not connected to the main electricity grid (= system of connected wires and power stations)

Solar power is useful in off-the-grid areas. 太阳能在主电网不接通的地区很有用。

not connected to any of the main utilities (= electricity, water, etc.) and having your own power and water supply

We're interested in independent self-sufficient living, off-the-grid. 我们对自给自足、水电自理的独立生活感兴趣。