Demand Side Units

A Demand Side Unit (DSU) is a demand site that can be instructed by EirGrid to reduce electricity demand. Instructions to reduce electricity demand are called dispatch instructions. Where a DSU consists of more than one individual demand site it is called an aggregated DSU. A DSU uses a combination of on-site generation and/or plant shutdown to deliver a demand reduction in response to an instruction from EirGrid.

DSUs that are available for demand reduction are eligible for a capacity payment in the Single Electricity Market (SEM). More information on the capacity payment mechanism in the SEM is available from www.sem-o.com.

Demand sites, with or without a Maximum Export Capacity (MEC), may be eligible to register as part of a DSU. A DSU must have a demand reduction capacity of at least 4MW. The maximum demand reduction capacity of an individual demand site in an aggregated DSU is 10MW. Demand sites with greater than 10MW demand reduction capacity may register as a stand-alone DSU.

The company registering the DSU, called the DSU aggregator, must be a licensed supplier and registered as a supplier in the SEM. It is not required to be the supplier of the individual demand sites. Information on becoming a licensed supplier can be found at http://www.cer.ie/en/electricity-retail-market-licences.aspx.

To become a DSU an application must be made to both EirGrid and the Single Electricity Market Operator (SEMO). The application to EirGrid can be made using the approved application form with all relevant documentation included. Information on the SEMO application process can be found at http://www.sem-o.com/joiningthemarket/Pages/default.aspx.

EirGrid requires real-time communications with the DSU to ensure secure power system operation and to issue dispatch instructions to balance generation and demand. A signal list is provided to the DSU when their application is finalised, so that the DSU can configure their control system to provide these signals. Dispatch instructions are issued by EirGrid via the Electronic Dispatch Instruction Logger (EDIL) that is accessed through a website. The method of communication installed between the individual demand sites and the DSU must be agreed with EirGrid in advance.

A DSU is required by EirGrid to be available 24 hours a day, year-round, unless an outage is agreed with EirGrid or if breakdown forces the unit to become unavailable. When the DSU is required it will be issued dispatch instructions specifying the amount of demand reduction required. Dispatch instructions are issued by EirGrid (via EDIL) at an aggregate level and the DSU aggregator then coordinates the reduction from the individual demand sites.

A DSU is required to demonstrate Grid Code compliance before they become commercially operational. This is achieved through a number of Grid Code tests that will be witnessed by EirGrid. EirGrid may also require testing as part of on-going Grid Code performance monitoring when the unit is commercially operational.