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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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  • first I live across the pond so I will ask the first question: what is, and how is the 'grid' paying you??

    this is rather important as my grid pays me per Kw at the same price they charge me. So it work out nice ie. if I draw 3 Kw and generate 5 Kw they pay for 3 Kw only. When i move into my new digs I bringing in 3 phase for the shop, etc. I take 2 legs for 220/110 and that where the switch  will be since they are looking at total load on the 3 phase any I generate on the back end gets credit. 

    I don't have times, or high/load times so I don't worry about it but you might have to. do you have different rates for different time of the day / night?

    . 

  • in reply to phoenixcomm

    Yes, £0.07 23:30 to 05:30 and £0.27 05:30 to 23:30. I can export at £0.15. The grid is just what we call the national electricity infrastructure here. The battery I have has the capacity to support the house between 05:30 to 23:30 with charge still remaining. So I basically pay £0.07 for all my electric. Any excess I can sell back at £0.08 profit (I expect to be a millionaire any day now Grinning). However, once late autumn and winter roll around my ASHP will consume a lot more and I expect to pull on the grid at the higher price. 

  • in reply to Andrew J

    How long does your battery last with that kind of activity, and how much does it cost to replace it when it wears out? I wouldn't calculate "profit" without knowing depreciation expenses...

  • in reply to bradfordmiller

    It's guaranteed for 15 years to be 80% usable.  And I'm not sure what you mean by "that type of activity" - it's a battery that is meant to be charged up and then discharged over time.  None of this is particularly stressful or beyond what it has been designed for.  The whole system is expected to have a payback period of 7 - 8 years, although obviously that is predicated on electricity prices staying the same or going up.  There's a reasonable probability they will come down over that sort of time period.  

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  • in reply to bradfordmiller

    It's guaranteed for 15 years to be 80% usable.  And I'm not sure what you mean by "that type of activity" - it's a battery that is meant to be charged up and then discharged over time.  None of this is particularly stressful or beyond what it has been designed for.  The whole system is expected to have a payback period of 7 - 8 years, although obviously that is predicated on electricity prices staying the same or going up.  There's a reasonable probability they will come down over that sort of time period.  

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