In the US, unless on Storm Watch, the PWs will not import power from the grid. This is because Tesla believes everyone will be taking the solar tax credit and you can only charge the PWs from a solar source. That decided to do this so we all did not have to keep detailed records of how much energy we got from the grid vs got from solar, implying it was 100%. Note this is theoretically only for 5 years so in the next few years we might see a shift in how this works.By setting the sell rate to zero it encourages the PWs to not export power to the grid for that period. Conversely, if the buy rate is set to the lowest value (e.g. $.01/kwh) does that encourage the PWs to import power from the grid to power the home during that period, rather than using stored PW energy?