Variation management for cost-efficient integration of variable renewable electricity

Licentiate thesis, 2020

The aim of this work is to improve our understanding of how wind power and solar photovoltaics (PV) can be integrated into the electricity system in a cost-efficient manner. For this, a techno-economic cost-minimising model of the electricity system is used for a set of case studies. The case studies cover a set of regions that have different conditions for wind and solar power and employ a range of strategies for variation management. The variation management includes the availability of complementing, shifting, and absorbing strategies internal to the electricity system, such as flexible bio-based generation, batteries, and transmission, as well as measures available from electrification of the industry, transportation, and heating sectors.  

The results show that there is a need for different variation management strategies in different system contexts. In regions with exceptionally good conditions for variable renewable electricity (VRE), wind and solar power integration benefits from absorbing strategies. In regions where the conditions for VRE are not sufficient to out-compete baseload generation, complementing technologies are needed to enable cost-efficient wind and solar power integration. Shifting strategies are primarily suited to the diurnal variations of solar PV. Variation management can increase the amount of cost-efficient VRE that can be integrated into the system while reducing the total cost of meeting the demand for electricity. The most valuable variation management strategy covered in this work involves optimising charging of electric vehicles and vehicle-to-grid (discharging from electric cars to the grid), which can reduce the total cost by up to 33% in a solar-dominated system but by only 8% in a wind power- and hydropower-rich region with inherent flexibility. The value of transmission lies in its abilities to smoothen wind variations between regions and to transfer electricity from electricity systems with superior wind or solar power resources. A scarcity of bioenergy would entail a high value being placed on available biomass for the purpose of complementing wind and solar power. To maximise the provision of flexibility by biomass, it could be utilised with negative emission technologies to enable the usage of fossil-derived natural gas. Biomass deployed to meet net-negative emissions targets would, however, not provide flexibility. The results of this work underline the importance of combining different technologies and strategies and the value of using them where they are best suited rather than deploying one strategy to resolve every situation.