HI< I dont mean to be facetious, applying for the grant is easy getting the money is difficult!!,. It is a long and tortuous road. for an example of what you have to provide please look at the agency website for Murcia, and every other region has there own set of rules, on something as low cost as a water heater it may not even be worthwhile applying given the pain. (If you speak fluent spanish, have connections in the region government, it may be a lot easier).
SOlar water heaters are now becoming very popular in Spain, mainly due to legislation that means virtually every new build or reform has to have some form of renewable energy, and most builders promoters see solar hotwater as a fairly low cost and easily installed answer,
In terms of effectiveness, from about now till about midOct( Dependent on weather) with a correctly sized system your hotwater cost should be very low if anything, as always its about capacity of the system and how much you use. You will need a booster Electric or gas etc for hotwater in the deptsh of winter.
I would beware of the low cost system offered by many companies as they tend to suffer badly from the harsh water and sometimes extremely cold condititons,
A quality system such as a Solahart is much better but again much more expensive, but will give you years of good reliable service.
you can put in a low cost imported system for around 1300?, and a Solahart would be about 2700?, ( but as I said you may have to pay again in about two to three years with a low cost system. due to corrosion of seals and particularly of the storage tank connections,,),, basically you get what you pay for!!
Mike
