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

Feasibility Assessment for the Replacement of Diesel Pumps with Solar Pumps
FINAL REPORT: September 2006
The bulk of the costs in both cases are the operating costs. As the operating hours increase,
the operating costs increase more significantly than the maintenance cost shows that fuel at
current cost levels is the main contributor to the LCC of DPs.
3.2.2 Life cycle cost comparison
The life cycle cost of different pumping options shows the true cost incurred over the project
lifetime for the same service rendered, i.e. an average of ‘x’ cubicmeter of water delivered
over a fixed head within a fixed period. Since the LCC varies with daily flowrate and head,
two daily flowrate examples have been selected. These are shown in Figure 3.6 for three
delivery heads each.
It can be seen that the LCC of the PVPs increase with increasing hydraulic load (note that
different PVPs have been used, always striving for the most optimal system). The increasing
LCC of PVPs is explained by the increasing power requirements.
Life Cycle Cost [1,000 N$]
600
500
400
300
200
100
-
Daily flow rate =
10m³/day
40 80 120
Head [m]
PVP
Figure 3.6: Life cycle cost for PVP and DP
DP
Life Cycle Cost [1,000 N$]
600
500
400
300
200
100
-
Daily flow rate =
20m³/day
40 80 120
Head [m]
The diesel pump hourly flowrates are set to a quarter of the daily flowrates, i.e. 2.5m 3 /hour
for 8 hours every second day means that the average daily flowrate rate is 10m 3 /day. This
yields a fairly efficient diesel pumping system and pumping every second day requires less
operator travel and time. However this also assumes that the borehole has the necessary
capacity to deliver at higher extraction rates since the solar pump would only extract at a rate
of a sixth of the daily flowrate, i.e. the maximum flowrate of the solar pump is about
1.7m 3 /hour at 10m 3 /day.
The LCC of the diesel pump systems remain fairly flat at lower hydraulic load (less than
1,000m 4 /day or in terms of hourly hydraulic load less than 200m 4 /hour). A diesel pump is not
efficient at such low power requirements and the fuel consumption remains more or less
fixed at the minimum rate of 0.7litres/hour. Once the hydraulic load increases above
200m 4 /hour the fuel consumption rate increases and the operating costs go up. The capital
cost also increases but the impact on the overall LCC is minimal.
The LCC is summarised in Figure 3.7 where the LCC for PVPs and DPs has been averaged
for different hydraulic loads. This is highly dependent on the selected pumping schedule
which is as follows:
• If the daily flowrate is less than 10m 3 /day, then the diesel pump will pump every 2 nd
day. If the daily flowrate is more than 10m 3 /day then it will pump every day.
o If the daily flowrate is less than 10m 3 /day, then the duration of the pumping
session will be 8 hours (pumping every second day).
o If the daily flowrate is less than 20m 3 /day but more than 10m 3 /day, then the
duration of the pumping session will be 6 hours (pumping every day).
PVP
DP
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