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CONSTRUCTION WORLD
AUGUST
2016
ENVIRONMENT AND SUSTAINABILITY
Conventional wisdom says the
panels should be orientated
towards north in the southern
hemisphere to gain maximum
benefit from the sun’s arc. More specifically,
solar panels should be pitched between 25
and 35 degrees (approximately equal to the
site’s latitude) to allow for the most efficient
power generation.
The result, from a power production
standpoint is a true ‘bell curve’ reflecting
power increases throughout the day peaking
at midday and gradually falling again to zero
at sunset.
However, in certain circumstances it
may be advantageous to point the panels
eastwards – or westwards.
In one such instance – a grid-linked
hybrid application in Johannesburg – an
east-west orientation was found to be advan-
tageous. The motivation was the limited elec-
trical power supply from the local provider
which was unable to meet full demand at
the business facility. Another challenge
presented to the solar PV design team was
the need to reduce the aggregate electricity
cost for the facility.
An iterative evaluation process was
undertaken which focused on testing various
solar PV system configurations. The tests
initially evaluated power production from
traditionally north-facing panels. Subse-
quently, various directions were tried culmi-
nating in a convention-breaking east-west
configuration.
The initial goal of the test programme
was to match energy production to the meas-
ured load profile, while the second objective
was to maximise the financial benefit.
For simulations conducted with an
equal number of panels and inverters, the
east-west configuration showed immediate
advantages as it provided power production
earlier in the day, with a slightly lower peak.
It was thus a better match for the facility’s
demand curve.
While a more advantageous match was
achieved, concerns were nevertheless raised
about the loss of yield. A number of different
angles of inclination were subsequently
tested and eventually an angle of 20 degrees
from the horizontal was chosen as the best
compromise between ‘flattening’ the produc-
tion curve and loss of yield.
That said, the east-west facing solution,
with a 20 degree inclination, showed a total
loss of yield of approximately 2,5% when
compared to the north-facing alternative.
Nevertheless, when this is compared
with the facility owner’s electricity tariff/
billing structure from power producer Eskom,
the east-west installation demonstrated the
following financial performance:
• In summer months a nett R6,50 per day
saving was achieved.
The benefits of
‘EAST-WEST’
solar PV installations
By Bevan Jones, Soltra Energy MD
In what direction should roof-mounted solar photovoltaic
(PV) panels be sited for optimum energy production?
>
• In winter months a nett R8,50 per day loss
was returned.
It is noteworthy that, as the summer tariff
benefits apply for nine months of the year,
the result is an approximate R1 050 per year
additional saving over a traditional north-
facing system.
When the capital cost of the system is
considered, this is a relatively small saving
and could be considered as a ‘break-even’.
However, there are a number of other advan-
tages presented by the east-west orientated
installation. These include:
1. The lower peak output of the system
means that the inverters can be over-
panelled by approximately 10% without
any change to the inverter system or
balance of plant. In a typical rooftop
system the panels and installation
comprise 70-80% of the turnkey cost.
2. The east-west installation results in
approximately 5% lower installation
cost because the brackets and mounting
material are used more effectively.
3. The panel density on the roof can be as
much as 30% higher, allowing for a higher
yield per square metre.
When the above factors are taken into
account, it is clear that the east-west
oriented system is comparable to a north-
facing system on a ‘cost of energy’ versus
a ‘kilowatts peak (kWp) installed’ basis.
(kWp is essentially the rate at which a solar
PV installation generates energy at peak
performance.)
Furthermore, when the added advan-
tages of over-panelling the inverters at a
fraction of the cost of the entire system is
maximised, and the lower cost of installation
is taken into account, an east-west orientated
installation is seen to provide significant cost
advantages over a north facing system.
One of the keys to the success of similar
installations going forward lies with their
management. Sophisticated ‘smart’ power
management solutions can now be installed
and tailored to users’ needs.
These systems will, for example, comple-
ment grid power with solar power when
necessary (at peak times), divert excess solar
power to possible battery storage for later
or after-hours use as appropriate, and fire
up a petrol or diesel generator to integrate
seamlessly into the power supply grid should
battery storage become depleted.
A range of micro smart-grid solutions
that measure the generated solar power
on a minute-by-minute basis, compare it to
current grid power availability and assess
current load states is available.
Soltra Energy technical director, Bevan Jones.