Integration of stochastic renewables in the Swiss electricity supply system (ISCHESS)

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Recently planned energy and climate policies encourage the deployment of renewable energy sources (RES).
RES, such as wind and solar, are inexhaustible, have a low carbon footprint and can operate on a small scale, enabling their usage in the distribution grid. They are however typically variable, producing uncontrollable and partly unpredictable amounts of electricity over time.
To ensure that the generated electricity matches the consumption on a second-by-second basis, additional stability measures will have to be provided for in future systems featuring a high share of RES. The ISCHESS project studies the optimal transformation of the current Swiss energy supply towards a more sustainable system through the integration of RES sources.
The first phase of the project focuses on local distribution while the second phase studies the problem in the context of the Swiss transmission grid. Simulation and optimization of detailed electricity grid models are used to evaluate alternative RES integration strategies including grid extension, the curtailment of RES energy and the use of storage technology. The goal is the identification of integration barriers and the assessment of operational, technological, environmental, social, economical and logistical aspects for the considered RES integration approaches.


To evaluate different integration strategies, grid performance indicators have been defined that serve as objectives and constraints for the case studies' assessment. Beside economic criteria for investment planning, they include measures for grid stability, environmental impacts and social aspects.
The analysis of future energy scenarios requires the simulation of the load demand and of available power injections (e.g. from PV sources) on an hourly basis over different time horizons. A tool was developed to generate typical future hourly profiles based on today’s measurements and aggregated predictions of key parameters, like the total Swiss load demand.
To evaluate RES integration strategies for future energy scenarios, it is necessary to perform a sequence of power flow simulations of the electrical power system, in order to verify the feasibility and performance of the selected scenario and strategy. A unified optimization formulation was developed for both the grid operation and the strategy selection. The formulation uses standard power flow tools and optimally selects the sizing and placement of storage components, distribution line upgrades and the degree of PV curtailment. The tool has been applied to a model of a large Swiss distribution grid, providing a simple investment planning paradigm for different cost estimates of storage components, distribution line upgrades and imported electricity.

ISCHESS - figure 1
Figure 1: Comparison of PV integration strategies: Usage cost per day for each strategy and combinations thereof (green surface) fitted to the simulated scenarios (blue stars) assuming an average electricity price of c =  55CHF/MWh, a cable degradation cost of pG = 55CHF/(km day) and a storage degradation cost of pS = 70CHF/(MWh day)


Current work studies the integration strategies on a more detailed level. The planning tool is developed to incorporate information on individual line elements, dynamic degradation costs of the batteries and regulatory constraints. On the scenario side, information on the geographic distribution of RES availability needs to be included in the transmission grid study. More in general, the study needs to investigate the sensitivity and robustness of the results to uncertainty in the modeling data, scenarios and, on the operational level, short term predictions. For the transmission grid study, the detailed bottom-up model developed at FEN will also be combined and synchronized with existing aggregated models and strategies developed at PSI.


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Sat Apr 29 13:14:36 CEST 2017
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