Methodology for Maximising the Use of Renewables with Variable Availability

A problem in exploiting renewable energy sources, as wind and solar radiation, is their fluctuating availability. To deal with it, the Heat Integration methodology for batch processes based on Time Slices (TS) was extended. Two approaches to identify the size and number of TS for variable renewable supply are investigated for solar energy. The first specifies a threshold load within which the fluctuation can be neglected. The optimal threshold value is selected from the trade-off between the overall inaccuracy and number of TSs. The second approach is to partition the measured/forecasted heat load curve using a large number of candidate time boundaries and approximate it by a piecewise-constant profile with high precision. The profile is supplied to a MILP formulation to screen the candidate time boundaries using binary variables of acceptance/rejection. The TS definitions are completed by approximating heat loads. The solutions are compared using several criteria including inaccuracies and numbers of TSs. The number of TSs and their sizes are ready to be used in Total Site analysis.