Thomas Massie runs off-grid home using wrecked Tesla Model S battery
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Here's the first one: https://youtube.com/watch?v=qpPYkqpe-Ms
I don't know if he mentioned how much it cost to get the conversion kit stuff, but looking at the site (evtv.me) makes me think it was several thousand dollars. It looks like 'standard electrical stuff' controlled by an arduino.
He has a propane-fueled generator for when the battery system is offline. He shows it and you can hear it running when he swaps out the old lead-acid battery system.
He's hoping to get 20 years out of the batteries. At several points you see the power draw on the system. At the end of the second video he did some verbal napkin math based on the number of cycles he'd already gone through. This was happening during the winter, his assertion being that winter would be the toughest time of the year.
You should watch the video series.
Sorry, but out of a technical perspective that makes absolutely no sense.