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The Solar Design Company

Home MCS 'Guide to the Installation of Photovoltaic (PV) Systems' Shading Method

The MCS Solar PV Guide

The MCS site-survey method to anticipate solar PV shading

The UK's Microgeneration Certification Scheme (MCS) has now released their Solar PV Guide called 'Guide to the Installation of Photovoltaic (PV) Systems' detailing new requirements for solar PV installations. The published version indicates that installers will be required to record a shade or horizon line on a sunpath diagram to present to clients. This change is planned to raise the level of certification on site surveys. The Solar Design Company now runs training courses in MCS Shading and Solar Surveying.

The Solar Design Company has created a special 52o latitude sunpath foil designed to fit their Solar Site Selector survey tool. The foil template is FREE to download for self-printing and can be used with the Solar Site Selector as an aid to the MCS method. Sunpath diagram from MCS PV Guide (p.63) The Solar Design Company Solar Site Selector foil

Download your FREE digital MCS-aid Solar Site Selector foil now

Frequently asked questions:

What is the Solar Site Selector? The Solar Site Selector is a small but useful tool for anyone wishing to quantify solar energy such as by solar thermal, PV and Passive Solar Heating installers.

The tool includes a sunpath diagram (the 'foil') which is printed on to a transparent acetate. This slots into the Solar Site Selector, which contains a fisheye lens and a compass and can also be used with a wide range of different 'foils' from 36o to 60o latitudes.

By looking through the lens, installers can identify objects in the scenery behind the foil which could obstruct solar radiation. The outline of these shading objects can be drawn on the foil with non-permanent marker so that it can be reused for each site.

The Solar Site Selector now comes with the foil to aid the MCS method included. If you already own the Solar Site Selector then you can download the digital foil now and print it on to an A4 sheet of acetate.

See here for more information about the Solar Site Selector.


Solar Site Selector:


Includes MCS-aid foil. All prices shown without tax or P&P (shipping) costs. UK P&P is £9.50. Contact us for more information or to purchase.

How does the MCS Solar PV Guide shading method work?

The MCS method uses boxes on the sunpath to estimate shading. Each box on the MCS diagram represents a part loss of system yield and the boxes are different shapes and areas. For each box that contains some aspect of a shading object, these are counted and multiplied to reduce the optimum output if there were no shading. Some of the boxes on the MCS diagram are crosshatched, which means that they should not be counted as part of the system yield loss. Shading objects that are within 10 metres of the centre point of the proposed array require a circle to be drawn onto the sunpath diagram. The apex of this circle should sit at the top of the shading object and the radius of the circle should be the height of the object (see image below). In this example, the red part of the line is within 10 metres of the proposed array, so a circle is added (dotted), with the top of the object at the apex of the circle. In total, this shading line passes though 6 boxes. Under the MCS method this represents a 6% loss of AC output yield. In this case the installer would multiply the total predicted optimum yield by 1 - (6*0.01) = 0.94. View a shading case study here to see the calculation process in more detail.

Note: the MCS method may be subject to change in later versions so please refer to the MCS Solar PV Guide when making calculations. Landscape sketches should be transferred on to the official MCS sunpath diagram and near-shading circling undertaken there.

