Bit more about it here http://elpais.com/elpais/2013/07/23/inenglish/1374591905_024635.html

but I am not sure if it makes anything clearer.

"Right now, it is possible to generate energy privately in Spain as long as it is used immediately - known as instantaneous self-consumption. The latest legislation on this option dates from 2011. Nobody did it before this because it wasn't worth it financially. But the cost of photovoltaic equipment has dropped as much as 80 percent in the last five years, while electricity bills have kept rising, making self-sufficiency an attractive option in these times of crisis. Cow farms use it, supermarkets use it, and even the odd private consumer uses it. Excess energy may not be stored in batteries as that is prohibited. When there is no sun or wind, consumers have to use the regular service and pay the bill."

Sorry but what?