Background: Integration of renewable energy sources in the frame of energy system transition
Figure 1: Counterbalance of fluctuating energy (adapted from Reuter, 2013)
• increasing need for an compensation of severely fluctuating power generation is as a result of ongoing extension of wind and solar power plants
• the decreasing amount of fossil fuel and nuclear leaded power generation as the dominating part of basic load is not only causing a gap in power generation but also in new challenges in flexibility and grid stability
The core objective of arrivee
• integration of widely available wastewater treatment plants (WWTP) with anaerobic sludge digestion into an optimized control reserve and storage concept to counterbalance those new challenges (Figure 1)
• by using a mathematical model of an existing pilot WWTP (Figure 2) the effects of external interventions for the supply of ancillary services under different conditions are tested.
• processes inside the plant and effects for the local net will be analyzed in detail
• these processes are complemented by new innovative plant elements to optimize a participation in the control reserve market (Figure 3)
energy output
time
renewable energy input
electricity demand power grid natural gas
grid (storage)
65% CH4
35% CO2
>90% CH4
electrolyzer
natural gas grid power grid electricity surplus
electricity shortage
digestion tank
digestion tank
CHP unit
CHP unit
Figure 5: Development of gas usage on WWTP in Germany and
calculated potentials for optimized electricity production Figure 3: Modules of WWTPs to provide control reserve
Wastewater treatment plants as system service provider for renewable energy storage and control energy in virtual power plants
Figure 4: Possible use of power-to-gas technology on WWTPs (incl.
methane conditioning)
Contact: Dipl.-Ing. Michael Schäfer, email: michael.schaefer@bauing.uni-kl.de, Tel.: +49 631/205-4643 Dipl.-Ing. Oliver Gretzschel, email: oliver.gretzschel@bauing.uni-kl.de, Tel.: +49 631/205-3831
Master new challenges with existing infrastructure
Power surplus in the grid:
• that energy is used in a first step to produce oxygen and hydrogen with an electrolyzer.
• hydrogen is used for processing high quality methane by Sabatier process (chemically) or inside the existing digestion tank (biological)
• purity of the raw gas is increased from about 65 % to more than 90% methane
• this SNG (synthetic natural gas) is compatible with the existing regular natural gas grid and the grid can be used as a nearly infinite gas storage (Figure 4)
Power shortage in the grid:
• non-vital plant components are shut down and the CHP-unit(s) are powered up
• emergency power systems on the plant can by powered up as well
CH4
electrolyzer
renewable energy power grid
natural gas grid (storage)
CHP unit
aeration tank gas storage
H2
gas storage
CH4 gas storage
CH4
digestion tank
• initial project results present a high potential of negative control reserve from WWTPs in Germany
• methods take account to: consideration of unused gas, efficiency improvements, conversion of WWTPs from aerobic into anaerobic sludge digestion and use of spare capacities of the digestion tanks
• rom 1990 the energy production increased by the factor of 1,5 from 0,8 to 1,25 TWhel/a. By utilizing this potentials electricity production could rise to 2,61 TWhel/a (Figure 5)
• under this boundary conditions calculations show that WWTP could provide negative control reserve of a magnitude of nearly 300 MW
Initial results show a substantial potential of WWTPs to provide ancillary services, by reshaping the existing infrastructure in a sustainable, ecological and economic way. This may contribute significantly to a stable operation of energy grids and a further integration of renewable energy sources in the frame of energy system transition.
According to demand - absorb or dispense
91,34
298,24
142,69
304,42
241,10 443,35
0 100 200 300 400
[MWel]
energy production minimum potential maximum potential
0 25 50 75 100 125 150
use of external fermentation substances sludge assembly centres efficiency improvements
use of unused gas conversion to anaerobic sludge digestion
[MWel]
max min
Figure 2: Pilot-WWTP Radevormwald
Project partners:
www.erwas-arrivee.de
CHP unit gas storage
digestion tank aeration tank
largest electricity consumer
control option:
· intermittent operation
· use of pure oxygen
provides constant CH4 production
control option:
· co-fermentation
· further methane conditioning by using H2
provides local storage capacities
control option:
· intermediate storage for proper operation of the CHP unit and the
electrolyzer
production of electric power and
heat
control option:
· activation of free power
capacities
· use of
redundant CHP- units and
emergency power generator
CO2 and H2 are converted into CH4
and H2O
control option:
· activation on energy surplus water is converted
into H2 and O2
control option:
· activation on energy surplus
· produced O2 can be used in the aeration tank; H2 is needed for methan conditioning
electrolysis sabatier reaction
