New paper: Unlocking energy flexibility of municipal wastewater aeration

A new paper from CITIES / DTU Compute & Krüger A/S – download for free the next few weeks!

A novel economic optimal control strategy suggests that the power consumption in wastewater treatment can be flexible since the water is treated in large tanks with long retention times where specialized aeration equipment is repeatedly switched on and off.

By controlling these switching times with respect to nutrient concentrations, electricity consumption can be predicted and shifted in time and hence provide short-term demand-side flexibility.

The proposed principle is used to reduce the operating costs of a wastewater treatment plant by enabling the flexibility to distribute the aeration load to periods with less expensive power prices.


  • Significant cost savings for wastewater treatment by shifting power consumption
  • Favourable to exploit instantaneous price differences in multiple power markets
  • Optimal energy consumption of wastewater aeration using switching times


Authors: Niclas Brok and Henrik Madsen from DTU Compute & Thomas Munk-Nielsen and Peter A. Stentoft from Krüger A/S.

Energy Webinar on System Integration and Energy Conversion

CITIES participate in this webinar series on System Integration and Energy Conversion. The first webinar is on Thursday, Oct. 29. Join us and hear the presentations from CITIES – Centre for IT-Intelligent Energy Systems IP Henrik Madsen and our partners Ørsteds (Ørsted Onshore North America) and Energinet and others. Find the link to sign up in the posting below

The Webinar Series begins on October 29th where Innovation Centre Denmark Boston, in collaboration with Massachusetts Institute ofTechnologyDTU – Technical University of DenmarkTufts UniversityEnerginet, and Energy Cluster Denmark, will host an Energy Webinar on system integration and energy conversion. We hope you will join us for this informative and worthwhile event.

Sign up for the seminar here:


After seven years of research CITIES project comes to an end. We are pleased to invite you to our annual meeting – and this year also – final conference Monday, November 9, 2020 – at DTU and Online.

This year we also collaborate with two other projects – DiCyPs and FED. Tuesday, November 10, 2020 CITIES invite you to join our joint conference at EWII in Kolding in person or online.

Check out our joint conference webpage GREEN DIGITALIZATION and learn more about the programs. And sign up! 

New CITIES-related project looks for a solution to reduce CO2 from data centres and server rooms

Although CITIES ends by the end of 2020 after seven years of research, CITIES’ research, findings and thoughts continue through several other projects based on research in CITIES or inspired of CITIES.  A brand new one is Cool-Data; a Grand Solution project supported by Innovation Fund Denmark with DKK 13 million.

Researchers at DTU Compute, DTU Management and DTU Civil Engineering will work with industrial companies to develop a new cooling and storage system for data centres and server rooms, which will be managed through artificial intelligence and reduce energy consumption and thus CO2 emissions.

Dominik Franjo Dominkovic, a postdoc at DTU Compute, is the project manager of Cool-Data. In CITIES he has been working with the technology and methodologies, latest together with one of CITIES partners, EnergyCool, and the electricity and heating company GEV in a demo case in Grindsted in Jutland. See more below

In ‘Cool-Data’ Dominik, EnergyCool and GEV continue the work with the two other DTU departments, and PURIX, Naviair, and Center Denmark. Learn more at the DTU website

Digitalisering i fjernvarmen bidrager til 2030-mål

ENGLISH version: District heating digitalization contributes to 2030 targets

Det sparer penge og CO2, når fjernvarmesektoren styrer temperaturen med data og lokale vejrudsigter i stedet for tegninger af ledningsnettet og mavefornemmelsen. Det viser forskningsprojekter, som CITIES er involveret i. Læs artiklen i DTU-magasinet DYNAMO

1, 7 mio. husstande i Danmark (ca. 64 pct.) bliver opvarmet med fjernvarme, der løber gennem 60.000 kilometer fjernvarmenet. Rejsen fra fjernvarmeværket til radiatorerne tager typisk flere timer, og derfor skal varmebehovet kunne forudsiges.

Man skal ikke skrue mere op for varmeproduktionen end nødvendigt, for det koster penge og er energispild, ligesom temperaturtabet i rørene er større ved højere temperaturer.

Samtidig skal vandet være tilstrækkelig varmt på de såkaldt kritiske punkter i udkanten af ledningsnettet. Så det er en videnskab at styre fjernvarmeproduktionen optimalt.

På DTU Compute arbejder CITIES centerleder professor Henrik Madsen og hans kolleger med datadrevet energi- og temperaturoptimering. Flere forskningsprojekter viser, at digitalisering forbedrer prognosen for varmebehovet markant og derigennem letter vejen til Danmarks 2030-klimamål.

NREL – CITIES Support: Cooperative Research and Development Final Report

The research in CITIES finally comes to an end after seven years of research. Now one of our partners ‘NREL’ points out in a report their support to CITIES with references to four scientific papers and the establishment of Center Denmark.

NREL – National Renewable Energy Laboratory National Renewable Energy Laboratory – operated by Alliance for Sustainable Energy for the U.S. Department of Energy (DOE).

Energy System Integration
Modeling, simulation and analysis of integrated energy system and evaluate the use of the Energy Systems Integration Facility (ESIF).

The ESIF is the first US research facility that can conduct integrated megawatt-scale research, development, and demonstration of the components and strategies needed to safely and seamlessly integrate clean energy technologies into energy systems infrastructure and utility operations at the speed and scale required to meet national goals.

In order to achieve the ambitious goal of a fully renewable Danish energy system, an overhaul of the operation, monitoring and planning of the entire energy system is necessary.

By moving from the traditional view of the power, heating, cooling, water and other systems as completely separate, centralized and mostly radial, to recognizing the significant opportunities for efficiency and emission reduction brought about by allowing these systems to fully integrate and interact with one another.

Integration of previously distinct energy systems allows for flexibility throughout the system, so that society’s needs for energy can be met while considering the fluctuating nature of many renewable energy resources.

Integrated Information and Communications Technology (ICT) powered systems offer the possibility of intermediate conversion and storage of energy in forms including power [sub-daily], heat (including the district heating network) [daily] and gas [seasonal], providing an essential service to balance the variations in wind and other forms of renewable energy production and ensure the security of energy supply. The high density and diversity of energy use and networks within a city environment, coupled with the expressed desire to achieve sustainability within cities maims them an ideal framework for this research activity.

“Energy System Integration: Defining and Describing the Value Proposition”, M. O’Malley, B. Kroposki, B. Hannegan, H. Madsen, M. Andersson, W. D’haeseleer, M. McGranaghan, C. Dent, G. Strbac, S. Baskaran, M. Rinker, NREL Technical Report NREL/TP-5D00-66616, June 2016,

Demand response
Additional results in the project focused on examining demand response (DR) as a way to increase flexibility in the operation of energy systems. DR proponents widely laud its prospective benefits, which include enabling higher penetrations of variable renewable generation at lower cost than alternative storage technologies, and improving economic efficiency.

In practice, DR from the commercial and residential sectors is largely an emerging, not a mature, resource, and its actual costs and benefits need to be studied to determine promising combinations of physical DR resource, enabling controls and communications, power system characteristics, regulatory environments, market structures, and business models.

The work during this project focused on the enablement of such analysis from the production cost modeling perspective. In particular, a bottom-up methodology for modeling load-shifting DR in production cost models was developed.

The resulting model is sufficiently detailed to reflect the physical characteristics and constraints of the underlying flexible load, and includes the possibility of capturing diurnal and seasonal variations in the resource.

“On the Inclusion of Energy- Shifting Demand Response in Production Cost Models: Methodology and a Case Study”, N. O’Connell, E. Hale, I. Doebber, J. Jorgenson, NREL Technical Report, NREL/TP-6A20-64465, July 2015,

Transactive Energy
The project also examined the concept of “Transactive Energy” (TE) and conducted significant work simulating transactive control in distribution systems. NREL, University of Colorado, South Dakota State and DTU performed their simulation using the Integrated Energy Systems Model (IESM) co-simulation platform.

The team implemented network-aware TE controls in the IESM co-simulation framework that manages distribution feeder voltages based on real-time optimal power flow. This is one part of a multi-timescale TE control approach that NREL is developing to reduce costs for both balancing power supply and demand and managing distribution feeder voltages.

This multi-timescale TE approach uses a price signal based on two components: an energy price based on wholesale prices and bids by participating DERs that adjusts on a 5-15 min market cycle, plus an incentive signal overlay for fast grid services, updated every 1-10s. For the TE Challenge, NREL simulated only the calculation of the incentive signals for voltage regulation services and used the time-of-use (TOU) price as the energy price.

More extensive analysis using a longer test period is required to determine appropriate levels of compensation for PV curtailment and reactive power support that will ensure fair compensation to houses that provide voltage regulation services.

“NIST Transactive Energy Modeling and Simulation Challenge Phase II Final Report” D. Holmberg, M. Burns, S. Bushby, A. Gopstein. T. McDermott, Y. Tang, Q. Huang, A. Pratt, M. Ruth, F. Ding, Y. Bichpuriya, N. Rajagopal, M. Ilic, R. Jaddivada, H. Neema, NIST Special Publication 1900-603,

Integrated energy planning with variable renewable energy
The research also examined the integration of a very large share of variable renewable energy sources into the energy system.

To do this, an integrated energy planning approach was used, including ice storage in the cooling sector, a smart charging option in the transport sector, and an excess capacity of reverse osmosis technology that was utilized in order to provide flexibility to the energy system. A unit commitment and economic dispatch tool (PLEXOS) was used, and the model was run with both 5 min and 1 h time resolutions.

The case study was carried out for a typical Caribbean island nation, based on data derived from measured data from Aruba. The results showed that 78.1% of the final electricity demand in 2020 was met by variable renewable energy sources, having 1.0% of curtailed energy in the energy system.

The total economic cost of the modelled energy system was similar to the current energy system, dominated by fossil fuel imports. The results are relevant to many populated islands and island nations.

“Integrated Energy Planning with a High Share of Variable Renewable Energy Sources for a Caribbean Island”, D. Dominkovic, G. Stark, B. Hodge, and A, Pederson, Energies 2018, 11(9), 2193,

Center Denmark
Finally, NREL points out the support for the establishment and design of Center Denmark, the new Danish national digitalization hub for data-intelligent and integrated energy systems.  

NREL mentioned Center Denmark has been heavily influenced by the research at NREL and their research facility;  Energy Systems Integration Facility (ESIF). See above.

Download the report
The report ‘NREL CITIES Support: Cooperative Research and Development Final Report‘ is available at no cost from the National Renewable Energy Laboratory (NREL).

Advice to the Danish Parliament: New framework conditions, energy taxes linked to CO2 emissions, and sector coupling

Yesterday Henrik Madsen and other researchers from DTU visited Folketinget to give an important message:

  • Denmark need to have new framework conditions as soon as possible.
  • Energy taxes should be harmonized and linked to CO2 emissions from the electricity we use per hour. This can be done now.
  • In addition, dynamic network tariffs must be introduced, which are linked to the physical challenges in the network.
  • Such framework conditions, digitalisation and sector coupling will contribute to both green growths and to reaching the target of 70 per cent CO2 reduction in 2030.

See the video from the meeting in Folketingets Klima-, energi- og forsyningsudvalg. Jump to time code: 11:25:30

See Henrik Madsen’s presentation (PDF) in the Danish parliament on September 21, 2020

Learn more in the DTU report from June 2020: Sector Development Project about Smart Energy Systems (English summary of report)

GREEN DIGITALIZATION 2020 – CITIES FINAL CONFERENCE and joint conference with DyCiPs and FED

The invitation is on its way. Save the dates!

Due to the COVID-19 situation:

Monday the 9th of November is CITIES final conference at DTU, Lyngby. The conference will be physical with streaming functionality in Zoom, so the IAB members and others can join online.

Tuesday the 10th of November will be an International Day – a partner conference with CITIES, the DiCyPs project (AAU), and the FED.  All three projects will be represented. The day has been changed from DTU to EWII, Kokbjerg 30, 6000 Kolding, Denmark. The meeting will be physical with streaming functionality in Zoom.

We reserve the right to act upon COVID-19 participation restrictions.

If you want to show up physical at DTU or EWII and need to book tickets and/or hotel please note that the meeting could be changed to a virtual meeting at short notice. We recommend that attendees from abroad stay home and join us virtually.

DTU and SDU move together with Center Denmark in Denmark’s Energy Silicon Valley

Center Denmark, which is a national meeting point for green research, has moved to new premises and has new cohabitants. Not long ago, the center’s employees moved together with the cluster organization Energy Cluster Denmark, and now both SDU and DTU join the green research community, which is physically located in Port House in Fredericia.

Learn more in the press release (Danish):

Opinion: Remember to give the tariffs a makeover #green-tax-reform

When the Danish politicians this fall negotiate green tax reform, they should look at #tariffs. Nothing is stronger than a well-designed price signal when you want to promote flexible energy consumption, writes Henrik Madsen in this opinion in Teknologiens Mediehus GridTech.

Today, tariffs make up a large part of the Danish consumers’ electricity bills. The pure electricity price is approx. 15%, tariffs approx. 20% and the rest are energy taxes. If politicians want consumers to change electricity consumption, it is also necessary to look at tariffs when negotiating green tax reform so that they set up a sensible incentive structure that encourages people to change behaviour.

Denmark should have a system where the price is high when there are capacity problems, large grid losses and so on. And low when there are no problems in the network.

See the Danish text here

#dkpol #dkenergi #dkgreen #smartenergy #data