Energy and budget balances for sweet potato-based ethanol production

Lima e Silva, Luis Felipe; Gonçalves, Wilson Magela; Maluf, Wilson Roberto; Resende, Luciane Vilela; Lasmar, André; Carvalho, Régis de Castro; Licursi, Vicente; Moretto, Paulo

doi:10.1590/S1678-3921.pab2019.v54.26521

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Crop Science • Pesq. agropec. bras. 54 • 2019 • https://doi.org/10.1590/S1678-3921.pab2019.v54.26521 linkcopy

Energy and budget balances for sweet potato-based ethanol production

Balanços energético e econômico para produção de etanol a partir de batata-doce

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract:

The objective of this work was to assess the viability of sweet potato (Ipomoea batatas) for ethanol production, as well as to estimate the energy and budget balances for the crop. Data from the agricultural and industrial production phases were evaluated. Those from the agricultural phase were estimated from a field experiment and used for comparison of sweet potato genotypes. Those from the industrial phase were estimated based on the literature on the fossil fuel energy and electricity consumed in the ethanol production process. With average yields of 35 Mg ha^-1 roots and 12 Mg ha^-1 dry stems, the output/input ratios were 6.64 and 1.93 for the energy and budget balances, respectively. For yields of 50 and 80 Mg ha^-1 roots (17 and 27 Mg ha^-1 dry stems, respectively), the indexes for energy balance were 7.16 and 7.68, respectively, and those for energy budget were 2.76 and 4.42. The obtained results confirm the great aptitude of the sweet potato crop for biofuel production.

Index terms: Ipomoea batatas; alternative energy sources; biofuel; corn; energetic sustainability; sugarcane

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[TFN1] ⁽¹⁾The costs with mechanized operations were estimated from the directly (fuel, labor, fertilizer, and agrochemicals) and indirectly (tractor and other machinery) embodied energy in the production system. ⁽²⁾The labor of one man per day is equivalent to 8 hours of manual work. ⁽³⁾By transforming liters into kilograms, this value represents a greater calorific power.

Investment		Unit	Embodied energy	Reference
		Agricultural phase
Mechanized operations⁽¹⁾
	Plowing	Hour machine	0.1715	Siqueira et al. (1999)
	Harrowing for leveling	Hour machine	0.0190	Siqueira et al. (1999)
	Fertilization and opening grooves	Hour machine	0.0199	Freitas et al. (2006) and Souza et al. (2008)
	Irrigation	kW h^-1	0.0036	Lima et al. (1999)
	Internal transportation	Hour machine	0.0055	Freitas et al. (2006)
Labor⁽²⁾
	Opening grooves	Day man	0.0063	Souza et al. (2008) and Gliessman (2000)
	Preparing and selecting seedlings	Day man	0.0100	Souza et al. (2008) and Gliessman (2000)
	Planting by hand	Day man	0.0063	Souza et al. (2008) and Gliessman (2000)
	Weeding by hand	Day man	0.0167	Souza et al. (2008) and Gliessman (2000)
	Harvesting	Day man	0.0167	Souza et al. (2008) and Gliessman (2000)
Inputs
	Nitrogen	kg	0.0670	Pimentel & Patzek (2005)
	Phosphorus	kg	0.0174	Pimentel & Patzek (2005)
	Potassium	kg	0.0136	Pimentel & Patzek (2005)
	Diesel	L	0.0477	Pimentel & Patzek (2005)
		Industrial phase
Electricity and fuel fossil energy when processing 1.0 L ethanol from starch		GJ L^-1	0.00669	Nguyen et al. (2007)
		Yield
Ethanol		L	0.0215⁽³⁾	Álvares Junior & Linke (2001)

Investment		Unit	Quantity	Cost (R$)	Total (R$)	Percentage
		Agricultural phase
Mechanized operations
	Plowing	Hour machine	1	50	50	2.02
	Harrowing for leveling	Hour machine	2	50	100	4.03
	Fertilization and opening grooves	Hour machine	3	90	270	10.89
	Irrigation	kW h^-1	808	0.18	146	5.89
	Internal transportation	Hour machine	0.5	50	25	1.01
Subtotal			-	-	591	23.84
Manual operations		Day man	40	25.00	1,000.00	40.34
Subtotal			40	25.00	1,000.00	40.34
Input
	N-P₂O₅-K₂O (4-14-08) fertilizer	kg	1,000	0.80	800.00	32.27
	Diesel	L	40	2.20	88.00	3.55
Subtotal					888.00	35.82
Total			-	-	2,479	100

Clones	Root productivity (Fresh matter - Mg ha^-1)				Dry steam (Mg ha^-1)
Clones	>50	50> 25	<25	Controls	Dry matter
UFLA07-12⁽¹⁾	98.0	-	-	-	20.0
UFLA07-43⁽¹⁾	95.0	-	-	-	20.3
2007HSF001-24	75.5	-	-	-	18.5
2007HSF002-05	70.1	-	-	-	13.6
2007HSF002-19	62.0	-	-	-	9.8
2007HSF010-12	55.6	-	-	-	10.5
CNPH Laranja	-	-	-	52.2	6.8
2007HSF022-19	59.2	-	-	-	15.9
2007HSF004-04	54.2	-	-	-	5.6
2007HSF030-02	52.8	-	-	-	23.0
2007HSF028-16	-	47.8	-	-	11.4
2007HSF027-16	-	42.8	-	-	18.8
2007HSF024-06	-	48.7	-	-	4.6
2007HSF031-04	-	38.6	-	-	29.1
2007HSF024-04	-	45.9	-	-	7.0
2007HSF004-17	-	46.4	-	-	10.6
Brazlandia Roxa	-	-	-	33.5	15.7
2007HSF025-04	-	41.1	-	-	9.0
2007HSF006-16	-	31.5	-	-	23.2
2007HSF002-14	-	40.6	-	-	9.8
2007HSF001-28	-	45.3	-	-	2.9
2007HSF010-33	-	38.1	-	-	18.4
2007HSF022-10	-	44.2	-	-	10.2
2007HSF010-41	-	37.9	-	-	6.1
2007HSF022-05	-	34.9	-	-	22.2
2007HSF014-05	-	30.9	-	-	22.8
Ufla07-49	-	31.5	-	-	13.9
2007HSF001-01	-	32.5	-	-	8.5
2007HSF022-09	-	35.9	-	-	13.4
2007HSF005-06	-	30.7	-	-	16.5
2007HSF020-08	-	33.1	-	-	17.9
Ufla07-53	-	32.5	-	-	11.8
2007HSF026-05	-	28.1	-	-	29.6
2007HSF002-04	-	27.8	-	-	13.1
2007HSF011-01	-	30.3	-	-	28.7
2007HSF021-01	-	31.1	-	-	67.9
2007HSF009-06	-	-	23.1	-	7.3
2007HSF001-26	-	27.6	-	-	35.7
2007HSF002-08	-	31.9	-	-	16.4
2007HSF004-06	-	26.3	-	-	24.6
2007HSF027-10	-	-	20.6	-	11.0
Itajubá-2012	-	26.4	-	-	43.8
2007HSF010-35	-	28.2	-	-	14.5
2007HSF010-47	-	-	21.7	-	13.4
2007HSF022-12	-	26.0	-	-	29.1
2007HSF010-06	-	-	22.6	-	6.3
2007HSF002-11	-	-	22.5	-	14.6
Ufla07-15	-	-	21.8	-	33.2
2007HSF020-07	-	25.6	-	-	7.9
2007HSF027-05	-	-	23.1	-	27.2
2007HSF028-05	-	25.7	-	-	3.0
2007HSF012-02	-	-	23.6	-	11.2
2007HSF020-12	-	-	22.5	-	28.1
2007HSF002-02	-	-	20.6	-	21.6
2007HSF010-23	-	-	20.0	-	13.2
2007HSF005-01	-	28.5	-	-	9.7
2007HSF010-31	-	26.1	-	-	13.4
2007HSF010-17	-	-	19.5	-	10.5
2007HSF029-01	-	-	21.4	-	14.6
2007HSF028-08	-	-	19.4	-	6.2
2007HSF027-07	-	-	17.2	-	20.7
2007HSF001-37	-	-	19.3	-	17.1
2007HSF011-05	-	-	19.3	-	13.7
2007HSF011-06	-	-	16.0	-	17.4
2007HSF027-12	-	-	17.9	-	19.7
2007HSF022-04	-	-	14.0	-	15.5
2007HSF001-21	-	-	13.0	-	36.2
2007HSF001-17	-	-	12.2	-	65.9
Palmas	-	-	-	13.5	11.9
2007HSF023-08	-	-	12.6	-	42.7
2007HSF026-02	-	-	12.5	-	23.8
2007HSF007-26	-	-	12.4	-	29.2
Brazlandia Rosada	-	-	-	8.5	5.8
2007HSF007-21	-	-	9.1	-	9.2
2007HSF006-13	-	-	8.8	-	42.6
2007HSF014-04	-	-	9.0	-	48.2
Álvaro-2012	-	-	12.2	-	4.9
2007HSF005-03	-	-	6.9	-	4.3
2007HSF001-40	-	-	7.4	-	6.6
2007HSF029-02	-	-	7.9	-	9.5
2007HSF010-01	-	-	0.7	-	9.6

Investment		Unit	Quantity	Consumption	Total
Mechanized operations
	Plowing	Hour machine	1	0.1715	0.1715
	Harrowing for leveling	Hour machine	2	0.0190	0.0381
	Fertilization and opening grooves	kW h^-1	3	0.0199	0.0597
	Irrigation	Hour machine	808	0.0036	2.9088
	Internal transportation	Hour machine	0.5	0.0055	0.0028
Subtotal			-	-	3.1808
Manual operations⁽¹⁾
	Opening grooves	Day man	1	0.0063	0.0063
	Preparing and selecting seedlings	Day man	2	0.0100	0.0200
	Hand planting	Day man	10	0.0063	0.0630
	Hand weeding	Day man	7	0.0167	0.1172
	Harvest	Day man	20	0.0167	0.3349
Subtotal			-	-	0.5414
Input
	Nitrogen	kg	40	0.0670	2.6796
	Phosphorous	kg	140	0.0174	2.4349
	Potassium	kg	80	0.0136	1.0919
	Diesel	L	40	0.0477	1.9092
Subtotal			-	-	8.1155
Total for agricultural phase			-	-	11.8377

Parameter		Unit	Quantity	Embodied energy	Total
Investment		30 Mg ha^-1
Fossil fuel energy and electricity		GJ L^-1	0.00669	5,600	37
Yield
	Ethanol	GJ L^-1	0.0215	5,600	121
	Residues	TDN (kg)	0.0184	3,899	72
	Stems	TDN (kg)	0.0184	7,341	135
Investment		50 Mg ha^-1
Fossil fuel energy and electricity		GJ L^-1	0.00669	8,000	54
Yield
	Ethanol	GJ L^-1	0.0215	8,000	172
	Residue	TDN (kg)	0.0184	5,570	102
	Stems	TDN (kg)	0.0184	10,488	193
Investment		80 Mg ha^-1
Fossil fuel energy and electricity		GJ L^-1	0.00669	12,800	86
Yield
	Ethanol	GJ L^-1	0.0215	12,800	276
	Residue	TDN (kg)	0.0184	8,912	164
	Stems	TDN (kg)	0.0184	16,780	309

Roots yield	Total energy (GJ)	Percentage (GJ)	Values (R$)
	Energy embodied in the agricultural phase
35 Mg ha^-1	11.84	24.01	2,475
50 Mg ha^-1	11.84	18.11	2,475
80 Mg ha^-1	11.84	12.14	2,475
	Energy embodied in the industrial phase
35 Mg ha^-1	37.46	76	-
50 Mg ha^-1	53.52	82	-
80 Mg ha^-1	85.63	88	-
	Total embodied energy
35 Mg ha^-1	49.30	100	2,475
50 Mg ha^-1	65.36	100	2,475
80 Mg ha^-1	97.47	100	2,475
	Yield
35 Mg ha^-1	327.36	-	4,788
50 Mg ha^-1	467.65	-	6,840
80 Mg ha^-1	748.25	-	10,944
	Balance
35 Mg ha^-1	6.64	-	1.93
50 Mg ha^-1	7.16	-	2.76
80 Mg ha^-1	7.68	-	4.42