DIY Green Energy

For PDF copy go to: www.joyfulcatholics.com/DIY Green Energy

Anyone anywhere can have complete energy independence by producing his/her own energy from manure and grain stems (all but the grain and the roots of wheat, rye, corn, oats, barley, etc.). Manure from two typical cows and two typical horses plus grain stems from about 12 acres (about 5 Hectare) can typically produce enough true green energy to power a typical US household plus two electric cars.

Anyone anywhere can accomplish such energy independence using a device called an anaerobic digester. Digesters can use microbes to digest almost any organic material, producing methane (also known as CH4) in the process. Methane is the chemical that gives natural gas its power.

THE NEEDS

As calculated below, independently fully powering a US household requires:

1,032 kWh methane/week for generating 220 kWh of electricity/week

360 kWh/week for non-electrical household energy

400 kWh/week for two electric cars

1,792 kWh/week total

THE SOURCES

I have looked at four sources of stuff to digest; cow manure, horse manure, human feces, and enough grain stems to weigh three times the combined weight of wastes.

# ofCOWSandsame# ofHORSES
# of 12410
HkgkWhkgkWhkgkWhkgkWh
U17641,0001,5201,9913,0323,9747,5689,923
M 108401,0961,5962,0873,1084,0707,64410,019
A501,1761,5221,9322,5123,4444,4957,98010,445
N1001,5962,0532,3523,0433,8645,0268,40010,976
S

The top left corner and bottom right corner can be read as:

  • One cow plus one horse plus one human plus stems will provide 764 kg of stuff to digest which can produce 1,000 kWh of energy.
  • 10 cows plus 10 horses plus 100 humans plus stems will provide 8,400 kg of stuff to digest which can produce 10,976 kWh of energy.

I have some ideas to get the more energy out of the material, but those are for another day.

ALTERNATIVE STUFF TO DIGEST

I think the best approach would be to:

  1. Raise grain (wheat, rye, corn, oats, barley, etc.)
  2. Harvest the food portion
  3. Put the stems into your digester
  4. Put the sludge as organic fertilizer on the grain field(s).
  5. Repeat

However, use any abundant and affordable organic material where ever you are. Almost any organic material can be used to make methane: food scraps, animal carcasses, grain stems, grass, straw, leaves, seeds, etc. Try whatever is available and cheap. For example, dirty bedding from cleaning out animal cages is perfect for in a digester.

How much methane you actually get will vary depending on several factors like:
• The particular type of organic material you use
• Whether you had a good or a bad growing season
• How well you prepare the stuff to be digested
• The temperature during digestion
• The acidity/alkalinity during digestion
• Etc etc etc

To really know your potential:
1. Get two barrels/buckets, one slightly smaller than the other
2. Fill the larger barrel half with stuff being tested and with half cow manure. Carefully measure the kg of each you put in.
3. Invert the smaller barrel into the larger barrel and get all the water out of the smaller barrel leaving the smaller barrel floating inside the larger barrel
4. Wait. The smaller barrel will rise as it captures biogas produced
5. When the smaller barrel stops rising, measure how high it rose. That height times the area of the bottom of the barrel will tell you how much biogas you got.
6. USE the biogas. Why waste it?
7. Subtract the amount of biogas you got from the cow manure to know how much you got from the stuff you are testing. If unsure about cow manure, do this once with only cow manure.
8. How much biogas you got from the stuff you tested divided by the number of kg of stuff you put in the barrel with tell you your liters of biogas per kg stuff to be digested.

ALTERNATIVE SOURCE OF DIGESTING MICROBES

If you cannot access cow manure, use horse manure, pig manure, etc. Relying on horse manure, methane production will start slowly. So, build your digester with something like 20% extra capacity. Wait until the first batch is producing lots of gas, which means it has lots of microbes. Then transfer the 20% extra into the second batch to give the second batch a faster start. Once you know how much to transfer from batch to batch, you should be able to get most batches done in four weeks even without cow manure.

If you can access neither cow manure nor horse manure, use human feces alone. This will give you a very very slow start, but again, once you have a batch producing well, transfer some of the digester contents to the next digester and so on.

PLEASE CHECK MY RESEARCH AND MY MATH

COW MANURE

“Generally speaking, a 1000 pound cow will produce about 82 lbs of manure daily. Most cows are bigger than this.”

https://farmandanimals.com/how-much-manure-does-a-cow-produce/

82 lbs/day manure / 2.2 lbs/kg = 37.2 kg/day manure.

I USE 20 kg/day cow manure to allow for leaving manure in the fields.

Table 1 “Beef Manure (Outdoor Pen) 10 Wet Mass Methane Potential (m3 CH4/1000 kg)” standard (1 atmosphere pressure and 20 C)

Table 1 https://extension.okstate.edu/fact-sheets/anaerobic-digestion-of-animal-manures-methane-production-potential-of-waste-materials.html

10 m3 CH4/1000 kg Wet Mass = 10 liters methane/kg manure

I USE 10 liters of methane/kg of cow manure.

I include cow manure mostly to get lots of the microbes that do the digesting. The four chamber stomachs of cows take the time to produce plenty of the microbes that do the digesting, but leave relatively little of the stuff to be digested.

1 cow * 20 kg/day manure * 7 days = 140 kg manure

140 kg manure * 10 liters of methane/kg of manure = 1,400 liters methane

1,400 liters methane * 0.044 mol/liter = 61 mol methane

61 mol methane * 0.247 kWh/mol methane = 15 kWh methane/cow/week

HORSE MANURE

“One horse (defined here as a 454 kg (1000 lb) animal) produces roughly 17 kg (37lb) feces and 9 L (2.4 gal) of urine per day”

https://rucore.libraries.rutgers.edu/rutgers-lib/26434/PDF/1/play/

“A 1,000-pound horse produces about 31 lbs of feces and 2.4 gallons of urine daily…”

https://extension.psu.edu/horse-stable-manure-management

Interesting to see the sources not match.

31 lbs horse manure/day / 2.2 kg/pound = 14 kg horse manure/day

I USE 7 kg/day horse manure to allow for leaving manure in the fields.

“methane production potential of horse manure averaged over all batch experiments was 139 ± 65 mL methane per g horse manure VS”

https://rucore.libraries.rutgers.edu/rutgers-lib/26434/PDF/1/play/

VS is basically the methane producing part of the stuff to be digested. VS varies widely so I have taken the minimum methane production from the experiments.

139-65 mL methane/g horse manure = 74 liters methane/kg horse manure

I USE 75 liters methane/kg horse manure.

The single chamber stomachs of horses process food more quickly than cows so they provide much less of the microbes, but have not removed as much of the stuff to be digested.

1 horse * 7 kg/day manure * 7 days = 49 kg manure

49 kg manure * 75 liters methane/kg manure = 3,675 liters methane

3,675 liters methane * 0.044 mol/liter = 161 mol methane

161 mol methane * 0.247 kWh/mol methane = 39 kWh methane

HUMAN FECES

“While the wet mass of feces excreted daily ranges between 70 and 520 g per person per day (g p− 1 d− 1), an amount of 350–400 g p− 1 d− 1 is generally considered as a reasonable average.”

https://www.sciencedirect.com/science/article/pii/S0973082615000939

0.128 kg of feces/day can be collected.

https://en.wikipedia.org/wiki/Human_feces

Interesting to note how the two sources do not agree.

I USE 0.3 kg/day human feces based on the 350-400 g/day feces average

“there is a possibility of potential biogas per kg human faeces becomes equal or higher than the manure, and the levels of methane in the biogas can reach 70%

file:///C:/Users/LEP/Downloads/a-review-of-recycling-of-human-excreta-to-energy-through-biogas-generation-indonesia-case.pdf

I USE the same 10 liters of methane/kg of human feces that I use for cow manure.

Human feces provide little, but not zero, of both the microbes and the stuff to be digested. Human feces are included primarily as a way to properly dispose of human feces.

1 human * 0.3 kg feces/day * 7 days = 2 kg feces/week

2 kg feces * 10 liters methane /kg feces = 20 liters methane

20 liters methane * 0.044 mol/liter = 0.88 mol methane

0.88 mol methane * 0.247 kWh/mol methane = 0.21 kWh methane

STEMS

“The system produced an average of 0.15 m3 of methane per kg of grass.”

https://pubmed.ncbi.nlm.nih.gov/11942700/

Note that this is methane per kg of grass. I ASSUME grain stems will produce approximately the same amounts.

I USE 150 liters of methane/kg stems

Stems provides no microbes, but lots of stuff to be digested. I have arbitrarily ASSUMED 3 times the weight of all three types of waste in weight of stems is a good balance for speed (from the cow manure) plus stuff to digest (from the horse manure and stems). What is your best guess?

140 kg cow + 49 kg horse + 2 kg human = 191 kg wastes/week

191 kg wastes/week *3 = 573 kg stems to add/week

573 kg stems * 150 liters methane/kg stems =85,950 liters methane

85,950 liters methane * 0.044 mol/liter = 3,781 mol methane

3,781 mol methane * 0.247 kWh/mol methane = 933 kWh methane

Table 1. Forage Realistic Yield Potential

2 to 4 Tons/acre/year Small Grains for forage (Oats, Rye, Wheat, Barley)

https://www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/nrcs143_014887.pdf

I USE 3 tons/acre/year

Because this is from the US government, I ASSUME 2,000 lbs/ton.

573 kg stems/week * 2.2 lbs/kg = 1,260.6 lbs stems/week

1,260 lbs stems/week * 50 weeks/year = 63,030 lbs stems/year

63,030 lbs stems/year / 2,000 lbs/ton = 31.515 tons stems/year

32 tons stems/year / 3 tons/acre/year = 10.6666 acres needed

I USE 12 acres.

METHANE

0.044615 mol/liter methane

at standard temperature and pressure (273.15 K, 101.325 kPa)

https://planetcalc.com/7916/

Note that the liters/kg is at 20C=293.15 K while mol/liter is at 0C=273.15 K. I have not increased the mol/liter to match, but effectively round against myself again by using mol/kg on the lower temperature.

I USE 0.044 mol/liter methane

“Heat of combustion -890.8 kJ/mol”

https://www.engineeringtoolbox.com/methane-d_1420.html

“1 kJ = 0.000278 kWh”

www.inchcalculator.com

890.8 kJ/mol methane * 0.000278 kWh/kJ = 0.247 kWh per mol methane

I USE 0.247 kWh/mol methane.

HOUSEHOLD ENERGY USE

In table: “In 2015, high US household energy use was 100 million Btu.”

https://www.eia.gov/energyexplained/use-of-energy/homes.php

“100,000,000 Btu = 29307.106944 kWh”

https://www.rapidtables.com/convert/energy/BTU_to_kWh.html

The average U.S. household consumes about 11,000 kilowatthours (kWh) per year. (of electricity)

https://www.eia.gov/energyexplained/use-of-energy/electricity-use-in-homes.php

29,000 kWh/year total – 11,000 kWh/year electricity = 18,000 kWh/year non-electrical energy.

18,000 kWh/year / 50 weeks/year = 360 kWh/week for non-electrical energy

11,000 kWh/year electricity / 50 weeks/year = 220 kWh/week of electricity

To get 220 kWh/week out of an 85% efficient generator requires 258 kWh/week put in to generator.

To get 258 kWh/week into a generator out of a 25% efficient engine requires 1,032 kWh/week put in to the engine.

I USE 1,032 kWh/week for generating electricity and 220 kWh/week for non-electrical energy.

ELECTRIC CAR ENERGY USE

“The average electric car kWh per 100 miles (kWh/100 mi) is 34.6. This works out as 0.346kWh per mile. In other words, on average, electric cars consume 34.6kWh to travel 100 miles and 0.346kWh to travel 1 mile.”

https://ecocostsavings.com/average-electric-car-kwh-per-mile/

I use 0.5 kWh/mile for an electric car.

“The average distance a US driver travels is 13,476”

ibid https://ecocostsavings.com/average-electric-car-kwh-per-mile/

“On average, there are 1.88 vehicles per U.S. household.”

https://www.statista.com/statistics/551403/number-of-vehicles-per-household-in-the-united-states/

I allow for two cars/household.

I allow for 20,000 miles/year/car.

20,000 miles/year/car * 0.5 kWh/mile = 10,000 kWh/year/car.

10,000 kWh/year / 50 weeks/year = 200 kWh/week/car

I USE 400 kWh/week for two electric cars.

Interesting to compare to gas car efficiency.

GASOLINE CAR EQUIVALENT

gallon of gasoline 1.3×10^8 Joules

https://www.ocean.washington.edu/courses/envir215/energynumbers.pdf

Heat of combustion-890.8kJ/mol-55528kJ/kg-23.9

https://www.engineeringtoolbox.com/methane-d_1420.html

I ASSUME 20 mpg as average fuel efficiency

I allow for 20,000 miles per year/car.

20,000 miles/year/car / 20 mpg = 1,000 gallons gas/year/car

1,000 gallons gas/year/car / 50 weeks/year = 20 gallons gas/week/car

20 gal gas/week/car * 1.3*10^8 J/gal gas = 2,600,00,000 J/week/car

2,600,00,000 J/week/car / 3.6*10^6 kWh/J = 722 kWh/week/car.

GENERATING ELECTRICITY

“there is a significant energy loss in converting energy from the gas form to the electrical form. Internal combustion engines are about 25 percent efficient and generators are about 85 percent efficient.”

https://extension.missouri.edu/publications/g1881

220 kWh/week electricity / 85% generator efficiency = 258 kWh input

258 kWh input / 25% engine efficiency = 1,032 kWh methane needed

SAFETY FIRST

Methane is dangerously poisonous whenever it is more than 0.5% of the air you breath. Methane can explode whenever it is more than 5% of the air around you.

https://www.wef.org/globalassets/assets-wef/direct-download-library/public/03—resources/wsec-2017-fs-002-mrrdc-anaerobic-digestion-fundamentals-fact-sheet.pd

No one can generate methane without danger. Methane is dangerous stuff. Methane has no color, no odor, no warning of its presence. So, PLEASE be very careful and build in all the safety measures you can.

If you have just a one in a thousand chance of being in danger at some time during a day, then you will be in danger once every 3 years (365 days/year * 3 years = 1,095 days).

Precautions you can take begin with:

  1. Flame trap(s) should be incorporated in pipes/hoses carrying methane
  2. Keep Digester(s) outside, not enclosed in a building
  3. Be sure pipes and hoses do not leak, Especially if in a building. Check them often.
  4. Keep the following away from methane:
    1. naked flames
    2. anything that can create a spark
      1. mobile phones
      2. electrical equipment not specially made to not allow sparks
      3. iron or steel tools
      4. power tools
      5. normal electrical switches
      6. static electricity

My research has been done online. The links below can help you get started with your research.

BACKGROUND

https://www.epa.gov/agstar/anaerobic-digesterbiogas-system-operator-guidebook

FinalAnearobicDigestionFactsheet_2E11FAB524961

https://attra.ncat.org/wp-content/uploads/2019/05/anaerobic.pdf?

DIY videos

https://www.researchgate.net/publication/345646026_Mini_Low-Cost_Bio-Gas_Digester_for_Household_Waste/link/5fa9d35aa6fdcc062420ac19/download

https://home-biogas.blogspot.com/

Note that I have not personally built a digester. This info is my best knowledge and belief from my “armchair research”. I am working on my digester design and will publish it when it is done.

You do not need me. If having your own independent source of power interests you, do your own research, develop your own approach,

BE CAREFUL, and make it happen! :-)

May God bless you, Phil