I have no doubt your friend has very probably assiduously tracked his output. I can think of quite a few variables, and I am of course unfamiliar with the local climate or specific site conditions in Spain. I have observed my own installations to produce less output in Winter, which I attribute to shorter days, and frequent cloud and extended mist and light rain. In Victoria this is the case certainly and whereas other States like SA and WA may have better solar farming resource (I have seen the subsidy-free large tomato green house at Port Augusta, with its large solar thermal setup, producing desalinated water and a couple of MW of power to run the Air Conditioners and hydroponic plant). The next solar thermal proof of concept with storage plant is expected to be built their. I dare say they will permit themselves a grid import if they need a help to get going. Cheaper than adding batteries...
But there are many household rooftop systems in Melbourne, for example, in obviously less than ideal orientations. This adds up over large number of installs to reduced output in Winter.
Now when you next get back to your desk, would you please describe the subsidies you perceive apply to some or any coal fired plant?
