3 RESULTS AND DISCUSSION
The two methods were subjected to a similar client
requirements and the component sizes calculated by
applying the above methods. Consider a client whose
DED is 904 Whrs and the total power consumed by all
appliances is 168 W. The insolation at the place is 5.5
kWhrs/m
2 .
3.1 The CCM method
On applying method 1 (CCM), we get an estimated
a charging current of 16.95 A and if for example the
modules available in the market are 80W, then from the
module specifications, the current at maximum power
point is 4.4 A. Thus, to generate the charging current
of 16.95, four modules are needed. The computation
on the battery bank capacity gives 1412.5 Ahrs and
assuming 200 Ahrs as our choice of batteries, then
seven of them are needed to create the battery bank
capacity calculated. This high battery bank capacity
takes into consideration 3 days of autonomy. Without
the days of the autonomy, only about two batteries of
similar size will be needed. The charge controller rating is calculated to be 26 A for a short current rating of
the modules of 5.2 A. In the market, one may not easily
get such a charge controller so the next higher rating
available in the market, 30 A, is chosen. The voltage
rating of the charge controller has to match the system
voltage of the solar system, in this case 12V. Lastly, the
inverter is rated depending on the devices that will be
powered by the solar system assuming they are all on
at the same time. The total power consumption in the
example is 168 W so the next higher inverter rating in
the market is obtained, for our example, a 200 W (VA)
inverter.
3.2 The EOM method
The Energy method when applied to the example above
assuming 80 W modules and 200 Ahrs batteries are
the ones available gives the total power from the modules as 302 W. This means four modules are required.
The computation gives a battery bank capacity of
1329.42 Ahrs, which is 6.65–7 batteries of 200 Ahrs,
factoring in 3 days of autonomy. Both the charge controller rating as well as the inverter ratings are obtained
as 30 A and 200 VA respectively.
3.3 Comments on the two methods
The two methods lead to the same results for each component as can be seen from above.The methods applied
here are not new but the CCM is the most commonly
used method (Michael Boxwell, 2019; Mark Hankins, 2010; Geoff Stapleton, Lalith Gunaratne, & Peter,
2002). In the CCM method, the technical specifications of the panel need to be known so as to make a
final decision on the exact size and number of panels needed. This may pose a challenge to a number
of installers and designers especially if they have no
access to these details which need either searching in
the internet or physically obtaining details in the shops.
This is a drawback for this method of sizing. On the
other hand, the EOM gives the total power needed
from the panels to meet the daily demand, a value
almost all dealers in solar PV easily identify with.
This means once the computation is done, one does not
need further details to make a final decision but can
just call the seller to confirm what sizes are available
and contact the client and advice on the combination
of panels needed. This is easier and more straightforward and is advantageous compared to the CCM
method.
In the real installation, care is taken to install solar
modules in a location where shading should not occur
at any time of the day. However, technically, modules have also bypass diodes installed to ensure that
in case some cells are shaded, the current flow from
the unshaded cells of the module bypass the shaded
cells to minimize power loss, since the shaded cells
act as loads and offer resistance. Again, once a solar
PV system is installed, its entire lifetime depends on
the individual components. For example solar modules have a factory warranty life span of 20–25 years,
batteries can last for 1–7 years depending on the maintenance, and a charge controller can last for 10 years,
while inverters can last for several years depending on
quality, usage, and maintenance.
4 CONCLUSION
Two methods of sizing a SHS have been discussed in
detail in this paper. It has been shown that the EOM is a
better and more straightforward method than the CCM.
The methods provide working estimates and that is
why they are more suited for small-sized solar systems.
More work still needs to be done to refine the methods,
for example, by taking real field data and using it to
size and compare with the initial sizing estimates. For
large solar systems, commercial sizing softwares are
recommended.
ACKNOWLEDGMENT
International Science Program, Sweden is thanked for
support.
REFERENCES
Chikh, M.,A. Mahrane, & F. Bouachri (2011), PVSST 1.0 sizing and simulation tool for PV systems, Energy Procedia
6, 75–84.
Geoff Stapleton, Lalith Gunaratne & Peter JM. Konings
(2002), The Solar Entrepreneur’s Handbook, Global Sustainable Energy Solutions
Justus Simiyu, Sebastian Waita, Robinson Musembi, Alex
Ogacho & Bernard Aduda, (2014). Promotion of PV
Uptake and Sector Growth in Kenya through Value Added
Training in PV Sizing, Installation and Maintenance,
Energy Procedia 57, 817–825.
234
The two methods were subjected to a similar client
requirements and the component sizes calculated by
applying the above methods. Consider a client whose
DED is 904 Whrs and the total power consumed by all
appliances is 168 W. The insolation at the place is 5.5
kWhrs/m
2 .
3.1 The CCM method
On applying method 1 (CCM), we get an estimated
a charging current of 16.95 A and if for example the
modules available in the market are 80W, then from the
module specifications, the current at maximum power
point is 4.4 A. Thus, to generate the charging current
of 16.95, four modules are needed. The computation
on the battery bank capacity gives 1412.5 Ahrs and
assuming 200 Ahrs as our choice of batteries, then
seven of them are needed to create the battery bank
capacity calculated. This high battery bank capacity
takes into consideration 3 days of autonomy. Without
the days of the autonomy, only about two batteries of
similar size will be needed. The charge controller rating is calculated to be 26 A for a short current rating of
the modules of 5.2 A. In the market, one may not easily
get such a charge controller so the next higher rating
available in the market, 30 A, is chosen. The voltage
rating of the charge controller has to match the system
voltage of the solar system, in this case 12V. Lastly, the
inverter is rated depending on the devices that will be
powered by the solar system assuming they are all on
at the same time. The total power consumption in the
example is 168 W so the next higher inverter rating in
the market is obtained, for our example, a 200 W (VA)
inverter.
3.2 The EOM method
The Energy method when applied to the example above
assuming 80 W modules and 200 Ahrs batteries are
the ones available gives the total power from the modules as 302 W. This means four modules are required.
The computation gives a battery bank capacity of
1329.42 Ahrs, which is 6.65–7 batteries of 200 Ahrs,
factoring in 3 days of autonomy. Both the charge controller rating as well as the inverter ratings are obtained
as 30 A and 200 VA respectively.
3.3 Comments on the two methods
The two methods lead to the same results for each component as can be seen from above.The methods applied
here are not new but the CCM is the most commonly
used method (Michael Boxwell, 2019; Mark Hankins, 2010; Geoff Stapleton, Lalith Gunaratne, & Peter,
2002). In the CCM method, the technical specifications of the panel need to be known so as to make a
final decision on the exact size and number of panels needed. This may pose a challenge to a number
of installers and designers especially if they have no
access to these details which need either searching in
the internet or physically obtaining details in the shops.
This is a drawback for this method of sizing. On the
other hand, the EOM gives the total power needed
from the panels to meet the daily demand, a value
almost all dealers in solar PV easily identify with.
This means once the computation is done, one does not
need further details to make a final decision but can
just call the seller to confirm what sizes are available
and contact the client and advice on the combination
of panels needed. This is easier and more straightforward and is advantageous compared to the CCM
method.
In the real installation, care is taken to install solar
modules in a location where shading should not occur
at any time of the day. However, technically, modules have also bypass diodes installed to ensure that
in case some cells are shaded, the current flow from
the unshaded cells of the module bypass the shaded
cells to minimize power loss, since the shaded cells
act as loads and offer resistance. Again, once a solar
PV system is installed, its entire lifetime depends on
the individual components. For example solar modules have a factory warranty life span of 20–25 years,
batteries can last for 1–7 years depending on the maintenance, and a charge controller can last for 10 years,
while inverters can last for several years depending on
quality, usage, and maintenance.
4 CONCLUSION
Two methods of sizing a SHS have been discussed in
detail in this paper. It has been shown that the EOM is a
better and more straightforward method than the CCM.
The methods provide working estimates and that is
why they are more suited for small-sized solar systems.
More work still needs to be done to refine the methods,
for example, by taking real field data and using it to
size and compare with the initial sizing estimates. For
large solar systems, commercial sizing softwares are
recommended.
ACKNOWLEDGMENT
International Science Program, Sweden is thanked for
support.
REFERENCES
Chikh, M.,A. Mahrane, & F. Bouachri (2011), PVSST 1.0 sizing and simulation tool for PV systems, Energy Procedia
6, 75–84.
Geoff Stapleton, Lalith Gunaratne & Peter JM. Konings
(2002), The Solar Entrepreneur’s Handbook, Global Sustainable Energy Solutions
Justus Simiyu, Sebastian Waita, Robinson Musembi, Alex
Ogacho & Bernard Aduda, (2014). Promotion of PV
Uptake and Sector Growth in Kenya through Value Added
Training in PV Sizing, Installation and Maintenance,
Energy Procedia 57, 817–825.
234