Solar thermal energy
Practical Action
Figure 2: Dispersion of solar irradiance through the atmosphere. Illustration: Neil Noble / Practical
Action (powerfromthesun.net).
Although potentially obvious, it is also useful to note that the majority of the solar water heating
will occur during daylight hours. This is not necessarily when it is demanded, thus solar hot
water storage tanks are normally required.
Daily, seasonal and geographical variations in solar insolation are an important aspect of solar
energy because of the influence on system design and solar energy economics. A useful
document which summarises the extent of the application of solar energy in 43 countries
around the world is the 2010 Survey of Energy Resources by the World Energy Council. The
document also notes the levels of solar radiation that can generally be expected in the countries
listed which may be useful as a quick reference.
Alongside journals and books, another useful source detailing solar insolation levels around the
world is a tool which has been developed by NASA and is free for public use. Below are images
produced by this tool which show the global variation in solar insolation.
November 2010
May 2011
2
February 2011
August 2011