High Sustainable Limit (HSL) is a name for a common telemetry signal sent to grid operators like CAISO in California and ERCOT in Texas. HSL is defined as a number, usually specified in megawatts (MW), that represents the continuous power delivery capability of a power generating facility such as a BESS (battery energy storage system) or a traditional power plant.
High Sustainable Limit (HSL) is a name for a common telemetry signal sent to grid operators like CAISO in California and ERCOT in Texas. HSL is defined as a number, usually specified in megawatts (MW), that represents the continuous power delivery capability of a power generating facility such as a BESS (battery energy storage system) or a traditional power plant.
In both ERCOT and CAISO, BESS projects telemeter an HSL signal to the grid operator on a regular interval, and the grid operator combines it with other telemetry signals to determine how to dispatch the BESS assets in order to settle supply and demand within the market. HSL is also a critical signal used by energy traders to inform market offers and bids, as it represents the maximum power the BESS asset under management can deliver continuously.
The precise definition for how HSL is computed varies by grid operator, but will take into account factors that impact both the power level (the number of megawatts) as well as the sustainable time period (how long the power level can be continuously delivered). For a BESS asset, these factors will typically include the number of inverters online, the power delivery capability of each AC or DC block within the asset, as well as the remaining energy available for discharge in each block.
For further reading, see this CAISO White Paper on HSL.
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