*3.3. Operation Schemes*

The addition of storage batteries improves the utilization of electricity. However, the configuration of storage batteries alone will increase the investment cost. Additionally, the smaller configuration size has less effect on electricity regulation. Therefore, this study proposes a CCHP system based on ESS service. The earnings of ESS come from two sources. First, the electricity used and stored in ESS is calculated for each CCHP system: charging in the form of electricity sales and purchases. Second, ESS charges a service fee for the electricity used and stored by the CCHP system. In this study, two other operation schemes are chosen for comparison. The three operation schemes are described as follows.

#### Scheme 1: ESS service model

Each CCHP system operates independently without configuring energy storage batteries, and the ESS services the CCHP system. Excess power is sold to ESS when PV and MT generation is sufficient. Conversely, electricity is first purchased from ESS when there is insufficient electricity. If the ESS does not have enough electricity, the customer purchases the shortage from the grid.

Scheme 2: Users configure energy storage equipment by themselves

Each CCHP system operates independently and is equipped with energy storage batteries. The operation process is similar to scheme 1. However, under this scheme, the cost of energy storage batteries needs to be included in the net investment cost.

Scheme 3: CCHP system is not equipped with energy storage equipment

Each CCHP system operates independently without the configuration of energy storage batteries. When PV and MT generation is sufficient, surplus electricity is wasted. Conversely, electricity is purchased from the grid if there is insufficient generation.

The heating and cooling load demands are met in the same way for the three operating schemes. First, it is determined whether the waste heat recovered by HR meets the system heat demand. If the waste heat is larger than the demand, the excess heat is saved in the TST. If the waste heat is insufficient, TST is given priority for heat release. When TST still cannot meet the demand, GB starts heat production.
