ORIGINAL ARTICLE

Use of Renewable Energy in Agricultural Processes to Produce Food

0000-0002-1371-4614Osvaldo André Paulo Ferreira-da Silva^I  , 0000-0003-3316-0898Pável Vargas-Rodríguez^{II  *}  , 0000-0003-4093-971XAbel Dorta-Armaignac^II  , 0000-0002-5114-7948Kaddiel Fernández-Hung^IV  , 0000-0003-3714-6989Ignacio Hernández-Ramírez^III  , 0000-0001-7906-8398Alberto Méndez-Jocik^V 

^IUniversidad de Ciego Ávila (UNICA), Centro de Estudios Hidrotécnicos, Ciego de Ávila, Cuba.

^IIUniversidad de Oriente, Departamento de Ingeniería Hidráulica, Santiago de Cuba, Cuba.

^IIIEmpresa Nacional de Proyectos Agropecuarios. UEB Ciego de Ávila, Cuba.

^IVGrupo de Difusiòn Tecnològica. Empresa de Cìtricos, Contramaestre. Cuba

^VEmpresa Nacional de Proyectos Ingeniería, Departamento de Diseño, La Habana, Cuba.

ABSTRACT

This work deals with the problem of food insecurity in the central region of Cuba, in a context characterized by the depletion of conventional energy sources and the negative effects of climate change. In Los Milian farm, Ciego de Ávila Province, the application of a closed cycle production process is foreseen for the production of food with the rational use of water and energy. It is conceived to use the surpluses of the biogas production process and to utilize dry matter as bio fertilizer. A system of treatment to reduce the pollutant load of the effluents, a domestic supply system coupled to a photovoltaic solar pump and an irrigation system compatible with the hours of least consumption of electricity are proposed. The results generate a positive social and environmental impact for Ciego de Ávila Province.

Key words: Water; Biomass; Solar Arrangement; Irrigation

INTRODUCTION

Ciego de Ávila is the province with the highest tourist activity in the country. The investments developed in Jardines del Rey Tourist Centre, foresee a short-term increase in the demand for agricultural products to meet the needs of development. This situation requires the rational and efficient use of water and energy through modern irrigation technologies (^{Tarjuelo, 1995}; ^{Tarjuelo & José, 2005}), taking into account the conservation of the region's natural resources and their protection against the consequences of climate change.

The soils that make up the region present disadvantageous conditions due to the presence of saline intrusion, as well as due to the mostly flat relief of its surface, which hinders its natural drainage, all of which contributes to identify more than 35% of the soils of the region in quality categories II and III, on the scale of soil agro productivity. Recent reports assure that the overexploitation of these resources, mainly those destined for agricultural irrigation, has led to a significant decrease in these reserves and the consequent penetration of marine wedge in coastal areas of the province. As agriculture is the largest water consumer, the use of efficient irrigation technologies is an imperative to achieve the rational use of water and energy (^{FAO (PMA); MINAG-Cuba, 1999}).

These reasons demand actions aimed to improving the management of water and energy in agricultural activities of the territory (^{Vanegas, 1988}; ^{Tarjuelo, 1995}; ^{Vigoa, 2001}; ^{Vargas, 2008}). The solution involves the use of a hybrid system, in which photovoltaic solar energy is used to supply water to the processes generated by livestock and domestic activities in the farm, the use of solid waste generated in pig farming, to obtain biogas, and the application of specific treatment systems to reduce the pollutant load of waste from the livestock process (^{Díaz, 2002}). Water coming from the well to guarantee the volumes necessary for the foreseen crops, will be pumped once filtered through a network pipes of HDPE conveniently designed to apply water to the irrigation plots.

MATERIALS AND METHODS

Milian farm, located on the periphery of Ciego de Ávila City, between coordinates 736039 North and 229762 East, with the entrance of the farm at 5½ km of the road that connects the capital city with Moron Municipality. The study case was described and energy consumption in the farm was characterized to determine the energy demand to be produced by biogas and the number of animals necessary to satisfy it. The supply system was also defined and the Soil -Water - Plant ratio necessary to design the irrigation system was characterized. The solar arrangement was defined and the dimensions of the photovoltaic module and its components, necessary to satisfy the water needs of the farm facilities were determined. They include the pig pens and the organs of treatment for the use of excreta in the biomass energy generation. Three Stabilization Lagoons were included as part of the treatment of domestic waste and irrigation activities.

Design Procedure for the Anaerobic Biodigester

Initially, the biodegradable potential was estimated to meet the need for cooking food, for lighting and as domestic fuel. The flow diagram of the Biogas Plant was selected based on the experience obtained from another similar system, taking into account climatological and hydro geological data, agricultural activities and their future projections for its implementation.

Calculation of Daily Biogas Demand of the Farm

The number of animals necessary to guarantee the daily residual volume and the biogas demand was determined without taking into account the residual product of the harvest or the breeding of other potentially useful animals. The area needed to produce 100% of the raw material required for feeding the pigs on the farm was estimated, so that there is sustainability in the process. The necessary biogas consuming equipment was identified and the consumption of each of them was estimated to determine the daily biogas demand of the farm. With these results, the number of animals necessary to guarantee livestock activities was calculated.

$C_B=\frac{N\times T_R\times P\times e}{1000}$ (1)

CB:	Biogas consumption per day (m^3/d)
TR:	Hours of use in the day (h/day)
N:	Number of artefacts.
P:	Consumption of the artefact).
e:	Artefacts efficiency (%)

TABLE 1 Average consumption and efficiency of the equipment (^{Malalasekera, 2015}) 

Equipment	Consumption (L/h)	Performance (%)
Kitchen burner Blanket Lamp (60W) Refrigerator de 100 L Gas Engine Infrared Lamp de 200W Cap Lamp Oven Burners Stove with 4 burners and 1 oven	300-600 120-170 30-75 0.5 m^3/kWh 30-40 100-120 420-500 1800-2100	50-60 30-50 20-30 25-30 80-90 30-50 20-30 20-40

Estimation of the Number of Animals Necessary to Supply the Demand for Biogas

Knowing the daily demand for biogas and using Table 1, the amount of excreta necessary was obtained, and the number of animals necessary to satisfy the demand, taking into account the parameters proposed in the following table.

TABLE 2 Properties and gas performance of some materials, (^{Acuña, 1984}) 

Material (Excrement)	Quantity (kg/animal)	Solid Content (%)	Rate C/N (carbon/nitrogen)	Yield (L/kg/d)
Cows Buffalo Pigs	15 - 20 18 - 25 1,2 - 4	18 - 20 16 - 18 24 - 33	24 - 25 24 - 25 12 - 13	15 - 32 15 - 32 40 - 60

$C_P=\frac{C_B\times 1000}{T\times e}$ (2)

Cp:	Number of animals needed.
CB:	Biogas consumption per day (m^3/d).
T:	Amount given per day (kg/animal).
e:	Daily yield (L/kg material).

The volatile solids content of the residual was assumed from affecting 25% of the fresh excreta mass, (^{Savran, 2005}).

Water Consumption of the Farm

The daily volume of water to be guaranteed for pigs was estimated in accordance with the Pig Breeding Manual and considering the fattening category, (45 L/d per animal); the water demand for the house was estimated for a supply of 100 L/d/p.

Biodigester Design Procedure

The biological demand of the effluent was obtained, considering maximum flow rate of the effluent, the volume of water necessary to use in the process, and the volume of sludge to be digested as well the volume of the biodigester.

$Qmax=Ch\times Qprom$ (3)

Average flow was computed by (4), assumed coefficient of irregularity (Ch = 2):

$Qprom=N_{50}\times q$ (4)

$Volumeofwater=\frac{\left[V\times (Pi-Pf)\right]}{(100-Pf)}$ (5)

$Volumeofsludge=Qprom-Vwater$ (6)

$Volumeofdigestedsludge=Vsludge\times \frac{(Pfresi-Pfdig)}{(100-Pfdig)}$ (7)

$Vdigester=Vsludge-\left[2/3(Vsludge-Vdig)\right]\times t$ (8)

${DBO}_{5}effluent={DBO}_5\times 0.4$ (9)

N 50:	Number of animals equivalent to 50 kg of weight.
q:	Allowance for each animal weighing 50 kg. (L/d)
Ch:	Irregularity coefficient.
Pi:	Approximate initial humidity of the residual (98.50%)
Pf:	Approximate final humidity of the residual (92.00%)
V sludge:	Volume of fresh sludge per day. (m^3)
V dig.slu.	Volume of sludge digested per day. (m^3)
t:	Digestion time (days) T ≥ 20 days;
V:	Volume of the Biodigester.

Calculation of the Biogas Storage Tank

Practical experience indicates that 40-60% of the daily biogas production normally has to be stored; therefore, a storage tank is required for it (^{Botero & Preston, 1986}). The size of the tank depends on the relative rates of generation and consumption of biogas and was sized to cover the peak rate of consumption: in this case the size was determined based on maximum gas consumption; the capacity of the tank was increased by 20 % as margin of safety:

${\mathrm{V}}_{\mathrm{m}\mathrm{a}\mathrm{x}\mathrm{c}}={\mathrm{G}}_{\mathrm{C}\mathrm{m}\mathrm{a}\mathrm{x}}\times {\mathrm{T}}_{\mathrm{C}\mathrm{m}\mathrm{a}\mathrm{x}}$ (10)

Gcmax:	Maximum hourly gas consumption (m^3/h).
TCmax:	Time of maximum consumption (h).

Post-Treatment of Effluents from the Anaerobic Reactor

It was planned to reduce the water content and facilitate the handling of the bio-fertilizer, as well as eliminate bad odours from it. Drying beds were used to dehydrate the sludge, and convert the volatile solids into biogas.

Calculation of the Daily Volume of Sludge that Reaches the Drying Beds (V L/d: m³/d)

Calculation of Drying Beds

$Vdrainday=\frac{\left[Vloddig\times (P_2-P_3)\right]}{(100-P_3)}$ (11)

$\mathrm{V}\mathrm{o}\mathrm{l}\mathrm{u}\mathrm{m}\mathrm{e}\mathrm{ }\mathrm{o}\mathrm{f}\mathrm{ }\mathrm{d}\mathrm{r}\mathrm{y}\mathrm{ }\mathrm{s}\mathrm{l}\mathrm{u}\mathrm{d}\mathrm{g}\mathrm{e}\mathrm{}=\mathrm{V}\mathrm{d}\mathrm{i}\mathrm{g}\mathrm{ }\mathrm{s}\mathrm{l}\mathrm{u}\mathrm{d}\mathrm{g}\mathrm{e}-\mathrm{V}drenday$ (12)

$\mathrm{V}\mathrm{o}\mathrm{l}\mathrm{u}\mathrm{m}\mathrm{e}\mathrm{ }\mathrm{o}\mathrm{f}\mathrm{ }\mathrm{d}\mathrm{r}\mathrm{y}\mathrm{ }\mathrm{s}\mathrm{l}\mathrm{u}\mathrm{d}\mathrm{g}\mathrm{e}\mathrm{ }\mathrm{p}\mathrm{e}\mathrm{r}\mathrm{ }\mathrm{y}\mathrm{e}\mathrm{a}\mathrm{r}=\mathrm{V}\mathrm{ }\mathrm{d}\mathrm{r}\mathrm{y}\mathrm{ }\mathrm{s}\mathrm{l}\mathrm{u}\mathrm{d}\mathrm{g}\mathrm{e}\times 365$ (13)

The area of the drying bed was obtained for sludge extractions every 26 days, 0.30 m thick and 14 extractions per year

$\mathrm{S}\mathrm{l}\mathrm{u}\mathrm{d}\mathrm{g}\mathrm{e}\mathrm{ }\mathrm{h}\mathrm{e}\mathrm{i}\mathrm{g}\mathrm{t}\mathrm{h}=\#\mathrm{ }\mathrm{o}\mathrm{f}\mathrm{ }\mathrm{e}\mathrm{x}\mathrm{t}\mathrm{r}\mathrm{a}\mathrm{c}\mathrm{t}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{s}\times \mathrm{a}\mathrm{c}\mathrm{c}\mathrm{u}\mathrm{m}\mathrm{u}\mathrm{l}\mathrm{a}\mathrm{t}\mathrm{e}\mathrm{d}\mathrm{ }\mathrm{t}\mathrm{h}\mathrm{i}\mathrm{c}\mathrm{k}\mathrm{n}\mathrm{e}\mathrm{s}\mathrm{s}$ (14)

$\mathrm{D}\mathrm{r}\mathrm{y}\mathrm{i}\mathrm{n}\mathrm{g}\mathrm{ }\mathrm{b}\mathrm{e}\mathrm{d}\mathrm{ }\mathrm{a}\mathrm{r}\mathrm{e}\mathrm{a}=\frac{\mathrm{V}\mathrm{o}\mathrm{l}\mathrm{u}\mathrm{m}\mathrm{e}\mathrm{ }\mathrm{o}\mathrm{f}\mathrm{ }\mathrm{d}\mathrm{r}\mathrm{y}\mathrm{ }\mathrm{s}\mathrm{l}\mathrm{u}\mathrm{d}\mathrm{g}\mathrm{e}\mathrm{ }\mathrm{p}\mathrm{e}\mathrm{r}\mathrm{ }\mathrm{y}\mathrm{e}\mathrm{a}\mathrm{r}}{\mathrm{S}\mathrm{l}\mathrm{u}\mathrm{d}\mathrm{g}\mathrm{e}\mathrm{ }\mathrm{h}\mathrm{e}\mathrm{i}\mathrm{g}\mathrm{t}\mathrm{h}}$ (15)

P 2 :	Initial humidity (92%)
P s :	Final Humidity (75%)
Vdig sludge:	Volume of digested sludge.
Vdrainday:	Volume drained daily.

Organic Load According to Total Volatile Solids (STV)

$\mathrm{S}\mathrm{T}\mathrm{V}=Sdigestedvolatile+Svolatiledepositing$ (16)

$SSvolatiledepositing=SVS\times 0.5$ (17)

$STV=\frac{STV}{Digestervolume}$ (18)

Design of the Stabilization Lagoons

The organic load of these lagoons for tropical countries can range 20 to 35 g/m²/d with depths between 1 to 2.5 m, the usual length: width (L/W) ratio is 2 to 2.5 m and the hydraulic retention times can reach 10 to 20 d according to the treatment objective. These systems remove 60 to 80% of the total DBO₅ from the feed in reference to the soluble DBO₅ at the outlet and eliminate between 4 to 5 logarithmic orders in the faecal coliforms depending on the retention times.

For the calculation of the Anaerobic Lagoon, the empirical design per load was used, this method is based on assuming the Organic Load with which the Lagoon will work. A retention time of 3.03 days was assumed.

For the design of the Facultative Lagoon, Cubillo Method was used, a depth = 5 m was assumed and the modified Gloyna expression was used to calculate the Applied Surface Load.

Aspects to Consider as Environmental Benefit

To analyse the environmental effect of the produced biogas, the volume of CH₄ that is no longer emitted into the atmosphere was considered, the protection of water sources from possible pollutants, the obtaining of organic bio-fertilizers, the reduction of the use of chemical fertilizers and the substitution of non-renewable energy sources.

Characterization of the Water - Soil - Plant - Climate Complex

The supply system was conceived to satisfy the needs of the crops and the consumption of the house, including the water needs for 400 piglets.

Supply Source

Water obtaining is from a well, with capacity = 2 L/s by means of a photovoltaic pump, selected to supply the farmer's home and for pig farming, the water will be driven to a tank raised 10 m high with the capacity for the required volume. For the irrigation system, it was planned to use another well with flow = 26 L/s coupled with a conventional pump. Water quality is adequate for irrigation and for household consumption, a value between 0.75 and 2.25 dS/m was assumed for design purpose (^{Pizarro, 2000}).

Characteristics of the Crops to Benefit

Tolerance to salinity: low 2.3 dS / m (for Guava crop because it is the most demanding). Flooding tolerance = 24 hours, (for tomato crop, because it is the most demanding). The following table refers other parameters of the crops (^{Pizarro, 2000}).

TABLE 3 Planting frame, crop coefficients and crop height (^{Allen et al., 1998}) 

Crops	P.F. (m×m)	Kc ini	Kc med	Kc fin	Height (m)
Guava	5 × 2	0.31*	0.93*	0.88*	2.0*
Cassava	0.9 × 0.9	0.3	0.8	0.3	1.0
Corn	0.9 × 0.4	0.7	1.2	0.6 - 0.35	2.0
Tomato	1.4 × 0.5	0.6	1.15	0.7 - 0.9	0.6
Water melon	0.5 × 0.4	0.4	1.0	0.75	0.4

* - Suggested values.

Hydro physical Properties of the Soil

General slope <1%, depth> 1.5 m, external and internal drainage was moderate to poor with depth. Moderately productive soils with a stabilized infiltration rate of 22.86 mm / h, a value of 2.3 dS/m was assumed, corresponding to a 90% reduction of the harvest in relation to the normal, (^{Pizarro, 1985}).

Climatic Characteristics

The monthly average series of evaporation and rainfall for 11 years provided by the Hydraulic Resources Institute in Santiago de Cuba, as well the temperature, wind speed and relative humidity data.

Design Procedure of the Irrigation System

A topographic survey was used, at 1: 2000 scale with level curves every 1m. HDPE lateral pipe of 20 x 16 mm diameter, with auto compensating drippers inserted at 0 75 m along the pipe, flow rate = 2.5 L/h and pressure range He = 98 to 294 kPa.

Agronomic Design

The procedure proposed by Keller and Rodrigo cited by Pizarro (1996) was applied to estimate the crops water needs, the criterion of ^{Allen et al. (1998)} and ^{Allen (2006)} was taken into account to calculate the correction coefficients of the net water needs in the critical period of crops. An extra dose to anticipate the leaching needs in the case of harmful saline levels was taken into account. The irrigation frequency was estimated daily, according to the irrigation technique and water management facilities. Timing irrigation was calculated for each crop, anticipating not applying irrigation during the peak hours set by the National Electro Energetic System (SEN in Spanish).

Hydraulic Design

It was conceived to the dimensioning of the installation for satisfying crop water needs defined in the Agronomic Design. In addition, the topography of the plots data was taken into account, besides total of crop water needs and the crops practices, let to choose the type of emitter and the most appropriate lateral arrangement, this also allowed to estimate the maximum number of rotational units. The hydraulic calculation was simplified due to auto compensating drip emitters are used, to guarantee that the pressures in the important points of the irrigation plot are kept within the compensation range of the drippers as a guarantee that they deliver the necessary flow. Boundary conditions in which the installation should operate were defined and the design of the irrigation plots was executed and their number, location, as well as the pressure and flow regime necessary for the design of the control station.

PV Pump System Design Procedure

Feasibility of the Solar Operation on the Farm

For the selection of the use of photovoltaic pumping, it was verified that the amount of solar energy available is appropriate, also the availability of other sources of energy in the area and that the intended use of the extracted water is for human consumption.

In accordance with ^{Bulté (1995)}, PV pumping systems are slightly cheaper than conventional ones for an operating time of 20 years, in the same way ^{Bloos et al. (1996}; ¹⁹⁹⁷⁾ confirmed that these systems are more reliable, autonomous and efficient.

Calculation and Selection of the Elements that Make up the PV Pumping System

To make the selection and sizing of the photovoltaic pumping system, it was taken into account the demand of the farmer's house and livestock activities, the convenient orientation of the photovoltaic panels and the power of the photovoltaic generator, as well as the number of modules in series and in parallel and the selection of the frequency converter and the conductors.

Calculation of the PV Generator Power: [PgFV (kW)]

$Pgfv=\frac{P_{ba}}{Ks}$ (19)

Pba:	water pump power (kW);
Ks:	safety coefficient (0.8 - 0.85 for Cuba)

This coefficient takes into account the total efficiency of the system (the average daily efficiency of the panel under operating conditions, the coupling factor, and the temperature coefficient of the cells). The selection of the solar arrangement was made with the Wincaps software.

Calculation of the Number of Modules in Series (Nms)

$N_{ms}=\frac{Tn}{Tnm}$ (20)

Tn:	nominal voltage of the installation (V);
Tnm:	nominal voltage of the modules (V).

Calculation of the Number of Modules in Parallel (Nmp)

$N_{mp}=\frac{Immax}{Ipmax}$ (21)

Im max:	maximum current demanded (A);
Ip max:	current for maximum power point (A).

Calculation of the Total number (Ntm) of Modules

$Ntm=Nms\times Nmp$ (22)

RESULTS AND DISCUSSION

The daily demand for biogas is 62.7 m³/d, and it is less than the volume of biogas produced, a part of it is destined for other users, or it can be stored.

TABLE 4 Daily demand of biogas in the farm 

Equipment	Consumption (L/h)	Quantity of Equipment	Hours of use (h/day)	Biogas Consumption (m^3/d)
Farmer’s house
Mantilla lamp (60W)	170	10	6	10.2
Refrigerator de 100 L	75	1	12	0.9
Kitchen / 4 burners	1800	1	4	7.2
Pigpens
Kitchen / 4 burners	1800	1	2	3.6
Mantilla lamp (60W)	170	20	12	40.8
Total				62.7

TABLE 5 Design of biodigestor 

Description	Unit	400 pigsof 100 kg
Digested sludge volume	m^3/d	3.50
Digestor capacity	m^3	96.67
Retention time	Días	20
Volume of gas produced	m^3/d	90.9
Storage tank	m^3	36.36

An excreta-water ratio of the final mixture of 1: 3 by weight was selected; this solution contributes to a better biodegradation of the excreta.

TABLE 6 Sizing of the drying bed 

Description	Unit	400 pigsof 100 kg
Daily drain volume Daily dry sludge volume Annual dry sludge volume Extraction period Amount of extractions Thickness of sludge accumulation Accumulated sludge area	m^3/d m^3/d m^3/d days U m m^2	2.38 1.12 408.80 26.00 14.04 0.30 97.07

9m² were assumed for each plot. The dehydrated sludge can be used as solid fertilizer and can be applied directly to the crop.

Design of Stabilization Lagoons

The Anaerobic Lagoon; designed to reduce the pollutant load of the crude residual, with a depth = 2.5 m and retention time = 3.03 d. The pollutant load of the effluent decreases to 9.48 kgDBO₅/m³ corresponding to a removal efficiency = 82.05 %, which is an acceptable value according to the design practice in Cuba.

The Facultative Lagoon 1 with a depth =1.5 m, but surface area greater than the anaerobic lagoon = 0.025 ha. For this case, the removal efficiency = 89.32 %, reducing the pollutant load to 0.06 kgDBO₅/m³. To avoid an increase in the pollutant load, a second Facultative Lagoon was planned with the same depth, but less surface area = 0.0157 ha and a retention time = 4.4 d. A removal efficiency = 79.02 % was obtained. It is important to check the bacteriological quality of the effluent before deciding its final destination, due to the risk of the presence of pathogens whose presence limits the reuse of the effluent in the irrigation of planned agricultural crops.

Table 7 shows the results of the agronomic design, Table 8 the results of the hydraulic design (20 × 16 mm) and Table 9 the exploitation parameters of the irrigation system.

Figure 1 shows the simulation of the hydraulic behavior of the farm's irrigation system and Figure 2 shows the general scheme of exploitation of the farm's irrigation area.

TABLE 7 Results of the agronomic design 

Crops	Irrigation Timing (h)	Irrigation Dose (L)	Total water needs (L)
Guava	6.1	40	39.97
Corn	2.3	3.07	3.07
Tomato	3.04	4.06	4.05
Cassava	1.56	4.67	4.66
Water melon	1.06	1.41	1.41

TABLE 8 Results of hydraulic design (lateral pipe 20 x 16 mm) 

CROPS	Lateral length (m)	Lateral discharge(L/s)	ho (kPa)	h mín. (kPa)	Pressure range
Guava	100	0.093	108.04	92.55	98 - 294
Cassava/ Corn	100	0.093	108.04	92.55	98 - 294
Tomato / Watermelon	100	0.093	108.04	92.55	98 - 294

TABLA 9 Parameters of operation of the irrigation system 

CROPS	Applying Flow (L/s)	Irrigation timing (h)	Irrigation Schedule (h)	Irrigation area (ha)
Guava	8.92	12	18:00 a 06:00	9.60
Cassava	16.38	6.24	06:00 a 12:24	7.80
Corn	16.38	9	06:00 a 15:00	7.80
Tomato	16.38	12	18:00 a 06:00	6.96
Water melon	16.38	4.24	06:00 a 10:24	6.96

FIGURE 1 Simulation of the hydraulic behavior of the farm’s irrigation system 

FIGURE 2 General scheme of exploitation of the farm´s irrigation area 

Next, the parameters of operation of the selected bomb are presented (Table 10).

TABLE 10 Operational parameters of the selected pump 

BRAND	Discharge (L/s)	Pressure (kPa)	Power (kW)	Efficiency 𝛈 (%)	NPSHr
Pump:6S181B/2B	25.3 L/s	406.7 kPa	7.1 kW	72 %	5.9 m

Analysis of the results of the selection of the photovoltaic solar arrangement

In the Tables 11, 12 and 13, the necessary parameters are described for the selection of the photovoltaic pump, parameters for the calculation of the necessary current and parameters of design of the solar arrangement, respectively

Pump Grundfus SQF 2.5-2 N, (Table 11a), encapsulated, stainless steel, maximum temperature = 40℃. Three-speed motor and protection against dry running. High performance engine of permanent magnet, and over-voltage and under-voltage protection. Protection against maximum power tracking point. Panels with 50 W of power of the polycrystalline and amorphous silicon type, inclined. Nominal power and voltage = 0.24 kW and 152 kW, respectively. Orientation (0° = south; 90° west; 180° north; 270° east) (Azimuth α = 0°) and Tilt angle β = 21°.

TABLE 11 Parameters necessary for the selection of photovoltaic pump 

Volume of water needed per day	6	m^3/d
Site insolation	8	h pico/día
Pumping regime	2	m^3/h
Static charge	6	m
Friction charge	4	m
Total charge	10	m

TABLE 11a Information of the set Pump -Engine 

Brand	Grundfus
Model	SQF 2.5-2 N
Pump type	Centrifuge
Engine type	MSF3 N
Operating voltage	30-300 V
Pump efficiency	80%

TABLE 12 Parameters for calculating the required current 

Need daily water volume	6	m^3/d
Total dynamic charge	10	mca
Hydraulic energy	23760	Wh/d
Pump efficiency	0.8
Energy of photovoltaic arrangement	32400	Wh/d
Nominal voltage of the system	300	volt
Electric charge	27.5	Ah/d
Driver performance factor	0.95
Corrected electric charge	28.6	Ah/día
Site insolation	8	h pico/d
Project current	7	Amp

TABLE 13 Design parameters for solar arrangement 

Project current	7	Amp
Modulus reduction factor	0.85
Module Current Imp.	0.329	Amp
Nominal system voltage	200	Volt
Voltaje del módulo	152	Volt
Serial modules	1	U
Parallel modules	3	U
Photovoltaic arrangement capacity	1.13	kW

Using biogas for cooking food and lighting, 33069 m³ of methane gas are no longer emitted into the atmosphere per year, in turn, the biomass energy produced, contributes to avoid the use of 5.7 Tn of equivalent oil per year, which constitutes a limited resource, and emits harmful gases towards the ozone layer such as NO_X; CO₂; HC and SO_2, which when burned can cause acid rain. The sludge from the digester is an excellent fertilizer, and it replaces the use of chemical fertilizers, saving time and financial resources for the farmer. The water treatment from the reactor removes a considerable amount of total volatile solids and DBO₅ and allow releasing according to the Cuban Standards.

Drip irrigation systems allow using water and energy efficiently and humanize the irrigation activities and apply irrigation outer the maximum electric consume, as well as increasing food production for markets and sale points. Photovoltaic solar energy is an ecological and economical solution in communities far from the SEN, it is expected to produce energy at 2.6 t/year of equivalent oil per year and contributes to reducing exports.

TABLE 14 Qualitative assessment of energy, water and environmental savings 

Anaerobic biodigester
Volume of methane retained from the atmosphere	33069	m^3/year
Equivalent energy produced from biomass	56940	kWh/year
Tons of oil saved	5.7	Tn/year
Emissions retained for oil savings
NOX	204.6	kg/year
CO2	13.8	kg/year
CO	47.9	kg/year
HC	5.00	kg/year
SO2	5.9	kg/year
Organic fertilizer produced	97.1	Tn/year
DBO avoided from receptor bodies	3168	kg/DBO/year
Photovoltaic generator
Produced energy	26280	kWh/year
Tons of oil saved	2.6	Tn/year
Emissions retained for oil savings
NOX	30.7	kg/year
CO2	2.1	kg/year
CO	7.19	kg/year
HC	0.75	kg/year
SO2	0.88	kg/year

CONCLUSIONS

• The proposed solutions favour the application of a closed cycle production process on Milian farm and contribute to the production of food through environmentally friendly alternatives.

• It is not convenient to reuse treated wastewater for irrigation of crops and other agricultural activities without taking into account the bacteriological quality of the effluent.

• The biogas plant allows the exploitation of the farm's biodegradable potentiality and entails a positive social and environmental impact.

• Photovoltaic arrangement is compatible with the supply needs of farms and it does not conceive a battery to store solar energy; furthermore, economic price is possible for solar module.

REFERENCES

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Received: March 02, 2021; Accepted: November 12, 2021

^*Author for correspondence: Pável Vargas-Rodríguez, e-mail: [e-mail]

Osvaldo André Paulo Ferreira-da Silva. Aspirante a Grado Científico. Universidad de Ciego de Ávila (UNICA), Centro de Estudios Hidrotécnicos, Ciego de Ávila, Cuba, e-mail: [e-mail]

Pável Vargas-Rodríguez, Profesor Titular, Departamento de Ingeniería Hidráulica, Universidad de Oriente. Santiago de Cuba, Cuba, e-mail: [e-mail]

Abel Dorta-Armaignac, Profesor Auxiliar, Departamento de Ingeniería Hidráulica, Universidad de Oriente. Santiago de Cuba, Cuba, e-mail: [e-mail]

Kaddiel Fernández-Hung, Especialista, Grupo de Difusión Tecnológica Empresa de Cítricos Contramaestre, Santiago de Cuba, Cuba, e-mail: [e-mail]; [e-mail]

Ignacio Hernández-Ramírez, Especialista en Proyectos. Empresa Nacional de Proyectos Agropecuarios. UEB Ciego de Ávila. hidrá[e-mail]

Alberto Méndez-Jocik, Jefe del Departamento de Diseño, Empresa de Proyectos Ingeniería, La Habana, Cuba, e-mail: [e-mail]

The authors of this work declare no conflict of interests.

AUTHOR CONTRIBUTIONS: Conceptualization: P. Vargas. Data curation: Osvaldo A. P. F. da Silva. P. Vargas. Formal analysis: Osvaldo A. P. F. da Silva. P. Vargas. A. Dorta. I. Hernández. A. Méndez. Investigation: Osvaldo A. P. F. da Silva. P. Vargas. A. Dorta. I. Hernández. A. Méndez. Methodology: Osvaldo A. P. F. da Silva. P. Vargas. A. Dorta. I. Hernández. A. Méndez. Supervision: Osvaldo A. P. F. da Silva. P. Vargas. A. Dorta. I. Hernández. A. Méndez. Roles/Writing, original draft: Osvaldo A. P. F. da Silva. P. Vargas. Writing, review & editing: Osvaldo A. P. F. da Silva. P. Vargas.