Abstract:
Solar energy is a viable alternative source of energy for socio-development of a
developing country like Lesotho. Investment in solar process applications, requires a
accurate solar radiation data for the successful implementation of solar process
projects. However, in Lesotho measured solar radiation datasets are not sufficient both
temporally and spatially as there are only seven solar radiation measuring sites, two
of which are not reliably operational.
This study solves the problem of the scarcity of solar radiation data in Lesotho, by
developing a solar radiation database for the country. It has a primary objective of
developing an accurate solar radiation database for Lesotho. This is achieved by
merging ground measured solar radiation data with satellite – derived solar radiation
data. The merged data is complimented by solar radiation data derived from sunshine
duration data. Merging solar radiation datasets is important because ground measured
data are sparsely distributed and cannot be interpolated accurately to represent solar
radiation at any location. Although satellite – derived datasets are spatially continuous,
they are not accurate as they are inferred from extra- terrestrial solar radiation modified
with atmospheric models. As a result, each of the databases cannot be relied up
unilaterally. Measured ground data is from five stations and sunshine duration derived
solar radiation is form twelve stations.
The improved database is validated using a leave one out cross validation technique.
Its reliability in estimating ground solar radiation is tested by relative bias error (rBE),
relative mean bias error (rMBE) and normalized root mean square error (NRMSE).
Results show that the database is credible as it has a maximum error of 2.7 % which
is comparable to other studies of similar nature in Africa.
An interpolation tool, increases the accuracy and reliability of interpolated solar
radiation as compared to manual reading of data from solar radiation maps. It has an
accuracy of 99.54%.
The improved database and interpolation tool can confidently be used in any solar
application process design and sizing in the country.
