Just Trees – paying it forward with solar

by | May 19, 2016 | Featured Slider, Latest, News

At Just Trees we have always been mindful of the positive and negative environmental impact that the running of our business has. Actions speak louder than words and we started addressing the negative impact by committing to becoming a Carbon Neutral company as early as 2010. Electricity usage was a major contributor to our carbon footprint and this is where the idea of solar power started gaining traction. The “load shedding” crisis of the 2013/14 season was the proverbial “nail in the coffin” and spurred us into action.

It started with a visit to a wine Estate that had installed a PV system in 2012 and information/tips were garnished from one of the Estate owners. Just Trees then initiated discussions with Solar System companies and a detailed impact assessment was conducted, including the following:

  • Detailed analysis of current electrical usage, (kWh) 24 hour cycles, kVA peaks, patterns of usage, day vs night usage, weekend usage
  • Determining critical loads, electrical configuration of existing infrastructure for these loads, kWh/kVA capacity
  • Detailed analysis of values to determine site specific Solar PV yield for the site
    • Specialised Solar PV Software was used to calculate the generation capacity of the solution. The basis of these calculations took the following into consideration:
      • Up to 20 years historical climate data from the region
      • Height above sea level
      • Exact GPS coordinates
      • Orientation of the Solar PV Solution
      • Gradient of the Solar PV Modules and influence of shading
    • a full financial model qualified by final design generation forecast

The following solution was put forward for consideration:

Grid-Tied system

  • Solar panels which will generate the energy (DC)
  • Grid tied inverters which would convert DC to AC and ensure that maximum power is generated from the panels. The AC energy would drive the pumps and all excess energy would be fed back into the grid.
  • Permission from local municipality was granted to tie into the grid for co-generation and net-metering
  • Standby generator to “assist” in times of high energy demand during load-shedding


However, after reading an article about farmers pumping water from the Orange River in the Northern Cape using only solar power and Variable Speed Drives (VSD’s), the question begged whether this solution, coupled with the input from current Municipal electricity could be considered. Consultation with VSD manufacturers confirmed that the VSD’s could be operated utilising both DC (Solar) and AC (Municipality) to drive the pumps together with a power management system (which would prioritize the available DC energy and use the AC to supplement the shortfall during non-peak solar periods).



After analysing the costs and benefits, we decided to go with the following solution:


Solar Assist PV/VSD system

  • 200 x Solar panels which will generate the energy (DC) of 51kWp
  • Variable Speed Drives to make use of power from both the grid (AC) as well as directly from a solar PV system (DC) to drive the pumps
  • PV not grid-tied – independent from grid
  • Standby generator to “assist” in times of high energy demand during load-shedding


The added advantage that the VSD provides is that system operating pressure can be kept at a constant by regulating the speed of the pumps motor. By adjusting the required system pressure (reference pressure) while irrigation is being performed in order to meet the actual required system pressure, this unlocks additional power savings thus optimizing the consumption of power.

VSD’s coupled with Solar PV solution for the pumps would amount to direct savings from installation of the VSD’s  and the additional savings attainable from direct feed of the Solar PV system to the VSD’s.


Having finally decided on a solution that we felt was best suited to our needs, we decided to partner with RenEnergy to design and implement the system for us.


To conclude, the system will have the following benefits to our business:

  • 87 Tonnes/year of CO₂ Emissions avoided
  • We will reduce electricity consumption by 20% through use of the VSD
  • Payback period directly via savings is 7.25 years



Since installing the VSD’s, we have already noted a 25% reduction in power needed to pump each liter of water onto our trees. We will be measuring PV electricity output over the next year to quantify exactly what the savings will be.


About Just Trees (Pty) Ltd


Just Trees is a wholesale tree nursery specializing in container grown trees. Just Trees works with landscape architects and landscape contractors who plant our trees knowing that they will contribute to their design becoming a reality. Contact: Carl Pretorius Tel: 021 871 1595 www.justtrees.co.za


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