The position of the Sun in the sky varies continually throughout the day and also changes signficantly over the course of a year. It is also very location-dependant, so it is critical that you know the latitude and longitude of your development site before you begin any calculations. Despite our fundamental physical understanding of solar position as a result of experiencing it every day, calculating it at any specific date and time is by no means a trivial exercise. The tilted rotation of the Earth and its elliptical orbit around the Sun add significant complexity to the equations required. Add the fact that one day isn't actually the time required for a full rotation of the Earth around its axis and that 365 days isn't actually the time required for a full orbit around the Sun, and we're in for some real fun and games.
This article discusses the processes involved in determining the luminous distribution of daylight and solar radiation over the skydome in order to accurately account for the effects of shading and reflections in and around a building site. It looks at the mathematical models used and their implementation, as well as some of the issues associated with aggregating multiple skies over longer periods.
Dynamic Daylight Simulation
This article presents the methodology used in the initial versions of the web-based dynamic daylight simulation tools and compares the results with those from Radiance using the exact same model. It is intended as a detailed supplement to a research paper with a similar title submitted to the PLEA 2017 Conference in Edinburgh, providing additional explanatory material, information and results to support the arguments made in the original paper.
RADIANCE and Daylight Factors
The freely available RADIANCE software is one of only a few lighting analysis tools able to accurately calculate illuminance levels on surfaces within a building model. This article explains how illuminance levels can be used to generate daylight factors in RADIANCE and presents a number of ways of doing this, including using ECOTECT as a modelling interface. It also shows how both illuminance levels and daylight factors calculated in RADIANCE can be read back and displayed interactively within your ECOTECT model.