Farmers Review Africa Sept/Oct 2018 FRA - September - October 2018 digital 5 | Page 41

to be operationally, financially, and
environmentally sustainable. In recent
years, the cost of solar technology has
dropped tremendously. Prices for the
solar panels used in these systems
have dropped up to 80%. In addition,
these panels last around 25 years, requiring
little maintenance throughout this time.
Renewable energy sources have
gained a lot of attention as a
replacement for fossil fuels or as a
supplement in hybrid systems. Solar-
powered (photovoltaic) systems are one
of the viable alternatives that have attracted
considerable attention in this regard.
Although photovoltaic (PV) systems
generally have a high investment cost,
it has many features, which make it
attractive as an alternative source of
power for water pumping. It is clean,
as it produces no carbon emission,
it generates no noise, and it has low
operational and maintenance cost.
The first solar pumps were installed
in the late 1970s. Since then, PV
water pumping systems have shown
significant advancements.
The first-generation PV pumping
systems used centrifugal pumps,
usually driven by DC motors or variable
frequency AC motors, with proven
long-term reliability and hydraulic
efficiency varying from 25 percent to
35 percent. The second generation PV
pumping systems introduced positive
displacement pumps, progressive
cavity pumps and diaphragm pumps
for smaller water quantities, generally
characterized by lower PV input power
requirements, lower capital costs and
higher hydraulic efficiencies.
Technological advancements
Current solar pumping technology
uses electronic systems and intelligent
software, which have further increased
the output power, performance and
overall efficiency of SPIS. The key
device is now the electronic controller,
which adapts the available power from
the solar generator to the solar pump.
Besides its controlling function, it
provides inputs for real-time monitoring
of various parameters, such as
borehole water levels and storage tank
levels, as well as pump speed.
When appropriately sized, solar pumps
can support drip, sprinkler, pivot or
flood irrigation methods. Depending
on the local conditions, a system can
also include filtration equipment. Solar
pumps are often combined with low-
pressure drip. The required pressure is
typically achieved by pumping water
into an elevated water tank and then
releasing it through gravity. However,
the tank presents an additional
expense and is often more expensive
than the pump itself.
Factors to consider
Determining the right choice of solar
generator, pump type and size, as well
as irrigation technology, is complex.
The system has to be well adapted to
the specific site conditions. Suppliers
endeavor to supply the whole system,
comprising the solar generator, pump,
controller and accessories, plus
the irrigation system.
Solar pumping systems
are continuously evolving
and improving, including
configurations with drip
irrigation, floating solar panels
or purely solar-driven center-
pivot irrigation machines. Suppliers
are increasingly optimizing the whole
system, including solar generator,
pump, controller and accessories, plus
the irrigation system.
Additionally, suppliers now often
provide technical support services
to satisfy the needs of end users.
Another trend goes in the opposite
direction: individual components – PV
panels, standard irrigation pumps and
available controllers – are offered on
the market and integrators provide
services to connect these components
into one irrigation system.
Moreover, online technologies will
further improve solar pumping systems
and make it more versatile. Monitoring
(e.g. groundwater), remote control and
extended communication platforms
can be expected to be part of even
small-scale applications at minimal
extra cost.
The key device is now the
electronic controller, which adapts
the available power from the solar
generator to the solar pump.
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