DER VET User Guide/Technologies/Compressed Air Energy Storage

Compressed air energy storage (CAES) is a type of storage that involves compressing air using an electricity-powered compressor into an underground cavern or other storage area. This compressed air is then expanded through a turbine to generate electricity. Usually, fuel is burned before the expansion process to increase the quantity of electricity produced and improve the overall efficiency. Similarly, heat losses from compression are sometimes re-captured and supplied to the air before expansion. The compressors and expanders may be sized independently from each other and from the cavern, decoupling all three size parameters. Additionally, some CAES designs allow for the compressors to run concurrently with the expanders, effectively turning the CAES into a combustion turbine (if compressed air production equals consumption).

CAES is available in the command line version of DER-VET only.

Note that when doing size optimization, the CAES is constrained to have an equal charge and discharge power capacity.

Inputs

HHV Heat Rate

Tag	Key	Description
CAES	heat_rate_high	Higher heating value (HHV) heat rate for the CAES system in BTU/kWh, which expresses how much fuel is required to generate each kWh of electricity. This only considers the energy content of the fuel, not any electricity that was used to compress the air. This, along with the CAES energy ratio determine the overall efficiency of the system.

Maximum Charging Power

Tag	Key	Description
CAES	ch_max_rated	The electric power consumption of the compressors (and other equipment used to "charge" the CAES) when charging at full power.

Maximum Discharging Power

Tag	Key	Description
CAES	dis_max_rated	The electric power produced by the expanders when discharging at full power.

Minimum Charging Power

Tag	Key	Description
CAES	ch_min_rated	The electric power consumed by a single compressor (and other equipment used to "charge" the CAES) when operating at its minimum level.

Minimum Discharging Power

Tag	Key	Description
CAES	dis_min_rated	The electric power produced by a single expander when operating at its minimum level.

Energy Capacity

Tag	Key	Description
CAES	ene_max_rated	The kWh of electricity produced when discharging the CAES from its maximum pressure to its minimum pressure. This can be more than the kWh used to fully charge the system due to the fuel input.

Upper Limit on State of Charge

Tag	Key	Description
CAES	ulsoc	Not as meaningful for CAES, this input allows the user to restrict the usable energy capacity of the CAES by setting an upper limit on SOC.

Lower Limit on State of Charge

Tag	Key	Description
CAES	llsoc	Not as meaningful for CAES, this input allows the user to restrict the usable energy capacity of the CAES by setting a lower limit on SOC.

Energy Ratio

Tag	Key	Description
CAES	energy_ratio	The energy ratio is the ratio of kWh of electricity generated by the expanders to kWh of electricity consumed by the compressors. This includes the addition of fuel, so the energy ratio is usually above 1.

Self Discharge Rate

Tag	Key	Description
CAES	sdr	Much like for the generic energy storage technology, this represents the decay in stored energy (%/hr) when the system is not operating.

Target SOC

Tag	Key	Description
CAES	soc_target	Much like for the generic energy storage technology, this represents the SOC the CAES system will return to at the beginning and end of each optimization window.

Startup Costs

Tag	Key	Description
CAES	startup	Much like for the generic energy storage technology, this binary input represents the decision about whether or not to apply startup costs, which will apply a penalty every time the system starts its compressors or expanders.

Charging Startup Cost

Tag	Key	Description
CAES	p_start_ch	Much like for the generic energy storage technology, this input represents the financial cost of starting the compressors, applied only if the startup input is 1.

Discharging Startup Cost

Tag	Key	Description
CAES	p_start_dis	Much like for the generic energy storage technology, this input represents the financial cost of starting the expanders, applied only if the startup input is 1.

Maximum Duration

Tag	Key	Description
CAES	duration_max	Much like for the generic energy storage technology, this input represents the maximum ratio of discharge power to energy capacity the optimization will select when doing size optimization.

Fuel Type

Tag	Key	Description
CAES	fuel_type	The type of fuel used to power the CAES. Either 'liquid', 'gas', or 'other'.