INCORPORATING COLD CHAIN
CONTRIBUTORS
Solar: A power(full)
alternative for the cold chain
By Hannes Enslin, Technical Product Manager at Auto X (Pty) Ltd; editing and introduction by Benjamin Brits
With the continual rise in conventional energy costs and slow electricity grid expansion in South Africa,
this power source is not only a convenient stand alone alternative, but importantly a green solution.
As businesses find different ways to
solve their power needs, and in
many cases lack of service in
outlying areas – and the dreaded load
shedding – solar power is in fact a very
suitable and reliable option that, like
most systems you would work with today,
comes in a variety of options – from full
stand alone to grid-tied.
The cold chain is a particular element
where solar power can be a solution and
especially in bringing cold stores closer
to the farmers or producers without
extreme measures to install the required
power infrastructure in remote areas.
In many instances, solar products
have the reputation of being
‘expensive’, but as technology and
demand has grown over recent
years, costs generally have come
down, and play on an equal par with
conventional and alternate supply,
and in some cases is a better and
cheaper overall solution.
With future developments, this
technology as well as its green aspect
will likely be a significant contributor
to the growing energy demand as
global growth of this energy solution
is expected to exceed 10% this year
(estimates pre-Covid-19 were at 14%).
COMPONENTS THAT FORM PART
OF A SOLAR SYSTEM
A solar power or solar energy generation
system consists of the following main subsystems/components:
• Photovoltaic (PV) panels (or
commonly referred to as solar
panels). These convert solar radiation
(photons – light energy) into electrical
energy (coulombs).
• Solar charge controller (SCC) – This
component regulates the PV voltage
and power to match the inverter or
battery energy storage system (BESS)
direct current (DC) bus voltage and
input power requirements.
• Inverter – An inverter converts the
DC energy from the SCC or ESS to
alternating current (AC) to power the
AC loads.
• Battery energy storage system (BESS)
– A battery bank for storing surplus
energy for later use.
• Balance of plant (BOP) – DC and
AC protection (breakers, fuses,
transfer switches), solar panel
mounting-structures, earthing and
lightning protection components.
• Monitoring and control system
Ag Funder
An example of Solar-powered cold rooms located in East and Southern Africa.
Many solar inverters nowadays have built-in
solar charge controllers, as well as monitoring
and control functions to enable gridsynchronisation.
Quite often they also have
an AC battery charger built-in to provide for
charging of the batteries from the grid or a
generator when solar energy is insufficient –
this is referred to as a hybrid inverter.
TYPES OF SOLAR POWER SYSTEMS
Solar system terminology can be confusing,
or often used incorrectly causing confusion,
but the main categories are as follows:
• Grid tied system: Inverters are
connected and synchronised to the
utility grid and must switch-off when
the grid fails. ‘Tied’ to the grid and not
allowed to function in ‘island’ or off-grid
mode. Typically used in large PV power
generation plants or larger roof-top PV
systems for self-consumption generation,
these systems reduce the energy bill
and potential maximum demand fee,
and export excess energy into the grid
if allowed by the service provider or
the municipality. Worldwide this type
of system is used from small residential
applications to a large utility scale.
• Off-grid system: The system is suitable
where no utility grid power is available
or the inverters and the AC loads it
serves are not connected to a grid.
These are typically used in rural and
remote areas and usually also are
installed with a larger BESS to provide
for longer autonomy (back-up power)
to compensate for any bad weather.
• Grid-assisted system: This is effectively
an off-grid system in the sense that the
inverter provides power to the load
in a ‘UPS’ mode and the load circuit
is isolated from the grid supply. The
inverter can however supplement
Amazon
power from the grid and/or charge
batteries from the grid when solar
energy is insufficient. The system can
operate in ‘island’ mode to provide
power to the load during grid failures
and load shedding. Some inverters
can also export excess energy to
the grid, again if allowed. This system
is used in the majority of smaller
scale domestic and commercial
applications for security of supply
during grid failures/load shedding and
reducing energy bills.
SOLAR POWER SYSTEMS AND
THEIR SUITABILITY TO THE COLD
CHAIN
As an alternative energy source for
refrigeration/cold storage, investment in a
solar energy system can contribute both in
terms of security of supply (provide power
to priority loads) during grid failures/load
shedding, as well as reducing the electricity
bill and maximum demand charges.
This applies to any electric energy
consumer including the refrigeration/cold
storage sector, where it can also provide
savings on generator fuel consumption
and maintenance costs due to the
criticality to maintain refrigeration/cooling
Distribution warehouses with rooftop solar
panels installed at one of the many Amazon
facilities in the US.
during grid outages to prevent/reduce
product spoiling and losses.
The same applies in remote/rural areas
where grid reliability is poor, and becoming
worse, and/or where service providers do
not plan capacity extension, or the cost
of the expansion outweighs the return on
investment of own (solar) generation to
meet business expansion needs.
There are ‘micro-grid’ and renewable
energy models on the market that are
internationally accepted by the World
Bank, US Aid, Power Africa, and the
EU, that can be used to design system
concepts and trade-off analysis with
bankable results.
For the logistics sector, solar panels
or flexible solar panels can theoretically
be fitted on refrigerated transport trucks,
trailers and container roofs. Limited
surface area/generation capacity,
potential material damage and theft
should to be taken under consideration
when determining the feasibility for use in
this application.
An onboard BESS with an inverter/
charger that can be recharged at
depots, fuel stations or even potentially at
EV charging bays along the national road
network is definitively something that we
may see in future as overseas developers
investigate ways to make this a reality.
We already have vast developments in
electric vehicles that too would make use
of this system.
THE MOST IMPORTANT
CONSIDERATIONS IN SIZING A
SOLAR SYSTEM
The most important parameter is always
money or access to funds: What can
you afford to invest (CAPEX) and what
is your expected break even term and
COLD LINK AFRICA • October 2020 www.coldlinkafrica.co.za 31