Use of renewable energy is becoming more economical today in both residential and commercial applications. The use of solar power backed up with a battery energy storage system (BESS) offers power plants more operational flexibility to reduce carbon emissions to meet their corporate sustainability goal.
Aspen Utilities Planner (AUP) is a modeling and optimization software package from AspenTech to optimize business processes involved in utilities system design, planning and operation. With newly developed custom models of SolarPanel and BESS by EMI Solutions, AUP can be extended to evaluate economic feasibility of adopting these new technologies in traditional power plants to tackle the carbon emission challenges.
In a simple hypothetical case study illustrated in Figure 1, Aspen Utilities flowsheet contains a Solar Panel model and a BESS model. The BESS model connects to the solar panel model to receive power in charging. The solar panel and BESS models are connected to a main power header to meet power demand. The rest of the power demand is met by the power import from the grid.
In SolarPanel model, standard information such as open circuit voltage, short circuit current, etc. at standard testing condition from manufactural datasheet is used to estimate parameters in the underlying equivalent circuit model. These parameters can then be used to predict the power output at any given irradiance and ambient temperature.
BESS model can be in either charging, discharging or idle state. It utilizes cell voltage vs. state of charge (SOC) performance maps to estimate battery cell voltage and battery current for a given SOC and battery power.
Once the flowsheet model is developed in Aspen Utilities Planner, a multi-period optimization model is configured via Aspen Utilities Excel Add-in as shown in Figure 2. The optimization results can be summarized and visualized in Figure 3.
The x-axis is the number of periods defined in optimization. In this case study, 24 periods are specified for optimization study in a typical summer day. Each period represents one hour. The grey and yellow line represents the power load and power imported from the grid respectively. The orange line represents the power price. Off-peak power price remains from midnight until 7 am and jumps up dramatically in the next two hours. The power price goes down and remain low until 3 pm and jumps to peak price until 11 pm.
The light blue line represents the power generation curve from the solar panel. The power generation from PV remains zero until 5 am. The power output starts to increase until 12 pm due to the increase of solar irradiance. It then is reduced gradually to zero around 8 pm upon the sunset.
According to battery SOC curve (dark blue line), the battery is charged from 5 to 7 am via PV power. Then it discharges power to reduce grid power import from 7 am to 8 am due to the higher power demand and price hike. After one hour of idle time, battery continuously charged by PV between 9 am and 3 pm by taking advantage of relatively low power demand and price to prepare for the upcoming power usage surge in the evening. Battery SOC reached 73% at 3 pm. After one hour of idle mode, the battery continuously releases power to meet high power demand in the evening along with the power import from the grid until battery SOC reaches prespecified minimum limit of 20%.
With the newly developed SolarPanel and BESS models, a multi-period optimization model in Aspen Utilities Planner is capable of having power plants to plan BESS charging/discharging operations by “seeing” the upcoming power price and power load variations.