Comparing Biogas and Propane gas

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From all the assumptions that we have accumulated, we decided to compare the cost and usage of biogas and propane gas. We visually wrote down our calculations on the board to have more clear sense of estimations:

 Then we listed out different scenarios of using these gas so that the community can decide a scenario more convenient for people. Below is all calculations, comparisons, and scenarios that we made during last class:

Assumptions for the Model

1.     8m^3 chamber produces 1m^3 gas

2.     This model requires 65kg of manure, provided by 4 cows

3.     1m^3 of gas covers 18 meals per day (3 meals for a household of 6 people)

4.     1m^3 of biogas = 2.19 lb

5.     Propane gas costs about $5 per m^3.

6.     Biogas costs about $0.87 per m^3.

People currently uses 25lb tank for propane gas, which provides a month of gas for a household. From assumption 1 and 4, we can calculate that for a 25lb tank of biogas, it takes 11.4 days (25lb/2.19lb=11.4) to produce from 8m^3 chamber. Using assumption 3 and 4, this also means that 25lb tank of biogas covers 18 meals daily for 11.4 days. 

To summarize the information above:

·      25lb tank of propane provides 30 days of usage for a household

·      25lb tank of biogas provides 11.4 days of usage for a household.

*For 30 days of usage, a household requires:

·      6m^3 of propane gas, which costs $40 (Assump 5). Each household may spend ½ day for a trip to buy the tank.

·      34m^3 of biogas, which costs $21 (Assump 6). Each household has to make three trips a month because users need to wait 11.4 days for biogas to be produced from the camber. This process can be further explained below:

o   Leave the chamber for 11.4 days ->make first trip and use biogas for 11.4 days

o   Leave the chamber for 11.4 days ->make second trip and use biogas for 11.4 days

o   Leave the chamber for 11.4 days ->make third trip and use biogas for 11.4 days

We thought of two different scenarios to compare the cost of using propane gas and biogas produced from 8m^3 digester.

Scenario 1: 1 household using 100% of biogas produced from the digester

·      The household will have to pay $21 for monthly usage of biogas.

·      If the household did not use biogas but only propane, it needs to pay $40 for monthly usage.

->All of these calculations come from the section above with *

Scenario 2: 4 families share biogas from 8m^3 digester while using other gas or methods of cooking (ex. Propane gas or firewoods).

·      The household will have to pay $5.25 (21/4) for using biogas three rounds of 11.4 days.

·      The household will have to use propane as simultaneously when using biogas for 11.4 days.  It will have to pay $15.2 ($40/30days=x/11.4days, x=15.2).

·      In total, the household will have to pay 5.25+15.2=$20.75 a month for using gas.

All of these calculations are for villagers to choose what they prefer to do. Would they prefer to pay $40 and make 1/2 day trip a month for propane gas? Would they prefer paying $20.75-$21 for using only biogas or using both biogas and propane simultaneously while making three trips a month to biodigester? This is their decision.