There are no comparison websites yet available in Spain. The main reason is that prices have not been totally deregulated for energy potencia of <10kwh. There is increasing compeition for properites (including many small businesses) with potencia >10kwh.
Many of the energy producers (eg Union Fenosa, Iberdrola) believe that residential prices might be liberalised at some point in the summer. However, nothing has been confirmed. Therefore, there is no business model for comparison sites similar to what you might find in UK and elsewhere, where they receive revenue from online advertising or commissions directly from the providers themselves.
regards
james