What procedure is applicable for the construction of a prototype of an electric propulsion aircraft?

You must apply for an experimental airworthiness certificate (please note that you will not subsequently be able to market the prototype or other identical units without a type-certificate): 

https://sede.seguridadaerea.gob.es/sede-aesa/catalogo-de-procedimientos/certificado-de-aeronavegabilidad-experimental-no-easa