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.there is a fundamental problem with Vehicle to home “power” - at least in north america…
Your information was so helpful and appreciated. I find this very interesting.there is a fundamental problem with Vehicle to home “power” - at least in north america…
the “key” scenario is as follows:
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…
- you want the car to provide power to your home when the grid is unavailable
- 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
- disconnect reasons are multiple
- safety - you don’t want power from your vehicle to electrocute the power grid workers attempting to restore power
- 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)
- once power is restored from the grid you want to automatically re-connect the home to the grid.
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…