user: Question: What is the lowest numbered hydroelectric power when the renewable electricity demand is 21.5%?
Columns: ['Autonomous Community', 'Hydroelectric power', 'Wind power', 'Solar power', 'Biomass power', 'Solid waste power', 'Total Renewable Generation', 'Total Electricity Demand', '% Renewable of Total Electricity Demand']
Types: ['text', 'real', 'real', 'real', 'real', 'real', 'real', 'real', 'text']
Sample row: ['Castile and León', 6960.0, 3840.0, 14.0, 274.0, 87.0, 11175.0, 15793.0, '70.8%']
SQL:

assistant: SELECT MIN("Hydroelectric power") FROM "Table" WHERE "% Renewable of Total Electricity Demand" = '21.5%';