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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 am kind of joining the party late and because I don't have an EV, the post and responses initially came across as a very unfamiliar George Jetson kind of world.  For instance I had not even heard of a house battery.  I am wondering one thing though... if someone didn't have an EV... is the setup scalable.... can someone have multiple house batteries which they charge up during the cheap time and sell back at a higher rate later in the day?

  • in reply to dang74

    It's not necessary to have an EV.  This is just part of a solar system that can be used to provide power to the house, with excess being sold off to the grid.  A battery helps support that by providing power (obtained at a cheaper, off-peak rate) during the night and winter months.  A battery can also provide power in the even of grid failure if provisioned properly.  My setup consists of 16kW of battery with approx 7.5kW of solar generation.  Having an EV gives me access to a tariff offering electricity at £0.07 otherwise I'd have to find an alternate that suited having this system plus an ASHP.   That gives me the ability to have all my electricity at £0.07 and sell excess back at £0.15.  In theory then my utility bill should drop to under 25% of what it would be without it.

    For an example of a house battery, check out the Tesla Powerwall. 

  • in reply to Andrew J

    Would you care sharing a (rough) estimate of what the battery cost? I already have the solar panels, micro inverters and monitoring system, but as I'm looking at quotes for a battery, I'm wondering if the given price is in the right ballpark.

  • in reply to obones

    Unfortunately the battery price wasn't broken out in my invoice, however looking back at emails, an 8kW pack cost £2350 and 5kW £1950.  This is ex-vat and doesn't include installation or other ancillary costs; also it was the price in January!

  • in reply to Andrew J

    Thanks for elaborating further.  It's very interesting but something I don't have experience with.

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