Usq Report Solar Power and Irrigation Systems
Usq Report Solar Power and Irrigation Systems
Usq Report Solar Power and Irrigation Systems
These reports do not provide a detailed address of grid connected solar PV rather
focussing primarily on potential for standalone solar PV and diesel hybrid
systems.
Solar irrigation must be considered in a holistic (whole of system) manner. Water
demand should be seen as the critical starting point. Understanding irrigation
demand is as important as understanding the technologies involved in the
conversion of solar energy to electricity, to meet this demand.
When considering solar irrigation the starting point is an analysis of current
energy usage. This is followed by an evaluation of energy conservation and
efficiency opportunities of the current system, before finally looking at
appropriate renewable energy technologies.
This report provides a technical summary of solar power and solar irrigation
systems in Queensland.
Queensland is geographically large, spanning a wide range of latitudes and
climatic zones. Solar radiation varies with latitude and has seasonal and daily
variations, which Queensland farmers must consider. This variability in energy
supply is important when designing a solar irrigation system to match variable
crop irrigation requirement. In irrigation, hybrid systems are generally used,
where solar is combined with power from the grid or a diesel generator to allow
continuous power delivery for pumping.
Diesel pumping is common in Queensland cotton irrigation, while electrical
pumping is more common in the sugar, dairy and horticulture industries where
there is generally better access to the electricity grid. Diesel systems are generally
more expensive to operate and maintain than electric systems and electrical
pumping offers benefits of easier integration with solar, lower running costs and
less maintenance.
Solar pumping systems are well suited to transfer operations in which pumps run
during daylight hours to fill a storage. The size of the storage needs to be
For this technical report, information on solar power and solar irrigation systems
from around Australia was reviewed and the range of configurations and standards
for solar powered irrigation, as well as other key factors, was documented. This
included a review of the benefits of renewable energy technology and the potential
for solar energy in agriculture. Various solar irrigation configurations and
components have been documented and factors influencing solar system feasibility
and sizing have been outlined.
Energy analysis
Energy analysis can be done at different levels of detail, including:
Energy Efficiency
An important aspect of energy efficiency is ensuring the right amount of water is
supplied to the crop at the right time. The pump must be suited to the job of
matching supply with demand. Irrigating 12ML/ha when the crop needs 8ML/ha
means that you are using 1/3 more energy than is necessary.
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Figure 3 Difference in solar radiation levels across the day between summer and winter in
Toowoomba
Figure 4 and Figure 5 depict typical Queensland solar radiation exposure for
winter and summer months. These figures show that in the irrigation regions in
Queensland there is reasonably high solar radiation and therefore substantial
potential for solar PV irrigation. The size of the system will need to be designed
for local conditions, to ensure that reliability of supply can be met. There is more
variability in the summer months due to Queensland’s summer dominant rainfall
and therefore cloud cover during this period.
Figure 6 Average daily solar exposure Annual (Australian Bureau of Meteorology, 2017).
Figure 6 shows the daily annual Australian sun exposure showing the range of
solar radiation across the other states and territories
Solar Alone
The solar panels provide power in the form of Direct Current (DC) due to
radiation from the sun. The DC power is then provided to a motor by a system
controller which regulates the panel(s) and motor, thereby controlling the pump
output (Figure 8). This type of system is typically used to provide a constant
water supply or for storage in a trough or dam and is ideally suited to stock and
domestic installations. This system is often relatively low cost, small and
independent of other systems, therefore is suited to use in remote areas (NSW
Farmers, 2015c).
Figure 8 Solar pumping configuration, using just solar as the energy source (NSW Farmers, 2015c).
Figure 10 Solar pumping configuration that uses a combination of solar and diesel as the energy
source (NSW Farmers, 2015c).
Figure 11 Solar pumping configuration, using a combination of solar and grid power as the energy
source (NSW Farmers, 2015c).
Figure 12 shows how a solar grid connected system can be scaled according to
requirements, costs and the proportion of power that could be exported to the
grid. Payback periods vary depending on how the system is sized (NSW Farmers,
2015c).
Floating Solar
The efficiency of solar arrays are dependent on temperature (among other
parameters), the cooler the array, the higher the efficiency or output. This,
combined with spatial constraints of large arrays, has led to the development
and use of floating solar arrays. By floating the solar array over an open water
body there are gains in panel efficiency, a reduction in evaporation water loss
and increased land availability, when compared to land mounted systems.
Floating systems can be implemented on almost any water body such as
irrigation dams, reservoirs or rivers.
The floating solar array consists of a raft or platform on which solar panels are
mounted. The electrical components are mounted on land, with the DC power
generated from the array transported via cable to the main switch board on land.
Variations on this design can include concentrator panels and solar tracking to
improve efficiency.
Floating solar systems have been used to power water treatment systems for
treating a variety of water quality issues (Infratech Industries, 2017).However
maintenance on a floating array may be high.
Polycrystalline cells are slightly lower in efficiency than monocrystalline cells, but
also have lower production costs. They are made from allowing molten silicon to
cool which gives it the unique segmented look and are often lighter blue in colour
(NSW Farmers, 2015c).
Location (shade)
Shading of the solar array will reduce the systems output. The shading can vary
throughout the day and season, therefore array placement has to be carefully
considered. Solar service providers are able to provide advice on correct
placement.
If an individual panel is partially shaded it can develop faulty cells, this will
reduce the panel or array efficiency. Possible sources of shading include:
• Vegetation – trees, bushes, long grass, leaves
• Structures – buildings, shelters, fences, power poles
• Landforms – hills, rocks
Orientation (tilt)
The orientation of each panel contributes to the efficiency of the whole system. A
typical rule of thumb is each panel should be north facing (in the southern
hemisphere) with the angle of tile equal to the latitude on the installation
location for best year round performance. This rule of thumb should be adjusted
to suit the energy use profile and individual requirements. For example if a famer
requires the most power during summer months the panel tilt should be lower
than latitude to take advantage of the higher sun orientation (NSW Farmers,
2015b).
Figure 17: Optimal Panel Tilt a) A lower tilt – greater solar power generation in summer; b) A tilt
equal to site’s latitude – greatest annual solar-power generation; c) A steeper tilt – greater power
generation in winter (NSW Farmers, 2015c).
Table 1 - Latitude and angle of tilt for optimum solar power generation in Queensland
Depending on use, panels should be adjusted from latitude by -10o to -15o for best
efficiency during summer months and conversely panels should be orientated +10o
University of Southern Queensland | Feasibility of Solar PV Powered Irrigation in Queensland
Report 1 Solar Power and Solar Irrigation Systems 21
to +15o during winter months for best performance. The panels can also be
directed to either east or west depending on highest use times.
Solar Tracking
Tracking systems can control either the angle of tilt, and/or the direction, that the
array (or individual panels) faces relative to the sun’s position in the sky, using
mechanical motors. This is achieved through either passive or active systems.
Passive systems can be pre-programed with sun data such as position and
intensity, to follow the sun and requires no more information to operate. Active
systems use the real time sun position to manoeuvre the panels or array into
position, this type of system continually feeds data to mechanical components to
orientate the panels for best performance.
Tracking systems can increase efficiency up to 10%, but can be expensive to
construct and install, tracking is more suitable to large-scale arrays and areas with
long sunlight hours. Alternatively a combination of both fixed and tracking system
can be used, with the tracking component used to prolong the output of the system
(NSW Farmers, 2015b).
The report Solar-Powered Pumping in Agriculture by NSW Farmers (2015c)
outlines the two main forms of tracking systems:
• Single-axis trackers rotate the array in the east-west axis only,
following the sun at a fixed angle of elevation from the time it rises in
the east until it sets in the west. Installing a single-axis tracker solar PV
array results in higher power output in the mornings and evenings.
• Dual-axis trackers rotate the array on an east-west axis and tilt it on
a second axis so that it is angled directly towards the sun at all parts of
the day.
Figure 18. The single axis tracker follows the sun from east to west (NSW Farmers, 2015c).
Figure 20: a) The I-V curve of a PV module (current is typically abbreviated as ‘I’ although its units
of measure are Amps); b) the maximum power point of the I-V curve is at the red dot. Note: This
point corresponds to the maximum point on the blue ‘power output’ curve (NSW Farmers, 2015c).
Inverter
Inverters make up approximately 20% of a typical solar system cost and are
used to convert the array Direct Current to more useable Alternating Current.
There are two main types of inverters; transformer type, and transformer-less
type. As the name suggest the transformer type incorporates a transformer; a
wire coil wrapped around a laminate iron core. These tend to be heavier and cost
less to produce. The transformer less type is a relatively new technology where
semiconductors (electronics) are used to convert the electricity. Transformer less
inverters are lighter, more efficient and react quicker to changes in power (Solar
Quotes, 2018).
The sizing of a solar pumping irrigation system needs to take account of a range
of factors. Guidelines on sizing solar pump systems and water storage have been
developed by NSW Farmers Association (NSW Farmers, 2013a).
Figure 21: Motor surge current in DOL configuration would either prevent a PV array from starting
the motor or result in an oversized PV array being installed (Global Sustainable Energy Solutions,
2015).
Current electronic systems and VSDs allow power to be drawn from either the solar
PV panels or simultaneously from the PV panels and grid or diesel generators (solar
assisted operation).
These systems draw energy from the PV panels to pump water, and if the output
energy of the PV array is not enough, the system switches on the AC input from
the generator or grid to “top up” and deliver all energy required by the motor. This
feature is especially important when the AC is supplied by a generator and
minimises diesel usage.
Figure 23: Switching power from solar PV to grid or diesel power in response to incident solar
radiation (Example – Power Electronics SP 7000SP brochure).
The VSD will reduce operating costs by allowing the pump to run efficiently at
varying loads, reduce maintenance cost due to less wear on pump/motor and
reduce operational costs such as refuelling and monitoring. If a VSD is
considered when installing a new system it can reduce the size of the required
1. QFF have published a number of case studies as part of the Energy Savers
program which aims to assist farmers reduce energy costs by supporting
the accelerated adoption of improvements in on-farm energy use. The
Program is funded by the Queensland Department of Natural Resources,
Mines and Energy, and The Department of Agriculture and Fisheries and
implemented by Ergon Energy in partnership with Queensland Farmers’
Federation
https://www.qff.org.au/newsroom/case-studies/
2. NSW Farmers the peak industry representative body for agriculture in New
South Wales, have published a range of case studies in their AgInnovators
web portal including ten on solar power systems for irrigation.
http://www.aginnovators.org.au/case-studies/
4. The company GEM Energy have included a case study on solar irrigation
for horticulture.
https://www.gemenergy.com.au/case-studies/
5. The company Solar Pumping Solutions has published some case studies
including a 100kW solar array powering a 55kW submersible pump at
Narromine NSW
https://www.solarpumping.com.au/projects/hybrid-solar-pumps-large-
scale-irrigation
6. The company Grundfos primarily serves the stock watering solar market
and a case study is included below.
http://au.grundfos.com/cases/find-case/Grundfos-providing-reliable-
water-supply-to-mid-north-cattlestud.html