Quiet place to work and study in central Madrid

I am currently staying very close to Sol and Parque Retiro. In my piso I do not have a great place to work or study. I'm looking for somewhere open to the public that I can sit down and concentrate with my books and laptop. I would also like to have access to wifi and if possible the ability to plug in my laptop as my battery doesn't last very long. Libraries in the US are good for this but I don't believe the library sytem here is equal in this regards. If anybody has any thoughts or suggestion please let me know. Thanks!