Mackay Okure, Fred Tuhairwe, Musinguzi W.B., Makerere University, Uganda.

1. Technical and Economic Viability of Biogas-based
Electricity Generation for Distributed Renewable Energy
Systems in Livestock Communities of Uganda
Presented by
FRED TUHAIRWE
13/10/2016 1
COLLEGE OF ENGINEERING, DESIGN, ART AND TECHNOLOGY
MAKERERE UNIVERSITY
Technical and Economic Viability of Biogas-based Electricity
Generation

2. Outline
• Background of the study
• Objectives of the study
• Case study of a pilot biogas-to-electricity generation plant
• Incorporation of a gas engine into a domestic biogas plant
• Developing a model for a dairy-farm-based biogas-to-electricity
mini grid
• Conclusion and recommendations
• Acknowledgements
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3. Background
• Access to modern energy services is still very low in communities
of Uganda, especially livestock keeping
• Generation and utilization of electricity from biogas is limited,
amidst the abundant resources.
• Pilot biogas-to-electricity schemes are not performing to the
expectations
• Biogas offers technical opportunities for decentralised approaches
to provision of modern energy services.
• The study was implemented through three interrelated cases:
Pilot/existing biogas-to-electricity plant,
Addition of gas engine generator to a domestic biogas system
Design of a new system for a livestock community with neither a biogas
system nor a electricity access.
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4. Study Objectives
• To establish the challenges faced by an existing biogas
production system for electricity generation that was
established a pilot case.
• To investigate the viability of incorporating a gas-engine
in a functioning domestic biogas system
• To develop a model for a dairy-farm-based biogas-to-
electricity mini grid
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5. 1. Performance of the existing biogas production system
for electricity generation
- A community-based biogas-to-electricity scheme established as
a pilot business model
-
The plug flow (PVC material) digester and a gas-engine generator
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6. Performance of the existing biogas production system
for electricity generation cont’d
The maize milling machine and the battery charging centre as
electricity load
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7. Performance of the existing biogas production system for
electricity generation cont’d
Criteria Quantity Performance Quantity
Volume of PVC bag 200 m3 volume of the
digester in use
37.2 m3
Expected feeding rate 1830
kg/day
Current feeding rate 257 kg/day
Expected gas
production per day
62.1 m3 Total gas production 11.6 m3/day
Expected electricity
per day
97 kWh Electricity
generated per day
18.0 kWh
Expected electricity
per month
29 MWh Electricity
generated per
month
541 kWh
Expected electricity
per annum
35 MWh Electricity
generated per
annum
6.5MWh
36.7
62.5
0.023
0.777
CO2 (%) CH4 (%) H2S (%) Others (%)
Performance of the biogas system for electricity generation
Mean percentage gas composition
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8. 0
5
10
15
20
25
30
0 2000 4000 6000 8000 10000 12000 14000
Efficiency(%)
Load (W)
Efficiency Vs load of the biogas generator
• Average pH was 7
• Average pressure was
1.35mbar.
• A full time
compressor was
availed
• System operated at
25% below its total
installed capacity
Performance - cont’d
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9. 2. Incorporating a gas-engine-genset in a functioning
domestic biogas system
Schematic diagram of the experimental design of the pilot project
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Existing system Added trial subsystem

10. Incorporating a gas-engine-genset - cont’d
The zero grazed cattle in a Kraal and a fixed dome biogas digester
-The domestic biogas plant
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11. Incorporating a gas-engine-genset - cont’d
The 3kW gas-engine with a gas meter and the electric loads under test
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12. Incorporation of a gas-engine-genset - cont’d
CH4
59.00%
CO2
40.30%
H2S
0.06%
Others
0.74%
Gas composition
CH4 CO2 H2S Others
• The net calorific value of the gas
was 21.3 MJ/m3
The gas bag containing biogas
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13. Incorporation of a gas-engine-genset – cont’d
0
2
4
6
8
10
12
14
0 500 1000 1500 2000
Efficiency(%)
Load (W)
Efficiency against load for the generator
• Performed adequately, however:
 Difficulties in maintenance and the
associated costs
 Presence of H2S, resulting into
corrosion
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14. 3. Developing a model for a dairy-farm-based biogas-to-
electricity mini grid
Map showing GPS locations of the livestock farms and cattle in the farms
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15. Particulars Unit Amount
Total initial investment USD 11,900
Specific Investment USD/kW 3967
Annual cost of O&M USD 200 (1.7%)
Annual electricity generated kWh 13,140 (13 MWh)
Discount rate % 10
Project life Years 12
Cost of electricity (Electricity export rate) USD/kWh 0.188
Equity Pay Back Period (PBP) Years 5.3
Simple Pay Back Period (PBP) Years 5.2
Pre-tax Internal Rate of Return (IRR) % 15
Net PresentValue (NPV) USD 3030
Benefit-Cost ratio (B-C) 1.25
Annual life cycle savings USD 445
Limited to the Financial Analysis using RETScreen
software
Developing a model for a dairy-farm based biogas-to-
electricity mini grid - cont’d
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16. Conclusion and Recommendations
• Low energy conversion efficiency
• Low capacity utilization and low gas quality
• A cluster of livestock farmers has potential for biogas as a S.PPS for DREs
• Capex needed to set up small DRE systems are within the means of the
farmers
• Designers and planners of biogas-based DREs must take sustainability of
the biogas plant into consideration
• Emphasis should be put on feedstock availability, management of O&M
and adequate capacity building
• Gas engine sets need gas cleaning systems for best performance
• All systems need a good business model with a proper system sizing
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17. • Renewable Energy Business Incubator (REBi) at CEDAT
• Centre for Research in Energy and Energy Conservation
(CREEC)
• Professor John Baptist Kaddu of JK-Farm
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Acknowledgements

18. THANKYOU!
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