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What is likely to happen, if anything, if I try and export to the grid and import from the grid simultaneously?

Andrew J

I have this scenario:  I want to export from a house battery to the grid during the period 23:30 to 01:00 at 3.6kW (until battery is empty.)  At the same time, I have my car plugged in charging at 7kW.  Would that have the net effect of pulling 3.4kW from the grid?  Is anything likely to fail?

As a basic summary, I can charge my house battery up at 7p from 23:30 to 05:30 and discharge it to the house during the rest of the day, thus I pay only 7p for electricity used.  I don't fully discharge the battery during this period so I can sell the remaining charge back to the grid at 15p before fully charging up again ready for the day.  However, I also need to charge my car up which I also do 23:30 to 05:30 - Note because of the tariff I am on I have NO control over when the charging actually occurs so I cannot configure it to avoid the time period where the house battery is discharging.  Re-configuring the battery to not discharge when I plug the car in is a laborious process which I want to avoid.  I only actually charge the car once or twice a week.

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  • I worked for a company that designed and manufactured a wide range of power inverter (up to 1 MW).  We would routinely do exactly what you are taking about.  We would power our inverter from the grid and generate power, pushing it back onto the grid.  We would only be charged for the loses in the system (based on efficiency and any other losses). Again, as others have mentioned, you need make sure that no limits are exceeded (wire gauges and fuses, etc.).

  • in reply to genebren

    It’s running now and all seems fine. I forgot to take the 8kW inverter into account so judging from what the control app is telling me, I’m pushing the full 8kW with the car taking 7kW and the grid 1kW. The export limit I have is 3.6KW so the inverter would normally limit to that when the load is low (nights I’m not charging for example)

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  • in reply to genebren

    It’s running now and all seems fine. I forgot to take the 8kW inverter into account so judging from what the control app is telling me, I’m pushing the full 8kW with the car taking 7kW and the grid 1kW. The export limit I have is 3.6KW so the inverter would normally limit to that when the load is low (nights I’m not charging for example)

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