PV example in the author's house

1 May : If I can encourage you to think more about PV, I could add that it's not only about saving your energy bills and making some revenue from feed in tariff. It becomes an interesting hobby, checking the weather, recording the statistics, matching the lifestyle to the performance (eg use appliances more when sun is shining) etc.
The last two months of Photovoltaic generation have been very good, both months exceeding the JRC expected amount by about 40%. (Helps us to forget the poor days of Jan and Feb.)

• March should have been 207 kWh but was 281. 
• April should have been 306 kWh but turned in a score of 429.

The amount by which these exceeded expectation were more than the entire months of Jan and Feb combined, which rather makes me think that you should not worry if sun angles or long shadows in the months of Dec and Jan are not going to be favourable. It seems better to optimise for the spring to autumn months.
Looking at the charts here, the final weeks of April were astonishing, we had a run of nine days in a row, all touching or above 20 kWh, apart from one freakishly cold dark day on 15 April. The lower illustration is a typical run of days, from April 15 to 21. Even though our roof faces east, the early morning sun gives us good performance. I notice a pattern whereby days often end with cloudier afternoons after a good start - enough to put me off recommending a west roof where an east one is available.