Storage via Power-to-Gas in Future Energy Systems: the Need for Synthetic Fuel Storage in Systems with High Shares of Intermittent Renewables

Rising global temperature concerns drive unprecedented changes in the electrical power system like the massive deployment of intermittent renewable energy sources. Such large-scale renewables deployment requires a variety of flexibility options for the electrical power system to be operated reliably. A possibly important flexibility option is storage. Next to battery storage and pumped hydro storage, which have a comparably small storage capacity, indirect energy storage via power-to-gas (P2G) might be interesting for long-term (seasonal) storage due to its large scale energy storage potential.

This dissertation studies the need for such energy storage via power-to-gas in future energy systems dominated by intermittent renewable energy sources, together with the operational impact of power-to-gas on the integrated electric power and natural gas systems. This overall goal is split in different sub-objectives: (i) Assessment of the value of electricity storage for an investor in a given electricity market. (ii) Identification of the circumstances which require electricity storage via P2G to justify the need for investing in P2G conversion. (iii) Once P2G would be installed, evaluation of the impact of such P2G units on the operation of both the electrical power and natural gas systems.

Several tools are developed to study each of the above mentioned research questions. (i) Three novel cost metrics, similar to the traditional levelized cost of electricity are presented to express the value of storage in an electricity market. (ii) An energy system investment model is presented to assess the cost optimal amount of installed storage capacity, and in particular P2G, in future energy systems under different environmental constraints. (iii) A novel integrated operational energy system model comprising the electrical power and natural gas sectors has been developed to analyze the impact of P2G on the operation of the natural gas network.

Applying the different cost metrics to storage technologies showed how those metrics can be used to assess the economic viability of different storage technologies. However, different examples also showed that it is not useful to apply such levelized cost metrics to storage units with small energy storage reservoirs like conventional batteries. For such technologies, a market price analysis with full temporal detail is recommended.

Portfolio optimization studies showed that investments in P2G are triggered by a requirement for large energy storage capacities which is typically related to long-term seasonal storage of surplus renewable generation. High shares of renewable generation could be installed as a consequence of an imposed renewable target (above 70%), or when high CO2 emission prices would occur (1000€/ton and above) in combination with an absence of CO2 sequestration possibility. Once P2G is installed, it can also be used for short-term storage cycles and deliver auxiliary services to the electrical power grid.

Short-term operational results indicate that the current Belgian gas network contains ample amounts of inherent flexibility to accommodate P2G integration in high renewable settings. The network can deal with possibly volatile gas injections from P2G without impacting the normal operation of conventional natural gas producers.