Implementing a photovoltaic system on ACOHOF Family Farm
School in Tatum, Cameroon
- A pre-study to evaluate a suitable system design
Project in Energy systems 1FA391 Uppsala University
Hampus Johansson Daniel Furén 23 September 2016
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Abstract
This study was conducted to serve as a pre-study to EWB (Engineers Without Borders) and their project to implement a PV (photovoltaic) system on AFFS (ACOHOF Family Farm School) located outside of Tatum in Cameroon.
Tatum is a rural village in the North-West region of Cameroon. Even though Tatum has a connection to the national electrical grid few households are connected to it since it is unreliable and the electricity expensive.
AFFS opened outside of Tatum in 2014 with the aim to offer education for unprivileged children exposed to poverty. Since the grid connection is poor, studying hours are restricted and computers are not possible to be operated. To enhance AFFS education possibilities, EWB in Uppsala has initiated a project which aims to install a PV system on AFFS, to provide a more reliable source of power. Prior to the installation, the size of the PV system must be determined, the availability of components researched and placing of them identified. Also, it is necessary to imbed the users of the system with its possibilities and disabilities.
To carry out the pre-study, different retailers of PV components were identified and their costs documented. A load profile was identified and modified, to reduce the energy consumption and the investment costs. The identified load profile peaked at 2.8 kW and consumed 29.4 kWh per day while the reduced load profile peaked at 1.5 kW and consumed 12.1 kWh per day. With an allowed capacity shortage of 10%, the identified load profile translated into a system solution of 6.85 kWp solar modules, 14 batteries with 200 Ah each and a 3.48 kW inverter at a total investment cost of 8 903 600 CFA (Central African franc) or 127 000 SEK (Swedish krona). With an allowed capacity shortage of 10%, the modified load profile translated into a system solution of 2.82 kWp solar modules, 5 batteries with 200 Ah and a 1.66 kW inverter at an investment cost of 3 522 700 CFA or 50 000 SEK. The solar modules were suggested to be placed on the roof of the poultry, since it offered a good direction toward sun and since it is located in a remote zone in the school area. For the system to sustain its life expectancy, it is important to stress for the users that the system is not an endless source of energy and that it is of great importance to not over dimension the load
The recommendation from the pre-study is to dimension the PV system with regard to the modified load profile and to accept a capacity shortage of 10%, which resulted in an investment cost of 50 000 SEK. The recommendation is motivated by the fact that the identified load profile hade a very high energy need during the night, which is not compatible with PV systems that generate electricity at daytime. Further, a capacity shortage limit of 10% would reduce the investment cost compared to a limit of 5% but would still be a big improvement from the existing capacity shortage of 16%, when the grid is the only power source.
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Acknowledgements
To all persons and organizations that made this study possible we are most thankful.
For the valuable feedback, advices and measurement equipment supplied we would like to thank our supervisor in Sweden, David Lingfors.
We are very thankful to our supervisors in Cameroon, Yongka Gilbert Kininver and Divine Verdzekov for supporting us and attending all of our needs.
Thank you Stefan Karnebäck for answering our questions and helping us with the measurement data.
We would also like to thank Justin Afoni and the ACOHOF organization for taking care of us and making us feel like home. Thank you, all the staff at ACOHOF for all help provided during our stay in Tatum.
At last, a sincere gratitude to SIDA for providing us with the financial support and to Engineers Without Borders Uppsala for introducing us to this project, making this field study possible.
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Table of contents
1. Introduction ... 5
1.1 Scope of the study ... 5
2. Background ... 6
2.1 Cameroon... 6
2.1.1 Tatum ... 6
2.1.2 The energy situation ... 8
2.1.3 Education ... 9
2.2 The ACOHOF organization ... 9
2.3 Engineers without borders project ... 10
3. Theory ... 11
3.1 Generating and storing electrical energy via photovoltaics ... 11
3.1.1 Solar cells and solar modules ... 11
3.1.2 Storage ... 12
3.1.3 Other components in a photovoltaic system ... 12
3.2 Measurements for solar energy potential ... 13
3.2.1 Pyranometer ... 14
3.2.2 Photodiode solar logger ... 15
3.3 Power quality and capacity shortage ... 16
3.4 Sustainability of PV systems ... 17
4. Fieldwork ... 18
4.1 Method and material ... 18
4.1.1 Measurements ... 18
4.1.2 Examining the power need ... 18
4.1.3 Physical research ... 19
4.1.4 Availability of PV components ... 20
4.1.5 Sustainability of the PV system ... 20
4.2 Results from fieldwork ... 21
4.2.1 Measurements ... 21
4.2.2 Power quality and capacity shortage... 23
4.2.3 Examining the power need of AFFS... 24
4.2.4 Physical research ... 26
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4.2.5 Availability of PV components ... 28
4.2.6 Sustainability ... 31
4.3 Discussion ... 32
5. Simulations ... 35
5.1 HOMER Energy ... 35
5.2 Method and material ... 36
5.2.1 HOMER Energy ... 36
5.3 Result ... 38
5.3.1 Identified load profile ... 38
5.3.2 Reduced load profile. ... 39
5.3.3 Cost of energy ... 39
5.4 Discussion ... 40
6. Conclusions ... 42
References ... 43
Appendix ... 46
A – Contact information for the retailers of PV system components ... 46
B – Power cuts ... 46
C – Electrical equipment and operating hours ... 48
D – Interview with the constructor, Clifford Brifee ... 50
E – Power need evaluation questionnaire ... 51
F – Interview with the program manager of ACOHOF, Gilbert Yongka ... 52
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1. Introduction
The energy provided through solar radiation each year to the earth is enough to supply the whole world’s energy demand and Africa is the continent that receives the highest amount of solar energy on its surface [1]. On average basis, most part of Cameroon experience solar irradiance of 5.8 kWh/m2/day [2], which provide good conditions for PV systems. Northern-more countries, e.g. Sweden, experience a wider variety in solar irradiance over the year, due to the difference in hours of sunlight over the year. However, to highlight the intense solar irradiation in Cameroon, on a yearly basis most parts in the south and middle of Sweden experience a solar irradiation of around 3 kWh/m2/day [3].
PV systems are generally differentiated between grid-connected- and stand-alone systems. While a grid-connected system is relatively easy to dimension, since the excess generation of electricity is assumed to be absorbed by the grid at all times, an off-grid system has to be accurately dimensioned in accordance with both energy consumption and the site-specific solar irradiation [3].
Renewable energy technologies, such as PV systems, have some major advantages compared to conventional energy technologies, the energy source used is practically inexhaustible and the technologies generally has low environmental impacts, e.g. CO2- emissions, when operated. A big disadvantage with some of the renewable energy technologies, e.g. PV and wind power, is the uncertainty and variation in supply due to the intermittent character of their energy sources.
In many African countries, where a big part of its population have poor access to electric grid and the grid has poor reliability, there is a need for other means than the conventional ones to access electricity [4]. PV systems are an alternative for rural areas to generate electricity without being connected to the national grid. To ensure availability at times with little or no sunshine, there is also a need for storage systems.
1.1 Scope of the study
This study was conducted as a pre-study on site in Tatum. The outcome of the project served as an input to EWB and the finalization of their project; installing the PV panels and educating local actors. To cover the various aspects of EWB: s project, the pre-study considered technical- and sustainable issues related to installing and maintaining a PV system in a rural area in Cameroon.
• The main technical scope of the study is to investigate the electricity need at the school, research local available components and from this design a suitable PV system.
• The sustainable scope of the study is to identify people eligible for operating and maintaining the system and identify their preexisting knowledge.
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2. Background
This report is based on a field study in Tatum, Cameroon. The study was conducted as a pre-study for EWB with the aim to determine the energy needs of AFFS and to further investigate the availability of solar modules and other PV components in the nearby area.
The data collected during the field study was used to simulate a PV system and to propose a suitable system design. Consequently, the report is divided into two separate method- and result parts, where the first part, containing the fieldwork, is being used to simulate PV system in the second part of the report.
2.1 Cameroon
Cameroon, i.e. Republic of Cameroon, lies within the Gulf of Guinea in the mid-western Africa and share its border with Nigeria in the north-west, Chad in the north, the Central African Republic in the east and the Republic of the Congo, Gabon and Equatorial Guinea in the south. Much because of its access to natural resources, such as oil, natural gas, mineral and agricultural products Cameroon is considered a lower middle income country [5] and a favorable economy in sub-Saharan Africa [6].
Approximately 23.7 million people inhabit Cameroon [5]. The north-west and south-west regions are Anglophone while the remaining regions are Francophone. Roughly 40% of the inhabitants of Cameroon is considered poor [5, 7] and are forced to manage their existence on expenses less than two US dollars per day. Compared to the bordering countries, this is a high share [5]. The access to modern health care is inadequate and unevenly distributed, the most frequent cause of death is Malaria and AIDS [7].
2.1.1 Tatum
Politically, Cameroon is divided into 10 regions, all of which is divided into divisions.
The divisions are further divided into sub-divisions [7, 8]. Tatum is the sub-divisional capitol of the Nkum sub-division, situated in the Bui division in the north-west region [9].
Nkum inhabits approximately 100,000 people [8] and is located at an altitude of approximately 2.000 m above sea level and the area experiences a climate favorable for agriculture, which occupy most of its inhabitants [8]. There are two seasons covering the year. The dry season range from mid-October to mid-March, the rainy season covers the rest of the year [8]. Whereas the wet season has an abundance of the dry season seldom experiences rainfall. The average annual rainfall is about 1800 mm and the average temperature ranges from 21 to 32 degrees over the year [8]. Like many of the rural areas in Cameroon, Nkum is characterized by poverty and lacks reliable infrastructures, health care, labor opportunities and other facilities associated with a decent living [9].
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Figure 1. Map of Cameroon, created using OpenStreetMap.
Figure 2. Map of Nkum sub-division, created using OpenStreetMap.
8 2.1.2 The energy situation
Even though Cameroon has access to oil, natural gas and hydropower, most Cameroonian households are using wood and charcoal as energy source for primarily: heating, cocking and warming water [4, 7], and since the household sector stands for the largest portion of the energy use in Cameroon, wood and charcoal is the most utilized energy resource [2].
The national electrical grid in Cameroon is not evenly developed and faces both technical and structural challenges [10]. Access to the national grid can normally only be obtained in urban areas while there are little development regarding electricity access in rural areas.
About 20% of the population has a connection to the national electrical grid [4, 10], in rural areas this share is 3.5% [10]. To further connect rural areas, large extensions of the national grid is central and investments in distributed hydro- and diesel power plants necessary according to [4].
The main actor on the Cameroonian electricity market is the integrated utility company ENEO Cameroon S.A. [10, 11], which prior to September 12th 2014 was known as AES- SONEL [11]. In July 2001 a concession agreement was sign that gave AES-SONEL the distribution rights to all middle- and low voltage costumers and the exclusive rights to operate the transmission network over a period of 20 years [11]. The generation of electricity is open for competition [10] but since the transmission network is discontinuous it is not possible to distribute the generated electricity over the whole country [10]. The transmission network in Cameroon consists of three separate grids: the southern interconnected grid, the northern interconnected grid and the eastern isolated grid [2, 10].
In terms of installed capacity, Cameroon is the second largest owner of hydropower in Africa, after the Democratic Republic of the Congo [4]. In 2010, the installed capacity of hydro electrical power plants was 729 MW in Cameroon, 48.4% out of the total 1505 MW installed capacity [10]. On an annual average, the hydro electrical power plants supply the transmission network with 75% of its electrical energy [4]. As of 2010, there were no other renewable technologies than hydro electrical power plants used to generate power to the transmission network, the other operated power plants in Cameroon were natural gas- or diesel driven thermal power plants [10]. A combination of the dependence on hydropower plants, their poor performance rate [12] and the seasonal dry periods makes the production of electrical energy unstable. Power cuts are a normality and it occurs that power distribution has to be regulated by ration [7].
Since the beginning of 1990’s there have been multiple failed tries to form different energy policies and frameworks in Cameroon, with the purpose of mobilize and utilize its energy resources [4]. Vision 2035 is a recent framework that emphasizes an increased production of electrical energy, oil and natural gas in order to be energy independent and increase the economic growth [13]. In 2012, the Cameroonian government recognized photovoltaics as a feasible source of electrical energy, as they signed a memorandum of
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understanding with a private developer to finance 500 MW of grid-connected and off- grid photovoltaic systems between 2012 and 2020 [10].
2.1.3 Education
Cameroonian kids start primary school at the age of six. The primary schools are run and funded by the government, Christian communities and private actors. Nevertheless, students have to pay for school uniforms and books [7, 8]. Even though the primary school is compulsory, only 70% finishes it [7]. Despite governmental investment in the school system, there is a general lack of teachers, classrooms and material. Furthermore, several schools in the northern parts of the country have shut down in the recent years, due to the violent situation [7].
First school and secondary school are the two stages following up the primary school.
Together, these stages last for seven years and are optional. Since these stages are subjected to surcharges for the students, few families can afford their children to attend [8]. Only 40% of the students graduated from primary school continues to the following up stages [7].
2.2 The ACOHOF organization
ACOHOF (Afoni Children of Hope Foundation) is a voluntary, non-profit making development organization based in the Bui-division in Cameroon. ACOHOF: s objective is to give under-privileged children better opportunities to make a decent living [9, 14].
In 2014 ACOHOF started the AFFS (ACOHOF Family Farm School) outside the village of Tatum. AFFS is a boarding secondary school with the aim to prepare children in the age between 12 and 20 years old for self-employment and entrepreneurship throughout a three-year educational plan [8, 9]. The education at AFFS alternates between theoretical- and practical learning by allowing the students a two-week in-school period with theoretical education and a following two-week period of practical work at home [14].
The purpose of the alternation is to allow students to put their learnings in practice and to not alienate them from their families and communities [8].
The site where the school is situated has no connection point to the national grid itself, but a line drawn from the closest connection point has enabled the school electricity. Due to the distance of approximately two kilometers to the connection point, the quality of power supply is poor and AFFS experience major voltage drops. Big enough to eliminate the schools’ intention to create a computer lab and provide sufficient reading- and security light [8].
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2.3 Engineers without borders project
EWB is a non-governmental organization that has multiple divisions in various countries.
EWB conducts and supports projects based on engineering, often in collaboration with local organizations and actors with the intention to find technical solutions with respect to the local conditions. An overall aim of EWB is to improve the possibilities of education by enhancing the study environment in school and at home, throughout volunteer based projects. [15]
During 2015 EWB: s division in Uppsala, Sweden, initiated a project together with the ACOHOF organization. The project aims to enhance the study environment at AFFS by installing a PV system. The PV system is intended to provide AFFS with enough power to run a few computers and to supply power for reading- and security lighting when the sun is set [16]. The project is to be finalized during the winter of 2016/2017, when the group coordinating the project at EWB: s Uppsala division travels to Tatum to install the PV system at AFFS.
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3. Theory
3.1 Generating and storing electrical energy via photovoltaics
There are mainly two types of PV systems. While one system is connected to the grid where it delivers its excess electricity, the other system is a stand-alone system connected to a storage system where the excess energy is stored for future use. A PV system connected to the grid usually consists of three main components, PV modules, an inverter and an energy meter [3]. A typical stand-alone PV plant consists of few more components due to the necessity to store the energy. The stand-alone PV system generally consists of PV modules, a charge controller, batteries, a deep-discharge protection and an inverter [3].
In addition to grid connected- and stand-alone PV systems, hybrid PV systems are a combination of both. In order for a stand-alone PV system to be available to deliver enough power continuously during a whole year, the installed capacity of solar modules and storage would in most cases need to be large and therefore costly. A hybrid PV system bridges the gaps in power supply from the PV modules by adding an alternative source of power, that is used when the irradiation is too low or the batteries are not charged [3].
In isolated areas not connected to a public grid, diesel generators are commonly used alternative source of power [17].
3.1.1 Solar cells and solar modules
The main component of a solar cell is the semiconducting material, most commonly silicon is used as semiconducting material in solar cells [3]. A semiconducting material allows for the electrons to transfer between the valence- and the conducting band in the atomic structure, the band gap [18]. Semiconducting materials found in solar cells are most commonly p-n doped [3]. P-n doping means that the semiconducting material is contaminated with atoms of other semiconducting materials to increase the number of available electrons and electron-holes, which makes it easier for the electrons to transit the band gap and thus increases the conductivity [18].
When in the valence band, the electron is in its natural state and bonded to the nucleus. If a light particle, a photon, with the corresponding amount of energy to the band gap, the energy difference between the two bands, hits the electron it will absorb the photon and excite to the conducting band [18]. When the electron is excited to the conducting band, it is given a higher potential energy. The increased potential energy is used in solar cells by leading the electron back to the valence band through an electrical circuit, and thus generating electricity [3].
A solar cell usually generates an open circuit voltage in the range of 0.5 volts [3]. To increase the voltage, multiple cells are connected in series allowing the overall voltage to be the sum of all individual cell voltages. Multiple solar cells connected to each other are referred to as a solar module. Since shading just one of the cells would drastically
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decrease the power output of the solar module, several solutions for such as bypass diodes can prevent that from happening [3]. In a similar manner as the solar cells are connected in the modules, the modules can be interconnected in series to form a PV generator.
3.1.2 Storage
Since it is only possible for solar cells to generate electricity when exposed to solar irradiation, means for storing the energy is necessary to be able to use the energy at the time it is needed. The most common and easily accessible solution to this is to use batteries. Other solutions such as flywheels and super capacitors among others are not included in this report and thus not investigated further.
There are many different types of batteries for different applications, such as lithium ion, lead-acid, nickel metal hydride to mention a few. The ones used in PV-systems are almost exclusively lead-acid batteries, due to its high energy density and low cost, compared to the other battery types [3, 19]. Lead-acid batteries are available in almost any size and voltage level, which in addition to the ability to supply high surge currents this contributes to the wide use of lead-acid batteries [19]. Also, the fact that the lead-acid batteries has been developed over more than 140 years contributes to a robust and reliable technology [19].
Each battery is individual in terms of lifetime, based on how the individual battery are treated. Among the parameters affecting the lifetime of batteries are: discharge rate, charge rate, state of charge and battery temperature during operation and idling [19].
Also, how deep the battery is being discharged affects the lifetime and aging of the battery [3, 19]. Frequent deep discharges can drastically decrease the lifetime, why most manufacturers recommend the batteries not being discharged to less than 40% of its capacity [3].
The drawbacks of lead-acid batteries are foremost the fact that it consists of lead, a toxic heavy metal with a high density that leads to heavy batteries and environmental risks [19].
If the battery is fully charged, and keeps getting charged, gassing occurs. Gassing refers to that hydrogen- and oxygen gas forms when the battery exceeds the end-of-charge voltage and for this reason the room where the batteries are stored must have sufficient ventilation, in order to prevent explosions [3, 19].
3.1.3 Other components in a photovoltaic system
As solar cells generate DC (direct current) and the electric grid as well as many electrical devices uses AC (alternating current) there is a need to transform DC to AC. This is usually done by an inverter. The sizing ratio of the inverter compared to the solar module peak efficiency should be more than 1 in order to reach maximum yields [3]. If the system is not connected to the grid, a DC-system can be used and an inverter would not be needed, instead a DC-DC converter can be used to transform the electricity to the desired voltage [3].
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For the batteries in a PV system to sustain its technical lifetime a charge controller is necessary. The charge controller has several tasks, namely: overload- and deep-discharge protection, prevention of unwanted discharging and state-of-charge monitoring [3].
Charge controller with additional features, such as DC/AC transforming, are available on the market and commonly referred to as a solar hybrid inverter [20].
Even though a PV plant on the roof of a house does not increase the risk of a lightning strike, it is of importance to protect the PV system from damage caused by high voltages.
The grounding should be carried out with a copper wire of at least 6 mm, in the shortest path to the grounding point [3].
3.2 Measurements for solar energy potential
To determine the potential for a PV system the irradiation from the sun needs to be measured. The amount of irradiation determines the potential power a solar module can generate.
The incoming irradiation can be divided into three components: direct irradiation, diffuse irradiation and reflected irradiation the sum of these components is called global irradiance, se Figure 3 for illustation.
• The direct irradiation is the irradiation from the sun which reaches the surface without any interference.
• Reflected irradiation on the other hand is irradiation which is being reflected on an area. The irradiance can be reflected on various types of areas with different amount of irradiation being reflected [3], this is called the albedo value which describes the resulting reflecting factor from the area.
• Diffuse irradiation is formed when the irradiance interacts with particles in the atmosphere and results in scattered irradiance. Therefore, diffuse irradiation arrives from all directions. How much diffuse radiation there is depends on how much particles there is in the atmosphere and how long distance the irradiance must travel through the atmosphere. Because of this, there is more diffuse radiation on cloudy days and when the sun height is low. Approximately 40% of the total irradiance is diffuse [3].
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Figure 3. Illustration of the different radiation types reaching the PV module.
Another important aspect of a PV system is to position the modules with regard to the path of the sun and the sun height angle [3]. Calculating the most favorable angle and direction for the modules enables a higher system yield, since more radiation can be absorbed by the modules [3]. Depending on at what time of the day the energy is needed the modules can be oriented in a favorable angle for that time of day. For example, if the energy is needed in the mornings the modules can be tilted towards the east, to utilize more of the solar energy in the morning.
To determine the irradiation behavior at potential sites for a PV system the global radiation at the site must be measured, to do this there are various types of sensors. Most sensors determine the global radiation which is the direct, diffuse and reflected radiation combined. One of the most common equipment used when measuring solar radiation is the pyranometer which is the most accurate device to measure global radiation [3].
An economical alternative to a pyranometer is to use a solar cell, a photo diode, as measurement equipment. The photodiode is short-circuited using a shunt resistor with low resistance, enabling the voltage drop at the resistor to be measured. Since the short circuit current is proportional to the irradiation it is possible to derive the irradiance [3].
3.2.1 Pyranometer
A pyranometer is a sensor that measures the global radiation. The heating of the absorber surface, caused by the sunrays, leads to a temperature difference between the absorber surface and the environment. The temperature difference is determined by the thermopile and allows the incident irradiance to be measured [3].
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Figure 4. Structure of a pyranometer.
∆𝜗 = 𝜗1− 𝜗𝐴 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡 ∗ 𝐸 (1)
∆𝜗 = 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒 𝜗1 = 𝑎𝑏𝑠𝑜𝑟𝑏𝑒𝑟 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝜗𝐴 = 𝑎𝑚𝑏𝑖𝑒𝑛𝑡 𝑡𝑒𝑚𝑝𝑒𝑟𝑎𝑡𝑢𝑟𝑒 𝐸 = 𝑖𝑛𝑐𝑖𝑑𝑒𝑛𝑡 𝑖𝑟𝑟𝑎𝑑𝑖𝑎𝑛𝑐𝑒
A pyranometer consists of two glass domes, an inside and an outside hemisphere which have two main tasks. Firstly, they ensure the absorber surface re-radiates as little heat as possible. Secondly, the hemispherical form makes so that the sensitivity depends on the incoming radiation, meaning the vertical irradiation will contribute with maximum effect while the horizontal contribution should be close to none. The drying cartridge is mounted to prevent misting of the glass cover, which would affect the results [3]. Even though the measurement spectrum of a pyranometer is limited to 300-2800 nm, the device is very accurate since this interval covers most of the solar radiation [3].
3.2.2 Photodiode solar logger
In contradiction to a pyranometer, a photodiode solar logger only measures a limited interval of the solar wavelength spectrum. The shell covering the photodiode reflects the irradiation with dependence of the angle of incidence, also the AM (air mass) at the specific site must be considered constructing such a device. Nevertheless, the disadvantages of a photodiode are also its benefits. Using a photodiode with the same technology as the intended PV modules yield a realistic measurement, since a photodiode measures the available irradiation for a PV model with the same technology as the photodiode [3 p.207].
A low-cost solar irradiance logger was supplied from the Department of Engineering Sciences at Uppsala University, its design is presented in Figure 5 and its image can be viewed in Figure 6. The components of the device are mounted on a double-sided circuit
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board which is placed in a water proof junction box with a window in the center of the lid, directly above the photodiode [21].
Figure 5. Solar logger design. Reproduced with permission [21].
Figure 6. Image of the photodiode solar logger used during the fieldwork. The batteries that supplies the device are underneath the circuit board, inside the junction box.
3.3 Power quality and capacity shortage
Power quality is a term that describes the fitness of electric power that drives electrical equipment [22]. Consequences of poor power quality might be unexpected power supply failures, equipment failure or malfunctioning, equipment overheating, damage to sensitive equipment such as computers, and many more possible consequences [24].
The power quality investigated in this report is of a basic essence, where the amount of power cuts serves as the measure. Documenting the number of power cuts and its duration leads to a capacity shortage fraction, which is expressed as a percentage of time when power is not available [23].
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3.4 Sustainability of PV systems
Sustainability is most often associated with the term sustainable development as first described in the Brundtland Report 1987 [31], in which human development goals is met without damaging the ability of natural systems to provide natural resources and ecosystem services.
In this report, however, sustainability does not have that broad meaning. Instead sustainability is here referred to as the durability of a PV system in terms of its technical lifetime, where it can be operated to generate electrical energy.
As a developing country with a poor electrical grid, Cameroon is in need of innovators and early adopters in order to develop a sustainable energy market [25]. As a part of this, PV systems could be a solution. The early adopters trigger the majority to continue to implement the new technology and are often younger, more positive and more willing to take risks [25]. Therefore, spreading the knowledge amongst the population could improve the implementation of renewable energy sources.
Maintenance of a PV system done by the users have bigger impact on the sustainability of the system compared to maintenance by the implementer [26]. In many programs implemented in rural areas of developing countries, a barrier for sustainable promotion of PV electrification can be found and a lack of knowledge about the technology [27]. If the load capacity of the PV system, limited hours of usage, is not communicated there is a risk that the expectations on the system will be over exaggerated and thus leading to disappointment when the system does not live up to the expectations [28]. If the users expect unlimited amount of electricity and no restriction on the usage the attitude towards renewable energies might be affected in a negative manner [28].
In order to successfully implement an off-grid PV system in rural areas it is necessary to include other parameters than good technology and reasonable financial prices. It also requires that attention is attended to social and political issues. Understanding the attitude of the community and the electricity needs but also to include the community could be a cornerstone in achieving a sustainable PV system [25].
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4. Fieldwork
The fieldwork was carried out in order to collect data and to make observations on site in Tatum. The fieldwork was conducted during an eight-week period in the summer of 2016 and is the first part of this project, followed up by a simulation part.
4.1 Method and material
The overall method used in this project was an on-site investigation of the different parameters. The various parameters were found using the different methods described below.
4.1.1 Measurements Solar irradiance
To measure the available solar irradiance on-site, a pyranometer and a photo diode was used. The pyranometer was installed prior to the fieldwork and located on the school area, close to where the solar modules were to be installed. Next to the pyranometer a photodiode solar logger was placed and used to gather data during the field work period.
The obtained data was extracted and refined using MATLAB, in order to visualize the solar irradiance data and to calculate the accumulated solar irradiance for the fieldwork period.
Power quality
The existing electrical connection to the school does not enable the school to use computers, but might be able to charge batteries in a PV system as a complement to the solar panels. Therefore, measurements of the availability of electricity were made. The measurements were conducted by observing all power cuts and document them during a 5-week period, from the 15th of June to the 20th of July 2016.
By documenting the number of power cuts and the length of each power cut, the total hours of power cuts were yielded, the mean duration of a power cut and the standard deviation for power cuts calculated. Further, the variability in repair time was calculated, which is the quota of the standard deviation and the mean duration and expresses the variability in power cut duration. This data is later to be used, to simulate the power available from the grid during a whole year. It should be noted that the Tatum-area generally experience more and longer power cuts during the dry season than during the wet season, which is when the pre-study was conducted.
4.1.2 Examining the power need
In order to get the necessary information about the current and future energy needs and the operating hours of AFFS, meetings, interviews and discussions were performed. The people subjected to these occasions were key-persons in the organization of the AFFS,
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and were thus familiar with the foreseeable future and direction of the school. The information about the energy needs and operating hours were used to create a load profile for AFFS.
The interview method used was semi-structured interviews. This method was used to encourage the interview objects to discuss with each other and with the interviewers, to come up with new ideas of what electrical equipment that are and could be needed at the school [30]. The question asked and discussed are to be found in Appendix E and the results from the interview are presented in Table 12 and Table 13 in Appendix C.
To identify the current energy need, the electrical equipment was evaluated in terms of power. The need was divided into categories with regard to equipment type. The operating hours for each equipment category was investigated through questions during the interview and meeting session.
The main categories investigated were:
1) Lighting 2) Computers 3) Televisions
4) Other electrical equipment
In order to get an accurate load profile, the investigated categories were divided into additional subgroups, where the equipment had the same operating hours. For example category 1) was further divided into reading- and security lighting.
The reading- and security lights were examined as well as the power of all existing lightbulbs and spotlight. The existing computers, computer screens and televisions were examined and their average power usage determined. The computers and their screens were assumed to have an average power consumption of 100 W. At last, various electrical equipment was examined and gathered in the last category.
In additional to the identified load profile, a modified load profile was created, were the potential reduction in power usage was taken into consideration. Operating hours-, power consumption- and number of lightbulbs were modified. The operating hours for the security lights were reduced by 50%, the light bulbs were assumed to be changed to low energy lightbulbs which assumed to use 11 W instead of 35 W. The number of security lightbulbs were reduced by 50%, meaning a reduction with 15 security lightbulbs. In the case of the reduced load profile, the computers not yet acquired were assumed to be less energy consuming and were assumed to use 50% less energy than the existing ones.
4.1.3 Physical research
To locate possible placements of the components in the PV system, a meeting with the constructor of the school properties was arranged. Since the school area still was under
20
construction, the meeting was necessary to determine where future structures were going to be placed. Furthermore, the strength of the roofs on the buildings had to be examined to make sure that they were eligible for placement of PV modules and the angle of the roofs had to be measured. The diagonal, length and height of a roof forms a triangle.
Measuring these dimensions for the prospected roofs enabled the use of trigonometric relations to figure out the angle.
Foremost, the placement of the PV modules was in focus during the interview but placements for batteries and other electrical components were examined as well.
In preparation for the meeting, a few general questions were formulated in order to have a ground for discussions. The questions discussed can be found in Appendix D.
4.1.4 Availability of PV components
To create a PV system in Cameroon and to make sure that local people can implement similar systems it is necessary to use local actors and buy local equipment. To find the available products that can be used in the system a field trip to Bamenda was made, the closest city with such equipment available. With help from locals, different retailers were visited and their products inventoried and documented. Three different stores were visited namely, SafeNet, Sono Inter System Commerce General and Tupecam Solar Energy. At all three stores the managers were asked what products they had to offer and at which prices. The PV system simulated will therefore be using the equipment that were available to buy in the local area.
4.1.5 Sustainability of the PV system
In order for the PV system to sustain its technical life span there are two main issues to address, one being the technical security and the other one the operating security. Both subjects focus on minimizing the risks of failure and ultimately breakdown. While the technical security refers to components in the system, the operating security refers to the manmade operation and maintaining of the system. The focus of the study was the operational security.
To make sure that the personnel operating the system have sufficient knowledge, a course will be held where the people attending will learn how to operate and maintain the system.
For this reason, interviews were held to find relevant people and to obtain information about their current knowledge, to assure they were eligible to attend the course and can operate the system in a secure way.
The people to attend the course were selected by consulting with Gilbert Yongka the ACOHOF manager. The persons were selected from both the organization as well as from the community. The people suitable for the course were mostly from the ACOHOF organization but to further anchor the knowledge and interest, some external persons with
21
existing knowledge about PV systems were selected to make sure that the understanding needed would exist in the area at all time.
4.2 Results from fieldwork
4.2.1 Measurements
To illustrate the irradiation on a single day, Figure 7 shows the irradiation on an arbitrary chosen day from the data provided by the pyranometer. Figure 8 and Figure 9 below illustrates the solar irradiance data gathered during the fieldwork. The instantaneous solar irradiance measured by the two devices differ quite a lot, especially regarding a peak between 200-300 hour for the photodiode solar logger, if one compares the area marked with a red dotted line in Figure 8 and Figure 9. The logging of the measurement data from the pyranometer started one day after the logging of the data from the photodiode solar logger, why each peak in Figure 9 corresponds to the peak next to the right in Figure 8.
By integrating all values from the different measurements, the total amount of accumulated solar irradiance during the field work period where 108.84 kWh/m2 for the photodiode and 108.55 kWh/m2 for the pyranometer. Meaning that, even though the differences in instantaneous irradiance, over time the photodiode and the pyranometer give similar results. In Table 1 the daily average accumulated solar irradiance from the photodiode and the pyranometer is presented along with value from the satellite derived data. The deviations between the measurements and the satellite derived data in Table 1 are further discussed in section 4.3.
Table 1. Accumulated solar irradiance, derived by measurement data from the two devices and satellite derived data collected from HOMER energy.
Device Photodiode solar
logger
Pyranometer Satellite derived data Accumulated solar
irradiance [kWh/m2day]
3.74 3.73 4.13
22
Figure 7. Irradiation during the second day of measurements, data from the pyranometer.
Figure 8. Irradiation measured by the photodiode solar logger.
Figure 9. Irradiation measured by the pyranometer.
23 4.2.2 Power quality and capacity shortage
According to the measurements at the school, the number of power cuts were 27 in 35 days. Overall, the power was cut for 137 hours which translates into a capacity shortage of 16%. Table 11 in Appendix B, each power cut and its duration during the fieldwork period is presented. The duration of a power cut during the fieldwork period varied from 5 minutes to 25 hours. Figure 10 illustrates all power cuts longer than 5 minutes. Table 2 presents parameters concerning the electrical grid and its reliability.
Even though the attempt to measure the voltage variations failed, due to equipment malfunctioning, the experience was that the voltage fluctuated a lot. However, since it was not possible to measure these voltage variations, no consideration to the voltage variation is being made in this report.
Figure 10. Graph of the available power at AFFS. The white areas show all power cuts during the fieldwork period.
Table 2. Electricity price and reliability parameters of the electrical grid in Tatum.
Measured and evaluated during the fieldwork period.
Electricity price [CFA]
Average duration of power cuts [min]
Standard deviation [min]
Variability in repair time [%]
92 272.8 398.92 146
To simulate the power quality in the simulation tool, later to be presented, the parameters in Table 2 was needed and therefore presented here, as explained under section 4.1.1. The standard deviation shows that the duration of power cuts was varying heavily, since it describes the deviation from the mean value.
15-jun 16-jun 17-jun 18-jun 19-jun 20-jun 21-jun 22-jun 23-jun 24-jun 25-jun 26-jun 27-jun 28-jun 29-jun 30-jun 01-jul 02-jul 03-jul 04-jul 05-jul 06-jul 07-jul 08-jul 09-jul 10-jul 11-jul 12-jul 13-jul 14-jul 15-jul 16-jul 17-jul 18-jul 19-jul 20-jul
24 4.2.3 Examining the power need of AFFS
The tables over the electrical equipment and their operating hours, Appendix C, were combined to form a load profile for AFFS. The load profile was based upon the conducted interviews and shows the desired power need of AFFS on an hourly basis. Even though some of the equipment are not used on a daily basis, e.g. student television, Figure 11 shows the load profile for a weekday when all of the electrical equipment is being used.
The peak load for the load profile was 2.8 kW and the daily energy consumption was 29.4 kWh.
Figure 12 shows the reduced load profile for AFFS where some possible energy saving measures were implemented. The peak load for the reduced load profile was 1.5 kW and the daily energy consumption was 12.1 kWh, the savings are presented in section 4.1.2.
25
Figure 11. AFFS load profile.
Figure 12. Reduced load profile for AFFS.
0 500 1000 1500 2000 2500 3000
00:00 01:00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00
Hourly mean power [W]
Indoor lights Classroom lights Security light Ad. Comp
Ed. Comp Fridge Staff tv Student tv
Projector Phone charging Blender Total power use
0 200 400 600 800 1000 1200 1400 1600
00:00 01:00 02:00 03:00 04:00 05:00 06:00 07:00 08:00 09:00 10:00 11:00 12:00 13:00 14:00 15:00 16:00 17:00 18:00 19:00 20:00 21:00 22:00 23:00
Hourly mean power [W]
Indoor lights Classroom lights Security light Ad. Comp
Ed. Comp Fridge Staff tv Student tv
Projector Phone charging Blender Total power use
26 4.2.4 Physical research
By consulting AFFS: s constructor, the suggested positioning for the PV modules was created. The primary positioning was considered to be on the roof of the poultry, which is located in the middle of the school area. The secondary suggestion was on the ground behind the poultry which is not being used. The poultry building is not yet finished and may therefore be adjusted to better fit hosting the PV modules.
The right side, according to Figure 13, of the roof is aligned in a south-east direction with a slope of 17.08°, which is good since a low angle is preferable in countries close to the equator. The angle was calculated using trigonometric relations and the measured values are presented in Figure 15. On the secondary position, on the ground, the angle could be modified in any angle.
Figure 13. The situation plan for AFFS with proposed positioning of the PV modules.
The red color indicates the primary location on the poultry roof and blue color the secondary location on the ground.
For storing the batteries, a new building was proposed. The new building was proposed to be located next to the poultry where the PV modules are suggested to be located. The constructor recommended building the battery storage room on either the north-east or the south-east side of the poultry as shown in Figure 14.
27
Figure 14. Part of the situation plan for AFFS with red rectangular squares where the battery storage is suggested.
Figure 15. Image of the poultry with the angle of the roof presented.
28 4.2.5 Availability of PV components
During the excursion to Bamenda three different retailers of PV system components were visited and their supplies inventoried. The available components are compiled in Table 3, Table 4 and Table 5.
In Table 3 the available PV modules are presented. The specifications are presented as they were found, some spaces are left blank since no specifications was available. The different PV modules were arranged with respect to technology, rated capacity and cost.
Table 4 lists the available batteries from the various retailers, the only technology available was 12-volt lead-acid batteries and the available batteries are arranged with respect to cost and maximum capacity. The available inverters with their parameters are presented in Table 5 some of the parameters of some inverters were not obtained, why some of the columns are left blank.
The retailers visited are listed below and the contact information to the retailers can be found in Appendix A.
1) SafeNet - value & power secured 2) Sono Inter System Commerce General 3) Tupecam Solar Energy
Table 3. Available PV modules and their obtained specifications.
PV module Rated Capacity
[Wp]
Cost [CFA/Wp]
Efficiency [%]
Nominal operating temperature
[°C]
Temperature coefficient
[%/°C]
Lifetime [Years]
Retailer
Su-kam monocrystalline
silicon
100-240 850 15 45 -0.4 25 1)
Su-kam monocrystalline
silicon
250-300 800 15 45 -0.43 25 1)
Sono inter system polycrystalline
100-200 900 - - - - 2)
Sunshine solar polycrystalline
100-250 700 - - - - 3)
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Table 4. Available batteries and their obtained specifications.
Battery Cost [CFA]
Voltage [V]
Maximum capacity
[Ah]
Maximum capacity
[kWh]
Retailer
Su-kam lead-acid
135 000 12 100 1.20 1)
Su-kam lead-acid
245 000 12 200 2.40 1)
Luminous lead-acid
220 000 12 200 2.40 2)
Network lead-acid
230 000 12 210 2.52 2)
Sun-Test lead-acid
70 000 12 65 0.78 3)
Sun-Test lead-acid
100 000 12 100 1.20 3)
Blue Gate lead-acid
200 000 12 200 2.40 3)
30
Table 5. Available inverters and their obtained specifications Inverter Capacity
[kVA]
Voltage [V]
Cost [CFA]
Efficiency [%]
Lifetime [Years]
Charge controlling
Retailer
Su-kam Solar
PCU
1 24 195
000
85 25 Yes 1)
Su-kam Solar
PCU
2 48 420
000
85 25 Yes 1)
Su-kam Solar
PCU
3 48 530
000
85 25 Yes 1)
Su-kam Solar
PCU
3 96 510
000
85 25 Yes 1)
Su-kam Solar
PCU
4 96 650
000
85 25 Yes 1)
Su-kam Solar
PCU
5 96 810
000
85 25 Yes 1)
Su-kam Solar
PCU
6 96 920
000
85 25 Yes 1)
Su-kam Falcon
1.5 24 230
000
- - Yes 2)
Unknown brand
2.2 - 250
000
- - Yes 3)
31 4.2.6 Sustainability
The sustainability research resulted in Table 6, a list of people suitable to participate in the education about PV systems held by EWB during the winter of 2016/2017. Table 6 shows the current knowledge and what purpose the person would have for the PV system.
All names and contact information have been removed for integrity reasons.
Table 6. Preexisting knowledge and purpose of the persons to attend the EWB course.
Name Occupation Electrical knowledge Purpose
Person 1
ACOHOF Community Radio technician /
broadcaster
No education; works as radio sound technician
Communicating knowledge and information to the community / Operating and maintaining the system Person
2
ACOHOF Community Radio technician /
broadcaster
No education; works as radio sound technician
Communicating knowledge and information to the community / Operating and maintaining the system Person
3
ACOHOF Family Farm School Project
Coordinator
No education; manages all the programs of ACOHOF, coordinates the ACOHOF Family Farm School project
Operating and maintaining the system
Person 4
ACOHOF Family Farm School Field
Supervisor
No education; supervises field activities of the ACOHOF
Family Farm School
Operating and maintaining the system
Person 5
ACOHOF Family Farm School Director
No education; coordinates the staffs and students of the ACOHOF Family Farm School
Operating and maintaining the system / Giving timely reports of any breakdown Person
6
ACOHOF Family Farm School ICT
trainer
No education; Teaches computer science to students of the ACOHOF Family Farm School
Operating and maintaining the system
Person 7
ACOHOF board member
None Operating and maintaining the system
Person 8
ACOHOF board member
None Operating and maintaining the system
Person 9
ACOHOF member None Operating and maintaining
the system Person
10
ACOHOF member None Operating and maintaining
the system
32 Person
11
External technician Working knowledge in Solar Panel Installations
External Support
Person 12
External technician Educated in computer maintenance and networking
External support
Person 13
External electrician Educated in electrical systems and works as an electrician
External support
Person 14
External support None Operating and maintaining
the system Person
15
External Technician Working knowledge in Solar Panel Installations
External Support
4.3 Discussion
Measurement
• Solar irradiance
The resulting data from the different measurement devices seams different when comparing them in Figure 8 and Figure 9. However, while the peaks are quite different the accumulated power measured are almost the same. This may be due to the reason that the photodiode solar logger measures the irradiance directly, while the pyranometer has a built-in inertia in the thermophile. The thermophile needs to get heated up which can take a couple of seconds, why sudden peaks that occur in the photodiode does not show in the pyranometer.
The results from the solar irradiation measurement shows a smaller accumulated irradiation than the satellite derived data obtained from HOMER energy. The pyranometer was calibrated in prior to the field study and from the results of the pyranometer a calibrating factor was calculated for the photodiode solar logger. This solution for calculating the calibrating factor weakens the purpose of using two measurement equipment, since one is normalized after the other.
The measured data shows very high peaks which may be a result from cloud diffuse radiation which appear when the sun is in the edge of a cloud. A solution from these problems would be to use a filter to remove the anomalies and smoothen out the curves.
The deviation between the measurements and the satellite derived data in Table 1 is explained by the fact that the measurements were conducted during one month while the satellite derived data is using values for a that month for several years to calculate a historical average for the solar irradiance for that month. This indicates that the period of time when the measurements were carried out experienced less solar irradiance, compared to the historical average.
33
• Quality of electricity
From measuring the amount and time that the power was out, a general understanding for how reliable the grid is in Tatum was attained. The measures show a great number of power cuts as well as a big variety in duration. According to the information beforehand, the grid was very unreliable and not suitable for powering computers for education, the measurements strengthens that claim. Since the measurements were done manually the error might be large, and a few data points might be missing. Even though the measuring might be inadequate the conclusion is that the grid is of very poor quality and not reliable.
Load profile
The load profile for AFFS resulted in an energy consumption that fits the incoming solar irradiance badly which can be seen when comparing the load profiles in Figure 11 and Figure 12 with the incoming solar irradiance in Figure 7. It can be seen in Figure 11 that, apart from the peak load around midday due to computer use, most of the energy is consumed during the night. This leads to an excessive battery storage need, so that the system can store enough energy during the day to provide for the energy need during the night. Not only excess batteries will be needed for such a system, there will also be a great need for PV modules, enough PV modules to provide the batteries with energy on days with low sun irradiation, this is further investigated under section 5.3.
To utilize a PV-system at its maximum potential, the usage should be distributed to match the incoming irradiation. A high peak-load during noon is therefore wanted, but it is still necessary to avoid a too high peak-load that might damage the system. Alternating between the various electrical equipment would result in a smoother energy use and a lower peak load which would provide a load profile less harmful to the PV system. For example, while using the computers all other electrical equipment should be turned off.
What is more important than to reduce the peak-load is that the electrical consumption is being matched with the production from the PV modules, to reduce the storage need.
The equipment category with the highest energy consumption were found to be the computers. The computers are only being used during a two-hour period of the day, at the same time as the sun approaches zenith and thus contributes with the highest irradiation- potential. Since the peak-load occurs at the same time as the irradiation potential is at its maximum, there are good conditions for the PV plant to generate electricity for the computers directly. A good way to minimize the peak load and thus system size would be to spread out the computer use over the day.
In Figure 12, a reduced load profile shows how some small changes, e.g. less energy consuming computers and less security lights as described in section 4.1.2, can affect the system. These changes could drastically decrease the peak load and the energy consumption and further the size of the PV system and its costs, without impacting the behavior of the users and the daily work at AFFS. The energy saving measures implemented in the reduced load profile are not deeply examined. Nevertheless, it is a visualization of what some small changes regarding operating hours and energy efficient equipment could lead to, regarding the size and cost of the PV system.
