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Integration of biogas systems into the energy system

Technical aspects of flexible plant operation

Jan Liebetrau Rytec

Peter Kornatz DBFZ

IEA Webinar 21 January 2021

www.ieabioenergy.com2

Authors:

Jan Liebetrau (Rytec, Germany),

Peter Kornatz (DBFZ, Germany),

Urs Baier (ZHAW, Switzerland)

David Wall & Jerry D Murphy (MaREI centre, University College Cork, Ireland)

https://task37.ieabioenergy.com/files/daten-

redaktion/download/Technical%20Brochures/Flex%20rep

ort_END_WEB.pdf

Find the report on the Task 37 web site under:

A Technical report from IEA Bioenergy Task 37

www.ieabioenergy.com3

• Introduction - Flexibility in the context of biogas systems

• Technical aspects of flexible plant operation

• Economics

• Exemplars of flexible operation

• Conclusion

Outline

Reasons for demand oriented operation

4

• Biogas based electricity as an facilitator for increasing share of

fluctuating renewables on different grid levels

• Direct supply of fluctuating demand of industrial facilities or

energy customers, also in areas with instable grid situation,

biogas as stand alone solution

• Reaction on maintenance shut down on site

• Biogas as a potential link between electricity and gas grid

(Power to gas - storage and distribution option)

Agora Energiewende: 12 insights on Germany's Energiewende February 2013

5

Electricity demand of a dairy farm in Summer (Neiber, 2020)

Demand electricity - different levels

• Depending on the energy customer required flexibility can have complete different requirements

• Grid connection or stand alone?

• Is on site storage (gas, electricity, heat) available?

6

Demand on the heat site

Development of main heat utilization in Germany for 2010-2017 (Daniel-Gromke et al., 2019a)Typical heat demand for heating and hot water supply of buildings with mixed

residential and industrial use (Jan Liebetrau, Rytec, own data 2020)

• Heat follows seasonal fluctuations, depending on the type of heat use

• Heat dominated CHP operation is done in Germany occassionally

7

Demand on fuel supply – fleet supply

Aggregated fuel demand function for a truck fleet and an agricultural business. (Gögköz et al., 2020)

• Only with fleets somewhat predictable

• Stand alone fuel station has to be developed.

Only relevant in case of stand alone fuel station

Technical options for flexibility on site

8

• Flexibility results in reduced capacity utilization or overcapacity is necessary

• This results in higher technical effort and costs, which have to be balanced by

the benefits

• Increase of CHP capacity (and grid access)

- in case of constant annual energy output

• Increase of gas storage capacity

• Control of biogas production rate

(controlled feeding,

storage of intermediates)

• Power to heat

• Biomethane

• Power to gas

Quality of flexibility – control aspects

9

Limited flexibility with standardized fluctuation(e.g. electricity market price oriented)

Flexibility on demand (e.g. ancillary services)

Prognosis step

IEA Bioenergy Conference 2015, Berlin October 2015

Time (h)

Time (h)

Ele

ctri

cal

cap

acit

yEl

ect

rica

lca

pac

ity

10

Schedules and markets

Weekly schedule Daily schedule Real time control

Brief description Weekly fixed scheduleNext day individually optimised

schedule Optimised during the day

Serviceable marketsDay ahead

Ancillary services

Day ahead

Ancillary services

Day ahead,

Intraday,

Ancillary services

Technical effort,

remote control

low,

optional remote control(ancillary services require remote

control)

Medium,

Indirect or direct remote control(ancillary services require remote control)

High,

Direct remote control (ancillary services require remote

control)

RestrictionsBiogas production (substrate availability), number of starts and stops of CHP, gas storage

capacity, heat demand, limits of capacity utilization, min/max performance

Flexibility/revenue low medium high

Main characteristics of basic schedules for flexible operation (Daniel-Gromke et al., 2019b)

11

• Preheating of cooling water and oil (min. 60 °C);

• Optimized starter and starting procedure of the CHP;

• Recirculation of air in air conditioning;

• Electric oil pressure build up prior to the starting procedure;

• Constructive condensation traps;

• Stainless steel finish at weak points due to sulphuric acid in condensate;

• Remote monitoring and control options for the CHP – PLC;

• Changing requirements for biogas quality (sulphur content, temperature, moisture).

CHP operation on flexible plants

12

CHP operation on flexible plants

Part load operation and efficiency of selected biogas CHPs (Tappen et al. 2017)

100 %

Load

(203 kW)

90 %

Load

(183 kW)

80 %

Load

(162 kW)

70 %

Load

(142 kW)

60 % Load

(122 kW)

Efficiency 33.7 % 31.6 % 31.3 % 29.5 % 27.4 %

CH4

slippage

0.47 % 0.52 % 0.58 % 0.65 % 0.74 %

Part load and methane slippage (Lichti et al., 2018)

Increasing capacity has higher electric efficiency - one large engine is more

efficient than two smaller engines combined

13

Flexible operation – gas management

• Gas storage balances deviation between gas production rate and gas

utilization rate

• Gas storage capacity is limited

• Gas management often not made for flexible operation

(e.g. effectively available gas storage capacity)

14

Potential measures to improve (Reinelt et al. 2019):

• Installation of additional (clean) gas storage;

• Upgrade of sensors for precise filling level evaluation;

• Installation of a gas management (transportation) system between the gas domes via

a controllable blower for inflation air;

• Upgrade of gas transportation lines;

• Upgrade of gas treatment devices.

Flexible operation – gas management

15

Flexible operation – gas management

• Gas storage balances deviation between gas production rate and gas

utilization rate

• Gas storage capacity is limited

• Feeding management can alter gas production rate to provide gas

when needed

• Model based control gives information on gas production rate of

substrate mixes

16

set variable:

substrate type

feeding amount

control variable:

gas storage filling level

Mauky et al: Chem. Eng. Technol. 2016, 39, No. 4, 652–664 DOI: 10.1002/ceat.201500412

Block diagram of the applied model predictive control (MPC) algorithm

Control of biogas production rate

Controlled biogas production

Gas

pro

du

ctio

n/g

as u

tiliz

atio

n(m

³/h

)G

as s

tora

gefi

llin

gle

vel(

m³)

Time (d)

Forward-looking process

management according to a

given schedule of energy demand

Component design needs to be

adjusted to variable energy

provision, flexibilisation can have

an impact on all components of

processing

Mauky et. Al, 2016: Model predictive control for demand driven biogas production in full scale, Chem. Eng, Technol. 2016, 39, No 4

45% Less gas storage

capacity

18

Process optimization including external factors

Source: DBFZ 2019

Flexibilisation

requires the

integration of

external factors and

internal limitations

Increasingly

complex

optimisation tasks

and complex

monitoring and

control tasks

Example for a more comprehensive process control considering technical and economic requirement (data from DBFZ) (EPEX: European power exchange – market for electricity)

Influence of solar radiation on gas storage capacity

SEITE 19

a) total view with normal

camera modus and

b, c, d): measured by

Infrared camera; cross

indicates the location of

the respective maximal

value

Source: Mauky/DBFZ

20

Influence of solar radiation on gas storage capacity

Based on Mauky et al. (2017)Demand-driven biogas production in full-scale by model predictive feed control.Conference Proceedings of the 25th European Biomass Conference and Exhibition (EUBCE), Stockholm, Sweden , S. 1845-1851

Up to 20 % difference in capacity

Intraday temperature difference [°𝐶]:5.1 → 29.7 = 24.6 March8.4 → 33.5 = 25.1 April8,7 → 37,7 = 29,0 April

11.0 → 34.2 = 23.2 May16.8 → 42.5 = 25.7 July 13,2 → 40,8 = 27,6 August23.6 → 43,4 = 19.8 September

7 %

13 %

20 %

21

Economics of flexible operationGeneral economics – aspects have to be considererd

Aspects have to be considered about

economy:

• Capex and opex for a given degree of

flexible operation

• Additional installation

• Additional maintenance effort

• Costs related to decreasing capacity

utilization

• Revenues and contracting conditions for the

energy products

• Long term prognosis of the energy marketsSource: Barchmann, DBFZ

22

Economics of flexible operationGeneral economics – difference between base load plants and flexible plants

concerning production cost

• Cost-based approach with new

constructed biogas plants

• no national specific assumptions

regarding funding systems

• 500 kW agriculture biogas plant

as example

• Feedstock: 30 % manure, 40 %

maize, 30 % sorghum

• One more CHP-unit at the

same annual power

production level, means

approx. 3 €ct/kWh higher

production cost

Reference

none 2 2 4

Base load operation Flexibilisation Downsizing Flexibilisation Upsizing Flexibilisation Upsizing

Installed power 500 500 1.000 2.000

Nummer CHP units 1 1 2 4

Operation time h/a 8.000 4.000 4.000 2000

Power sold kWh/a 3.960.000 1.980.000 3.960.000 3.960.000

Component Investment Investment Investment Investment

[€] [€] [€] [€]

CHP 453.902 453.902 907.804 1.815.608

Flare 123.288 77.163 123.288 123.288

Pumpstation 64.844 41.173 64.844 64.844

Solid feeding unit 336.956 186.622 336.956 336.956

Digester 505.077 297.236 505.077 505.077

Digestate Storage 379.326 228.615 379.326 379.326

Gasstorage 95.320 95.320 170.213 680.853

Sum of investment 1.958.713 1.380.031 2.487.508 3.905.952

Planing and constrution preparation 195.871 195.871 195.871 195.871

Complete investment for biogas plant 2.154.585 1.575.902 2.683.379 4.101.823

Annual cost (20 years operating time)

Capex [€/a] 294.618 223.029 394.032 687.831

Opex feedstock and resources [€/a] 403.479 201.740 403.479 403.479

Opex misc [€/a] 42.395 42.395 42.395 42.395

Sum [€/a] 740.492 467.163 839.906 1.133.705Specific cost

Power production cost [€/kWh] 0,187 0,236 0,212 0,286

Difference to reference[€/kWh] x 0,049 0,025 0,099

Flexibilisation factor

Flexibilisation options

23

Taking part in the electricity market leads

to a so called „double hump“, which define

the times of high prices and the preferred

times of electricity feed in

Demand translates into price development

Example of daily price development of day ahead market in 2020 (Auction

Day Ahead, 60 min, Germany, 31 of January 2020, Baseload (Source: EPEX

SPOT))

24Example of daily price development of day ahead market in 2020 (Auction Day Ahead, 60 min, Germany, 31 of January 2020,

Baseload (Source: EPEX SPOT))

Economics of flexible operationGeneral economics – revenues of flexibilisation (market)

economic efficiencythreshold for double flexible

option

Activation time CHP (6h)

Activation time CHP (6h)

• higher expenses must be compensated

by interacting with the volatility of the

market

• Market potential is very limited for the

payment of flexibility

• Expected additional revenues approx. 0.5

till 1.5 €cent/kWh in average

• Maximum values can be much higher

• Possibility for additional revenues

depends on price spread

25

Economics of flexible operationGeneral economics – revenues of flexibilisation (market)

Source: Dotzauer, 2020

• higher expenses must be

compensated by interacting with

the volatility of the market

• Market potential is very limited for

the payment of flexibility –

additional revenues needed!

(Heat, Summer Winter etc .)

• Expected additional revenues

approx. 0.5 till 1.5 €cent/kWh in

average

• How will the future look like?

Conditions for market products

26

Source:Barchmann et. al. 2016

• Different market options with different requirements for participation

• Biogas plants have individual constructive and operational designs –

which define the limits of flexibility

9/2018:

2.927 Plants (biogas+biomethane)

eligible for extra tariff „Flexprämie“

(app. 2,02 Gwel)

0

250

500

750

1.000

1.250

1.500

1.750

0

500

1.000

1.500

2.000

2.500

3.000

Insta

llie

rte

ele

ktr

isc

he

An

lag

en

leis

tun

g [M

We

l]

An

zah

l B

HK

W [n

]

Anzahl Biogas-BHKW, [n] Anzahl Biomethan-BHKW, [n]

install. el. Leistung Biomethan-BHKW, [MWel] install. el. Leistung Biogas-BHKW, [MWel]

Σ Biogas-BHKW n = 2.678

Σ Biomethan-BHKW n = 342

© DBFZ 08/2018

Incentives for technically „standby“;

this does not mean process

flexibilisation in operation

Number of biogas CHPNumber of biomethane CHP

Install. el. capacity biogas CHP (Mwel)Install. el. capacity biomethane

CHP (Mwel)

Exemplars of flexible operationDevelopment of flexibilisation in Germany (CHP and biomethan-CHP)

Source: DBFZ, based on annual power generation in respect to BNetzA 2012 – 2016, plant register of BNetzA 08/2018 and monthly reports of power trading companies 2012 - 2018

Number of biogas CHP

28

Bioenergie Langwedel GmbH & Co. KG

Basic information:

•Commissioned in 2010;

•Substrates include for over 50% liquid cattle slurry and dung, less than 30% corn silage with the

remander of feedstock comprised of cereal crop silage and cereals;

•Flexibile operation in place since February 2019;

•The average output is 486 kW;

•Installed capacity of 2,356 kW via three CHP units;

•The maximum gas storage capacity (at average gas production) is 16 hours;

•The volume of storage is 5.000 m³

•Heat storage of 1,000 m3 of hot water

Marketing concept:

•Individual electricity market oriented operation for the following day (day ahead market) and participation in “intraday” market;

•Both CHP units have approximately 1,800 h/a full load operation;

•Remote control from electricity trader;

•The contractor can directly access the process and process relevant parameter;

•Additional income expected in 2019 of more than 1.5 ct€/kWh;

•Operate with a maximum of 2 starts per day with a minimum of 1 hour of operation with both CHP units in full load, shift of electricity production to winter;

•The heat from the CHP unit is used to heat buildings and barns and dry digestate;

•95 % of available heat is used.

Exemplars of flexible operationExamples for flexible biogas plants

29

Bioenergie Hotteln GmbH & Co. KG

Basic information:

•Commissioned in 2018;

•Substrates include maize and suger beet

•Flexibile operation in place since February 2019;

•The average output is 486 kW;

•Installed capacity of 2,356 kW via three CHP units;

•The maximum gas storage capacity (at average gas production) is 14 hours;

•The volume of storage is 5,000 m³;

•Heat storage of 250 m3 of hot water

Marketing concept:

•Individual electricity market oriented operation for the following day (day ahead market) and participation in “intraday” market;

•Both CHP units have approximately 1,800 h/a full load operation;

•Remote control from electricity trader;

•The contractor can directly access the process and process relevant parameter;

•Additional income expected in 2019 of 0.5 ct€/kWh;

•Operate with a maximum of 2 starts per day

•The heat from the CHP unit is used to heat residential buildings an two hotels, furthermore a drying unit is included

•100 % of available heat is used.

Exemplars of flexible operationExamples for flexible biogas plants

30

The Swiss virtual power plant “Fleco Power” represents a marketplace to match flexibility of

producers and users of new renewable energy.

The flexibility of over 80 biomass, small hydroelectric and photovoltaic plants with a nominal power

of 30 MW is bundled and marketed as control energy to Swissgrid, the Swiss electricity grid

operator.

Fleco Power Structure to combine flexibility of decentralized installations

Exemplars of flexible operationFlexibilisation in Switzerland – Virtual Power Plant

Source: IEA Bioenergy 2020

31

Example of a 1-day flexibility control time course of a biogas installation in Switzerland in Autumn.

green: peak load time windows. blue/red: Historical load curves of electricity demand.

violet: biogas CHP timetable

Exemplars of flexible operationFlexibilisation in Switzerland – Virtual Power Plant

Source: IEA Bioenergy 2020

www.ieabioenergy.com32

The perception of the role of biogas has changed from traditionally seen as a means of treatment of a range of wet organic wastes towards a source of renewable energy as part of a new energy system.

In the near future the integration of energy vectors will be essential in facilitating PV during daylight hours, wind power on windy days and renewable sources of dispatchable energy such as from bioenergy.

The biogas plant operation itself can be controlled extensively and with this control comes high levels of flexibility.

Biogas systems can be a node of integration between electrical and natural gas grids in providing a sink for electricity (through power to gas systems) that would otherwise be curtailed or constrained.

The flexibility of biogas systems can facilitate energy delivery to:

• the electricity grid as close as possible to the electricity demand profile

• heat to consumers facilitating the seasonal demand profile of heat;

• to the gas grid to decarbonize gaseous fuels for various purposes;

• Biomethane directly to local consumers such as for transport biofuel for haulage and buses;

• Biogas can play an essential role as part of a virtual power plants.

Conclusion

www.ieabioenergy.com

Thank you for your interest

Contacts:

Jan Liebetrau

Rytec GmbH

jan.liebetrau@rytec.com

Peter Kornatz

DBFZ

Peter.Kornatz@dbfz.de