What affects solar panel output?

In the UK, panels facing south capture the most sunlight across the day and produce the most over a year. East and west-facing roofs still generate well, spreading output toward morning and afternoon respectively, which can actually suit businesses whose demand peaks early or late. North-facing slopes generate least and are usually avoided.

Roof pitch, the angle of the slope, also plays a part. A tilt somewhere around 30 to 40 degrees tends to work well at British latitudes, balancing summer and winter sun. Flat roofs are fine too, because panels can be mounted on angled frames set to a chosen orientation and pitch. A survey models your specific roof rather than relying on rules of thumb.

Shade is the enemy of output. A chimney, parapet, neighbouring building, tree or even a tall vent can cast a shadow that cuts generation, and on some wiring layouts shading part of a string affects more than just the shaded panels. Good design routes strings to minimise this, and microinverters or optimisers can limit the damage where shading is unavoidable.

Dirt, moss, leaves and bird droppings reduce output too by blocking light. In most cases British rain keeps panels reasonably clean, but sites near trees, industry or heavy dust may need occasional cleaning. Under a PPA, monitoring and maintenance usually sit with the funding partner, so a drop in output should be spotted and addressed.

Output follows the seasons. Long, bright summer days generate far more than short winter ones, so a system produces a surplus in summer and less in the darker months. Annual figures average this out, but your month-by-month generation will swing, which is worth understanding when matching solar to your demand.

Temperature has a counter-intuitive effect: panels are slightly less efficient when very hot. That is why a cool, bright spring day can produce strongly. It does not undo the benefit of summer sun, but it explains why peak output is not simply about heat. Cloud cover reduces output as well, though panels still generate useful power in bright overcast conditions.