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I'm wondering if it is possible to use solar panels with an inverter hooked up directly to the Bolt's EVSE to charge it? Given that the panels are unlikely to be able to provide the full 12 (or even 8 amps) that the EVSE expects, my guess would be no, but I'd like to be sure. The idea would be to install panels on the gazebo where I park my car. Given both the complexity of permitting and the instability of the grid in northern California (thanks Pacific Gas & Electric), directly attached panels seems a lot more appealing than a traditional grid-tied system.

As a corollary, I'm wondering if there's a way in general to force the EVSE to use less current, e.g. limit draw to 500W or so. Obviously this would result in very slow charging, but it seems like it could be useful in an emergency.

Thanks.
 

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Yes, you need to have a battery in between. My suggestion would be to tie panels to a 12 V LiFePO4 battery using an MPPT and run your EVSE off of a pure sine inverter. You want at least a 100 Ah battery and a 1000 watt continuous power inverter, and that's just to charge 120 V @ 8 A. You could also use two 75 Ah batteries in parallel with a 1500 watt continuous power inverter to charge at 120 V @ 12 A.

Will is a really good resource for this sort of thing:

 

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Yes, you need to have a battery in between. My suggestion would be to tie panels to a 12 V LiFePO4 battery using an MPPT and run your EVSE off of a pure sine inverter. You want at least a 100 Ah battery and a 1000 watt continuous power inverter, and that's just to charge 120 V @ 8 A. You could also use two 75 Ah batteries in parallel with a 1500 watt continuous power inverter to charge at 120 V @ 12 A.

Will is a really good resource for this sort of thing:

...and probably at least 2000W of PV. I'd probably bump up the battery bank capacity, too. You're probably into the small residential off-grid system category now, too. Turnkey systems abound.

IMO, asking a 1000W inverter to source 960W continuous is asking for trouble. I like a significant design margin, and would go for 1500W and 2000W for 8A and 12A charging respectively. But that's just me...a belt and suspenders kind of guy.
 

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...and probably at least 2000W of PV. I'd probably bump up the battery bank capacity, too. You're probably into the small residential off-grid system category now, too. Turnkey systems abound.

IMO, asking a 1000W inverter to source 960W continuous is asking for trouble. I like a significant design margin, and would go for 1500W and 2000W for 8A and 12A charging respectively. But that's just me...a belt and suspenders kind of guy.
Yeah, it's really going to depend on the inverter (some can handle their rated continuous load better than others). It has to be rated for at least 1000 W continuous. I'd probably prefer a 1200 to 1500 W personally. Again, that's for 8 A.

As for the solar array, yes, it needs to be the right size as well, but 2000 W is likely overkill (both from a power production and price perspective). A 100 Ah LiFePO4 battery will only have about 1.2 kWh stored, so even running at a slight deficit (say 800 to 900 W coming from the panels), you'd be able to run on 120 V @ 8 A for most of the daylight hours. There's so much variance in panels and setups too, that it's hard to say get XXXX watts of such and such solar panels. I'd say the baseline would need to be 1000 W, but even at 120 V @ 12 A, running 1500 W should be good enough.

The battery is where I would run the absolute smallest possible because it's the most expensive component that is really only acting as a buffer. The only reason I would suggest a 100 Ah is because many of the LiFePO4 are only rated for a 1 C continuous discharge (I'm not sure whether feeding power in from the MPPT concurrently reduces the effective discharge rate). In order to run a 12 V inverter at 960 W, you'd be looking at an 80 A constant discharge.

Building from the ground up, it might actually be worth considering a 24 V to 240 V inverter, which of course would increase the cost and decrease mobility, but it would also provide much faster charging rates. A 3500 W, 240 V pure sine inverter could max out the Bolt EV's stock EVSE running on 240 V @ 12 A. At that point, yes, 2000 W might be too small of a solar array, and you'd probably want a 150 Ah 24 V LiFePO4 battery.
 

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You will need a low battery cutoff device between the battery and the inverter. This will protect the battery at around 11.5 to 11.75 volts on cloudy days and may be all you need to shut the inverter off automatically at night. If you want your deep cycle AGM to last longer you may want to terminate charging at 12 volts or 24 volts for the 24 volt system. Full River batteries get pretty good reviews.
 

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You will need a low battery cutoff device between the battery and the inverter. This will protect the battery at around 11.5 to 11.75 volts on cloudy days and may be all you need to shut the inverter off automatically at night. If you want your deep cycle AGM to last longer you may want to terminate charging at 12 volts or 24 volts for the 24 volt system. Full River batteries get pretty good reviews.
I would advise against using any lead battery for this. Yes, LiFePO4 is more expensive (really, only about double AGM), but LiFePO4 is lighter, you can use more of its available energy, it typically has at least six to eight times the cycle life of lead, it has better Coulombic efficiency (>99% versus ~90% for lead), and they typically come with an internal BMS with low-voltage cutoffs. You're right that you might want an additional low-voltage cutoff between the battery and the inverter, but many pure-sine inverters already include a low input voltage setting.
 

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Yes, basically everything you mention is true except lighter doesn’t matter and an inverter’s low voltage cutoff is not adjustable like some of the better stand alone units. Also an AGM as a first battery keeps the cost down until you decide if the system is really working for you. Once it is ”payed for”, solar is basically free, and Coulombic efficiency is not such a big deal in a stationary application. After 1500 or so cycles, you can decide wether or not to upgrade. That’s how my mind works anyway.
 

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Yes, basically everything you mention is true except lighter doesn’t matter and an inverter’s low voltage cutoff is not adjustable like some of the better stand alone units. Also an AGM as a first battery keeps the cost down until you decide if the system is really working for you. Once it is ”payed for”, solar is basically free, and Coulombic efficiency is not such a big deal in a stationary application. After 1500 or so cycles, you can decide wether or not to upgrade. That’s how my mind works anyway.
I guess I just have to disagree. One of the main reasons to consider this type of system is mobility (e.g., camping). A >60 lb AGM battery with less usable capacity than a <30 lb LiFePO4 battery is a significant constraint.

The shortened lifecycle is also a major consideration. This setup would burn through an AGM battery in a year or two, whereas the LiFePO4 battery could last upwards of 10 years.

And losing up to an additional ~9% of the energy (due to Coulombic inefficiencies) gathered from an already inefficient PV system is huge. Just with the losses from the inverter and the Bolt EV's onboard charger alone, you're looking at over 70 kWh your panels will need to generate to fill a 60 kWh Bolt EV. Adding another ~9% inefficiency into that system is a significant loss. That's 10% fewer solar panels you need to buy (and for the sake of mobility, pack) for the same outcome.
 

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The shortened lifecycle is also a major consideration. This setup would burn through an AGM battery in a year or two, whereas the LiFePO4 battery could last upwards of 10 years.
I completely agree with your conclusion, and this is why. In the long term, Lead will actually be more expensive. Over 10 years, you have used one set of LiFePO4 batteries, but 5 AGM batteries. So if LiFePO4 is 2x the cost, the AGM actually cost 2.5x as much over 10 years. Going with AGM is penny wise / pound foolish.
 

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I guess I just have to disagree. One of the main reasons to consider this type of system is mobility (e.g., camping). A >60 lb AGM battery with less usable capacity than a <30 lb LiFePO4 battery is a significant constraint.

The shortened lifecycle is also a major consideration. This setup would burn through an AGM battery in a year or two, whereas the LiFePO4 battery could last upwards of 10 years.

And losing up to an additional ~9% of the energy (due to Coulombic inefficiencies) gathered from an already inefficient PV system is huge. Just with the losses from the inverter and the Bolt EV's onboard charger alone, you're looking at over 70 kWh your panels will need to generate to fill a 60 kWh Bolt EV. Adding another ~9% inefficiency into that system is a significant loss. That's 10% fewer solar panels you need to buy (and for the sake of mobility, pack) for the same outcome.
The OP wasn't talking about camping, he wants to be able to charge his Bolt during a normal day in California... ie bright sunshine for the solar panels coupled with power outages, wild fires, civil unrest... you know, the normal stuff you deal with in California :)

His system should have minimal cycling of the battery since he will be charging for the most part while the sun is shinning, using the battery as a buffer rather than a deep cycle power source.

Your mindset seems to be "stationary system = 15 KW or more power plant on my roof, anything smaller must be for camping" Me and RichardC are looking at it from the perspective of getting a newbie into the Solar lifestyle at a low cost of entry vs him saying "screw it" and getting a gasoline backup generator that would serve his current needs for less cost.

If he gets into it and likes it when his AGM batteries wear out in two to five years and need replacement he can get "old fashioned" lithium ion batteries instead of the new fangled solid state batteries that you will be urging on people :D

Keith

PS: I have looked into solar in my area, power is so cheap here that even with the reduced pricing Tesla solar has recently announced, I would just break even over the life cycle of the solar panels. And just when power become free I will drop dead of old age! For me the solar power for off grid camping is the only solar that makes sense.
 

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I also believe lithium batteries are better suited to your application. I have a lithium battery based off-grid system that I use to charge the Bolt and also power my Cottage that works really well.. An openevse is controlled through MQTT to turn charging on and off and set the charge rate. Then software takes the state of charge of the buffer battery, the amount of solar power and the load on the system to set the charge rate. In this way the wear on the buffer battery is minimized and the maximum amount of energy is sent to the Bolt. However it's not for the faint of heart if you aren't used to working with electronics and writing software. The Bolt is charged between 6 and 12 amps at 240v using a 3500 watt inverter and 3500 watts of solar.
 

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The OP wasn't talking about camping, he wants to be able to charge his Bolt during a normal day in California... ie bright sunshine for the solar panels coupled with power outages, wild fires, civil unrest... you know, the normal stuff you deal with in California :)

His system should have minimal cycling of the battery since he will be charging for the most part while the sun is shinning, using the battery as a buffer rather than a deep cycle power source.

Your mindset seems to be "stationary system = 15 KW or more power plant on my roof, anything smaller must be for camping" Me and RichardC are looking at it from the perspective of getting a newbie into the Solar lifestyle at a low cost of entry vs him saying "screw it" and getting a gasoline backup generator that would serve his current needs for less cost.

If he gets into it and likes it when his AGM batteries wear out in two to five years and need replacement he can get "old fashioned" lithium ion batteries instead of the new fangled solid state batteries that you will be urging on people :D

Keith

PS: I have looked into solar in my area, power is so cheap here that even with the reduced pricing Tesla solar has recently announced, I would just break even over the life cycle of the solar panels. And just when power become free I will drop dead of old age! For me the solar power for off grid camping is the only solar that makes sense.
The assumption I'm making is that, if there is a grid connection (i.e., stationary system), a battery-tied inverter and solar panels might not be the best solution. The better solution in that case might be a string inverter with direct power take off, such as SMA. At that point, you have the benefit of a grid-tied solar array with a 120 V power outlet that is available when the grid connection is shut off (for whatever reason). As long as the array is generating enough power, the string inverter can power the 120 V EVSE.

The moment someone says "off grid," I'm assuming that they want to use it someplace where a grid connection is not available (i.e., a mobile system). In either case, though, if using a battery as a buffer, LiFePO4 presents a far higher value than an AGM, even if that AGM is half to a third of the upfront cost.
 

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I want a system that can feed extra power to the grid, but be off grid during outages. I don't mind throwing a knife switch for it to switch over, depending on the cost of an automatic switch over device.

Our lights are LED, the Bolt, a refrigerator, the furnace blower motor, a 55" tv, a laptop and desktop computer are our main electricity uses.
 

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The OP wasn't talking about camping, he wants to be able to charge his Bolt during a normal day in California... ie bright sunshine for the solar panels coupled with power outages, wild fires, civil unrest... you know, the normal stuff you deal with in California :)

His system should have minimal cycling of the battery since he will be charging for the most part while the sun is shinning, using the battery as a buffer rather than a deep cycle power source.

Your mindset seems to be "stationary system = 15 KW or more power plant on my roof, anything smaller must be for camping" Me and RichardC are looking at it from the perspective of getting a newbie into the Solar lifestyle at a low cost of entry vs him saying "screw it" and getting a gasoline backup generator that would serve his current needs for less cost.

If he gets into it and likes it when his AGM batteries wear out in two to five years and need replacement he can get "old fashioned" lithium ion batteries instead of the new fangled solid state batteries that you will be urging on people :D

Keith

PS: I have looked into solar in my area, power is so cheap here that even with the reduced pricing Tesla solar has recently announced, I would just break even over the life cycle of the solar panels. And just when power become free I will drop dead of old age! For me the solar power for off grid camping is the only solar that makes sense.
I was just about to say the same thing in other words, thank-you. You are not trying to run a cottage at night here nor keep a refrigerator cold. You are only trickle
charging the EV when the sun is out. You need to think about it like a solar powered garden fountain that only runs when the sun is out. A small battery keeps it going if the sun goes behind the clouds for 10 or 15 minutes. Simple system.

A Full River 55ah battery (($175) has 2000 cycles with 30% DOD and 3000 cycles At 20% or 8 years of 365 days a year trickle charging. A 35ah battery is only $120

I would take the Money for a Li battery and instead put it into one extra solar panel. Remember if you size the array for the Inverter inefficiency and the EV load you can probably reach a point where the battery is hardly discharged and the beauty of an adjustable low battery shutoff is I can set as high as I want it, say 12 volts and the AGM will hardly feel any strain. This is a get it while you can type system, not life and death.

No, I still disagree, take the difference between an AGM and a LiFe and buy an extra panel. The battery is only a buffer, not a source. ****, I would be tempted to try panels directly into an inverter if I could find one that could handle the unregulated output of the panels.

Too bad this would not work in my neck of the woods, not enough good sunny days to make it pay off.
 

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I was just about to say the same thing in other words, thank-you. You are not trying to run a cottage at night here nor keep a refrigerator cold. You are only trickle
charging the EV when the sun is out. You need to think about it like a solar powered garden fountain that only runs when the sun is out. A small battery keeps it going if the sun goes behind the clouds for 10 or 15 minutes. Simple system.

A Full River 55ah battery (($175) has 2000 cycles with 30% DOD and 3000 cycles At 20% or 8 years of 365 days a year trickle charging. A 35ah battery is only $120

I would take the Money for a Li battery and instead put it into one extra solar panel. Remember if you size the array for the Inverter inefficiency and the EV load you can probably reach a point where the battery is hardly discharged and the beauty of an adjustable low battery shutoff is I can set as high as I want it, say 12 volts and the AGM will hardly feel any strain. This is a get it while you can type system, not life and death.

No, I still disagree, take the difference between an AGM and a LiFe and buy an extra panel. The battery is only a buffer, not a source. ****, I would be tempted to try panels directly into an inverter if I could find one that could handle the unregulated output of the panels.

Too bad this would not work in my neck of the woods, not enough good sunny days to make it pay off.
If that works for you, fine. There are a number of ways to set up the system for each person's unique budget and needs. What you sacrifice is ultimately up to you.
 

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If that works for you, fine. There are a number of ways to set up the system for each person's unique budget and needs. What you sacrifice is ultimately up to you.
This isn't about "what works for you" (meaning RichardC) it is about what the OP was asking about. I will not be going Solar because it is not economical in my area of the country, and power outages are very rare. If I were to go renewable here, wind would be a more viable option. Because I am not going solar, I am not laser focused on what would be the "best" system to invest in... so I aswered the OP's question rather than steering him towards an expensive "better" system.

The point is, RichardC and I are in line with the OP's goals, and what he stated in his first post, and re-affirmed in his replies. Neither RichardC or I are saying that our ideas are the best, or that they are most economical in the long run for someone "going solar"... they just meet the needs of the OP as stated by the OP. Not a full home setup. Not a camping setup. The setup the OP specified... still being able to charge his Bolt during a power outage, and supplementing his power supply when the grid is available.

Keith
 

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This isn't about "what works for you" (meaning RichardC) it is about what the OP was asking about. I will not be going Solar because it is not economical in my area of the country, and power outages are very rare. If I were to go renewable here, wind would be a more viable option. Because I am not going solar, I am not laser focused on what would be the "best" system to invest in... so I aswered the OP's question rather than steering him towards an expensive "better" system.

The point is, RichardC and I are in line with the OP's goals, and what he stated in his first post, and re-affirmed in his replies. Neither RichardC or I are saying that our ideas are the best, or that they are most economical in the long run for someone "going solar"... they just meet the needs of the OP as stated by the OP. Not a full home setup. Not a camping setup. The setup the OP specified... still being able to charge his Bolt during a power outage, and supplementing his power supply when the grid is available.

Keith
At which point, I would reaffirm not using batteries at all. If it's a stationary system, simply use a string inverter that has a power takeoff (such as a SMA Sunny Boy) and use a main disconnect.
 

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At which point, I would reaffirm not using batteries at all. If it's a stationary system, simply use a string inverter that has a power takeoff (such as a SMA Sunny Boy) and use a main disconnect.
So, during a power outage the power from the inverter will be smooth enough (clouds, etc causing output variations) to run the EVSE without causeing a fault? I admittedly am not a solar expert, but I though doing a direct PV to EVSE without a batter to smooth the output would cause problems.

Keith
 

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So, during a power outage the power from the inverter will be smooth enough (clouds, etc causing output variations) to run the EVSE without causeing a fault? I admittedly am not a solar expert, but I though doing a direct PV to EVSE without a batter to smooth the output would cause problems.

Keith
In theory, yes. Part of that is due to the amount of power that it outputs. It's only 120 V and 15 or 20 A, I believe (I'd have to dive into the spec sheets to confirm), so the output power is far under the size of the array and inverter (typically 3 kW to 6 kW). If anything, I think it's under powered, but at ~25% to 50% of the array's rated power, a few clouds or slightly overcast day shouldn't prevent it from outputting 960 to 1,440 W.

And again, in my opinion, LiFePO4 is still a better option if tying an inverter to a 12 V battery that is charged off solar panels using an MPPT. That's regardless of whether the system is stationary or mobile (yes, I was projecting a bit because I already have one of these systems in mind to build, and I want mine to also be mobile). Regardless, sure, you can get a cheap 12 V lead acid, but running in the same conditions, it will always be less efficient with a far shorter service life than LiFePO4. Basically, for me, it's as much a question of waste as budget.

Let's be honest. If the discussion is about hooking up an EV to solar panels mounted on a gazebo, a $200 to $400 difference in battery cost is a non-issue. Especially when then more expensive battery will likely last 4 to 5 times longer in that use case under those conditions. Part of the reason we buy EVs and solar panels is because, despite the higher upfront cost, they actually cost less than the alternative over time.
 

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Get a generator instead of batteries, so you can get higher capacity and run the whole house, and so you can ride through days of grid outage instead of a few hours.
I have 50 solar panels being installed, and bought a natural gas generator to supplement them, because Portland's electric utility is very unreliable.
The cost of a single Tesla 14 kWh battery is US$5600 (it's the lowest cost per kWh), which would more than pay for installation of a 10kW or larger generator.
 
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