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

Feasibility Assessment for the Replacement of Diesel Pumps with Solar Pumps
FINAL REPORT: September 2006
PVPs in Namibia after concluding the cost benefit analysis, the existing data will be
extrapolated to the recorded 51,500 boreholes in Namibia since that is the most reasonable
approach available.
Figure 4.1 presents the number of boreholes which are in use and which have an acceptable
chemical composition for livestock. The total number of boreholes of use are therefore
41,760 (81% of 51,500). The data shows that about 95% of the boreholes in Namibia have a
depth of between 0m and 200m. The remaining 5% of boreholes are deeper than 200m.
Number of boreholes
8,000
7,000
6,000
5,000
4,000
3,000
2,000
1,000
-
0 - 20
20 - 40
40 - 60
60 - 80
80 - 100
100 - 150
150 - 200
Head [m]
200 - 250
250 - 300
300 - 400
400 - 500
Figure 4.1: Number of boreholes in use at different borehole depths
In order to determine how many of these boreholes can be serviced with PVPs the number of
boreholes falling within the hydraulic load curve of 1,000m 4 /day and 3,000 m 4 /day are
established. This is approached as follows:
1. The total number of boreholes on the database is 51,500. There are more boreholes
as some have not been registered. No estimates on the number of additional
boreholes are made here.
2. It is assumed that 10% of the boreholes are no longer in use (overuse, collapsed etc).
3. The chemical analysis is extrapolated to the total number of boreholes (realising that
this will potentially contain a large error). It is therefore assumed that 90% of all
boreholes in use are suitable for livestock consumption.
4. It is assumed that the rest water level is 20m above the bottom of the boreholes.
5. The number of boreholes within each head range is queried by assuming that the
abstraction rate is 66% of the borehole yield (safe yield).
6. About 60% of the database information contains head and borehole yield. The
analysis is conducted with 60% of the data and then extrapolated to the total number
of boreholes.
This yields the total number of boreholes that fall to the “bottom and the left” of the constant
hydraulic load curve (refer to Figure 3.2). These boreholes would be fully and sustainably
utilised through PVPs at 66% of the borehole’s capacity, based on the Division of
Geohydrology’s abstraction rate design principles. Therefore boreholes with yields in excess
of what a PVP at a particular head is able to deliver are not taken into account and would
require other pumping technology to utilise fully (e.g. diesel or electrical pumps).
500+
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