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).