HESKH: The hospital as a hybrid energy storage system

The problem is well known: On the one hand, the growing share of renewable energies in the electricity mix increases the risk that the demand cannot be covered at all times. On the other hand, there is an oversupply in many sunny and windy hours. The approach that Stadtwerke Bochum GmbH and Fraunhofer UMSICHT are investigating, however, is new: In the project, “Hybrid Energy Storage Hospital“ (HESKH) they are investigating the question of whether and how the supply systems of hospitals can be used for electrical energy balancing. In addition to determining the potential itself, the project also examines the importance of precise heat load forecasts for the planning of flexible system operation.

In almost 2000 German hospitals, supply systems are available - from CHP plants, chillers and in future also heat pumps to heat and cold storage tanks. Compared to other consumers (e.g. residential and office buildings), their size makes them ideally suitable to compensate gaps in the power grid with little effort or for making economical use of an excess supply of renewable energies.

Compensation for supply shortfalls in the electricity grid

The project partners' aim is therefore to develop the potential of hospitals for electrical energy balancing and at the same time improve the economic efficiency of energy supply in the facilities. Using the example of the Protestant Hospital in Hattingen as well as simulation and optimization tools, they are investigating how existing storage capacities can be used to decouple the supply of heat and cold from current demand. This flexibilization makes it possible, on the one hand, to adapt electricity generation in CHP plants and, on the other hand, the electricity consumption of chillers, heat pumps and electrical heat generators to the current situation in the power grid. By integrating forecasts of the heat demand into the calculation of the optimal plant operation schedule, it is ensured that the hospital's heat requirement is covered at all times. The detailed data collection for the modelling as well as the creation of a simulation model to illustrate the energy consumption will also help to identify efficiency measures.

For hospitals, additional sources of revenue can arise from the optimized and flexible system operation. Furthermore, by analyzing the hospital's energy efficiency, it is possible to identify and quantify easy-to-implement saving measures that reduce energy consumption and energy costs. Another advantage of energy balancing concepts in hospitals is that old, inefficient and not ideally sized systems can be replaced in the course of a new design of the existing systems. In this way, energy efficiency and profitability can be increased further.

Improve the economic efficiency of energy supply

For network operators, this provides an opportunity to compensate for imbalances in the electricity grid to some extent by changing the use of consumption and supply systems. Hospitals are far more suitable than small systems in residential buildings. While micro- and mini-CHPs for residential buildings have an electrical output of approx. 5 to 20 kWel, the output of most hospitals is between 200 and 600 kWel. This results in significant advantages in terms of plant acquisition and implementation, since the effort required for energy management and information and communication technologies is significantly lower than for small plants.

In a first step, the researchers are collecting the relevant inventory and consumption data of the hospital in Hattingen and are incorporating these into a physical model of the building. From this, they gain a better understanding of the composition of the energy consumption and can derive efficiency measures. In addition, they carry out extensive measurements of electrical power and thermal energy flows in order to generate input and comparative data for the modelling and also to be able to forecast the heat demand based on this data.

From data acquisition to model development and simulation

In order to be able to plan the operation of hospital facilities based on the requirements of the electrical grid and the energy markets, the next step is to create both an operation optimization model and a forecast model. With the help of the forecast model, the heat demand for the next few days can be predicted and incorporated into the optimization model. Since ideal forecasts are impossible, the forecasts will always differ from the actual demand, so that special attention is paid to the investigation of the effects of these differences on the system operation planning. In this way, conclusions can be drawn as to the necessary accuracy of the forecast models and the uncertainties can be taken into account in the optimization model.

For the subsequent evaluation of the energy balancing concepts, the project partners define suitable criteria - e.g. energy balancing potential, flexibility, primary energy demand, costs and revenues. They also define various balancing scenarios and targets. On this basis, they develop possible balancing concepts for the subsequent optimization calculations. The results of these calculations are evaluated with regard to the selected criteria and the concepts are compared. In a final step, the transferability of promising concepts to other hospitals is examined and assessed in terms of technical and economic feasibility.

In particular, the Stadtwerke Bochum play an important role as a practical partner: they evaluate the results from the user's point of view and thus ensure that the methods and concepts developed are meaningful and feasible in practical implementation.

• Stadtwerke Bochum GmbH
• Evangelisches Krankenhaus Hattingen