Energy Storage System for Thermal Load Fluctuation Balancing

Cogenerative geothermal power plants can supply thermal energy required by energy-intensive activities, such as greenhouses heating. The required thermal load in these systems usually follows the daily temperature trend, leading to not negligible load fluctuations on the power plant side that need to be managed, in case a constant electric output from the plant is required (e.g. because the energy has been already sold on the dayhead electric energy market). The supplied heat flow rate must be constant to avoid a fluctuating operation of the cogeneration system. This paper investigates the opportunity of using a thermal storage to manage this load fluctuations and keep the system stable. Results show that even an oversized storage tank may not be sufficient to reach the desired set point conditions, especially if the load forecasting is incorrect. For this reason, it is necessary to increase the supplied heat flow rate to reduce energy shortages and use a cooler to dissipate energy surpluses. Results show that it is possible to achieve setpoint conditions by increasing the supplied heat flow rate by 20 % and using a cooler do dissipate thermal energy surplus. This performance worsens when the load forecast is not accurate, though shortening the period with a fixed heat flow rate can be beneficial.