Power your home

daveo4EV

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there is a fundamental problem with Vehicle to home “power” - at least in north america…

the “key” scenario is as follows:
  1. you want the car to provide power to your home when the grid is unavailable
  2. safety requires that if you have your own generator (in this case the car is a “generator” that can provide power) - you have to disconnect your home from the grid
  3. disconnect reasons are multiple
    1. safety - you don’t want power from your vehicle to electrocute the power grid workers attempting to restore power
    2. if you don’t disconnect from the grid you’ll be providing power to your home and all your neighbor’s homes (this is likely to overwhelm your generator and you’ll get a brownout or complete drop offline)
  4. once power is restored from the grid you want to automatically re-connect the home to the grid.
this is why grid tied solar drops offline when there is no grid power - they don’t want all the roof top solar electrocuting the power-company workers attempting to restore power by working on the lines…

in order for _ANY_ home backup power system to work it _MUST_ have a grid disconnect switch. Most US homes (99%) DO not have a grid disconnect system (other than the main breaker) - and idealy you want it to be automatic…you must disconnect before bringing generation sources online - otherwise you risk back feeding power to the grid (not safe) and the entire neighborhood will “see” your power and attempt to use it - overwhelming your generator and causing all sorts of nasty electrical problems…

Once you have disconnected your home from the grid, you are free to provide power to said home via any means you like (gas generator, windmill, solar panels, batteries, children on exercise bikes, etc…)

however for an optimal experience you also want a home power coordinator - that is monitoring the home’s usage, and balancing demand with supply and automatically switching things on and off…and this system needs to be able to talk to the car to tell it to provide or not provide power and know the state of it’s battery - it also needs to know how much power it can provide - which means it need to know the size of the breaker the car is connected to…

this is all 100% technically feasible, straight foward, and very very useful - but MOST residential homes are not built/configured this way - and it’s expensive to reconfigure most homes to accommodate this type of system.

How do I know?

Well I have sucha system installed - it’s called a Powerwall - and the key breakthrough of a Tesla Powerwall is _NOT_ the batteries - it’s the Powerwall gateway - which is a smart device that you install between the power meter and your home’s main panel - and the Gateway “watches” your home’s usage and the grid, and when the grid goes down throws an automatic relay that instantly disconnects the home from the grid, and then the batteries all kick in and start providing power to the home - this happens in about 1-5 milli-seconds and most of the time even appliance clocks don’t notice the power drop

without inserting an automatic cutoff between the grid and the home and having some software system that can coordinate demand/supply this great idea will continue to go no where…and most people aren’t willing to pay for an electrician to reconfigure their home electrical system to have a “gateway cutoff” - and so far only Tesla is delivering a system that offers an “off the shelf” solution that kinda “just works” to run the home’s power systems when disconnected from the grid…

people who have whole home generators know about automatic disconnect relays (or manual ones) but most of those systems don’t have any “smarts” to talk to a battery system or solar panels and direct power from multiple power sources (generator, car battery, solar panels, home batteries) to home demand (powerwalls for example let solar panels run during the day and split power from the panels to charge the batteries and power the home - you’d want some similar smarts for the car battery management)

also on a small note - if hte car is providing power - it would back feed through the PMCC (or similar devices) and could only provide as much power as the breaker on the “charger” - if you have a 50 amp breaker on your PMCC - the vehicle could only provide 50 amps of power to the home…

so while the whole system is technically feasible - and forseeable - it still requires quite a bit of planning and software and communications support from all the elements of the system: the master gateway, the grid disconnect relay, the vehicle’s on board software, the EV charger, the solar inverters and home power managemenet computer that co-ordinates all this stuff...and your home’s electrical system has to be designed to have multiple power sources (solar, battery, vehicle power as a source, power grid) - and all these sources have to be switchable so that they can be brought online/offline under software/hardware control - they also have to provide data channels so the central power management computer knows your Taycan is at 5% battery and isn’t really a reliable source of power anymore…

for those interested I’ve had powerwalls for 2 years and to day from Feb. 14th, 2018 they have bridged over 30 hours of grid outage at my home in the Santa Cruz area - the system works great and I love it - and my neighbors are jealous (3 have installed their own systems) - so I have some insight as to what is possible here and how well it can work - the main problem is it’s basically a redesign of your entire home’s electrical system - and a few new devices that need to installed, supported and maintained to allow all this seamless switching from multiple power sources and do it safely such that your home does not back feed power to the grid when it shouldn’t…

Porsche’s existing vehicle software doesn’t support this
Porsche’s existing vehcile charger doesn’t support this
There is no powermanagement system that can talk to the vehicle or charger
and there is no standard whole home grid disconnect relay that can talk to these systems…

I know it can work, I’d love it to work, but it’s not quite ready for prime time with out the full support of the vehicle manufacturers…
 
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daveo4EV

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I’d be happy to speak at length with anyone curious about a solar/battery whole home Tesla system - mine have worked great - and it’s the best fully functional system available to date in my opinion - but from having the system and seeing what it takes to really make this ready for prime time - and being a sofware engineer and technical person myself - we’ve got a longs ways to go until all the pieces are in place for this type of system to be standardized and just work for the average home owner…

just witness the confused and frustration at trying to explain you need a 50 amp breaker for a NEMA 14-50 plug to charge your Taycan (or any other EV) - and how many porsche dealers can’t even ge that right - and getting an electrical system setup for “back feed” is even more complex (and beyond the experience/skill of 98% of residential electricians) - and the lack of building codes, and standards make this a bleeding edge configuration for residential deployment…

we all know this can be done, but at the moment it’s way beyond societies general awareness as to how to do it…we are in early days...

any claims like the one in this thread - that doesn’t discuss/address the need for vehicle software support. software support in the eV chargers, and a whole home power management computer, and the cost to retrofit into existing homes is simply naive IMHO…
 

daveo4EV

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here is the backup history of my Santa Cruz Powerwall system…57 “grid outages“ in two years - totalling 30.5 hours of “offline” - in each case the powerwalls stepped in and the powerwall gateway cut off the home from the grid, and allowed my solar panels and batteries to continue to power the home during the outage…my wife LOVES it -and in particullar last year during thanksgiving day the system bridged a 4 hour outage while we had the entire familiy to our home for thankgiving dinner - there was ZERO interruption thanks to the Solar and the Powerwalls…

sign me UP if I could use my Taycan’s 93 kWh battery as part of this system, but I’m not holding my breath and Porsche would need to release software for both the vehicle and the vehicle charger to allow power to be backfed, and communicate with the home power management system.

I look foward to the day- but that day is not today.

BDBD0455-2003-49A8-BDE4-8DB037C53E23.jpeg
 
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daveo4EV

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here is the visulization of the powerwall’s master control computer for your home - note the “idle” powerwall at the bottom on the picture - if the grid drops offline - the powerwall gateway computer will isolate the ”grid” and allow the the battery to “feed” the home along with the solar - it also allows the solar to “charge” the battery if the home’s demand is less than the production - excess solar is automatically redirected to charge the batteries - allowing the system to run indefinately for many days as long as the day time solar production can charge the battery from overnight usage…adding a EV battery as a potential alternative power source would be beyond awesome!!!

even including smarts to charge the EV battery during the day when there is excess solar

the possibilities are enticing, but I’m aware of very few systems that have the total picture in mind and are on their way to market in such a manner than people could actually install it in their home…

again I reference the confusion/angst caused by people simply trying to understand how they are going to charge their EV at home, and that doesn’t require redesiging their home’s entire electrical system, just adding a 240V 50 amp circuit…

4E8F13A8-93DC-4DDD-933D-E8D3D65720D2.jpeg
 

daveo4EV

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I’m super excited for something like this - but dubious that anyone has a total system ready for market anytime soon

Tesla is the best and furthest along, and they still have a long ways to go if you want to start including vehicle batteries in the equation, and they are the best positioned to deliver it and so far haven’t…

but they have:
  1. the software platform in the vehicle - OTA update to add this feature
  2. the communciations connectivity in the vehicle - Wifi internet
  3. a software driveng EVSE (Tesla Wall Charger Gen3 has wifi and backfeed ability)
    1. charger has WiFi to talk with a Powerwall gateway or cloud server
  4. the charger hardware (Tesla Wall charger Gen3)
  5. Whole home automatic relay with Connectivity and auto switching (Powerwall gateway)
  6. already has communication with TEsla vehicles and Powewalls to only charge your EV when you are off grid if there is excess solar…and dyamically adjust the vehicle charge rate to match the exact amount of excess solar so you don’t take away from the home/battery
Tesla is very very close - closer than anyone in this space - but it will only work for their existing powerwall customers with gateways and the cutoff switches…which to suggest is a small user base doesn’t even begin to suggest how small that is…

I really want it - but not sure when it will be there - but honestly Tesla is the furthest along and the only company I know that has all the pieces “in the market” place, but still hasn’t quite stiched them together yet…
 

daveo4EV

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here is a simplified diagram of a home self back up system - you could put any EV in to this picture on the generator side of this diagram if the vehicle’s software and charging infrastructure supported back feeding…which most do not as of this writing…you would add the “car” next to the Powerwall battery’s in this diagram - but you still need a communcation channel “to the car” for the Powerwall Gateway - tell the car to switch on/off as the home demands go up/down…

we lack a standard “gateway” specification - so at the moment systems like this require a lot of vertical integration - all made by the same manufacturer…the Porsche Powermanager available in europe is intriguing to me…but Porsche still has a long ways to go…

the red arrow in this diagram is the “key” element (between the PG&E meter panel) and the Powerwall gateway - this connection can be severed in less than 5 miliseconds by the gateway (relay switch) which instantly turns the home into a “micro-grid” with dual power sources (solar & batteries) and the gateway can direct power from either source to the home’s main breaker panel…

my wife’s coffer maker keeps working and she doesn’t care where the power comes from - and honestly doesn’t even notice when we’re off grid…

AC1D7B18-2A0F-49BE-9C92-18B5AFE44902.jpeg
 

Scandinavian

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there is a fundamental problem with Vehicle to home “power” - at least in north america…
Thanks Dave for quite a detailed summary of the issues facing anybody that wants to add some back up power, whether PowerWall or your EV battery.

It certainly Is not only a North America challenge, it is universal. It is a challenge and needs standards for safety reasons that you have outlined.

This is very similar to inverter installations in boats. If the shore power or generator does not provide enough power, it is complimented or totally supplied by the vessels batteries. Of course such an installation requires multiple safety aspects to be considered, but it is available to install today!

What I found most interesting was that the Quasar was a DC charger, bidirectional. Not sure about the price level but it it certainly was small. The problem with this unit though and the Taycan is the fact it is DC. That means the car loses all control of charging to 85% or whatever. DC will be direct charging. Probably a simple update in Software for Porsche to be able to adjust charging levels. They have shown so much innovation in SW functionality already? NOT!

As was stated somewhere in the video they are discussing the issues with the specification for the CCS standard. But the issue that I see is how will it effect the guarantee for the battery? I mean there could be more charging cycles on the battery without driving the car?

Still an interesting concept I think, but it is certainly not ready by a long shot for general use and deployment.
 
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  • Thread Starter
  • #9
there is a fundamental problem with Vehicle to home “power” - at least in north america…

the “key” scenario is as follows:
  1. you want the car to provide power to your home when the grid is unavailable
  2. safety requires that if you have your own generator (in this case the car is a “generator” that can provide power) - you have to disconnect your home from the grid
  3. disconnect reasons are multiple
    1. safety - you don’t want power from your vehicle to electrocute the power grid workers attempting to restore power
    2. if you don’t disconnect from the grid you’ll be providing power to your home and all your neighbor’s homes (this is likely to overwhelm your generator and you’ll get a brownout or complete drop offline)
  4. once power is restored from the grid you want to automatically re-connect the home to the grid.
this is why grid tied solar drops offline when there is no grid power - they don’t want all the roof top solar electrocuting the power-company workers attempting to restore power by working on the lines…

in order for _ANY_ home backup power system to work it _MUST_ have a grid disconnect switch. Most US homes (99%) DO not have a grid disconnect system (other than the main breaker) - and idealy you want it to be automatic…you must disconnect before bringing generation sources online - otherwise you risk back feeding power to the grid (not safe) and the entire neighborhood will “see” your power and attempt to use it - overwhelming your generator and causing all sorts of nasty electrical problems…

Once you have disconnected your home from the grid, you are free to provide power to said home via any means you like (gas generator, windmill, solar panels, batteries, children on exercise bikes, etc…)

however for an optimal experience you also want a home power coordinator - that is monitoring the home’s usage, and balancing demand with supply and automatically switching things on and off…and this system needs to be able to talk to the car to tell it to provide or not provide power and know the state of it’s battery - it also needs to know how much power it can provide - which means it need to know the size of the breaker the car is connected to…

this is all 100% technically feasible, straight foward, and very very useful - but MOST residential homes are not built/configured this way - and it’s expensive to reconfigure most homes to accommodate this type of system.

How do I know?

Well I have sucha system installed - it’s called a Powerwall - and the key breakthrough of a Tesla Powerwall is _NOT_ the batteries - it’s the Powerwall gateway - which is a smart device that you install between the power meter and your home’s main panel - and the Gateway “watches” your home’s usage and the grid, and when the grid goes down throws an automatic relay that instantly disconnects the home from the grid, and then the batteries all kick in and start providing power to the home - this happens in about 1-5 milli-seconds and most of the time even appliance clocks don’t notice the power drop

without inserting an automatic cutoff between the grid and the home and having some software system that can coordinate demand/supply this great idea will continue to go no where…and most people aren’t willing to pay for an electrician to reconfigure their home electrical system to have a “gateway cutoff” - and so far only Tesla is delivering a system that offers an “off the shelf” solution that kinda “just works” to run the home’s power systems when disconnected from the grid…

people who have whole home generators know about automatic disconnect relays (or manual ones) but most of those systems don’t have any “smarts” to talk to a battery system or solar panels and direct power from multiple power sources (generator, car battery, solar panels, home batteries) to home demand (powerwalls for example let solar panels run during the day and split power from the panels to charge the batteries and power the home - you’d want some similar smarts for the car battery management)

also on a small note - if hte car is providing power - it would back feed through the PMCC (or similar devices) and could only provide as much power as the breaker on the “charger” - if you have a 50 amp breaker on your PMCC - the vehicle could only provide 50 amps of power to the home…

so while the whole system is technically feasible - and forseeable - it still requires quite a bit of planning and software and communications support from all the elements of the system: the master gateway, the grid disconnect relay, the vehicle’s on board software, the EV charger, the solar inverters and home power managemenet computer that co-ordinates all this stuff...and your home’s electrical system has to be designed to have multiple power sources (solar, battery, vehicle power as a source, power grid) - and all these sources have to be switchable so that they can be brought online/offline under software/hardware control - they also have to provide data channels so the central power management computer knows your Taycan is at 5% battery and isn’t really a reliable source of power anymore…

for those interested I’ve had powerwalls for 2 years and to day from Feb. 14th, 2018 they have bridged over 30 hours of grid outage at my home in the Santa Cruz area - the system works great and I love it - and my neighbors are jealous (3 have installed their own systems) - so I have some insight as to what is possible here and how well it can work - the main problem is it’s basically a redesign of your entire home’s electrical system - and a few new devices that need to installed, supported and maintained to allow all this seamless switching from multiple power sources and do it safely such that your home does not back feed power to the grid when it shouldn’t…

Porsche’s existing vehicle software doesn’t support this
Porsche’s existing vehcile charger doesn’t support this
There is no powermanagement system that can talk to the vehicle or charger
and there is no standard whole home grid disconnect relay that can talk to these systems…

I know it can work, I’d love it to work, but it’s not quite ready for prime time with out the full support of the vehicle manufacturers…
Your information was so helpful and appreciated. I find this very interesting.
Thanks
 

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