pass inspection. The only way to legally obtain backup power from the R1T would be to run an extension cord out to it and plug that into one of the bed outlets. These are rumored to be able to supply 15 A @ 120 V equal to 1.8 kW. A fully charged 180 kWh battery can supply that much power for 100 hours (4 days and 4 hrs).

    As mentioned in No. 19 the average Texas house consumes 14 MWh/yr. That works out to an average demand of 1.6 kW. A 13.5 kWh back up battery will, therefore, last, on average, 13.5/1.6 = 8.4 hours unless you institute some sort of load shedding when the utility goes down. Were it legal to draw energy from the vehicle (and were the modifications made to the truck and the EVSE to allow this) a fully charged 180 kW battery would supply an average load of 1.6 kW for, on average, 4 days, 16 hours and 30 minutes. The big difference between the powerwall or the proposed illegal truck hookup is that they will supply the brief peak loads (such as a 6 kw air conditioner cycle) whereas the legal truck hookup is limited to a peak draw of 1.6 kW.

    Thus a power wall is great for short outages (as many tend to be) but pretty useless when the power goes out for a couple of days unless you impose strict shedding or install multiple power walls. For longer outages you still need a generator.
     

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