This is an extract from a translation which I did. Basically it is saying that the National Grid is obliged by law to buy a proportion of the energy it supplies from "green" (renewable) sources, and to pay a premium price that is determined by regulations:

Royal Decree 436/2004 establishes a policy of subsidies for electrical production in photovoltaic plants, which are intended to boost the development of this renewable energy source. Under the Decree the following tariffs are laid down:
 Tariff for photovoltaic solar facilities of up to 100 KW (0.4235 €/KWh) which corresponds to 575% of the average or benchmark electrical tariff and which goes up annually with the Consumer Price Index (cost of living index) for energy. Guaranteed for the first 25 years.
 80% of the amount after 25 years and for an indefinite period. The legislation referred to sets out the method of systematizing the legal and financial regulations of the business of producing electrical energy in the form of a special set of regulations, which obliges electrical companies to buy the energy generated by photovoltaic solar facilities.

And this is a text from a U.S. website:

It's no accident that SunPower has set its sights on Spain and other European markets. Spain and Portugal, for instance, offer simple so-called feed-in-tariffs that pay solar power plant operators a ***premium rate*** -- typically for 15 to 20 years -- for producing renewable energy.
http://blogs.business2.com/greenwombat/solar_energy/index.ht...