Research Projects
Local Load Management and Distributed Generation
Initial considerations
The limited availability of fossil fuels and the necessity to mitigate climate change by reducing greenhouse gas emissions pose great challenges for the transformation of today’s electrical energy systems. One of the key strategies for “decarbonizing” the electricity production is a rapid increase in renewable energy generation, which has been taking place in many countries over the recent years.
Due to the decentralized nature of many renewable energy carriers and the intermittent characteristics of wind and photovoltaic power generation, significant adaptations of power system operation and control have to be made when a high share of renewables shall be accommodated. Although the infeeds from intermittent sources can be predicted quite well, additional control flexibility is needed on various time scales in order to compensate for forecast errors and high infeed ramp rates. However, a flexible mid-load operation of conventional power plants, as well as the usage of active power control reserves, is usually quite costly.
The outlined situation has triggered a rising interest in control methods that utilize flexibility on the side of the load instead of the generation. Traditional “Demand Side Management” (DSM) methodologies, which have been known in power systems research for decades, are a good basis for these activities. They usually consist of user-incentive-based or automatic remote deactivation of certain appliances during peak hours. However, the control methodologies must be extended substantially when a tight control over the temporal consumption characteristics of electrical appliances shall be achieved, and not only the shifting of a certain portion of load.
Outline of the project
The project “Local Load Management” (LLM) is aimed at developing novel methodologies to exploit demand-side flexibility in power systems. It is being conducted by a team from ETH Zurich, University of Applied Sciences North-Western Switzerland (FHNW), Atel Netz AG and Landis+Gyr since 2006. Financial support is provided by swisselectric research. The current project phase is called ''Electricity grid security and operation taking into account distributed loads, in-feeds and storages'', which commenced in 2007.
In this project phase, a suitable communication infrastructure for applying a sophisticated load management scheme in private households is developed. As depicted in Figure 1, interface units in the individual appliances provide a link to a central control entity which can influence the appliance operation through external commands.
For cooling and heating household appliances such as freezers, refrigerators, water boilers and heat pumps, a coordination strategy is developed. It allows a controlled reduction or increase of the aggregated active power consumption of a large set of such appliances by transmitting switching impulses (ON to OFF or OFF to ON) to selected appliances, allowing the group to act like a “virtual distributed energy storage”. This approach does not violate the usual temperature range of the appliances; only the duty cycle is shortened by the compulsory switching. Thus, the user comfort remains relatively unimpeded.
The coordinated control is complemented by a device-dependent load shedding which is activated in the case of a network disturbance. For that scheme, also non-thermal household appliances may be considered, the deactivation of which causes comfort losses for the user. This may be justified if the load shedding scheme appears to be an effective measure to prevent the loss of load in entire regions.
The possibilities of unifying the load management concepts with the control of storages such as batteries and Distributed Generation units will be investigated as well. Furthermore, arising power system control issues in distribution grids will be addressed. Apart from that, economical considerations and strategies for the regulatory or market-based introduction of Local Load Management into today's electricity systems are elaborated in the project.
References
[1] S. Koch, M. Zima, G. Andersson. Local Load Management: Coordination of a Diverse Set of Thermostat-Controlled Appliances. Extended Abstract and Poster presented at Smart Energy Strategies 2008, Zurich/Switzerland, September 2008.
[2] S. Koch, D. Meier, M. Zima, M. Wiederkehr, G. Andersson. An Active Coordination Approach for Thermal Household Appliances – Local Communication and Calculation Tasks in the Household. Submitted to PowerTech 2009, Bukarest/Romania, June/July 2009.
[3] S. Koch, M. Zima, G. Andersson. Active Coordination of Thermal Household Appliances for Load Management Purposes. Submitted to IFAC Symposium on Power Plants and Power Systems Control, Tampere/Finland, July 2009.
[4] F. Kupzog, C. Rösener and P. Palensky. Konzepte zur koordinierten Nutzung verteilter Energiespeicher. Presented at 5. Internationale Energiewirtschaftstagung an der TU Wien - (IEWT2007), 2007, pp. 219 – 230
[5] M. Stadler, W. Krause, M. Sonnenschein, U. Vogel. Modelling and evaluation of control schemes for enhancing load shift of electricity demand for cooling devices. Environmental Modelling & Software 24, 2009, pp 285 – 295 (available online).
Project Partners: swisselectric research, ATEL Netz AG, Fachhochschule Nordwestschweiz, Landis+Gyr
