Depends where you are, of course, but here on the south coast of the UK, between November and Feb there just simply aren't enough available hours of daylight, especially not in the two weeks either side of the solstice - then there are the deep dark days where the clouds ensure hardly a photon gets through. From practical experience, this is why I chose to supplement the solar with wind power  

 I'm all for diversification in power sources! I hope to eventually find property with year-round running water to have a small hydro setup.  

 I really like the idea of a boom I can drop over the side with turbines to generate power as the water passes the hull - hydro is so underutilised I reckon  

 Yup.