Forget electric showers here. Generally they are rated at 10Kw and a typical house power supply here is 5.75Kw.  All houses in the UK get a 12Kw supply as standard but here you contract what you want, at a price!

Where your house is I very much doubt you would get anything over 5.75Kw

Also, as you are doing a serious renovation, the architect is almost certainly going to require a solar hot water installation to be installed before the house obtains its 'cedula de habitabilidad' (this is now part of the building regulations here) and all of these come with a stored water system.

Nigel