Use case: Electricity-price-driven operation of biogas plants with CHP units
Using BioCash as an example, we show how electricity price forecasts can be combined with plant-specific operating data and process engineering constraints. Factors considered include expected biogas production, the status of the gas storage system, substrate management, and technical and biological operating limits. On this basis, a CHP operating schedule is calculated that enables economically optimized plant operation while remaining within process constraints. The most economically suitable operating mode does not depend on the electricity price alone.
The interaction of the following factors is crucial:
- forecast electricity prices
- available and expected biogas production
- status and capacity of the gas storage system
- output and operating limits of the CHP unit
- substrate availability, substrate costs and methane yield
- substrate composition and feeding strategy
- biological stability of the digester and potential process overload conditions, assessed using an ADM1-based process model
- additional operational and process engineering constraints
Another focus is the evaluation of the electricity price forecast used. BioCash updates the forecast regularly and stores the respective forecast snapshots for the coming seven days. Once the published electricity exchange prices are available for the corresponding period, they can be compared with the previously stored forecast values. This makes it possible to investigate how accurately the price level, high- and low-price periods and their timing were predicted. At the same time, it is possible to evaluate how forecast quality changes as the forecast horizon increases. The resulting historical forecast and comparison data can be used for validation and, in the future, also for the further development of forecasting models.
However, it is not only the accuracy of the electricity price forecast that matters. It is also important to determine whether and how forecast deviations affect the CHP operating schedule calculated from it. For this reason, we investigate whether, for example, CHP start times and operating durations, use of the gas storage system or the achievable contribution margin change. Not every deviation between the forecast and the published electricity exchange price automatically leads to a different operating decision. If, for example, a high-price period is misjudged or forecast at the wrong time, the optimum operating time of the CHP unit may shift and the available biogas may be used less economically. The electricity price forecast can therefore be evaluated on two levels: How accurate is the forecast itself, and what actual influence do forecast errors have on plant operation and the economic result?