IEA TCP WIND Task 25 ”Design and Operation of Energy Systems with Large Amounts of Variable Generation” compiled Recommended Practices for power system impact studies, what has traditionally been called wind and solar integration studies. In this work we compare the recommended practices to actual modeling practice using a recent wind and solar integration study for Sweden carried out by PhD students, post docs and senior researchers at Chalmers university of technology. The aim is to highlight key challenges and trade-offs when performing studies of energy systems with large shares of wind and solar power.

The case study of Sweden investgates electrification of industry and transport. Sweden benefits from a carbon-neutral electricity system composed by hydropower nuclear power and wind power. However, with a large energy-intensive industry, including iron and steel as well as petro-chemical industry, which need to move away from fossil-fuels the electricity demand is expected to double.

To analyse the changes in the electricity and energy system that electrification of the industrial and transport sectors entails, a large geographical range is required to capture trade flows and a long time horizon that reflects changed conditions for investments in new electricity production and storage with associated infrastructure over time. At the same time, a high geographical resolution is needed to represent transmission constraints in the electricity grid and a high time resolution to capture the variability of weather-dependent electricity production. To cope with this, the analysis in is based on three different electricity system models in combination; a European investment model to study the development of the electricity system based on today's capacity mix up to the year 2065 followed up by calculations with an investment model with high geographical resolution for the Nordic electricity system from which results are used to calculate flows of active and reactive power in an electricity grid simulation model and to check that the calculated electricity systems are physically and electrically reasonable in normal operation and to identify the need for reactive power compensation.

The latest update of the IEA TCP WIND Task 25 Recommended Practices, Edition 3, includes recommendations for very high shares of wind and solar – wind and solar dominated power systems, with energy system coupling. This matches well with the Swedish case study with wind and solar power supplying more than 50 % of the electricity demand from 2035 and in which the sector coupling to industry and transport both add new loads bout also new sources for flexibility. We will go through the different modelling choices made in the study, relate them to the recommended practises, discuss the implications on results and future work.

The suggestion is that this is a joint session with the two authors using two presentation slots. We have therefore submitted one abstract each.