Thread by @OliverRuhnau

The final version of our paper
"#Storage requirements in a 100% #renewable electricity system: extreme events and inter-annual variability"
is now published in Environmental Research Letters 🎉
Joint work with @QvistStaffan
doi.org/10.1088/1748-9…
@IOPenvironment #energytwitter

Regarding 100% renewable electricity systems, prolonged periods with persistently scarce supply from wind and solar resources have received increasing academic and political attention. Our article explores how such scarcity periods define energy storage requirements.

We contrast time series analysis with system cost optimization model, based on a German 100% renewables case study using 35 years of hourly time series data ➡️ Much more data than in usual energy system analyses

Our findings on extreme events #Dunkelflaute:
- periods with persistently scarce supply last no longer than 2 weeks BUT
- the max. energy deficit extends over 9 weeks -> multiple scarcity periods in a row
- storage must bridge a max. of 12 weeks -> losses and charging limitations

What this means for #storage requirements:
- need to supply 36 TWh of electricity in DE
- most of this is hydrogen storage in salt caverns
This is the result of cost optimization solving the trade-off between overbuilding (and curtailing) renewables and building more storage ⚖️

Adding other sources of flexibility, the duration of the period that defines storage requirements lengthens to more than one year.
We show this for bioenergy but I assume it's similar for demand response and interconnectors ➡️ further research needed to confirm

When optimizing system costs based on a single year rather than a multi-year time series, we find substantial inter-annual variation in the overall storage requirements, with the average year needing less than half as much storage as calculated for all 35 years together.

We conclude that focusing on short-duration extreme events or single years can lead to an underestimation of storage requirements and costs of a 100% renewable system.

Here is a thread on an earlier version of this paper with more details and figures:

https://twitter.com/QvistStaffan/status/1427625795355349004

🙏 Thanks to @KittelMartin for discussions and feedback!

💡 Inspired by and adding to similar work by @WPSchill, @nworbmot, @JackieADowling, and many more