UPDATE: new law that regulates the Bono Social has come into force in October 2017. The new Bono Social for Vulnerable Consumers knows three different categories, each with a corresponding discount percentage, ranging from 25 to 50% and available for those in their usual residence, with contracted power up to 10 KW and on VPSC tariff. All those already receiving the Bono Social have until 8.10.2018 to re-apply under the new criteria. Until then they will continue to receive it, but if not renewed before then, or not able to meet the requisites, your contract will automatically revert to the VPSC tariff (voluntary price small consumer), without discount.
Iberdrola Bono Social (in Spanish, as the English version on the website has not been updated with data from the new law.