Advances in Phytochemistry, Textile and Renewable Energy Research for
Industrial Growth – Nzila et al. (Eds)
© 2022 Copyright the Author(s), ISBN: 978-1-032-11871-0
Open Access: www.taylorfrancis.com, CC BY-NC-ND 4.0 license
Photovoltaic off-grid solar home system sizing using the charging current
and total energy methods: A comparison of the two sizing methods
Sebastian Waita
Condensed Matter Research Group, Department of Physics, University of Nairobi, Nairobi, Kenya
ABSTRACT: Kenya receives some good sunshine owing to its location in the tropics. Solar energy, being
environmentally friendly and an inexhaustible source of energy, has the potential to change people’s lives for
the better, especially in the rural communities in Kenya. Solar energy is converted to useful electrical energy
using solar panels exposed to the sun’s radiation. The solar panels and the other balance of system components are usually interconnected to provide this energy for powering loads. This connected system, popularly
known as a Solar Home System (SHS) is creating a lot of impact in the rural communities in Kenya. Although
the system’s installation is key in the overall system performance, the system has to be well designed and
sized as well for it to perform optimally. A number of commercially available sizing softwares are complex
and way beyond the average person in terms of cost. There are two main sizing methods: the charging current method, herein abbreviated as CCM, and the total energy method, abbreviated as EOM, which could
be easier and more accessible to solar designers and installers. In this paper, we have presented a comparison of the two sizing methods to assess if there is any significant difference between the two methods. On
applying both methods to an example, it has been found that they give the same sizing details of the components. Furthermore, the EOM appears more appealing since it provides the total power rating of the system,
the most commonly used and understood term in rating solar panels. The method is recommended for estimating the components for small solar PV systems. Large solar PV system sizing needs commercial sizing
software.
Keywords: Solar Home Systems, Solar energy, communities, sizing, method, off-grid, charging current, total
energy
1 INTRODUCTION
Since the Kenyan government enacted the energy act
in 2006 through the sessional paper number 4 of 2004,
and thereafter gazetted the renewable energy policy
in 2012, there has been an upheaval of activities in
the renewable energy sector in Kenya, especially on
photovoltaic solar systems. The creation of the Energy
Regulation Commission (ERC) (now renamed Energy
and Petroleum Regulatory Authority (EPRA)) to regulate the energy sector created a “solar energy rush” to
meet the EPRA requirements for licensing to deal with
solar photovoltaic energy systems. As a result, a number of institutions are involved in the training of solar
technicians mostly at the technician 2 (T2) level. The
Department of Physics, University of Nairobi, through
the solar academy has also been involved in training solar Photovoltaic technicians since 2012 (Justus
Simiyu, et al., 2014).
An off-grid photovoltaic solar system (popularly
called stand-alone solar system) has a number of
key components: (1) the solar modules—they generate the required electricity on irradiation through
the photoelectric effect; (2) the charge controller—
it protects the battery bank from overcharging and
over discharging; (3) the Battery bank—batteries store
the energy for use at night or in the absence of sunlight during the day; (4) the inverter—it converts
the direct current (DC) into alternating current (AC)
(can be omitted if AC is not needed); (5) the load—
the appliances powered by the solar system; and (6)
the cables—they interconnect the various components
(Michael Boxwell, 2019; Kefa V.O. Rabah, 2005).
A well-designed, sized, and installed solar system will serve the client satisfactorily. However, in
cases where the client complains, it is about low performance and poor operational condition. Whereas
some cases relate to component failures and are not
within the installers’ control, most of the above cases
are due to failure to visit site, system design, sizing errors/oversights/mistakes, and incomplete understanding of solar systems (Kenya Renewable Energy
Association KEREA, Report, 2009).
A professionally installed solar system has to go
through a number of steps: site visit, system design,
sizing and installation, testing, commissioning, and
230
DOI 10.1201/9781003221968-31
Industrial Growth – Nzila et al. (Eds)
© 2022 Copyright the Author(s), ISBN: 978-1-032-11871-0
Open Access: www.taylorfrancis.com, CC BY-NC-ND 4.0 license
Photovoltaic off-grid solar home system sizing using the charging current
and total energy methods: A comparison of the two sizing methods
Sebastian Waita
Condensed Matter Research Group, Department of Physics, University of Nairobi, Nairobi, Kenya
ABSTRACT: Kenya receives some good sunshine owing to its location in the tropics. Solar energy, being
environmentally friendly and an inexhaustible source of energy, has the potential to change people’s lives for
the better, especially in the rural communities in Kenya. Solar energy is converted to useful electrical energy
using solar panels exposed to the sun’s radiation. The solar panels and the other balance of system components are usually interconnected to provide this energy for powering loads. This connected system, popularly
known as a Solar Home System (SHS) is creating a lot of impact in the rural communities in Kenya. Although
the system’s installation is key in the overall system performance, the system has to be well designed and
sized as well for it to perform optimally. A number of commercially available sizing softwares are complex
and way beyond the average person in terms of cost. There are two main sizing methods: the charging current method, herein abbreviated as CCM, and the total energy method, abbreviated as EOM, which could
be easier and more accessible to solar designers and installers. In this paper, we have presented a comparison of the two sizing methods to assess if there is any significant difference between the two methods. On
applying both methods to an example, it has been found that they give the same sizing details of the components. Furthermore, the EOM appears more appealing since it provides the total power rating of the system,
the most commonly used and understood term in rating solar panels. The method is recommended for estimating the components for small solar PV systems. Large solar PV system sizing needs commercial sizing
software.
Keywords: Solar Home Systems, Solar energy, communities, sizing, method, off-grid, charging current, total
energy
1 INTRODUCTION
Since the Kenyan government enacted the energy act
in 2006 through the sessional paper number 4 of 2004,
and thereafter gazetted the renewable energy policy
in 2012, there has been an upheaval of activities in
the renewable energy sector in Kenya, especially on
photovoltaic solar systems. The creation of the Energy
Regulation Commission (ERC) (now renamed Energy
and Petroleum Regulatory Authority (EPRA)) to regulate the energy sector created a “solar energy rush” to
meet the EPRA requirements for licensing to deal with
solar photovoltaic energy systems. As a result, a number of institutions are involved in the training of solar
technicians mostly at the technician 2 (T2) level. The
Department of Physics, University of Nairobi, through
the solar academy has also been involved in training solar Photovoltaic technicians since 2012 (Justus
Simiyu, et al., 2014).
An off-grid photovoltaic solar system (popularly
called stand-alone solar system) has a number of
key components: (1) the solar modules—they generate the required electricity on irradiation through
the photoelectric effect; (2) the charge controller—
it protects the battery bank from overcharging and
over discharging; (3) the Battery bank—batteries store
the energy for use at night or in the absence of sunlight during the day; (4) the inverter—it converts
the direct current (DC) into alternating current (AC)
(can be omitted if AC is not needed); (5) the load—
the appliances powered by the solar system; and (6)
the cables—they interconnect the various components
(Michael Boxwell, 2019; Kefa V.O. Rabah, 2005).
A well-designed, sized, and installed solar system will serve the client satisfactorily. However, in
cases where the client complains, it is about low performance and poor operational condition. Whereas
some cases relate to component failures and are not
within the installers’ control, most of the above cases
are due to failure to visit site, system design, sizing errors/oversights/mistakes, and incomplete understanding of solar systems (Kenya Renewable Energy
Association KEREA, Report, 2009).
A professionally installed solar system has to go
through a number of steps: site visit, system design,
sizing and installation, testing, commissioning, and
230
DOI 10.1201/9781003221968-31