Project Partner:

Carbon Offset

Soil Biodiversity

Native

May 2023

Project Summary:

Su.re.co installs small-scale biodigesters with local Indonesian farmers, turning their cow & pig manure into organic fertilizers and biogas, providing a sustainable alternative to firewood, LPG gas, and chemical fertilizers.

Carbon offsets from biogas are a result of the carbon saved from LPG and firewood usage, the carbon saved from chemical fertilizer usage, and the carbon saved from manure degradation, subtracted by carbon emitted by burning biogas and carbon emitted by the bioslurry (organic fertilizer) (see Formula Below). Further sources can be seen in the appendix next to each parameter.

OCS: Carbon saved from old cooking source (LPG/firewood)

CF: Carbon saved from chemical fertilizer

CMO: Carbon prevented from setting free when cow manure decomposes (cow manure offset)

BF: Carbon emitted by bio-fertilizer

BG: Carbon emitted by cooking with biogas

Following this scheme, the carbon offset per biodigester is approximately 1 tCO2e/year (precisely: 0.96 tCO2/year).

This value of 0.96 tCO2 is the theoretical result for a digester running under ideal circumstances.

The gasmeter formula reduces the assumption of “Flow rate * average gas production” of 90 minutes per day.

Therefore, precise gas consumption includes non-ideal parameters, such as a lower feeding rate, shorter cooking times, colder temperatures, etc. In the calculation.

The formula, which includes the gasmeter data, is the following:

Carbon Offset [tCO2] = 0.004437758 * Gas Consumption [m^3]

(1.)

x [m^{3}]

y [tCO2]

225.338994

1

2253.38994

10

22533.8994

100

(2.)

It is important to understand that the calculations are estimates based on existing data and assumptions. Therefore, the following assumptions contribute largely to the variability of carbon offset estimate results.

- Ideal Feedrate of 15L/day of manure (total with water is 26 L/day)

- Usage factor of 50 % firewood and 50 % LPG

- Average feedstock: 50 % cow manure and 50 % pig manure

- Slurry rate: 15 L/day

- 90 minutes cooking time per day

- Ideal retention time of 25 days (how much time it takes for all the slurry to be replaced)

The Gasmeter formula also follows the previous assumptions, plus several new ones. Since the gasmeter data replaces average cooking time, it only influences BG (biogas emissions) and OCS (cook stove). The gasmeter formula thus contains the slope 0.004437758.

This calculation is a rough estimate by Su-re.co and is not yet validated by external experts. As knowledge and data are updated by us and others, the following areas can help us refine our calculations.

- Parameters used in the cow manure management calculation need to be updated to current standards. Furthermore, some data still uses agricultural data from the US, which need to be changed to data for Indonesia.

- We need to include emissions of biogas production subtracted by emissions of LPG and Chemical fertilizer production. This would require a proper LCA (Lifecycle assessment) analysis.

- Su-re.co can also reduce the assumptions by collecting more data about the manure type usage and type of the replaced cooking source. By starting a survey, the assumption will be replaced by specific data. Besides that, examining the consistency of our biogas and slurry would help get even more detailed results.

These measurements, however, will be costly and require extensive monitoring.

In short, regardless of the calculations' details, the results remain an estimate. Using the final estimates needs careful communication and transparency in the process.

The carbon saved by replacing the old cooking sources LPG and firewood comprises two parts.

The replacement of LPG multiplied by the usage factor of LPG (FLPG), and the replacement of firewood multiplied by the usage factor of firewood (FFW).

This calculation is based on the assumption of the following usage factors: LPG 80% and Firewood 20%.

The saved carbon comprises the mass of the old fuel that was burned multiplied by the emission factor of that source (EF). The energy needed for cooking is based on the assumption that it is possible to cook 90 minutes per day with the biogas. (not always true, e.g., on colder days).

The energy is, therefore, a product of the cooking time (tcooking), the supplying flow rate, the density of biogas (rhoBG) (the amount of gas used), and the heating value of biogas (HHVBG).

To calculate the carbon offset of the chemical fertilizer, we first need to know how many hectares can now be supplied by the bioslurry fertilizer. For this, we first calculate the amount of bioslurry produced per day (SO), using the level of bioslurry in the digester (2/3) divided by the retention time (ideally 25 days). The produced bioslurry multiplied by the density (rhoBS) will result in the mass of bioslurry fertilizer that can be used. By dividing this by the fertilizer needed per hectare (UBS), the number of hectares that can be theoretically supplied with the bioslurry per day is calculated.

In reality, this bioslurry (x25) can only be used every 25 days, not per day. Once we know the supplied hectares, we can calculate the chemical fertilizer usage for this area, which is prevented by multiplying it with the chemical fertilizer usage (UU). The calculation is based on the assumption that urea was used as fertilizer before, but this could be more specified if wanted. Lastly, multiplying this with the emission factor of kgCO2/kgurea will lead to the prevented chemical fertilizer offset.

The carbon emitted when cooking with biogas can be easily calculated by multiplying the amount of biogas needed for the daily cooking time of 90 minutes (energy needed for cooking as calculated before divided by the heating value of biogas and biogas stove efficiency) with the emission factor for biogas (EFBG).

Cow/Pig Manure, when left on the field will release N2O and CH4. Therefore, by reusing cow/pig manure for the bioslurry it is not released into the atmosphere and can be included in our carbon offset calculation.

This calculation is again divided into two parts, one regarding pig manure and one regarding cow manure.

The factors FC and FP include each farmer's usage factor of the two manure types.

The theoretical calculation per digester is based on the assumption that pig and cow manure are used 50:50; for the COC, since gasmeters are calculated, the factors are calculated based on actual usage.

In the formula, the amount of emission of CH4 in cow manure (ECCH4) and in pig manure (EPCH4), as well as the emission of N2O in cow and pig manure (ECN2O/EPN2O), are multiplied by the related global warming potential (GWP).

To calculate ECCH4/EPCH4 and ECN2O/EPN2O, Su-re.co used the following formulas from GHG Protocol: Global Protocol for Community-Scale Greenhouse Gas Emission Inventories. The results are all based on the ideal feedrate of feedstock per day, calculated by dividing the slurry level in the digester by the retention time.

The calculation for carbon emitted by bioslurry fertilizer is similar to the calculation for chemical fertilizer. The daily slurry outcome (SO) is multiplied by the emission factors for CO2/m3 slurry used and CH4/kg slurry. As the emission factor for CH4 is given in a different unit (per ha on which bioslurry was applied), Su-re.co included the density of bioslurry (rhoBS) and usage factor of bioslurry (kg/ha) to calculate the hectares that can be fertilized by the given bioslurry per day. Additionally, the global warming potential is included again to receive only kgCO2.

Parameter [u]

Abbreviation

Value

Source

Volume [m^{3}]

V

1

Su-re.co

Slurry level [m^{3}]

V_{slurry}

0.666666667

Su-re.co due to filling system

Biogas level [m^{3}]

V_{biogas}

0.333333333

Su-re.co due to filling system

Hydraulic retention time slurry [days]

HRT_{slurry}

25

Ideally

Parameter [u]

Abbreviation

Value

Source

Pig manure density [kg/m^{3}]

rho_{PM}

1004

Pig manure emission factor [kgCH4/(pig*year)]

EF_{PCH4}

7

Pig manure emission factor [kgN/(1000 kg pig*day)]

EF_{PN2O}

0.4

Pig manure usage factor +

F_{P}

0.5

Calculated from customer sample data

Manure produced per pig [kg/day]

MPP

4.78

Typical weight pig [kg]

75

Fraction of total annual nitrogen managed in MMS for cows

MS_{P}

0.02

Parameter [u]

Abbreviation

Value

Source

Cow manure: water ration = 1:1

0.50

Su-re.co's instructions for farmer.

Cow manure density [kg/m^{3}]

rho_{CM}

990

Ideal feedrate [m^{3}/day]

V̇_{FS}

0.015

Cow manure gas emission factor [kgCH4/(cow*year)]

EF_{CCH4}

31

Cow manure gas emission factor [kgN/(1000kg cow*day)]

EF_{CN2O}

0.47

Cow manure usage factor +

F_{C}

0.5

Assumption based on Su-re.co’s experience

Manure produced per cow [kg/day]

MPC

27

Typical weight cow [kg]

m_{c}

600

Fraction of total annual nitrogen managed in MMS for cows

MS_{C}

0.02

Emission Factor from manure management (solid storage) [kgN2O/kgN]

EF

0.005

Parameter [u]

Abbreviation

Value

Source

Density [kg/m^{3}]

rho_{CH4}

0.6442

CH4 share in biogas

F_{CH4}

0.6

Global warming potential [kgCO2/kgCH4]

GWP_{CH4}

25

Parameter [u]

Abbreviation

Value

Source

Density [kg/m^{3}]

rho_{CO2}

1.773

CO2 share in biogas

F_{CO2}

0.4

Parameter [u]

Abbreviation

Value

Source

Global warming potential N2O [kgCO2/kgN2O]

GWP_{N2O}

298

Parameter [u]

Abbreviation

Value

Source

Biogas consumption [m^{3}/year] **

BGC

98.55

From gasmeters, here in theory calculated for 90 min cooking time.

Average consumption [m^{3}/day]

BGC_{daily}

0.27

From gasmeters, here in theory calculated for 90 min cooking time.

Heating value biogas [MJ/kg]

HHV_{BG}

18.2

Density [kg/m^{3}]

rho_{BG}

1

Biogas emission factor [kgCO2/kgfuel]

EF_{BG}

8.57E-01

Calculated with Environmental Protection Agency data below. (includes N2O, CO2 and CH4 emissions from biogas).

Emission factor biogas [kgCO2/mmBtu]

52.07

Emission factor biogas [gCH4/mmBtu]

3.20E+00

Emission factor biogas [gN2O/mmBtu]

0.63

Parameter [u]

Abbreviation

Value

Source

Heating value LPG [MJ/kg]

HHV_{LGP}

49.3

Heating value Firewood [MJ/kg]

HHV_{FW}

16.2

LPG emission factor [kgCO2/kgfuel] ******

EF_{LPG}

2.75E+00

Calculated with Environmental Protection Agency data below. (includes N2O, CO2 and CH4 emissions of LPG)

Firewood emission factor [kgCO2/kgfuel] ******

EF_{FW}

1.39E+00

Calculated with Environmental Protection Agency data below. (includes N2O, CO2 and CH4 emissions of firewood)

Firewood Usage Factor ****

F_{FW}

0.5

Assumption based on Su-re.co’s experience

LPG Usage Factor ****

F_{LPG}

0.5

Assumption based on Su-re.co’s experience

Density LPG [kg/m^{3}]

rho LPG

1.882

Emission factor LPG [kgCO2/mmBtu]

61.71

mmBtu conversion [mmBtu/MJ]

9.00E-04

Emission factor LPG [gCH4/mmBtu]

3

Firewood emission factor [kgCO2/mmBtu]

93.8

Firewood emission factor [gCH4/mmBtu]

7.2

Emission factor LPG [gN2O/mmBtu]

0.6

Emission factor firewood [gN2O/mmBtu]

3.6

Parameter [u]

Abbreviation

Value

Source

Stove efficiency

μ_{BG}

0.3492

Center for Energy Studies** (2001)**, Institute of Engineering, Tribhuvan University, Pulchowk, Lalitpur

Cooking time [min/day]

t_{cooking}

90

Assumption based on Su-re.co’s experience.

Flowrate [L/min]

3

Assumption based on collected gasmeter data is legitimate (between 2-3)

Parameter [u]

Abbreviation

Value

Source

LPG stove efficiency

μ_{LPG}

0.4506

Firewood stove efficiency

μ_{FWS}

0.135

Parameter [u]

Abbreviation

Value

Source

Density [kg/m^{3}]

rho_{BS}

993.5125

Slurry outcome [m^{3}/day]

SO

0.015

Assumption based on experience (half of ideal feedrate as 50 % is water)

Emission factor bio slurry [kgCH4/ha]

EF_{BSCH4}

4.52

Fertilizer needed per hectar [kg/ha]

UBS

10000

Emission factor bioslurry [kgCO2/m^{3}]

EF_{BSCO2}

0.15

Emission factor digestive fluid [gCO2/m^{3}]

EF_{BSCO2}

150.32

Parameter [u]

Abbreviation

Value

Source

Emission factor [kgCO2-C/kg urea]

EF_{CO2urea}

0.2

Urea usage [kg/ha]

UU

250

Density [kg/m^{3}]

rho_{CF}

2310

Conversion CO2-C into CO2 emissions

44/12

The livelihood benefits are the benefits that farmers get from the reduction of cost and time spent on getting LPG and / or firewood. The livelihood benefits scope of calculation follows the one stated in this Gold Standard document.

There are some assumptions made in this calculation that enable us to make our co-benefits tangible:

1. The usage factor of biogas replaces a prior use consisting of 50% firewood and 50% LPG

2. Farmers are cooking using biogas for 90 minutes / day

3. All the farmers used urea as fertiliser before we installed a biodigester

4. The output of organic fertiliser (Bioslurry) is 15L / day, assumed to reduce the amount of chemical fertiliser

5. Time spent collecting firewood interferes with working hours (farming).

Livelihood benefit = LPG + FW + CF + TS

LPG : cost reduction of LPG

FW : cost reduction of Firewood

CF : cost reduction of Chemical Fertilizer

TS: cost of time saved from searching firewood

We acknowledge other important impacts (gender, education, access to energy) but not taken into quantitative manner.

Parameter

Value

Unit

Source

Consumption of LPG without biogas

12_{}

kg/month

Biogas baseline interview

Consumption of LPG with biogas

9

kg/month

Feasibility Study

Cost of LPG in Bali (subsidised)

6666.667_{}

IDR/kg

Monthly cost reduction of LPG

20000

IDR/MONTH

Parameter

Value

Unit

Source

Replacement of chemical fertilizer with bioslurry

200_{}

kg/year

Feasibility Study

Price of urea chemical fertilizer (subsidised)

2250

IDR/kilo

Local price

Monthly cost reduction of Chemical Fertilizer

37500

IDR/MONTH

Parameter

Value

Unit

Source

Consumption of firewood without biogas

53

kg/month

Biogas baseline interview

Consumption of firewood with biogas

35.33333

kg/month

Reduction is around 1/3 of the initial usage

Monthly average spending for firewood

56.60377_{}

IDR/ kg month

Biogas baseline interview

Reduction of firewood with biogas

1000

IDR/MONTH

Parameter

Value

Unit

Source

Hours spent searching firewood without biogas

18.8

h/month

Hours saved of seraching firewood with biogas

6.266667

h/month

Biogas baseline interview

Average income of small holder coffee and cacao farmers

1264500_{}

/month

Calculation

Average working hour for small holder farmers per month

144

h

Avarage salary

8781.25

IDR / hour

Monthly potential additional of revenue for farmers

55029.17

IDR/MONTH

Parameter

Value

Unit

Cost reduction of LPG

20,000

IDR/month

Cost reduction of firewood

1,000

IDR/month

Cost reduction of chemical fertilizer

37,500_{}

IDR/month

Cost Time saved

55,029

IDR/month

Total saving=

113,529

IDR/MONTH