Con Edison determines if your building is on a spot or isolated network
A spot, or isolated, network is a utility installation designed with multiple high-voltage feeders and transformers tied to a common bus to ensure reliable electric service for large electric load users. The network protectors on these transformers are designed with an automatic safety feature where the network protector will open when energy feeds back from the low voltage bus toward the high-voltage feeder, which is indicative of a fault on the high-voltage cable. If a PV system were installed on a spot or isolated network and solar production were to exceed building load at any given time, the network protectors would sense the export of PV power as conditions analogous to those during a high-voltage feeder fault and would open automatically, causing the electricity service to that building to go out.
In the past, Con Edison would require the installation of a reverse power relay (32R device) to trip solar inverters offline whenever incoming power dropped below a certain minimum amount in order to prevent any possibility of back-feed of power to the network protectors. Over the last few years, Con Edison has been able to offer a technical solution to allow export (and therefore net metering) of solar generation at these locations. This smart grid solution includes lightening the sensitivity of the network protectors to prevent them from opening under normal PV export conditions, installing SCADA monitoring and communications equipment, and anti-islanding relays in some cases. This smart grid technology solution would be an alternative to installing a 32R relay device and would allow systems installed on a spot or isolated grid to net meter. While the relative cost of $50,000 - $100,000 for the smart grid solution is higher than a reverse power relay (typically under $10,000), the economic benefits of net metering are often large enough for developers to choose this option.
In some cases where the building is served by street ties (typical network service) in addition to dedicated transformers, a lower cost option may be available if the street ties are able to handle the export from the PV system. If possible, this will be discussed with the contractor during the engineering review. Back to current process