Cabin Solar - How To -

[Skvez]

Unfortunately you have made the very common blunder of assuming that you will get 70W out of a 70W solar panel.
Solar panels are rated under ideal circumstances. Ideal being equatorial sunlight, which we *never* get in the UK even on our brightest cloudless summer day.
A sunny cloudless day in winter in the UK (which lets be honest are pretty uncommon) will get you a lot less than 70W exactly how much less depends a bit on the technology of the solar panel.

On the tests I did back in 2011 I was getting about 12Wh *per day* from a 100W panel in December. Your calculations assume 280Wh from a 70W panel (or over 33 times more power than I measured in a real world environment)

People complain that I say Solar doesn't work, I don't, solar is great but you need to have realistic expectations of what it will provide, especially in Northern Climates in Winter when performance is very poor compared to ideal.