"Cool" perhaps but a money losing proposition for sure. Typically, the only sensible reason go off grid is if there is no grid available. It's easy to calculate how much solar you need. The first thing you need to do is calculate how much PV you need on your roof. Assume that it takes up to 18kWh to charge your Spark's battery, then to pvwatts.nrel.gov, to calculate how PV you need on your particular roof. It's pretty accurate.
Here's my system:
https://easyview.auroravision.net/easyview/index.html?entityId=7466210
As I write this, my 9.2kW / 41 solar panel system has generated ~20kWh. It was a cloudy morning, but the sun is shining now.
As for going off-grid, keep in mind that with net metering; your power co will bank the power you export to the grid - which in a sense is like a virtual battery (that you don't have to buy or maintain), allowing you to use that power when the sun goes down and on cloudy/rainy days.