This paper was written with the aim to present a short study about the real efficiency of electric and thermal energy produced by a state-of-the-art Biogas Plant as well for evaluating the real usage of agricultural land that is used today for all actually installed Biogas plants in Germany. Germany was used because statistics and specific data were best available for this type of study. info@biz-consultant.net www.biz-consultant.net

1. Is Biogas an efficient green source of energy?
By Georges SEIL, PhD
Abstract
This paper was written with the aim to present a short study about the real efficiency of electric
and thermal energy produced by a state of the art Biogas Plant as well for evaluating the real
usage of agricultural land that is used today for all actually installed Biogas plants in Germany.
Germany was used because statistics and specific data were best available for this type of study.
Introduction
Biogas, biofuels (bioethanol, biodiesel), and biohydrogen production and usage is indeed a
critical subject, worth to be more developed and analysed detached from a political or climate-
oriented activity organizational context.
In Europe Biogas is mainly produced from crops, specifically it is corn, and, in some places, it is
even genetically modified corn. Biogas is then used in gas combustion engines driven generators
for producing mainly electricity. Electricity is fed into the electricity distribution grid and the energy
producer benefits from a substantially important subsidized “Feed-in tariff”. Where no possibility
for a residential heating network is given or alternatively no agricultural use in greenhouses is
required, the thermic energy produced by the gas engines is in most cases lost.
The present efficiency evaluation considers that biogas (or any other biofuel product) is produced
by using as input harvested corn. This is the situation at >90% of the European located biogas
plants. Some numbers provided by a study from the EU Commission1
are:
“Biogas production has increased in the EU, encouraged by the renewable energy policies, in
addition to economic, environmental and climate benefits, to reach 18 billion m3 methane
(654 PJ) in 2015, representing half of the global biogas production. The EU is the world leader in
biogas electricity production, with more than 10 GW installed and several 17,400 biogas plants,
in comparison to the global biogas capacity of 15 GW in 2015. In the EU, biogas delivered 127 TJ
of heat and 61 TWh of electricity in 2015; about 50% of total biogas consumption in Europe was
destined to heat generation. Europe is the world's leading producer of biomethane for the use as
a vehicle fuel or for injection into the natural gas grid, with 459 plants in 2015 producing 1.2
billion m3 and 340 plants feeding into the gas grid, with a capacity of 1.5 million m3. About 697
biomethane filling stations ensured the use 160 million m3 of biomethane as a transport fuel in
2015.”
In case most of the production is coming from agricultural waste, then wide boundary analysis
could exclude ground preparation and sowing. If grass silage is collected, then wide boundary
should include harvesting.
Most net energy efficiency calculations for biogas plants are limited on close boundaries and do
not consider the wide boundary that includes ground preparation, sowing, harvesting and
transportation. All wide boundary factors are substantially contributing to primary energy
consumption and thus reducing the total energy efficiency of the process.
In the present research paper, it is assumed that a total energy required for corn production
including fuel consumption reaches 2.168 – 2.732 MJ/hectare land.2
1
European Commission, Joint Research Centre, Directorate for Energy, Transport and Climate,
Via E. Fermi 2749 – TP 450, Ispra, VA 21027, Italy.
https://www.sciencedirect.com/science/article/pii/S096014811830301X
2
Bradley Justin Stubbs, Master Thesis: ENERGY USAGE OF AGRICULTURAL MACHINERY FOR CORN AND
SOYBEAN PRODUCTION IN BRAZIL, INDIA, USA AND ZAMBIA.

2. Other assumptions3
Methane yield per tonne of whole crop corn: 205-450 m3
Production per hectare land of corn: 9-30 tons dry matter
Wide boundary energy elements:
E1: ground preparation
E2: sowing
E3: harvesting
Minimum evaluation
Primary energy evaluation
From the above assumption, we use a minimum of 2.168 MJ per hectare for primary energy
consumption on E1-E3 of the wide boundary.
Minimum methane production per ton: 205 Nm3
Corn production per ha: 9 tons
Methane content per ha: 9*205= 1,845 Nm3
Energy content in Methane per ha: 9*205*18= 33,210 MJ or 9.2 MWh
Biogas Plant with 2 MWh capacity
Operating hours per year: 8,000 hours
Total electric production per year: 8000*2= 16,000 MWh or 16 GWhe
With 16 GWh of electric energy @35% system efficiency, the total energy input will be
16 / 0.36= 45.71 GWhT
Total required harvesting area for corn in ha: Total energy demand / Energy content/ha
45,710 / 9.2= 4,968 ha
Total primary energy used in GJ: 4,968 ha*2.168= 10,771 GJ or 2.991 GWh => 3 GWh
% on prime energy to total energy used: 3 / 45.71= 7%
Reverse calculation from fnr.de site4
for 2017 production
Total harvested land for Biogas production: 1,374,000 ha
Total installed electric capacity: 7,200 MW or 7.2GW
Total electric production in 2017: 51.4 TWh or 51400 GWh
From this practical case, we learn that Germany in 2017 used 26.73 ha per GWhe produced.
In our calculated case, we use 4,968 / 16 GWhe = 310 ha per GWhe produced, which is far
above the measured values from fnr.de.
Now let’s go to the next step for the maximum evaluation.
3
Biogas from Crop Digestion, 2011. Jerry Murphy, Rudolf BRAUN, Peter WEILAND, Arthur WELLINGER-
www.lee.lu
4
www.bioenergy.fnr.de

3. Maximum Evaluation
Primary energy evaluation
From the above assumption, we use a minimum of 2.732 MJ per hectare for primary energy
consumption on E1-E3 of the wide boundary.
Minimum methane production per ton: 450 Nm3
Corn production per ha: 30 tons
Methane content per ha: 30*450= 13,500 Nm3
Energy content in Methane per ha: 30*450*27= 364,500 MJ or 101 MWh
Biogas Plant with 2 MWh capacity
Operating hours per year: 8,000 hours
Total electric production per year: 8000*2= 16,000 MWh or 16 GWhe
With 16 GWh of electric energy @47% system efficiency, the total energy input will be
16 / 0.47= 34.04 GWhT
Total required harvesting area for corn in ha: Total energy demand / Energy content/ha
34,040 / 101= 337 ha
Total primary energy used in GJ: 337ha*759= 255,783 kWh or 0.256 GWh
% on prime energy to total energy used: 0.256 / 34.04= 1%
Reverse calculation from fnr.de site5
for 2017 production
Total harvested land for Biogas production: 1,374,000 ha
Total installed electric capacity: 7,200 MW or 7.2GW
Total electric production in 2017: 51.4 TWh or 51400 GWh
From this practical case, we learn that Germany in 2017 used 26.73 ha per GWhe
produced.
In our calculated case, we use 337 / 16 GWhe = 21 ha per GWhe produced, which is almost
the same rate as for the measured values and thus confirms an agricultural ground usage
of 21-30 ha per GWhe produced.
Emissions Evaluation - Minimum
From primary energy production, we calculated a total energy content of 45.71 GWh, equals to
164.56 TJ
According to The Journal of Environmental Science and Health6
, Biogas emission factors are shown
as below:
5
www.bioenergy.fnr.de
6
Journal of Environmental Science and Health, Part A- 2018
Toxic/Hazardous Substances and Environmental Engineering
ISSN: 1093-4529 (Print) 1532-4117 (Online) Journal homepage: https://www.tandfonline.com/loi/lesa20

4. Accordingly, from our 2 MWe biogas plant, we generate a minimum of:
CO production: 164,560 * 256 = 42 tons
SO2 : 164,560 * 25 = 4 tons
NOx: 164,560 * 202 = 33 tons
Volatile compounds: 164,560 * 10 = 2 tons
CH2O: 164,560 * 8.7 = 1 ton
If the same energy would have been produced by wood as chips or pellets or timber, the CO
production would have been: 164,560 *14000 = 2,303 tons
With LPG: 164,560 * 820= 135 tons

5. Emissions Evaluation - Maximum
From primary energy production, we calculated a total energy content of 34.04 GWh, equals to
122.54 TJ
According to The Journal of Environmental Science and Health7
, Biogas emission factors are shown
as below:
Accordingly, from our 2 MWe biogas plant, we generate a minimum of:
CO production: 122,540 * 310 = 38 tons
SO2 : 122,540 * 25 = 3 tons
NOx: 122,540 * 540 = 66 tons
Volatile compounds: 122,540 * 21.15 = 3 tons
CH2O: 122,540 * 14 = 2 tons
If the same energy would have been produced by wood as chips or pellets or timber, the CO
production would have been: 122,540 *14000 = 1,715 tons
With LPG: 122,540 * 820= 100 tons
7
Journal of Environmental Science and Health, Part A- 2018
Toxic/Hazardous Substances and Environmental Engineering
ISSN: 1093-4529 (Print) 1532-4117 (Online) Journal homepage: https://www.tandfonline.com/loi/lesa20

6. FEEBIZ-energy Sankey of a Biogas Plant

7. Conclusion
Biomass systems like a Biogas plant are useful systems with substantially lower production on
emissions compared to Wood8
or Coal. However, when calculating the actual total installed power
capacity of biogas plants as to reach approx.. 61 TWh*1.3/0.35 = 227 TWh only in Europe, the
required agricultural area is minimum equal to:
61000 * 25ha/GWhe = 1,525,000 ha land used for Biogas plants.
Biogas system efficiency is in average 30% lower than for traditional natural gas power plants.
Biogas systems are only efficient with 30-35% electric efficiency and some 60% thermal efficiency if
and only if thermal energy may be fully used, either externally by heating/cooling networks or
internally by using thermal energy for dewatering the liquid effluents, demineralizing the effluent
and using it for irrigation. The solid part of the liquid effluents will then have to be used for
producing fertilizer pellets. Fertilizer pellets will be spread on the surface of the agricultural land and
thus offer the advantage to activate the fertilizer effect only at a limited penetration of some 20 cm,
just at the level where the plants can absorb the nutrients.
Pellets fertilizer do not enter to ground water levels.
Fertilizer pellets are a by-product of the Biogas process. Granular fertilizers provide accurate dosing
of fertilizer on agricultural land at the top level of the plantation and thus avoid over-nitrification of
soils. The pelletizing process protects the environment and avoids spreading pathogens by
converting liquid manure to demineralized water and dried fertilizer pellets.
Biogas plants include at least three major weak points:
Point-1: low energy efficiency versus natural gas
Point-2: liquid effluents; if the liquid effluents are spread untreated to the agricultural lands, they
provoke contamination of agricultural and proximity land with phosphorus, nitrogen, metals,
pathogens, sediment, pesticides, salt, BOD1, trace elements (e.g. selenium).
Point-3: Excess usage of agricultural land for biogas crops limits the use of land for food culture. This
is already to be seen in some Western European countries.
Point-2 may be solved immediately by mandatory linking the investment subsidies to the inclusion of
effluent treatment up to demineralized water level and production of dried fertilizer pellets.
Georges Seil, PhD
02 October 2020
Copyrights by BIZ-Consultant sàrl – Luxembourg – 2020
8
Wood should not be considered as CO2 neutral because not all wood related emissions produced by
combustion processes or for energy production are to be considered as being neutralized by planning new
trees. The issue lies in the asynchronous use and re-growth of the wood substance.