Construction World March 2015

ENVIRONMENT

ABOVE: SMA solar PV inverters (Powermode is the official distributor for SMA in South Africa). RIGHT: John Hope-Bailie, Powermode.

structure for a more cosmetically-pleasing result. Many examples exist of the ‘ex post facto’ connection of PV panels resulting in a distinct lack of aesthetic integrity. A good guideline is that the colour and texture of the solar PV system should be consistent with all other materials with which it is associated. Taking the concept a step further, the entire appearance of the building should be consistent with the PV system used. In a traditional building, for example, a tile-type solar PV system will often be more visually appealing than large modules which, on the other hand, may well suit a modern, high- tech construction. Integrating PV systems into roofing structures is better done at the design phase when the slope of the roof can be angled optimally and attention can be paid to the strength of supporting structures. Ideally the roof should accommodate an additional loading of 20 to 25 kilogrammes per square metre to adequately and safely support PV panels. Some roof coverings are better suited to the mounting of PV systems than others. This is particularly true when water proofing has to be taken into account. In commercial and industrial buildings, solar PV modules can form part of the watertight skin. Dubbed building-integrated photovol- taics (BIPV), these modules are formed from materials that can replace conventional building materials in parts of the building envelope such as the roof, skylights, façades, sunshades, louvers and canopies. These panels are available from a number of specialist manufacturers, although there is a price premium which has possibly limited their uptake – to date – in South Africa.

tects as well as the contractor, engineers, electricians, roofers and other installers associated with the project to have a clear understanding of the responsibilities of each party in the building process. They also need to have specific details of the energy yield objectives associated with the project. These usually include goals for the reduction of grid-linked energy consump- tion to a point approaching zero with a view to ultimately generating more energy than the building uses so that in future – should the law ever permit it via a feed-in tariff (FIT) or similar scheme – the surplus can be sold to the electricity company. Determining project objectives The main starting point is to determine the maximum power that is required to be gener- ated. Power is related to size and the designer has thus to allow for a certain number of solar PV modules to achieve a given energy output. Will there enough surface area avail- To maximise the power output from a solar PV array – to optimise sunshine all year round – particular attention should be paid to its orientation and to that of the building to which it mounts. Solar arrays should be orientated towards ‘the solar window’ to achieve the maximum amount of solar radiation available at any site at any time. The solar window represents the range of sun paths for a specific latitude between the winter able to install a given size PV array? Optimising the solar window

and summer solstices. The closer an array surface faces the sun throughout every day and over a year (without being shaded), the more energy the system will produce – and the more cost effective it becomes compared to other power sources. The ideal orientation of a solar array is defined by two angles. The array azimuth angle is the angle it should face based on a compass heading. North in the southern hemisphere, for example. A south-facing array could lose as much as 40% of its effi- ciency. That said, the perfect angle for South African installations – per rule-of-thumb – is a few degrees east of north. The tilt angle is the angle between the array surface and the horizontal plane. Generally, the higher the site latitude, the greater the optimal tilt angle to maximise solar energy gain. If optimal gain is expected in cloudless winter days (such as found in Johannes- burg, for example), the optimal tilt angle will be slightly more than the local latitude, say between 25 and 27 degrees. On the other hand, if optimal gain is in the spring and summer months (in winter rainfall areas such as the Western Cape) then the optimal angle would be slightly less than the local latitude. In Cape Town, for instance, this would be slightly more than its latitude of 34 degrees. As you move towards the equator, the angles become flatter. Very precise measurements can be made using industry-developed algorithms avail- able from solar PV specialists. Integrating solar panels The integration of solar PV panels can be done with a view to optimising the aesthetics of a

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CONSTRUCTION WORLD MARCH 2015 I