looking to get a new EV with 100kwh battery, which has a 6.5kw output from the vehicle. I could use this 6.5kw to run the house at night but would need a V2H bidirectional charger which are currently expensive and not yet approved for Australia.
Question i have is it possible to use the Dc directly from the EV ( 400v or 800V DC) and plug this into existing solar inverter which is capable or up to 1000vDC. This way i plug the DC into spare MPPT port at night and the DC gets invertered to AC to run the house like normal in the day when the suns out?
Maybe you have looked into it, and it doesnt make sense, but it seems it would be more sensible to install a transfer/isolayion switch and plug so the AC outlet of car could plug into switchboard. A fairly common thing for plugging a generator into home in places where outages are not infrequent.
There may well be ways yo make the switching wirelessly through wifi or bluetooth.
6.5Kw! That’s a game changer.
Well no, connecting an EV’s traction battery to an MPPT input on your solar inverter would be very hazardous!
A bit of theory: a photovoltaic panel is a current source (over most of its I/V characteristic). The MPPT periodically adjusts the impedance of the inverter’s input in an attempt to maximise the power, and this varies the voltage of the connection between the PV array and your inverter. One of the (many!) considerations when connecting a PV array to an inverter is to avoid an overcurrent situation – when the PV array is offering “too much amperage” for the inverter to handle.
The spec sheet on your inverter might say it’s designed to handle up to 20 amps. That’d be 10kW at 500V, or just 8kW at 400V.
The traction battery on your BEV is designed to supply tens or even hundreds of kW – depending how grunty it is. A Tesla Model 3 has a motor rated for 210kW – that’s somewhat more than 500 amps at 400V. That’s way way more than any household’s PV inverter can handle. What happen if you connected such a low-impedance 400V supply to one of its MPPT inputs? Might blow a fuse. A wire might melt. The MPPT socket might catch on fire. OMG. Let’s not find out!
However it’s not all bad news… it’d not be rocket-science to design a combo PV inverter/EVSE, where the EVSE (“EV supply equipment”) can accept power either from the PV array or from the household AC supply, and where the PV inverter can accept V2G power from the EV. I’d expect such devices to appear pretty quickly on the market after the power electronics (and design-engineering, and regulatory approvals) are well-sorted for V2G. For the time being, the closest we get are spendy V2H devices (without wide applicability, due to the complexities of grid regulation – for both technical and legal reasons); and DC-coupled EVSEs such as the 30kW unit from Ampernext (Innovative 30kw DC-DC EV Charger - DC Input - Ampernext). A firm in the USA is making noises about a 12.5kW unit (North American Clean Energy - DC-coupled EV charging solution ).
I’m holding out for a much smaller (3.6kW) DC fastcharger – which eventually will become quite affordable when AC-powered. Despite the inefficiencies of the DC-AC-DC conversion in the PV inverter and the DC fastcharger, it’ll be much more efficient than my current AC trickle-charging setup for my e-NV200 on my home’s wee 1.8kWp solar array… but it’s not yet available. I can hope!
Hi, yes i already have a generator input with a changeover switch for blackouts etc, but the EV only has a 6.5kw external 240v output, which would be fine for the majority of the house, but more would be better.
Use the High voltage from the EV battery and using thru my existing Fronius 22kw inverter seems like a easier solution. this way if the house is drawing more then 22kw it will use mains ( just like when the sun is out ).
Hi and thanks
I checked the links you provided but they dont seem to be bidirectional chargers.
Maybe ill just use the standard 6.5kw 240v outlet and use that with a transfer switch on the house, but then i would need another cable running from the car.
Not sure how you came.to think i was suggesting connecting the V2L to the inverter via the MPPT terminals, because there is nothing that remotely implies that.
My understanding is that these type of connections allow a generator to stand in for the grid, not replace the PV modules/inverter, AC supply to home loads and battery charging.
If the battery is forced charged from the grid, except the changeover switch has switched over to a generator that is providing enough energy, it will charge the battery just as the grid would.
Are you suggesting that somewhere between the this and the battery there is some hardware that blocks it because it recognises its not the grid at all but an ICE generator or even V2L energy from an ev?
Indeed, your answer to the OP’s question didn’t reference their idea of connecting the HV from a BEV to a spare MPPT terminal on their PV inverter. We both agree that’s a non-starting idea!
However… I am suggesting that a changeover switch that’s designed for use with a backup genset might not work well if its “backup generator” input is connected to an AC supply from a BEV’s V2L. The challenging part of the design is to “sync up” the two supplies of power, in cases where the grid supply is still active (but perhaps with unstable voltage or phasing) when the V2L supply is powered-up. When the two supplies are 180 degrees out of phase, oh dear. An uninterruptable power supply (UPS) has the circuitry required for this, but not a Powerwall or a V2L. So… unless there’s something with UPS functionality (e.g. a supply that’s rated “V2G” and compliant with grid-supply standards in your country or state) I’d say it’s very important to make sure your household is in full blackout (disconnected from the grid) before throwing the switch that connects the backup supply to the house.