Energy-Sponge-Bruck (Energieschwamm Bruck an der Mur)

Starting point/Motivation

Developments in the area of grid-connected energy supply for small to medium sized cities with 10,000-25,000 inhabitants were not carried out to the same extent as the urban development itself. In contrast to cities and quarters, where there are clear strategies concerning future developments, this important fundamental work has not yet been performed in the municipal sector.

Contents and Objectives

The key objective of the exploratory study "Energieschwamm Bruck" of the urban region Bruck an der Mur and Oberaich was the establishment of a clear basis for the development and flexibilisation of the future communal energy system. The City Bruck/Mur has over 15,000 inhabitants and is suitable as a testing area for the development of an integrative and smart energy supply. It is an industrial site and transport hub where many different energy sources are utilized. This study evaluates technological as well as organizational and market-based issues. Examples of the performed investigations are the analysis of strategic possibilities to support local energy suppliers, or the importance of the acceptance of new technologies. Besides, a general evaluation method for cities with 10,000-25,000 inhabitants was established.

Methods

The project is divided into three sequential parts. First, the status quo of the current energy system of Bruck an der Mur, the potentials for integrated renewable energy flows and the necessity for a grid extension are detected. The energy consumption, the energy generation as well as the potentials of renewable energies are analyzed with a cellular approach, which was especially designed for this case, and provides temporal and spatial information. Second, on the basis of the status quo, three scenarios that show possibilities for future developments in the communal energy system of Bruck an der Mur, are developed. The scenarios are evaluated energetically and economically. Third, with the results from the first two parts, a list of possible implementation projects for Bruck/Mur is defined. In addition to that, all used methods get summarized and generalized. This guidance can then be used to set up development strategies for energy systems of other urban regions.

Results

The energy supply (electricity, gas, thermal energy) of the city Bruck/Mur is provided by different market operators, which are Stadtwerke Bruck, Brucker Biofernwärme, Energie Steiermark, private small hydropower plants and private photovoltaic systems. They have to adapt to communal as well as commercial market forces, and have to face with various success factors and obstacles. The results of the three investigated scenarios show possible future development opportunities of the energy system for Bruck/Mur.

In the first scenario, the net-system, high shares of electricity from photovoltaic systems are fed into the grid. Additionally the achievable rates of energy and power autonomy are evaluated. In Bruck/Mur there are many suitable roof top areas that can be used for photovoltaic plants. At the moment only a small proportion of it is used. Depending on the share of used area, the rate of power autonomy can be increased from currently 27% to 55%, and with using of options in flexibility even 68% can be reached. Although Bruck/Mur has a high potential for feeding electricity from photovoltaic systems into the grid, the full feeding-in of the produced energy is economically not favourable, because of actual circumstances for private households (price, funding, etc.). Consequently, an important issue is the use of appropriate storage facilities, not only for private homes, but also for the overall system. The rate of energy and power autonomy can be increased significantly by a storage in the area of private households. This makes the usage of solar energy economically more attractive. Due to the fact that, at present the investment costs for such storage technologies are relatively high, companies have the opportunity to provide storage capacity centrally and integrate households.

The second scenario analyses the substitution of natural gas boilers, which provide thermal energy for multi-family dwellings, by combined heat and power plants. The annual heat demand of these objects is 1.7 GWh. Besides heat, additional 706 MWh of electricity can be produced. The primary energy efficiency of the combined heat and power plants is 95%. Compared to that, the same amount of electricity and heat supplied by the grid or from a gas boiler has a primary energy efficiency of 77%. Replacing boilers with CHP units results in a more efficient use of energy, since domestic heat and also electricity is produced (for self-consumption as well as for feeding into the grid). A point of discussion of CHP units is the used primary energy source. Based on the Sustainable Process Index (SPI) method, the substitution of currently operating boilers with CHP units leads to two effects. Taking into consideration the whole life cycle, the operation with natural gas or wood chips leads to a smaller land utilisation and the contribution to the greenhouse effect decreases (status Quo vs. Natural gas: about 8% less land area, Status Quo vs. Wood chips: about 99% less land area).

The third scenario involves the inclusion of a thermal energy storage into the heating network. At present, heat is provided by a paper mill as waste heat and by two biomass boilers, which operate from November to March. In the model year 2014, the heat demand was 19.7 GWh. Already with the inclusion of a 150 m³ hot water storage the heat demand can be solely covered by waste heat, including consumption peaks in the morning and in the evening. However, if there is a rise in the heat demand of more than 30%, the needed storage size will increase significantly. In this case surplus covers and undersupplies have to be compensated for longer time periods. The storage scenario focuses on two parties, the biological district heat and Norske Skog. These are especially relevant, if the heat demand in Bruck/Mur will increase.

At the end, the study provides a list of suggestions for different technologies and their market maturity. There are market-ready technologies available for every investigated scenario. Furthermore, the study serves proposals for business models. The generalized methods used in the project can be applied to other cities of comparable size.

Prospects / Suggestions for future research

The study "Energieschwamm Bruck" investigates three scenarios of possible future energy supplies from local sources. All scenarios lead to a greater energy independence of the city Bruck/Mur. In addition to that, the resource efficiency rises and the CO2-Emissions decline. An appropriate usage of the available local resources results in an unexpected high rate of energy and power autonomy. Since the applied instruments and methods are generally valid, guideline values for similar locations can be derived from the results.

This project is a solid basis for holistic and transdisciplinary considerations of municipal energy systems, which include technical as well as socio-economic factors. Furthermore, other methods like the cellular concept were developed, which is applied in other projects.