Evaluation of solar powered water pumping system: the case study of three selected Abattoirs in Ibadan, Nigeria

ABSTRACT

In this paper, detailed and comprehensive analysis of the technical, environmental and economic benefits of providing adequate water supply using solar PV system for three selected abattoirs (Bodija, Akinyele and Iyana church abattoirs) in Ibadan are presented. First, an estimate of average daily water requirement for slaughtering and cleaning cattle is obtained for each of the abattoir. This was achieved through oral interviews conducted at the different abattoirs to arrive at a reliable estimate. Thereafter, the total water requirement, the water storage capacity and the electrical load requirement necessary for the sizing of solar PV system that will enhance the smooth operation of the abattoir are determined. Some of the key results revealed that the water requirements of the abattoirs are 208,780, 91,632 and 78,590 l/week, respectively. The most suitable submersible pump for the three abattoirs is 60GS50 (5hp, 60gallon/min Goulds series). The cost of pumping water and providing lighting for smooth operation of the abattoirs are $0.23, $0.21 and $0.19, respectively. The results also show that 16,300, 15,200 and 14,600 kg/yr of carbon dioxide as well as 46.37, 43.36 and 41.45 kg/yr of carbon monoxide could be avoided, respectively with the implementation of the project.

KEYWORDS:

• Abattoir
• Water requirement
• PV system
• economic analysis
• environmental benefit
• Ibadan

1 Introduction

In recent years, there has been increase in water requirements all over the world as a result of increase in population, rising agricultural demand and rapid urbanisation. Also, the fast declining in infrastructure for water supply (Postel, Daliy, and Ehrlich 1996) has pushed water availability to its limits. One of the wide areas where water is required is in the operations of the abattoirs. An abattoir is a premise approved and registered by controlling authority for hygienic slaughtering and inspection of animals, processing and the effective preservation of meat products storage for human consumption (Adeyemo 2002). The efficient and undisrupted operation of abattoirs is hinged to the availability of adequate potable water. Unfortunately most abattoirs especially in Sub-Sahara Africa are operating without adequate clean water supply. This has become one area of concern due to the associated health implications that may arise to this effect.

In Nigeria, most abattoirs are located near water sources such as streams and rivers in order to gain unrestricted access to water needed in processing the animals. This location ensures that water is guaranteed for the slaughtering process. However, these water sources (streams and rivers) are unhygienic (Adeyemi and Adeyemo 2007) and therefore raise concern for health issues. In resolving the issue of potable water shortage for abattoir in the country, most abattoirs are now provided with either the bore hole or well water with storage facilities with the intention of clean water supply. The source of electrical power to these water projects is the national grid backed-up with diesel generators. However, the incessant national grid failure as well as incessant increase in diesel cost has led to most of the water project being abandoned in search of alternatives. Due to the challenges associated with lack of access to potable water in the abattoirs and the concern for energy shortage in the country, the use of renewable energy resources as an alternative energy source has become imperative. Of the various renewable energy sources, Solar is identified as the most viable (Ayodele and Ogunjuyigbe 2015) in South Western Nigeria.

The uses of photovoltaic water pumping systems have been studied by different authors (Bouzidi 2011): Systematic procedure for efficient design of electric water pumping systems fed by PV or/and WECS has been carried out by (Skretas and Papadopoulos 2008). In their work, hybrid electric water pumping system was designed and investigated using the proposed systematic procedure and Matlab software for the purpose of an installation under consideration for the city of Xanthi (Thrace Region), Greece. The result was compared with that of photovoltaic powered electric water pumping system only and wind powered electric water pumping system only. The result revealed that the hybrid water pumping system was more practical and better. Mokeddem et al (Mokeddem et al. 2011) carried out an experimental study on the performance of directly coupled PV water pumping system. The system was monitored at different conditions of varying solar irradiance values and two static head hydraulic system configurations. The system is a low-cost design, using local components without any complex electronic control and auxiliary systems. It was concluded that the system is suitable for low delivery flow rate applications. Similarly, Belgacem (Belgacem 2012) evaluated the performances of a direct photovoltaic pumping system based on an asynchronous motor driving a centrifugal pump. The system was tested for a short test period while operating under local climatic conditions. The results revealed that the variations in the solar radiation intensity could change the overall efficiency and the pumping flow. The analysis is thought to be useful for selecting a suitable motor and load for a water pumping application in remote areas under tropical climatic conditions. An overview of the occurrence of different groundwater sheds, water quality, and availability in Nigeria has been presented by Sodiki (Sodiki 2014). In his work, he discussed the viability of solar-powered groundwater pumping systems in Nigeria especially in localities where the national electricity grid is not yet connected.

Most of the aforementioned studies are concerned with the performance of water pumping system vis-à-vis the availability of solar irradiation. In this present work, the water requirements for the operation of three selected abattoirs in Ibadan is established, and the application of solar water pumping system in the provision of potable water to meet the needs of the abattoirs are presented. The economic implication of such project and the environmental benefit compared to the use of diesel generator is also carried out. The paper can serve as an eye opener to the government and private investor in the country on the viability of solar water pumping system at improving the quality of products coming from Nigerian abattoirs.

2. Estimation of water requirement for abattoirs

Water need of an abattoir can be evaluated from the knowledge of the total number of cattle slaughtered and the quantity of water required per slaughtered cattle. In this study, oral interview was conducted in three main abattoirs (as presented in Table 1) that deal with slaughtering of cattle in Ibadan. The abattoirs were selected because they are the main abattoirs by which most meats in Ibadan market are organised for sale.

Table 1. Abattoirs selected for the study.

Abattoir 1	Bodija
Abattoir 2	Akinyele
Abattoir 3	Iyana Church

The responses were used to estimate the average quantity of water needed for each of the abattoirs every day. It was generally observed that the day of the week influence the numbers of slaughtered cattle with the number reaching its highest during the weekends (Friday and Saturday). No activities go on in the abattoirs on Sundays.

To this end, the total number of cattle slaughtered per day ($N_c$) can be estimated as:

(1) $N_c=N_{wd}+N_{ww}$(1)

where $N_{wd}$ is the number of cows slaughtered from Monday to Thursday and $N_{ww}$ is the number of cows slaughtered on Friday and Saturday. Sunday is not accounted for, based on the fact that cattle are not slaughtered on this day in some western states of Nigeria, hence (1) can be re-written as:

(2) $N_c=4n+2m$(2)

where n and m are the average number of cattles slaughtered from Monday to Thursday and Friday to Saturday, respectively. The values (n, m) are estimated from the physical visits to the abattoirs and oral interview of the stake holders. The quantity of water required ($Q_t$) for the operation of an abattoir can be expressed as:

(3) $Q_t=a(q_c+q_f+q_m)$(3)

where a is the assumed factor of safety usually 1.2 to cater for the special periods like Christmas, Easter and Ramadan periods, $q_c$ is the average quantity of water required in cleaning up one cattle, $q_f$ is the average, and quantity of water required in washing the abattoir floor and gutters per cattle and $q_m$ is the average quantity of water required by an abattoir worker to clean himself up after the whole process per cattle. The average values of the various quantities of water were determined as (4), respectively.

(4) $q_{c,m,f}=\frac{\sum _{i=1}^k{q}_{c,m,f}(i)}{k}$(4)

where k is the number of abattoirs visited, in this case k = 3.

2.1. Alternatives for water pumping system and electricity generation for abattoirs

The long history of water pumping system has led to the development of many methods for pumping water with minimum efforts and energy over the years (Abdelmalek Mokeddem et al, 2011). The alternatives for water pumping application range from a simple hand pump to high efficiency electric pumps (Moechtar, Juwono, and Kantosa 1991, Abdelmalek Mokeddem et al, 2011). In remote rural areas where access to electric supply is not practical, the use of diesel pumps is very common. However, as a result of problems associated with diesel water pumping system such as the fuel transportation (Ayodele and Ogunjuyigbe 2016) and operating cost (Ayodele, Ogunjuyigbe, and Babatunde 2016), renewable energy operated water pumping system provides an alternate. Various alternatives for water pumping systems have been developed and tested around the world. These includes: wind water pumping system where water pumping is achieved through the use of energy in the mass of moving air, solar water pumping system which makes use of available solar irradiation for water pumping. Also, hydropower, biomass, and biofuels have also been identified as feasible sources of energy to pump water. However their use is less prominent in the developing country due to their high initial capital cost (Cloutier and Rowley 2011). Of these various renewable energy sources which could serve as alternative energy sources for water pumping as well as electricity generation for abattoirs, solar is the most prominent for the city of Ibadan (Ayodele et al. 2017).

2.2 Solar energy resources

In order to appropriately size solar water pumping system for any water project, adequate knowledge of the solar irradiation is required. The solar irradiation data used for the study was observed from weather stations close to the abattoirs and was obtained from the International Institute of Tropical Agriculture (IITA), Ibadan with longitude and latitude of 3°99ʹE and 7°42ʹN respectively. The solar data collected for the study span over a period of 9 years (2005–2013). The monthly variation of the solar irradiation is as depicted in Figure 1 while the annual mean value is depicted in Table 2.

Table 2. Annual mean value of solar irradiation of Ibadan (MJ/m²/day).

Year	2005	2006	2007	2008	2009	2010	2011	2012	2013	Average
Values	14.60	14.43	14.20	14.22	14.33	14.23	13.27	13.92	14.67	14.21

Figure 1. Monthly variations of the solar irradiation over a span of 9 years (2005–2013).

The figure reveals that solar irradiation is high in the months of March and lowest in the month of August. This is expected as they correspond to the peak of dry and raining seasons, respectively. The table shows that there are variations in the average annual values of solar irradiation which varies from13.27 MJ/m²/day in 2011 to 14.67 MJ/m²/day in 2013. The average value over a period of 9 years is 14.21 MJ/m²/day. This value reveals that there is a considerably decent amount of solar irradiation throughout the year in Ibadan, the area of study.

3. Selection and sizing of PV water pumping system components

The schematic diagram showing the PV system used for water pumping as well as electricity generation for a typical abattoir is depicted in Figure 2.

Figure 2. Schematic diagram of PV based water pumping system with electricity generation.

The figure shows the mechanical pumping system as well as the electrical system. The pumping system consists of the submersible pump, storage tank and the pipes that convey water from the well to through the storage tank to the abattoirs. The electrical section consists of PV modules, inverter, battery storage system, battery chargers and the cables. In order to ensure optimum performance of these components, they are required to be appropriately sized to match the solar regime of the intended site of deployment.

3.1 Estimation of electrical energy need for lighting

This is more like the benchmark for any solar PV system design. Based on personal sight visit and direct interview of the stake holders, the electrical needs of the abattoirs were estimated. The electrical loads consist of mainly the lighting point to allow the butcher work into the late hours in the evening or start work early in the morning and the pumping machine needed to draw water into the storage tank. The total electrical load (E_D) of the abattoir can be determined as:

(5) $E_D=E_L+E_p$(5)

where E_L and E_p are the electrical energy required for lighting up the abattoirs and for pumping water, respectively.

The electrical load required for lighting based on the requirement of abattoirs is depicted in Table 3–5. The tables reveals that the total electrical energy ($E_L$) Wh/day) required for lighting the abattoirs 1, 2 and 3 are estimated to be 4.8kWh/day, 2.88kWh/day and 1.62kWh/day, respectively.

Table 3. Estimation of the electrical energy need for lighting abattoir 1 ($E_L$) Wh/day).

Electrical load with power rating	No of units	Total power (Watt)	No of operating hours/day	Equivalent Wh/day
Lighting lamps(60W)	5	300	6	1800
Compact Fluorescent Lamp (CFL, 30W)	10	300	10	3000
Total Electrical load ($E_L$Wh/day)				4800

Table 4. Estimation of the electrical energy need for lighting abattoir 2 ($E_L$) Wh/day).

Electrical load with power rating	No of units	Total power (Watt)	No of operating hours/day	Equivalent Wh/day
Lighting lamps(60W)	3	180	6	1080
Compact Fluorescent Lamp (CFL, 30W)	6	180	10	1800
Total Electrical load ($E_L$Wh/day)				2880

Table 5. Estimation of the electrical energy need for lighting abattoir 3 ($E_L$) Wh/day).

Electrical load with power rating	No of units	Total power (Watt)	No of operating hours/day	Equivalent Wh/day
Lighting lamps(60W)	2	120	6	720
Compact Fluorescent Lamp (CFL, 30W)	3	90	10	900
Total Electrical load ($E_L$Wh/day)				1620

3.2 Estimation of electrical energy needed for water pumping

The electrical energy need for pumping water ($E_p$wh/day) depends on the ratings of the pump to be selected among the commercially available ones and must be well sized to match the local solar regime of the location. However, selection of pumps in a solar powered water pumping project depends on several factors including: availability of water supply, size of the available water storage system depending on the water needs, total dynamic head, diameter of well and the population size demand. In this paper, submersible pumps are used in order to have a properly sized pumping system and it is assumed that the pump will be in operation only during the peak sunshine hours. To determine the best efficient pump in the market, the system total dynamic head ($H_{system}$) must be determined and matched with the data sheets of the commercially available ones. The pump whose characteristics best matches the total system dynamic head will be selected. The system dynamic head can be evaluated as

(6) $H_{system}=H_{pipef}+H_{vaf}+H_{vel}$(6)

where $H_{pipef}$ is the head loss due to pipe friction, $H_{vaf}$ is the frictional head loss due to pipe valves and fittings, $H_{vel}$ is the vertical elevation of the pipe from the submersible pump to the storage tank. The head loss due to pipe friction, $H_{pipef}$ can be estimated as:

(7) $H_{pipef}=\frac{133.4d_o{{ }^{-0.017}}^{{ }^{\left(\frac{l_o}{d_o}\right)\frac{v^2}{2g}{\left(\frac{1}{v{d}_o}\right)}^{0.15}}}}{C^{1.85}}$(7)

where $d_o$ is the pipe internal diameter (m), $l_o$ is the pipe length (m), $v$ = is the flow velocity (m/s), $g$ is the acceleration due to gravity (m/s²), $C$ is the Hazen William’s coefficient. The flow velocity can be determined as:

(8) $v=\frac{4Q_o}{\pi {d_o}^2}$(8)

where $Q_o$ is the discharge rate of the selected pump in m³/s which is estimated using:

(9) $Q_o=\frac{Q_t}{t}$(9)

where $Q_t$ is the quantity of water required by the abattoir as determined in section 2, $t$ is the time required for the pump to be in operation which is usually in the range of the average sunshine hours.

The frictional head loss due to pipe valves and fittings, $H_{vaf}$ is given by:

(10) $H_{vaf}=\sigma \frac{v^2}{2g}$(10)

where $\sigma$ is the dimensionless fitting loss factor and $g$ is the acceleration due to gravity. The various constants used in selecting the pump as obtained from literature and suitable for the location, are given in the Table 6.

Table 6. Values of constants.

Variable	$l_o$(m)	$H_{vel}$(m)	$d_o$(m)	C	$\sigma$
Value	1	75	0.0254	150	1

Various pumps have, in their data sheet, specific total dynamic heads, efficiencies and capacities. Pump charts are used to match the estimated total dynamic head ($H_{system}$) to the best efficiencies possible.

3.3 PV array sizing

The size of the PV required depends on the electrical energy need of the abattoir that the solar modules are expected to supply and this can be calculated as:

(11) $E_{LL}=1.5\times E_D$(11)

where E_LL is the total load (kWh/day), the solar PV modules are expected to meet, E_D is the estimated total electrical energy need of the abattoir (kWh/day) and the value ‘1.5ʹ is the factor of safety introduced to cater for the extra load unaccounted for in the original load design estimation (Mandapati 2012).

The required PV array area, $P{V}_{Area}$ required by the abattoir can be estimated as:

(12) $P{V}_{Area}=\frac{E_{LL}}{G_{av}\times TCF\times {\eta }_{pv}}$(12)

where $G_{av}$ is the average daily solar irradiation, (kWh/m²/day) of the location, $TCF$ is the temperature correction factor and ${\eta }_{pv}$ is the PV energy conversion efficiency. The average array efficiency is determined from the rated module characteristics for each specific solar panel technology. Values of $G_{av}$ are obtained from site solar radiation data over a certain period of time. Typical values of ${\eta }_{pv}$ are in the range of 6–15% with a theoretical maximum value of 20% (Sodiki 2014). The values of $TCF$ corresponding to various PV cell temperatures can be obtained from the PV manufacturer data sheet as depicted in Table 18 in appendix. The PV array peak power$P_{(peak)}$can be obtained from the estimated PV area as:

(13) $P_{(peak)}=PVarea\times 1000\times {\eta }_{pv}$(13)

Table 7. Unit cost of components making up the PV system for water pumping.

Item	Cspv	Csbatt	Cicc	Cv
Cost($)	1.2/Wp	4/Ah	5.8/A	0.18/W

Table 8. Specific emission per unit of diesel and gasoline and the cost of the fuel (US Energy 2014).

Specific Parameters	$S_{C{O}_2}$(kg/L)	$S_{CO}$(kg/L)	$P_d$($/L) (@ N150 per dollar)
Diesel	2.7	0.00766	0.97

Table 9. Estimate of number of cattle slaughtered per week.

	$N_{wd}$ (Mon. to Thur.)	$N_{ww}$ (Fri. and Sat.)	$N_c=N_{wd}+N_{ww}$
Abattoir 1	800	500	1300
Abattoir 2	400	430	830
Abattoir 3	280	300	580
Total	1480	1230	2710
Average	494	410	904

Table 10. Variations of water requirement from different abattoirs visited per cattle.

	$q_c$(litres)	$q_f$(litres)	$q_m$(litres)	$Q_t$(litres)
Abattoir 1	150	0.6	10	160.6
Abattoir 2	100	0.4	10	110.4
Abattoir 3	125	0.5	10	135.5
Total	375	1.5	30	406.5
Average	125	0.5	10	135.5

Table 11. Estimated of average water requirement for the abattoir based on numbers of cattle slaughtered taking into consideration the factor of safety (a = 1.2).

	$Q_t$(litres/week)	$Q_t$(litres/day)	$Q_t$(litres/sec)	$Q_t$(m^3/day)	$Q_t$(m^3/sec)
Abattoir 1	250,536	41,756	0.48324	41.7560	0.000483288
Abattoir 2	109,958	18,326	0.21216	18.3264	0.000212112
Abattoir 3	94,308	15,718	0.18192	15.0983	0.000181920
Average	146,990	24,498	0.28356	24.4984	0.000283548

Table 12. Total dynamic head and flow rates for pump selection for the abattoirs.

	Flow velocity (m^3/sec)	Total dynamic head (m)
Abattoir 1	0.7048	76.1191
Abattoir 2	0.5384	76.0251
Abattoir 3	0.2992	75.9697
Average `	0.4663	76.0053

Table 13. Estimation of the electrical energy need for water pumping (E_p) for each of the abattoir.

Electrical load with power rating	No of units	Total watt	No of operating hours/day	Equivalent Wh/day
Water Pump(3.75kW)	1	3750	6	22,500

Table 14. Estimate of the electrical energy need based on number of cattle slaughtered per week.

	$E_L$ (Wh/day)	$E_P$ (Wh/day)	$E_D$(Wh/day)
Abattoir 1	4800	22,500	27,300
Abattoir 2	2880	22,500	25,380
Abattoir 3	1620	22,500	23,100

Table 15. Table mean solar irradiation, PV area, PV peak power and the battery storage capacity calculated for the abattoirs.

Abattoir	Mean solar irradiation $G_{av}$  kWh/m^2/day	$P{V}_{area}$(m^2)	PV peak power $P{V}_{peak}$  (kWp)	Storage capacity$S_{batt}$ (Ah)	Average sunshine hours (hr)
Abattoir 1	4.3	62.54	10.38	3.31x10^3	6
Abattoir 2	4.3	58.13	9.65	3.07 x10^3	6
Abattoir 3	4.3	55.36	9.19	2.93 x10^3	6

Table 16. Table Sizing of PV system components.

Abattoir	No of PV module$N_m$	No of battery$n_{batt}$	Charger rating$I_{ch}$ (A)	Inverter size$P_{inv}$ (kVA)	Cost of fuel per annum,$C_F$ ($)$\times$ 10^3	Life cycle cost (LCC) ($)$\times$ 10^4	Cost of energy ($/kWh)
Abattoir 1	42	14	430	5	5.87	6.05	0.23
Abattoir 2	38	12	400	5	5.49	5.63	0.21
Abattoir 3	36	12	380	5	5.24	5.37	0.19

Table 17. Environmental benefit of PV system over the diesel generator.

Abattoir	Fuel saved per annum (L/annum)$\times$ 10^3	Carbon dioxide emission saved$C{O}_{2em}$ $E_{C{O}_2}(kg/yr)$$\times$ 10^4	Carbon monoxide $CO$ emission saved$E_{CO}(kg/yr)$	Carbon credit on project,$C_{em}$ (kg/yr) $\times$ 10^3	Break-even point$B_{ep}(yr)$
Abattoir 1	6.05	1.63	46.37	4401	10.3
Abattoir 2	5.66	1.52	43.36	104	10.2
Abattoir 3	5.41	1.46	41.45	3942	10.1

Table 18. parameter of a 250Wp solar module.

S/N	Parameters	Values
1	Maximum Power	$P_{max}$	250Wp
2	Open Circuit Voltage	$V_{oc}$	37.8V
3	Maximum Power Point Voltage	$V_{mpp}$	31.1V
4	Short Circuit Current	$I_{sc}$	8.28A
5	Maximum Power Point Current	$I_{\mathrm{m}\mathrm{p}\mathrm{p}}$	8.05A
6	Module Efficiency	${\eta }_{pV}$	14.91%
7	NOCT		48°C
8	Operating Temperature	$T_{op}$	−40°C to 85°C

*STC: 1000W/m², 25°C, AM 1.5

The total number of PV modules ($N_m$) needed can be obtained from the division of the PV array peak power by the rated reference peak power of the selected solar module obtained from the data sheet at standard test conditions (1000W/m² and 25°c) and can be calculated as:

(14) $N_m=\frac{P_{(peak)}}{P_{ref}}$(14)

It should be noted that the solar module should be selected from the commercially available ones in such a way that it gives precise number of modules that is economical and the mounting area is good enough to give good overall efficiency. The modules are to be connected in series and parallel depending on the desired system voltage. The number of PV modules in series can be estimated as:

(15) $N_{ms}=\frac{V_{DC,bus}}{{V_{DC}}_{,\mathrm{r}\mathrm{e}\mathrm{f}}}$(15)

where ${V_{DC}}_{,\mathrm{r}\mathrm{e}\mathrm{f}}$ is the rated reference PV module voltage (V) obtained from the PV data sheet and $V_{DC,bus}$ is the rated DC bus voltage (V). For the number of PV modules connected in parallel, the following equation holds:

(16) $N_{mp}=\frac{I_{DC,bus}}{{I_{DC}}_{,\mathrm{r}\mathrm{e}\mathrm{f}}}$(16)

where ${I_{DC}}_{,\mathrm{r}\mathrm{e}\mathrm{f}}$ is the rated reference current of the PV module which can also be obtained from the manufacturer data sheet. The combination of these two parameters should give the total number of PV modules as estimated above. They are combined as:

(17) $N_m=N_{ms}\ast N_{mp}$(17)

3.4 Estimation of the size of required inverter

The inverter to be selected should have the capability to withstand the maximum AC load of the selected pump ($P_{max}$) and lighting with a factor of safety of 1.2 of the inverter output (Ayodele, Ogunjuyigbe, and Amusan 2018) to cater for the possibility of surge. Therefore, the power rating of the inverter ($P_{Inv}$) can be estimated as:

(18) $P_{Inv}=\frac{1.2\ast P_{max}}{pf}$(18)

where $pf$ is the power factor

3.5 Sizing of the battery storage capacity

The use of batteries in a PV system ensures that solar energy is available for use at all time of the day and at every period round the year. This covers for the months of the year with very little solar irradiation and for periods of the year where more water is needed as demanded by increased number of slaughtering. Typically, the batteries employed for use in solar PV operations is the deep-discharge type designed to provide moderate currents continuously for a long period of time and can be discharged almost completely without any damage. For safety purposes, a depth of discharge (DoD) of 0.9 is used as obtained from Sodiki (2014). The total capacity of the batteries to be used ($S_{Batt}$) can be estimated as:

(19) $S_{Batt}=\frac{1.5\ast N_c\ast E_{LL}}{24\ast DoD\ast {\eta }_b\ast {\eta }_{inv}}$(19)

where $N_c$ is the highest number of non-sunshine pumping hours in the day over the year as obtained from the observed meteorological data, $DoD$ is the maximum permissible depth of discharge of the battery, ${\eta }_b$ is the efficiency of the battery, ${\eta }_{inv}$ is the efficiency of the inverter. The total numbers of batteries ($N_{nb}$) can be obtained from the estimated total storage capacity as:

(20) $N_{nb}=\frac{S_{Batt}}{A_{Batt}}$(20)

where $A_{Batt}$ is the ampere hour rating from the manufacturer data sheet of a selected battery.

These batteries can be connected either in series or in parallel, depending on the application the batteries are to serve. The number of series connected batteries and parallel connected batteries can be obtained as follows (Sodiki 2014; Ayodele, Ogunjuyigbe, and Amusan 2018):

(21) $N_{nbs}=\frac{V_{DC,bus}}{v_b}$(21)

(22) $N_{nbp}=\frac{N_{nb}}{N_{nbs}}$(22)

where $N_{nbs}$ is the number of batteries connected in series, $V_{DC,bus}$ is the DC bus voltage of the system, $v_b$ is the DC output voltage of the battery system, taken to be 24V, $N_{nbp}$ is the number of batteries connected in parallel.

3.6 Sizing of the battery charge controller

The battery charge controller is important as it guarantees that the batteries are safely charged in order to ensure longer life span is maintained. The battery charger must be capable of carrying the short circuit current of the installed PV arrays and also to maintain the DC bus voltage. The charging current for the system, ${\mathrm{I}}_{char}$ can be determined as:

(23) ${\mathrm{I}}_{char}=\frac{P{V}_{app}}{V_{DC,bus}}$(23)

4. Economic analysis of utilising PV system for water pumping

Decision making is vital in the design of a PV system and hence, adequate knowledge of the economic cost for the total project cycle period is essential to determine the likelihood and feasibility of the design implementation. The adequacies of the PV water pumping system have to be established before investment is committed to the project. The system should be capable of pumping water for abattoirs at the most subsidised rate. The unit cost of the individual component making up the PV system has to be considered to achieve this and some other diverse costs acquired ranging from the installation cost (drilling cost, charge per personnel head), operation and maintenance cost and the miscellaneous cost. A comparison between various geographical locations is possible with this mode of analysis and the prospective investors will be able to select the location of best fit and the one that offers the best overall yield.

The life cycle cost gives a detailed economic feasibility analysis based on the cost incurred from the implementing the project over the total cycle period it is supposed to last. It can be estimated as:

(24) $\mathrm{L}\mathrm{C}{\mathrm{C}}_{\mathrm{p}\mathrm{v}\mathrm{s}}=C_{p.v}+C_{bat}+C_{bcc}+C_{inv}+C_{in}+C_m$(24)

where $C_{p.v}$ is the cost of PV array, $C_{bat}$ is the cost of battery, $C_{bcc}$ is the cost of battery charge controller, $C_{inv}$ is the cost of inverter, ${C_{in}}_s$ is the installation cost, $C_m$ is the maintenance and operation cost. The cost of PV array can be determined as:

(25) $C_{p.v}=P{V}_{app}\ast {\mathrm{N}}_{\mathrm{m}}\ast {\mathrm{C}}_{\mathrm{s}\mathrm{p}\mathrm{v}}$(25)

where ${\mathrm{C}}_{\mathrm{s}\mathrm{p}\mathrm{v}}$ is the specific cost of the PV array. Also, the cost of battery can be estimated as:

(26) $C_{bat}=S_{batt}\ast C_{sbatt}$(26)

where $C_{sbatt}$ is the specific cost of the battery ($/Ah)

Typically, a battery life spans is about 5 years and considering the probable project life cycle is about 20 years, therefore, in addition to the original battery bank set, three extra set of batteries will be required before the lapse of the project’s time frame. The cost of these extra set of batteries, each having a life span of 5 years has to be included in the overall system cost and can be determined as:

(27) $C_{batt}=C_{bat}\mathit{\ast }\left[{\left(\frac{\mathit{1}\mathit{+}inf}{\mathit{1}\mathit{+}int}\right)}^{\mathit{5}}\mathit{+}{\left(\frac{\mathit{1}\mathit{+}inf}{\mathit{1}\mathit{+}int}\right)}^{\mathit{10}}\mathit{+}{\left(\frac{\mathit{1}\mathit{+}inf}{\mathit{1}\mathit{+}int}\right)}^{\mathit{15}}\right]$(27)

where $inf$ and int are the inflation rate and e interest rate, respectively and can be obtained from the data sheet of Central Bank.

The inflation rate and the interest rate are taken to be 0.09 and 0.13 respectively as used in (Ayodele, Ogunjuyigbe, and Amusan 2018). Since the projected life span of the system is 20 years, the maintenance and operation cost, $C_m$ is evaluated as:

(28) $C_m=C_{oma}\times \left(\frac{1+inf}{1+int}\right)\times \left\{\frac{1-{\left(\frac{1+inf}{1+int}\right)}^l}{1-\left(\frac{1+inf}{1+int}\right)}\right\}$(28)

where $l$ is the life span of the PV system (20 years), $C_{oma}$ is the annual system maintenance and operation cost which is about 1% of the project cost as stated in Ayodele and Ogunjuyigbe (2015). It is expressed as:

(29) $C_{oma=}0.01\ast C_{p.v}$(29)

The life cycle cost for a year is given by $ALC{C}_{pvs}$ and can be calculated as:

(30) $ALC{C}_{pvs}=C_{pvs}*\frac{\left\{1-\left(\frac{1+inf}{1+int}\right)\right\}}{\left\{1-{\left(\frac{1+inf}{1+int}\right)}^l\right\}}$(30)

The remaining component costs, the battery charge controller, inverter and installation costs are calculated as (Pranav Birajda 2013):

(31) $C_{ch}=I_{char}\ast C_{icc}$(31)

(32) $C_{inv}=P_{Inv}\ast C_v$(32)

(33) $C_{in}=0.1\ast C_{\mathrm{p}.\mathrm{v}}$(33)

The unit costs of the various components of the PV system as obtained from market survey and literature are depicted in Table 7 (Ayodele and Ogunjuyigbe 2015).

The unit cost of pumping water per cubic meter ($C_{cmc}$) using solar PV system can be calculated as:

(34) $C_{cmc}=\frac{ALC{C}_{pvs}}{Q_t\ast 365}$(34)

where $Q_t$ is the quantity of water delivered per day as determined in section 2.

The cost of energy can be estimated from:

(35) $C_{COE}=\frac{ALC{C}_{pvs}}{E_{LL}\ast 365}$(35)

5. Emmision comparison of the PV project with diesel generator

The environmnetal benefit of ultilising solar PV for water pumping in the abattoir instead of diesel generator is explored in this section.

5.1 Quantity of fuel consumed by diesel generator when replaced with PV system

The quantity of fuel (L/hr) that would be required for diesel generator to pump water if we have opted for diesel generator rather than the PV system can be determined as:

(36) $F=A_G{P}_{PV}+B_G{P}_{Gen}$(36)

where $F$ is the fuel consumed in L/hr by the diesel generator, $A_G$ and $B_G$ are constants and are the coefficients of the fuel consumption curve in L/kWh. The values has been experimentally determined as 0.246 and 0.08145 (Ismail, Moghavvemi, and Mahlia 2013),$P_{PV}$ is the rated power of the PV system in kW to replace the diesel generator and $P_{Gen}$ is the rated power of the diesel or gasoline powered alternate replacement geneator in kW. The selection of diesel generator is based on the required electrical load to be met in the abbattoir. The amount of fuel consume per annum and the cost of fuel are given as (37) and (38), respectively

(37) $F_{annum}=F\ast 8760$(37)

(38) $C_F=F_{annum}\times P_d$(38)

where $P_d$ is the current price of diesel per litre ($/L)

5.2 Carbon emission

The amount of carbon dioxide (CO₂) and carbon monoxide (CO) that would be emmited if diesel generator is adopted rather than the PV system can be estimated as follows:

(39) $C{O}_{2em}=F_{annum}\times S_{C{O}_2}$(39)

(40) $C{O}_{em}=F_{annum}\times S_{CO}$(40)

(41) $C_{em}=0.27\ast C{O}_{2em}$(41)

where $C{O}_{2em}$ and $C{O}_{em}$ are the quantity of carbon dioxide and carbon monoxide that would be emmited (kg/yr) by the diesel generator, respectively. $S_{C{O}_2}$ and $S_{CO}$ are the specific quantity of carbon dioxide and carbon monoxide emitted per litre of fuel (kg/L), $C_{em}$ is the quantity of carbon emitted (kg/yr). The specific emissions ($S_{C{O}_2}$ and $S_{CO}$) for diesel fuel are as depicted in Table 8 (Ayodele and Ogunjuyigbe 2015)

5.3 Break-even point

The break-even point of the project can be estimated if assumed the cost of project is offset from the cost expended on fuel consumption per annum as:

(42) $Bpt=\frac{\mathrm{L}\mathrm{C}{\mathrm{C}}_{\mathrm{p}\mathrm{v}\mathrm{s}}}{C_{{ }_F}}$(42)

6. Results and discussions

In this section, the results of water requirements of the abattoirs are discussed and the sizes of the various components of PV system that can support the smooth operation of the abattoirs are given. Results of sensitivity analysis are presented to give insight into the behaviour of the PV system to change in certain inputs such as change in diesel price, change in cost of PV panel etc.

6.1 Water and electrical energy requirement of the abattoirs

The results from the oral interview conducted at the abattoirs for the estimation average number of cattle slaughtered in a week and average quantity of water required for a typical abattoir in Ibadan are furnished in Tables 9 and 10, respectively. Table 9 revealed that an average total of 2710 cattle per week are slaughtered in the three abattoirs with abattoir 1 being most utilised one with an average value of 1300 cattle per week. This is expected as it is the largest abattoir in Ibadan with highest patronage of customers, because it is located within the largest market in the city of Ibadan.

Table 10 gives an estimate of the water usage of the abattoirs for the purposes of cleaning up a cattle ($q_c$), washing the slaughter floor ($q_f$) after the day’s job per cattle and water requirement by the butchers for cleaning up their body after the slaughtering process ($q_m$) per cattle. These estimates are obtained from personal site visit and oral interview of the stakeholders in each of the abattoir. Graduated bowls and buckets (in litres) are employed for use in the abattoirs to access water and these are calculated and turned into numerical values. These various quantities of water allow us to determine the minimum required water storage capacity of each abattoir. Consequently, allowing us to determine the appropriate submersible pump and other components that make up solar water pumping system. Presently people are employed to fetch water from the stream or well as the case may be to fill existing bowls as depicted in Figure 3.

Figure 3. Meeting the water need in a typical abattoir in Ibadan.

The total estimated quantity of water needed by the abattoirs as estimated using (4) are given in Table 11. Other conversions are also obtained using the right conversion ratios.

The flow velocities for each abattoir was estimated based on water requirements of the abattoirs and the total system dynamic head was subsequently calculated using (7). The results are presented in Table 12. Total system dynamic head is basically needed in selecting suitable water pump for the abattoirs.

All pumps model have standard system head–flow rate curves in which suitable pump can be selected. Some of submersible pumps available in the market are Shakti, Falcon, Unnati, Rovatti and Figh, Lubi, Goulds, Kiwi and Amos pumps. However, Goulds pump model 60Gs as depicted in Figure 4 is selected for the three abattoirs because of its high relative flow velocities. Based on the estimated total dynamic system head, Goulds submersible pump series 60GS50 was selected for each of the three abattoirs.

Figure 4. Goulds pump chart with best efficiency at 60GPM.

The pump (60GS series) has its best efficiency point at 60 gallons per minute (GMP) with GS being the pump series type. The horsepower rating of the pump is given by the concluding number following the pump series type. It ranges from 1.5 to 7.5 horsepower. The specific pump selected is the 60GS50 with a rating of 5hp and this corresponds to 3.75kW (1hp = 0.7457kW). Therefore, the estimated electrical energy required by submersible pump is 3.75kW for each of the abattoirs. ($E_p$wh/day) considering 6 h of usage is furnished in Table 13.

Therefore, the total electrical energy requirements of the abattoir (E_D) as determined using (6) are furnished in Table 14

6.2 Sizing of PV system components for water pumping

The three abattoirs in this study are located in the city of Ibadan, South Western Nigeria with average solar irradiation of 4.3kWh/m^2/day and average sunshine hour of 6hrs. The solar module type employed in this study is the 250 Wp mono-crystalline cell while the battery is Surette series with 250Ah per battery. The other parameters of the PV module at STC, relevant to this study are furnished in the manufacturer data sheet in Tables 18–19 in the appendix. Based on the electrical energy requirement of the abattoirs and the solar regime of their locations, the required PV area, PV peak power and the battery storage capacities are calculated using (11)–(16) and (19). The results are displayed in Table 15. The table reveals that the required PV area ranges from 55.36–62.54m² while the PV peak power ranges from 9.19–10.38 kWp and the battery storage capacity ranges from (2.93–3.31) x 10³Ah.

The required numbers of PV modules, battery charger ratings and inverter size were determined for each of the abattoir and the associated life cycle cost over a life period of 20 as well as the cost of energy for water pumping was calculated. The results are shown in Table 16. The result revealed that abattoirs 1 to 3 require 42, 38 and 36 numbers of PV module, respectively with 14, 12 and 12 corresponding numbers of battery. The cost of energy for water pumping water is 0.23, 0.21 and 0.19 $, respectively. Although the cost is a little higher compared to unit cost of the local grid, however, it availability and reliability are better guaranteed.

The environmental advantage of the PV water pumping system for abattoir application was explored. The benefits were determined based on the amount of diesel fuel, carbon dioxide and carbon monoxide that would be avoided compared to when the water project is powered by diesel generator. The results are presented in Table 17. The table revealed that if the cost of buying diesel fuel is used to offset the cost of the project, then the project will break even half (about 10 years) into the project life time. The physical implication of this is that the project is viable and attractive for investors. It is also observed that an average of 16,300, 15,200 and 14,600 kg of CO₂ are saved by the abattoirs per annum, respectively while 46.37, 43.36 and 41.45 kg of CO are prevented from polluting the environment per annum.

6.3 Sensitivity analysis

The sensitivity analysis shows the dependency of a given system characteristic on some defined input variable (Ogunjuyigbe and Ayodele 2016). Various sensitivity analyses were performed on the PV system using different input variables. The results are presented in Figure 5–7. Figure 5 (a) reveals that the cost of energy and the break-even point increase linearly with the increasing cost of PV while Figure 5(b) shows that the longer the project life time, the lesser the cost of energy, however, life cycle cost increases with the project life time..

Figure 5. Sensitivity analysis showing the relationship between (a) Cost of Energy in pumping water and the break-even point with the unit cost of PV (b) Cost of energy and life cycle cost with the project life time.

Figure 6. Sensitivity analysis showing relationship between (a) CO₂ emission and CO emission with the solar irradiation at the location of the abattoir (b) PV peak power and cost of energy to the solar irradiation.

Figure 7. Sensitivity analysis showing the relationship between (a) fuel costs per annum and diesel price (b) break-even point and the diesel price.

Figure 6(a) indicates that both the CO₂ and CO reduce if the solar irradiation of the site increases. This is expected as the higher the solar irradiation the lesser the need to use diesel generator and hence the lesser the emission. Figure 6(b) shows that the required PV peak power reduces indicating that lesser PV modules are needed if the solar irradiation increases. This will indirectly reduce the cost of energy. Figure 7 shows that the break-even point reduces with the increase in diesel price. This is because the break-even point was calculated based on how much would be saved in off-setting the cost of the project if PV is used for water pumping instead of diesel generator

7. Conclusion and future research

Providing water for abattoir improves the health status of a nation. The technical viability, economic potential and the environmental advantages of utilising solar PV system to provide water for the smooth operation of three selected abattoir in Ibadan have been presented. The average total water requirements of the abattoirs in providing safe slaughtering practices have also been determined. Based on the studies, the followings specific conclusions are made:

1. An average number of 1300, 830 and 580 cattle are slaughtered in abattoir 1, 2 and 3, respectively in a week. This requires 208,780, 91,632, 78,590 l of water for the operation of the abattoir per week.

2. The average total water requirement per cattle for abattoirs 1, 2 and 3 located in Ibadan are 160.6, 110.4 and 135.5 l.

3. Total energy requirement of 27,300, 25,380 and 24,170 Wh/day are required to provide potable water and lighting for the abattoirs, respectively.

4. Goulp pump 60GS50 with specification of 5hp (3.75kW), delivering 50gallons in a minute is the best pump for each of the abattoirs based on the solar regime of the sites.

5. The cost of energy to ensure efficient operation of the abattoirs are $0.23, $0.21 and $0.19, respectively while the life cycle cost over a period of 20 years are$ 60,500, $56,300 and $53,700, respectively.

6. The CO₂ emissions saved by using PV system for water pumping instead of diesel generator are 16,300, 15,200 and 14,600 kg/year, respectively while the CO emissions saved are 46.37, 43.36 and 41.45 kg/year, respectively.

This present study focuses on the use of battery as the only storage device in the PV based water pumping system. One of the challenges of utilising PV system for water pumping applications is the cost of battery. Batteries are often replaced when used for water pumping compared other domestic home application such as washing and lighting due to the high current that is drawn from the battery as a result of the nature of operation of the induction motors which are often used in pumping application. This increases the overall life cycle cost of the PV system which makes generation of electricity from PV sources to be unattractive for water pumping application. The future research will focus on the use of hybridised storage technology using supercapacitor and battery instead of battery only. In this way, the supercapacitor with high power density but low energy density characteristics will complement battery with high energy density but low power density. The complementary characteristics are expected to improve the battery lifetime and also reduce the life cycle cost of a PV/Battery system for water pumping application.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Notes on contributors

Temitope Raphael Ayodele

Temitope Raphael Ayodele holds Bachelor of Engineering (B.Eng) in Electrical & Electronic Engineering from the Federal University of Technology (FUTA) and a Master of Engineering (M.Eng) in Electrical Power and Machine Engineering from the University of Benin, Nigeria.He obtained his doctoral degree (Doctor Technologiae) from Tshwane University of Technology, Pretoria, South Africa. His research interests are in Renewable energy resource assessments, grid integration of renewable energy, economic analysis of energy sources, Power system stability and power quality assessments.

Ayodeji Samson Olatunji Ogunjuyigbe

Ayodeji Samson Olatunji Ogunjuyigbe is with the Department of Electrical & Electronic Engineering, University of Ibadan. Dr. Ogunjuyigbe has 23 years of professional experience encompassing University teaching, research, inclusive of 2 years in consulting. Dr. Ogunjuyigbe was a Lecturer at the Faculty of Engineering, Ladoke Akintola University of Technology, (2006-2009), a consulting Engineer with SGI Consulting for the reinforcement of Nigerians Utility power Transmission Network. Dr. Ogunjuyigbe is presently team leading the power, Energy, machine and Drive (PEMD) Research group at the Department of Electrical & Electronic Engineering of University of Ibadan. The group is focused on researches in the core area of Power analysis, Energy conversion and its efficient Utilisation.

Omolola Anuoluwa Adeniran

Omolola Anuoluwa Adeniran holds B. Sc in Electrical & Electronic Engineering from University of Ibadan, Ibadan, Nigeria. Her research interest are in the area of Renewable Energy, Energy resource assessment and variability studies.

Appendix Table 18. Parameter of a 250Wp solar module.

S/N	Parameters	Values
1	Maximum Power	$P_{max}$	250Wp
2	Open Circuit Voltage	$V_{oc}$	37.8V
3	Maximum Power Point Voltage	$V_{mpp}$	31.1V
4	Short Circuit current	$I_{sc}$	8.28A
5	Maximum Power Point Current	$I_{\mathrm{m}\mathrm{p}\mathrm{p}}$	8.05A
6	Module Efficiency	${\eta }_{pV}$	14.91%
7	NOCT		48°C
8	Operating Temperature	$T_{CF}$	−40°C to 85°C

aSTC: 1000W/m², 25°C, AM 1.5