Hello, name is Dave. Need help building a system to supplement the charge on a Tesla

[Dave162]

Looking for suggestions on supplementing the charge on a Tesla

 

[curiouscarbon]

Dear Dave,

cool idea; are you able to share more details about your situation and what you wish to achieve?

EV charging can be done at relatively low rates like 1000-2000W even if to the car that’s a trickle charge.

what’s the setup right now? 240v wall charging? do you already have solar panels set up?

cheers and hope you may drive by the power of the sun soon

 

[svetz]

Welcome to the forums!

 

[rickst29]

If you want to add a lot of Solar PV Watts to assist in charging the Tesla, then you must either grid-tie (with expensive licensing and permits, possibly requiring PV installation from a relatively small number of licensed-and-approved PV contractors) -- OR you may build a totally separate system, with either a 120V or 240V Converter supplying "AC" Voltage into the Tesla charge cord. That would need the following components:

1. PV Array.
2. MPPT Solar Controller(s), feeding a battery bank.
3. Battery Bank (preferably "48V" rather than "12V" or "24V", because that allows for smaller wiring between the Battery Bank and the Inverter.)
4. A big Inverter.

They do make some Inverters with built-in Transfer switches, but these are more for "grid backup" than "fully utilizing the Solar". You can program the Tesla to both a maximum Input Current value and a Maximum voltage shortfall value, and these can be separate values for 120v for 240v input. The Inverters also shut down the battery Voltage drops "too far", although this value is too low for most kinds of battery banks. (Some Inverters are programmable, and that's a very good feature).

I feel that a battery bank is mandatory, for two reasons: First, many MPPT Solar Controllers can't even get started until a battery is connected; and second, the battery bank needs to hold up Voltage on the Inverter Input whenever clouds pass overhead for a short period. On the output side, I "feel" that pure Sine Wave Inverter output is pretty much mandatory - although I have no proof that Tesla's internal charger can't handle "Modified Sine Wave" from the 120/240V input, I'd hate to try it and then break it. Your Inverter output needs to look like the grid (pure Sine wave), with extremely low distortion and harmonics.

 

[DerpsyDoodler]

If you want to add a lot of Solar PV Watts to assist in charging the Tesla, then you must either grid-tie (with expensive licensing and permits, possibly requiring PV installation from a relatively small number of licensed-and-approved PV contractors) -- OR you may build a totally separate system, with either a 120V or 240V Converter supplying "AC" Voltage into the Tesla charge cord. That would need the following components:

1. PV Array.
2. MPPT Solar Controller(s), feeding a battery bank.
3. Battery Bank (preferably "48V" rather than "12V" or "24V", because that allows for smaller wiring between the Battery Bank and the Inverter.)
4. A big Inverter.

They do make some Inverters with built-in Transfer switches, but these are more for "grid backup" than "fully utilizing the Solar". You can program the Tesla to both a maximum Input Current value and a Maximum voltage shortfall value, and these can be separate values for 120v for 240v input. The Inverters also shut down the battery Voltage drops "too far", although this value is too low for most kinds of battery banks. (Some Inverters are programmable, and that's a very good feature).

I feel that a battery bank is mandatory, for two reasons: First, many MPPT Solar Controllers can't even get started until a battery is connected; and second, the battery bank needs to hold up Voltage on the Inverter Input whenever clouds pass overhead for a short period. On the output side, I "feel" that pure Sine Wave Inverter output is pretty much mandatory - although I have no proof that Tesla's internal charger can't handle "Modified Sine Wave" from the 120/240V input, I'd hate to try it and then break it. Your Inverter output needs to look like the grid (pure Sine wave), with extremely low distortion and harmonics.

You sure about all those statements? I thought grid tie meant feeding electricity back to the grid. If you are not grid tying, I’ve read from many that permits often are not required. At any rate, I strongly suggest OP should refer to his local municipal codes to determine what his options are and at the very least seek 2nd and 3rd opinions on this (and/or other) forums.

 

[rickst29]

Thanks, Derpsy. I did fail to include the option of a using a Transfer Switch, preventing grid-tie but using the grid connection when input 120-VAC (or 240-VAC) is "unavailable" from the battery bank and Inverter.

Except for that case, however, if your PV panel is connected to the same Tesla outlet (120V or 240v) which is powered from the Grid, through a grid-connected home circuit breaker panel - than you ARE grid-tied, and there is no way for your home distribution panel to distinguish between "feeding into the shared outlet" versus "feeding into the Grid" when current is present.

In some cases, maybe, a particular Electric Utility provider and Municipality might allow you to provide power into them "for free", giving you no credit (by leaving a dumb meter and dumb billing in place). But Grid-tie is the mere attachment of a grid-compatible power generation device, and not necessarily feeding back power for credit.

Without a transfer switch to prevent connection, I can't imagine any electric utility which would let you connect an unqualified power-generating Inverter into "their" grid through "your" panel. A lower-quality Inverter (incapable of locking phase with the Grid, or with a bad waveform and too much THD) would be a disaster - for them. So the Tesla Solar outlet needs to be separate, or it needs to be connected through an automatic Transfer/Disconnect switch, or it needs to be officially grid-tied.

I hope this correction clears things up. With this offered as an addendum, I am quite sure about all of my statements so far. I have a pretty big grid-tie array on my own house, and I have wired another house (only from the Panel outwards), with special charging current, voltage-drop limits, and time-of day limits programmed into his model-S for connection for that particular outlet (which is recognized by its geographical location). It's been working great, and it was built right.

 

[DerpsyDoodler]

Thanks, Derpsy. I did fail to include the option of a using a Transfer Switch, preventing grid-tie but using the grid connection when input 120-VAC (or 240-VAC) is "unavailable" from the battery bank and Inverter.

Except for that case, however, if your PV panel is connected to the same Tesla outlet (120V or 240v) which is powered from the Grid, through a grid-connected home circuit breaker panel - than you ARE grid-tied, and there is no way for your home distribution panel to distinguish between "feeding into the shared outlet" versus "feeding into the Grid" when current is present.

In some cases, maybe, a particular Electric Utility provider and Municipality might allow you to provide power into them "for free", giving you no credit (by leaving a dumb meter and dumb billing in place). But Grid-tie is the mere attachment of a grid-compatible power generation device, and not necessarily feeding back power for credit.

Without a transfer switch to prevent connection, I can't imagine any electric utility which would let you connect an unqualified power-generating Inverter into "their" grid through "your" panel. A lower-quality Inverter (incapable of locking phase with the Grid, or with a bad waveform and too much THD) would be a disaster - for them. So the Tesla Solar outlet needs to be separate, or it needs to be connected through an automatic Transfer/Disconnect switch, or it needs to be officially grid-tied.

I hope this correction clears things up. With this offered as an addendum, I am quite sure about all of my statements so far. I have a pretty big grid-tie array on my own house, and I have wired another house (only from the Panel outwards), with special charging current, voltage-drop limits, and time-of day limits programmed into his model-S for connection for that particular outlet (which is recognized by its geographical location). It's been working great, and it was built right.

you can also connect your system such that grid feeds the inverter, then the inverter feeds the house main. This eliminates any chance of backfeed with no need for manual or automatic intervention.

 

[Ampster]

Looking for suggestions on supplementing the charge on a Tesla

What are you using now and what size is the internal charger on your car? Depending on the model of Tesla you may be limited to 40 Amps. Tesla has changed that configuration over the years. I have used Clipper Creek, JuiceNet, the Tesla mobile connector and several others with success on both of my Teslas.

 

[Ampster]

I have wired another house (only from the Panel outwards), with special charging current, voltage-drop limits, and time-of day limits programmed into his model-S for connection for that particular outlet

To clarify by, "outwards" I assume you mean behind or away from the meter in the direction of the loads. I have played around with turning my EVSEs on and off based on solar production but not had any luck modulating output. I would be interested in hearing more, but don't want to hijack this thread. However what you are doing may be relevant to what the OP means by using th word "supplement".

 

[Ampster]

You can program the Tesla to both a maximum Input Current value and a Maximum voltage shortfall value, and these can be separate values for 120v for 240v input.

I have two Teslas and I can only adjust the input current on the screen on the car. Where do you find the adjustment for "maximum voltage shortfall value"?

Are you talking about the car settings or the EVSE settings?

 

[curiouscarbon]

I too am curious what "supplement" signifies. Haven't seen many resources about modulating charging based on battery state.

 

[rickst29]

To clarify by, "outwards" I assume you mean behind or away from the meter in the direction of the loads. I have played around with turning my EVSEs on and off based on solar production but not had any luck modulating output. I would be interested in hearing more, but don't want to hijack this thread. However what you are doing may be relevant to what the OP means by using th word "supplement".

You are correct, and I described three different things into a single sentence: The Tesla can specify a maximum charge current (not otherwise tunable) and a single spread of off/on operating hours for a given location. The "minimum Voltage" requirement was with regard to the Inverter on the DC input battery pack side, and it is also an off/on function. In going to a dedicated Outlet, power into the Tesla adapter will vanish when the Inverter shuts down.

And, if sent through a Transfer switch in order to share a single plug, the Tesla has no way to tell whether power is being drawn from the Solar and Inverter (good) or from the Grid at high noon on a Cloudy day (when rates are high). If there's power and it's within the allowed hours before "departure", it WILL pull in power, to try and meet that departure time at the maximum default charging capacity you specify.

But Tesla model-S Software 4.3.3 (and later, AFAICT) allow only one charging period per day, everything else requires a "when I plug it in" override of the period preceding the imaginary departure time. So, if used for only one Tesla socket, through a Transfer switch, you are unable to set two different charging periods (off peak/night, and peak Solar). That's the main reason why I recommend that a Solar System which isn't inherently grid-connected should be done with separate outlets.

But there is no question that grid-connected is best, as long as you can pay for the higher cost installation AND get a decent rate of payback. Having gotten into game with a Nevada Tier-2 "Payback" at a full 88% of retail (probably forever), it will actually be best for me to charge my upcoming EV at night (paying 100% of the lowered off-peak night rate). By doing that, even though my peak Solar Energy is totally "free" within the house, giving them ALL of my "leftover" Kwh at 88% times the peak daytime rate "earns" more credit than i spend at night, even though my spending rate is 100% of the lower night rate. (It's simple math, the daytime rate is more than 12% higher than the nighttime rate).

It all depends on the tariff which is available to you, and your increased installation costs. That's entirely a local thing, and wer'e all waiting for a little more info from Dave162, in order to add anything else.

 

[Diysolar123]

I thought that even the "trickle charge" option (days to get a full charge) for a tesla was a couple killowatts!!
Normal charging was 10-20kw (240vac 40+amps).

those cars really suck the power; you will need a lot of panels to charge a tesla.
Have you considered just installing "Mr. Fusion"?

 

[Ampster]

you can also connect your system such that grid feeds the inverter, then the inverter feeds the house main. This eliminates any chance of backfeed with no need for manual or automatic intervention.

I am trying to picture how that would work assuming you are talking about a grid tie inverter. In the case where you describe the grid feeding the GT inverter there is no way that I know of to make that a oneway path. By the very nature of a grid tie inverter it is a bidirectional connection. A GT inverter needs to be able to export to the grid as a buffer since it is only designed to produce the maximum power from the solar.

In the case of a hybrid inverter with a transfer switch the connection from the grid would have to come from a circuit breaker before the main panel and the main panel would have to be wired as a critical loads panel and it would be limited in current based on the inverter and what extra current could be passed through the hybrid inverter from the grid. Some hybrids can be adjusted to zero export mode but that requires automatic intervention of software. Perhaps I am misunderstanding your connection scheme. Do you have a single line diagram?

 

[curiouscarbon]

I thought that even the "trickle charge" option (days to get a full charge) for a tesla was a couple killowatts!!
Normal charging was 10-20kw (240vac 40+amps).

those cars really suck the power; you will need a lot of panels to charge a tesla.
Have you considered just installing "Mr. Fusion"?

have verified a test of charging at 1.5kW from a 3kWh goal zero pack for a short period of time. floating ground had to be addressed for error code to abate.

50,000Wh/1500W -> 33hr
70,000Wh/1500W -> 47hr

50,000Wh/20,000W -> 2.5hr
70,000Wh/20,000W -> 3.5hr

 

[Ampster]

I thought that even the "trickle charge" option (days to get a full charge) for a tesla was a couple killowatts!!

I just checked and the lowest i can set my internal charger is 5 Amps. That assumes 240 volts so that is 1200 Watts. Depending on the car I can get as much as 20 kWhrs overnight which can be 100 miles of range at that rate. I just checked and the max rate is 32 Amps which easily can put 200 miles of range into that car (Model 3) in less time than my TOU low rate window.

 

[Ampster]

So, if used for only one Tesla socket, through a Transfer switch, you are unable to set two different charging periods (off peak/night, and peak Solar). That's the main reason why I recommend that a Solar System which isn't inherently grid-connected should be done with separate outlets.

The simple workaround for that is to set the car to always ready and use a programmable switch to control a relay to turn on the power to the plug in which the Tesla is attached. I did that before I had a Tesla because my other EV had no programmable charging. I kept using that system because it was easier.

 

[Ampster]

70,000Wh/20,000W -> 3.5hr

That rate is moot for a Tesla since the internal chargers are mostly limited to a lot less than that. On the other hand DC charging at a Supercharger can be as high as 250kW but briefly tapers down. Even then that is 37 minutes from 5% to 90%.

 

[Ampster]

I too am curious what "supplement" signifies.

Me too. If he is talking about DC fast charging that would not be optimal from solar. .

Haven't seen many resources about modulating charging based on battery state.

My interest is finding a way of modulating charging based on solar production. I have no interest in charging my Tesla from my house bank of batteries. Even during a power outage I would rather do that from solar once my house batteries are full.
From a grid tie perspective some of the Solaredge GT inverters come with a J1772 charging cable that allows some priority setting between grid export and the charging port.

 

[curiouscarbon]

thought 11.52kw was practical max for most usa wall charging due to one phase.

tesla models outside of usa can have 3 phase charging

please refer to 6m15s

240V * 48A -> 11,520W