A preliminary design and feasibility study has been conducted for a 200 kWe solar thermal power plant for operation in Ontario. The objective of this study is to assess the feasibility of small-scale commercial solar thermal power production in areas of relatively low insolation. The design has been developed for a convention centre site in Toronto, Ontario. The plant utilizes a portion of the large flat roof area of the convention centre to accommodate the collector array. Each power plant module provides a constant electrical output of 200 kWe throughout the year. The system is capable of maintaining the constant output during periods of low insolation, including night-time hours and cloudy periods, through a combination of thermal storage and a supplemental natural gas heat source. The powerplant utilized the organic Ranking cycle (ORC) to allow for relatively low source temperatures from the solar collector array. A computer simulation model was developed to determine the performance of the system year-round using the utilizability-solar fraction method. The ORC powerplant uses R245fa as the working fluid and operates at an overall efficiency of 11.1%. The collector is a non-concentrating evacuated tube type and operates at a temperature of 90°C with an average annual efficiency of 23.9%. The system is capable of achieving annual solar fractions of 0.686 to 0.874 with collector array areas ranging from 30 000 to 40 000 m2 and storage tank sizes ranging from 3.8 to 10 × 106L respectively. The lowest possible cost of producing electricity from the system is $0.393 CAD/kWh. The results of the study suggest that small-scale solar thermal plants are physically viable for year round operation in Ontario. The proposed system may be economically feasible given Ontario’s fixed purchase price of $0.42 CAD/kWh, but the cost of producing electricity from the system is highly dependent on the price of the solar collector.
Thermodynamic Analysis and Sizing of a Small Scale Solar Thermal Power System Based on Organic Rankine Cycle
