Inverter replacement.

 The grid tie solar inverter’s working principle is just like a conventional solar inverter but with a significant difference: a grid tie inverter converts the DC output of your solar panels directly into AC. Then it synchronizes this AC with the utility grid frequency.  

• During peak sunlight hours, the electricity produced by your solar panels may exceed household demand. In this case, the extra power will go to the grid, and you’ll receive a credit from your utility company.
•  At night or during cloudy weather, when your solar panels are not producing enough power to meet your household demand, you’ll pull electricity from the grid as you normally would.
•  An on-grid solar inverter must be able to shut down automatically when the utility grid goes down, as feeding electricity into a downed grid can be dangerous.