In order to maximise the direct beam component of the incident radiation involves calculations depending upon the latitude position of the location of the modules and the season of collection. In Scotland irradiance falls mainly on south facing facades and roofs. Therefore to maximise solar energy all installations should be made facing south ( 30o) in Scotland (or anywhere North of the Equator).
Seasonal variations of the solar intensity are almost entirely to due with the fact that the Earth's axis of rotation is not perpendicular to its plane of rotation around the Sun. The diagram below shows the earths rotation around the Sun.

The variations in the solar rays received at the Earth during Midsummer and Midwinter are shown below.

The location of Glasgow is 56o North, so using this in conjunction with the above allows the diagram below to be drawn, which enables the inclination angles to capture the maximum direct beam irradiance (during midwinter and midsummer only) to be calculated.
Below shows the incident radiation during both midsummer and midwinter along with the location of Glasgow and the angles f and d which the modules should be inclined at to receive the maximum direct beam radiation.

The calculation of the angles f and d just require the use of simple algebra. Equations 1 and 2 below show the calculations for the optimal angles to capture the maximum direct beam radiation.

Equation 1

Equation 2

In order to capture the maximum direct beam component of the incident radiation during midwinter and midsummer the modules should be aligned at 79.50 and 32.5o respectively.

Any modules will tend not to be inclined at these optimal angles for midwinter and midsummer but inclined at a pre-determined value permanently. In most urban solar installations there is no choice in the inclination angle, or scope for variation during seasonal changes. The determining factor is the slope of the roof. An estimation that the inclination angle of 40o is the average slope of a household will be used. Another factor that is very likely outwith an urban installations control is the size of the array. The installation could be made on the roof of a mansion where a vast area could be utilised, or on the roof of a small one-bedroom house, therefore very limited area. Calculations will be made to show approximately the cost of an installation per m2.

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