Solar PV water pumping study - FINAL REPORT ... - UNDP, Namibia

Impact on Years-tobreakeven
Feasibility Assessment for the Replacement of Diesel Pumps with Solar Pumps
40%
30%
20%
10%
0%
FINAL REPORT: September 2006
-10%
5.00 7.00 9.00 11.00 13.00 15.00
Diesel price [N$/litre]
Figure 3.10: Indicative relationship between fuel price and breakeven
The calculation is based on the current diesel price of 6.70N$/litre (0% impact) and
represents an average impact of fuel price variations on the years to breakeven. For different
operating points the impact is different since the pumping schedule, the capital cost and the
replacement costs vary over the range of operating points. The relationship indicates a 5%
reduction in the years to breakeven for every 10% increase in the fuel cost. This holds true
for up to 50% fuel increases where after the impact of an increase in fuel price lessens.
The use of tracking arrays to increase the daily output of the PVP is a popular option with
PVP systems. Tracking arrays can be passive or active, single or double axis, all of which
determines the increase of the daily energy harnessed. The increase can be in the region of
10% to 15% for a passive, single axis tracker and to 25% to 30% for an active, dual axis
tracker. If the pump is a centrifugal pump (pump efficiency sensitive to operating point) then
the daily efficiency of the pump will improve more than the daily efficiency of a helical rotor
pump, which has a flatter efficiency curve.
Capex cost savings [N$]
16.0%
14.0%
12.0%
10.0%
8.0%
6.0%
4.0%
2.0%
0.0%
- 1,000 2,000 3,000 4,000 5,000
Hydraulic load [m4/day]
Figure 3.11: PVP capital cost reduction when using a tracking array with 20% increase in
solar irradiation
For the cost comparison it is assumed that the tracking does not increase the water delivery
but allows a reduction in the size of the solar PV array (this is a practical approach adopted
here since the average daily flowrate between the PVP and DP need to remain the same for
comparison sake).
Figure 3.11 shows that the cost savings at low hydraulic load and consequently low PV array
size is small and increases as the size of the hydraulic load and therefore the PV array size
increase. For example, the PV array size needed for a PVP to deliver at a hydraulic load of
1,000m 4 /day is about 1,200Wpeak. The capital cost of the system decreases by about 10% if
tracking arrays are used to decrease the PV array size for the same amount of water per
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