Why can’t I use my solar panels during an outage???

Does solar work in a power outage?
There are two reasons that ordinary grid-tied solar will not work during a grid failure. The first is a technical reason and the second is a safety and regulatory issue.

First and foremost is the technical reason. The electronics that control a solar electric system constantly adjust voltage and current in order to keep the panels operating at their most efficient and powerful operating point through a range of varying sunlight conditions. To do this, the system needs to be able to produce quantities of power that are not dependent on how much your house is actually using at the time. In a grid-connected system, that excess power is put back onto the grid for others to use, and Naturgy credits you on your bill for that power.

Solar power output varies directly with sunlight levels. So, even if you disregard the need for efficiency, connecting this variable resource directly to your home’s electrical system would cause your lights to blink, damage your refrigerator, and wreak havoc on your computers and television.

The second reason that solar shuts down during a blackout is safety.

During a power outage, the power utility sends out repair crews to find and fix the points of failure. The linemen can be jeopardized if there is a local power generator (like your solar system) leaking power onto the grid lines. Therefore, utility rules mandate that in the event of a power outage, solar arrays must automatically shut down. Solar systems have detectors that sense whether power is coming across the grid, and whenever grid power is down, they automatically shut down too, to protect utility workers.

(thanks to: http://www.thirdsunsolar.com for this great explanation)