Design-stage assumptions for good off-design performance of a binary geothermal power plant

© 2018 University of Minho. All rights reserved. In the literature, several studies exist on the design of a binary geothermal power plant. However, most of them do not (properly) account for its off-design operation. Even for a baseload geothermal power plant, frequent off-design operation occurs due to the changing environment conditions. Therefore, in this work, we propose a two-step optimization methodology which allows optimizing the design of an air-cooled binary geothermal power plant as well as the operating conditions during a typical year. In the first step, the design of the shell-and-tube heat exchangers and the air-cooled condenser are optimized towards maximal Net Present Value (NPV). The NPV is chosen as the optimization objective since it accounts for the size of the components, the economic parameters and the time value of money. However, assumptions have to be made regarding the economic parameters, such as the electricity price, and the environment conditions. In the second step, we optimize the operating conditions (temperatures and flow rates) of the binary power plant during a typical year towards maximal net electrical power output. Here, we take into account the Belgian hourly weather data and electricity prices for 2016. If we calculate the NPV in a post-processing step, accounting for the real hourly electricity prices and weather conditions, the value is different from the value in step 1. The real NPV is the highest for an ORC which was designed for the average electricity price (of 36.57 EUR 2016 /MWh). The electricity prices are not a priory known, but for a design assumption close to the average electricity price (30-60 EUR 2016 /MWh), the NPV is not more than 10% lower than the optimal value. The influence of the environment temperature assumption on the real NPV is small (<1.3%).

ISBN:9789729959646

Publication year:2018