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15
CONSTRUCTION WORLD
MARCH
2015
I
ENVIRONMENT
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-
able to install a given size PV array?
Optimising the solar
window
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
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
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.
ABOVE:
SMA solar PV inverters (Powermode is
the official distributor for SMA in South Africa).
RIGHT:
John Hope-Bailie, Powermode.