What is the total capacity (MW) of the windfarm located in the state/province of Gansu?
CREATE TABLE "other_notable_onshore_wind_farms" (
  "wind_farm" text,
  "capacity_mw" real,
  "country" text,
  "state_province" text,
  "notes" text
);
SELECT SUM("capacity_mw") FROM "other_notable_onshore_wind_farms" WHERE "state_province"='gansu';