A different perspective is that it isn't a good idea to have 'loopholes.' If you can make money from solar tax free but not from other sources then this will give people an incentive to invest in solar and not in other things.
I believe the hybrid system that both Rolfe and I have is 48V. The battery seems to go up to 54V.I agree, but there could be a caveat in that as Rolfe's installer said it is not possible it could be that Rolfe's system uses HV batteries, rather than standard 15S or 16S "nominal 48V" low voltage system. As far as I can see, Givenergy have both LV and HV systems
Thanks for clarifying.
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IMHO, no. For reasons mentioned in my posting below...
Provided the PSU is voltage adjustable to not exceed battery or vehicles current limit, the existence of the PSU will be invisible to the inverter, thanks to Kirchoffs Current Law
No voltage control and very crude output filtering, generally resulting in AC ripple superimposed over the DC square wave, causes all sorts of confusion to sophisticated electronics, generally resulting in a shut down because it just doesn't like the dirty signals it is seeing.
'Some bloke in Lincolnshire' told you it can be done with any batteries. The nominal 48v DC coming out of your batteries to the inverter is supplemented by another source of 48vDC from the MG4. The inverter doesn't know or care where the energy comes from, the batteries will simply see a reduced demand from the inverter.
The easy way Terry is to increase the voltage output of the power supply until you reach the desired load coming from the car eg 2kW or 3kW etc, do this when the house batteries are at circa 75%. Once set, the car can be connected and as the house batteries discharge the load is transferred to the car.
1) It will definitely have voltage control
The reason for requiring the adjustable voltage control is to stop the 48vdc charger, that the BMS has no control over, pushing a cell into the cell damage voltage zone. This will cause the BMS to shut down the system, the very thing the system owner is trying to avoid.
Hence why I suggested that the system is started up and with house battery down at 75% the voltage from the power supply is increased until the required output current is achieved eg 40 amps for 2kW. If the load on the inverter is less than 2kW or Solar starts to generate, the battery voltage would start to rise and the current from the car would reduce. In my system, at 80% the current from the power supply drops to zero, at 75% I'm pushing 3 kW into the Inverter / Battery combination. LifeP04 as you know has a very flat charge / discharge curve so it happens very quickly.
Some allowance has to be made under the described no load conditions but thats not the real world. With the slightest load applied they work absolutely fine. My system runs on some DELL ex server power supplies and is absolutely fine, no reliability problems at all. A bigger concern is the quality of power from the MG, that does leave a little to be desired.
Not in my experience. Generators with the exception of Honda Inverter one have loads of distortion on their outputs. Using a generator to feed the power supply above would IMHO make it very suitable for charging the batteries. THD is pretty much irrelevant when it's being fed into a switched mode power supply, it's only converted to DC at the input.
Makes you wonder why all modern tech uses switch mode power supplies if theyre so bad? how does anything manage to work? Even the car charger is switch mode.
Well at least it gets some discussion going doesn't it? To be absolutely honest, the only time I have used our MG5 and the DC charging of house batteries has been during Christmas Day and Boxing Day. It has worked flawlessly without the slightest concern anywhere. The idea is really simple and carries very little risk. That said it's hardly worth bothering about for the amount it saves and financially probably not worth it. I'm in the fortunate position that I have access to the power supplies from my I.T. business, they cost me nothing and I can do the installation myself being a retired electrician from a previous life in my late teens / early twenties.
And that is absolutely fine but it's not a reason NOT to have the discussion?
Absolutely, the real consideration is that the DC voltage that come from the battery, the inverter wont care where it comes from, DC is DC no matter what as long as the voltage is ok then it will be fine.
It is not the inverter seeing the charger voltage or current, it's the fact you have tapped into a line that will move current both ways. If the inverter does use all the charger output, it will flow back to the battery.
Correct but that isnt a problem, in my setup as the batteries approach 80% charge the current is almost zero from the power supply,
The power supplies generally will have a voltage trim adjustment, I would adjust the voltage as above so that the house batteries wouldnt reach fully charged.
Not really practical to have the whole house load applied to the V2L of the MG4, well not in my case with heatpumps etc. My suggested operation is simply to add battery capacity to the house inverter from the car. In my case I run at 3 kW from our MG and whilst it's not sufficient to supply the whole load it does provide a healthy 36 kWh over a 12 hour period which nicely keeps us away from peak rate energy costs.
It wouldnt achieve what I wanted to do. I do have auto switching on the grid input to my system to cover mains failure etc. The car connection is an easy way to effectively double my battery capacity for high energy us days (such as Christmas) or extended power outages (about 6 years ago we had a grid fault on Christmas eve that lasted all the way through to boxing day).
Yes, I did say previously that a power supply was what was needed, not the battery charger that you believed would be fine for the job Should we get more home battery capacity?
Not meant as an attack here, but your understanding of LFP battery/cell behaviour is letting you down ...... I'm interested in how you determine the voltage of an LFP pack @ 75% to 80% SOC?
