Can a UPS feed power into the mains power supply?

If an uninterruptible power supply has a bi-directional rectifier then it may offer the ability to feed power into the mains power supply as part of the National Grid’s Demand Side Response (DSR) program. The site receives a fee for having energy available upon demand and when used. Larger datacentre uninterruptible power supply installations can also support the electricity supply grid frequency by disconnecting and running on battery power. Again this is on demand and can generate revenue for the datacentre operator.