The results under objective function of annual basic cost

The optimal configuration of the ICE and the BESS with increasing PV penetration and their costs under F1 (ABC only) are presented in Fig.5-10.

a)

b)

Fig.5-10 The simulation results of F1: a) annual basic cost changes with increase of PV penetration; b) optimal configuration changes of the ICE and the BESS with increasing PV

penetration.

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(Note: The U.S. dollar exchange rate against RMB is 1:7)

With the increase of the PV penetration, the annual basic cost is decreased initially but then raised, illustrated in Fig.5-10a). Obviously, when PV penetration is 30%, the ABC is the least. Fig.5-10b) shows the optimal configuration of the ICE and the BESS under different PV penetration scenarios.

Under the low share of PV penetration scenarios (0 to 20%), the optimal installed capacity of ICE gradually decreases with the rising of PV output, and then it sharply drops to 0 at PV penetration of 20%. At the same time, the optimal capacity of BESS spurts suddenly, but then diminishes with the growth of PV penetration.

From the proportion of various costs in ABC under the different PV penetration scenarios as described in Fig.5-11, we can see that at lower PV penetration, the energy consumption cost dominates overall cost, and the proportion of annualized investment cost gradually increases with the rising of the PV penetration. When PV penetration is high, the increase of the DES investment cannot bring ideal energy-saving benefits, which cause the waste due to excessive installed capacity of equipment.

Fig.5-11 Cost proportion changes with the increase of the PV penetration under the optimal configuration results of F1.

The optimization results of the configuration are depended on the economic performance of the ICE and BESS. Fig.5-12 shows the unit capacity profit change of the ICE and BESS with the increase of the PV penetration. The economic performance of the PV is better than that of the ICE.

When the PV penetration increases, the operating hours of the ICE decrease and the unit capacity profit of the ICE becomes worse. When the PV penetration reaches 20%, the ICE takes no economic advantage. Therefore, the optimal installed capacity of the ICE decreases with the increase of the PV penetration and finally becomes 0. As the installed capacity of the ICE gradually decreases, the BESS needs to replace it as the main energy supply system at peak time. At the same time, overproduction of the PV system had occurred shown as Fig.5-13. Therefore, the economic benefit of BESS improves due to recovering surplus PV production. As a result, when the PV penetration is 20%, the installed capacity of the BESS sharply increases.

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Fig.5-12 Unit capacity profit of PV, ICE and BESS under the optimal configuration results of F1.

Fig.5-13 BESS recovered surplus PV production and PV waste under the optimal configuration results of F1.

However, when the penetration of PV continues to raise, the increase of surplus PV production leads to the decline of PV benefits. Although the BESS can improve its own profit by storing the surplus PV production, the amount of the increased profit cannot make up for the loss of PV benefit.

Moreover, due to the increase of PV penetration, the average cost of electricity purchased from grid decreases (as presented in Fig.5-14), which reduces the profit space of BESS, resulting in the decrease of installed capacity of BESS.

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Fig.5-14 The average cost of electricity with increase of PV penetration.

Since the peak load cost and CO2 emission cost are not included in the objective function F1, the optimal configuration results of the ICE and the BESS are only determined by their own operation benefits. The peak shaving rate and CO2 emission reduction rate of different PV penetration scenarios are displayed in Fig.5-15.

Fig.5-15 Peak shaving rate and CO2 emission reduction rate of different PV penetration scenarios under the optimal configuration results of F1.

The introduction of the DES can realize peak shaving and CO2 emission reduction. When the PV penetration is less than 20%, the peak load is greatly reduced due to the power generation of ICE, which is above 40%. When PV penetration is more than 20%, ICE is no longer installed, and peak shaving is only carried out by PV and BESS in the daytime. However, the power load increases at night because of the ‘peak discharge and low valley charging’ operation mode of BESS, which led to a rapidly falling in peak shaving rate at the 20% PV penetration. Then, with the continuous

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increase of PV penetration, the output of PV power increased in peak time. There is more overproduction of the PV system, which can be charged to BESS instead of importing power from the grid at night. Therefore, the peak shaving rate increased. The peak shaving and CO2 emission is 19% and 31% respectively under the optimal combination of the DES which PV penetration is 30%.