Renewable energy generation potential of stormwater detention basins

The purpose of this project is to determine if implementing hydropower at a stormwater detention basin outlet in Toowoomba is technically and financially feasible. A detention basin has been designed using DRAINS and currently acceptable techniques and standards by Toowoomba Regional Council. The detention basin under investigation is part of a residential subdivision and has been designed using the Extended Rational Method (ERM) hydrological model. The ERM hydrological model is an acceptable model for use in designing on-site stormwater detention within the Toowoomba Regional Council area. Historical pluviograph rainfall data was acquired and input into DRAINS to create historical storm events. The ILSAX and Initial Loss – Continuing Loss (IL-CL) hydrological models were used to calibrate and produce more realistic hydraulic results for energy generation calculation with respect to rainfall runoff. The ILSAX hydrological was created by Geoffrey O’Loughlan in 1993 and uses the time area method and Horton infiltration procedures to calculate rainfall runoff. The IL-CL hydrological model applies initial losses and continuing losses to a catchment and applies the same time area calculations. The outflow hydrograph for the detention basin was extracted from DRAINS for the ILSAX and IL-CL models and the power energy equation applied at each timestep of the outflow hydrograph for each storm event. The results show that for each storm event that generates flow through the detention basin outlet, energy was theoretically generated when the hydropower generation system was applied. The energy generated was applied to various storage options and was insufficient using the IL-CL model to offset the 48kW consumed daily by the street lights in the subdivision. The low frequency of runoff producing rainfall events resulted in the system being heavily constrained by the available energy storage. The costs associated with energy storage increases disproportionately to the energy stored and costs savings applied. Therefore, it was determined that the lower storage options between 25kW and 100kW provided the most efficient cost savings relative to the energy storage option. Implementing the proposed hydropower system in a residential subdivision in Toowoomba is unlikely to be financially viable at current implementation costs due to the low energy generation relative to the cost of commercially supplied power. As the technology advances, it is anticipated that implementation costs will reduce and therefore the system may eventually become feasible in the future